WEBVTT 00:00:00.000 --> 00:00:01.979 align:middle line:90% [SQUEAKING] 00:00:01.979 --> 00:00:03.951 align:middle line:90% [RUSTLING] 00:00:03.951 --> 00:00:05.923 align:middle line:90% [CLICKING] 00:00:05.923 --> 00:00:17.580 align:middle line:90% 00:00:17.580 --> 00:00:18.960 align:middle line:90% JUEJUN HU: OK. 00:00:18.960 --> 00:00:21.760 align:middle line:84% Thank you all for joining this semester's class, 00:00:21.760 --> 00:00:24.045 align:middle line:90% 3071 Amorphous Materials. 00:00:24.045 --> 00:00:25.420 align:middle line:84% So what I'll do in this lecture-- 00:00:25.420 --> 00:00:27.080 align:middle line:84% I will start by giving you a little bit of an overview, 00:00:27.080 --> 00:00:29.063 align:middle line:84% introduction of class and then proceed 00:00:29.063 --> 00:00:31.730 align:middle line:84% to talk about, essentially, the fundamentals of amorphous state, 00:00:31.730 --> 00:00:32.230 align:middle line:90% OK? 00:00:32.230 --> 00:00:34.880 align:middle line:84% The way the lecture class is going to be organized 00:00:34.880 --> 00:00:37.200 align:middle line:84% is I will try to cover both fundamental science as well 00:00:37.200 --> 00:00:40.180 align:middle line:84% as practical applications based on the fundamental insights. 00:00:40.180 --> 00:00:41.160 align:middle line:90% OK? 00:00:41.160 --> 00:00:43.118 align:middle line:84% So later on, you'll see that I have essentially 00:00:43.118 --> 00:00:45.800 align:middle line:84% have one lecture focusing on the fundamentals and then one 00:00:45.800 --> 00:00:48.080 align:middle line:84% lecture to talk about what are the applications based 00:00:48.080 --> 00:00:50.960 align:middle line:84% on those scientific knowledge, OK? 00:00:50.960 --> 00:00:51.600 align:middle line:90% All right. 00:00:51.600 --> 00:00:54.580 align:middle line:84% So here is just a quick introduction about myself. 00:00:54.580 --> 00:00:56.680 align:middle line:84% Some of you probably already know me. 00:00:56.680 --> 00:00:58.200 align:middle line:90% You can call me JJ. 00:00:58.200 --> 00:01:00.980 align:middle line:84% I will not try to ask you to pronounce my first name. 00:01:00.980 --> 00:01:02.760 align:middle line:84% That's the first homework assignment. 00:01:02.760 --> 00:01:03.380 align:middle line:90% No. 00:01:03.380 --> 00:01:05.260 align:middle line:90% Don't worry about it. 00:01:05.260 --> 00:01:08.140 align:middle line:84% You also don't have to call me Dr. Hu or Professor Hu. 00:01:08.140 --> 00:01:10.580 align:middle line:84% I have no connection whatsoever with BBC. 00:01:10.580 --> 00:01:12.920 align:middle line:84% Any of you have seen the BBC series, Doctor Who? 00:01:12.920 --> 00:01:13.580 align:middle line:90% [LAUGHTER] 00:01:13.580 --> 00:01:14.200 align:middle line:90% That's not me. 00:01:14.200 --> 00:01:14.700 align:middle line:90% OK? 00:01:14.700 --> 00:01:15.380 align:middle line:90% That's not me. 00:01:15.380 --> 00:01:18.600 align:middle line:84% In terms of what I do, in my lab, 00:01:18.600 --> 00:01:21.340 align:middle line:84% we work with light, just like that. 00:01:21.340 --> 00:01:22.500 align:middle line:90% OK? 00:01:22.500 --> 00:01:25.540 align:middle line:84% Now, for real, what we are doing-- we work a lot 00:01:25.540 --> 00:01:27.100 align:middle line:90% on new optical materials. 00:01:27.100 --> 00:01:29.600 align:middle line:84% And amorphous materials, of course, is something I work on. 00:01:29.600 --> 00:01:32.780 align:middle line:84% That's why this class is very dear to my heart. 00:01:32.780 --> 00:01:35.720 align:middle line:84% We use these materials for all types of applications, 00:01:35.720 --> 00:01:37.660 align:middle line:84% ranging from sensing, spectroscopy, 00:01:37.660 --> 00:01:40.680 align:middle line:84% to high speed communications, imaging, you name it. 00:01:40.680 --> 00:01:43.020 align:middle line:90% OK? 00:01:43.020 --> 00:01:43.600 align:middle line:90% All right. 00:01:43.600 --> 00:01:46.020 align:middle line:90% Comes back to this class. 00:01:46.020 --> 00:01:49.580 align:middle line:84% We have a few reference texts, OK? 00:01:49.580 --> 00:01:53.620 align:middle line:84% These are not required because between the Google Books and MIT 00:01:53.620 --> 00:01:55.020 align:middle line:84% library, pretty much, you can get 00:01:55.020 --> 00:01:57.560 align:middle line:84% access for all these resources pretty much for free. 00:01:57.560 --> 00:01:58.487 align:middle line:90% OK? 00:01:58.487 --> 00:02:00.070 align:middle line:84% The main text we are going to use here 00:02:00.070 --> 00:02:04.030 align:middle line:84% is the Fundamentals of Inorganic Glasses. 00:02:04.030 --> 00:02:05.030 align:middle line:90% There are two versions-- 00:02:05.030 --> 00:02:05.950 align:middle line:90% 1994. 00:02:05.950 --> 00:02:08.210 align:middle line:84% A few years back, they actually have a newer version, 00:02:08.210 --> 00:02:10.030 align:middle line:90% an updated version. 00:02:10.030 --> 00:02:11.430 align:middle line:90% So either one is fine. 00:02:11.430 --> 00:02:12.030 align:middle line:90% All right? 00:02:12.030 --> 00:02:14.590 align:middle line:84% I've included the Google Books links there. 00:02:14.590 --> 00:02:16.270 align:middle line:84% The other text we're also going to use 00:02:16.270 --> 00:02:20.350 align:middle line:84% is the Introduction to Glass Science and Technology. 00:02:20.350 --> 00:02:21.990 align:middle line:90% There are two versions, again. 00:02:21.990 --> 00:02:25.330 align:middle line:84% I've included a link for the 2005 version. 00:02:25.330 --> 00:02:27.470 align:middle line:84% You actually get free access through MIT 00:02:27.470 --> 00:02:28.730 align:middle line:90% for the 2005 version. 00:02:28.730 --> 00:02:31.150 align:middle line:84% 2020 version-- there's no electronic version 00:02:31.150 --> 00:02:34.210 align:middle line:84% you can access freely, but you can borrow it from MIT library. 00:02:34.210 --> 00:02:35.590 align:middle line:90% OK? 00:02:35.590 --> 00:02:37.050 align:middle line:90% Another couple of texts here. 00:02:37.050 --> 00:02:38.330 align:middle line:90% This is another one here. 00:02:38.330 --> 00:02:41.830 align:middle line:84% This one is a bit older, but again, good reference. 00:02:41.830 --> 00:02:43.430 align:middle line:90% Now, the last one here-- 00:02:43.430 --> 00:02:47.470 align:middle line:84% this is a little bit of shameless self-promotion. 00:02:47.470 --> 00:02:50.330 align:middle line:84% Now, I put the text there not because I'm one of the editors. 00:02:50.330 --> 00:02:52.310 align:middle line:90% OK? 00:02:52.310 --> 00:02:53.210 align:middle line:90% A couple of reasons. 00:02:53.210 --> 00:02:55.350 align:middle line:84% One is this actually a very comprehensive text. 00:02:55.350 --> 00:02:57.610 align:middle line:84% If you want to learn one specific area 00:02:57.610 --> 00:02:59.430 align:middle line:84% in amorphous materials with greater depth, 00:02:59.430 --> 00:03:01.430 align:middle line:84% this is actually a very good reference to go to. 00:03:01.430 --> 00:03:01.930 align:middle line:90% OK? 00:03:01.930 --> 00:03:05.208 align:middle line:84% As a matter of fact, this book is so comprehensive 00:03:05.208 --> 00:03:06.250 align:middle line:90% that I actually weigh it. 00:03:06.250 --> 00:03:08.730 align:middle line:90% It weighs 8 pounds. 00:03:08.730 --> 00:03:11.362 align:middle line:84% So that's why normally, even for myself, 00:03:11.362 --> 00:03:13.070 align:middle line:84% I would just read the electronic version. 00:03:13.070 --> 00:03:15.570 align:middle line:84% You get free access through MIT library 00:03:15.570 --> 00:03:16.782 align:middle line:90% again for the entire book. 00:03:16.782 --> 00:03:17.990 align:middle line:90% You don't have to buy it, OK? 00:03:17.990 --> 00:03:21.250 align:middle line:84% In fact, I have a couple of copies of that book in my home 00:03:21.250 --> 00:03:23.570 align:middle line:84% because the publisher sent it to me. 00:03:23.570 --> 00:03:26.010 align:middle line:84% The main application-- my wife actually 00:03:26.010 --> 00:03:27.790 align:middle line:90% uses them as yoga blocks. 00:03:27.790 --> 00:03:28.730 align:middle line:90% [LAUGHTER] 00:03:28.730 --> 00:03:29.290 align:middle line:90% OK? 00:03:29.290 --> 00:03:30.750 align:middle line:90% I just read electronic version. 00:03:30.750 --> 00:03:31.490 align:middle line:90% All right. 00:03:31.490 --> 00:03:34.330 align:middle line:84% OK, so that's about the reference texts. 00:03:34.330 --> 00:03:36.630 align:middle line:84% Now, about this class-- we're going to have lectures. 00:03:36.630 --> 00:03:38.050 align:middle line:90% OK? 00:03:38.050 --> 00:03:40.530 align:middle line:84% We're also going to have a lot of in-class demos. 00:03:40.530 --> 00:03:45.455 align:middle line:84% We also have one joint session with the MIT Glass Lab. 00:03:45.455 --> 00:03:47.330 align:middle line:84% I will be talking about it, but we will have, 00:03:47.330 --> 00:03:48.930 align:middle line:90% essentially, some projects. 00:03:48.930 --> 00:03:51.390 align:middle line:84% And then we will have a few individual project meetings. 00:03:51.390 --> 00:03:53.330 align:middle line:84% There's a final project presentation. 00:03:53.330 --> 00:03:55.800 align:middle line:84% And I will talk about the pick-your-own-topic lectures. 00:03:55.800 --> 00:03:57.240 align:middle line:90% OK. 00:03:57.240 --> 00:03:58.740 align:middle line:84% I have already posted all the course 00:03:58.740 --> 00:04:01.920 align:middle line:84% materials, including the lecture slides, on the Canvas website. 00:04:01.920 --> 00:04:04.260 align:middle line:84% You will also find, essentially, templates for project 00:04:04.260 --> 00:04:06.680 align:middle line:84% proposals, project reports, everything. 00:04:06.680 --> 00:04:07.480 align:middle line:90% It's all there. 00:04:07.480 --> 00:04:09.260 align:middle line:90% OK? 00:04:09.260 --> 00:04:11.640 align:middle line:84% All right, now, let me talk a little bit about these 00:04:11.640 --> 00:04:13.340 align:middle line:90% pick-your-own-topic lectures. 00:04:13.340 --> 00:04:15.787 align:middle line:84% So normally, in a class, instructors 00:04:15.787 --> 00:04:17.079 align:middle line:90% will be giving you assignments. 00:04:17.079 --> 00:04:18.412 align:middle line:90% And then you go and complete it. 00:04:18.412 --> 00:04:21.740 align:middle line:84% I decided to do this in a little bit of an inverse manner. 00:04:21.740 --> 00:04:24.820 align:middle line:84% What I'll do is that I will leave, essentially, 00:04:24.820 --> 00:04:27.900 align:middle line:84% one lecture worth of time at the end of the semester 00:04:27.900 --> 00:04:30.460 align:middle line:84% where you actually propose a topic, like what 00:04:30.460 --> 00:04:33.340 align:middle line:84% you want to learn about amorphous materials. 00:04:33.340 --> 00:04:35.480 align:middle line:84% I will actually go ahead, do the literature survey, 00:04:35.480 --> 00:04:38.340 align:middle line:84% look at the field, come back, essentially present to you 00:04:38.340 --> 00:04:40.140 align:middle line:90% about what I found out. 00:04:40.140 --> 00:04:41.420 align:middle line:90% OK? 00:04:41.420 --> 00:04:43.473 align:middle line:84% Now, in terms of topic selection, 00:04:43.473 --> 00:04:45.140 align:middle line:84% I want you to submit your topic proposal 00:04:45.140 --> 00:04:47.960 align:middle line:84% by April 15, the same time as you submit your tax forms. 00:04:47.960 --> 00:04:49.980 align:middle line:90% So don't forget that. 00:04:49.980 --> 00:04:53.460 align:middle line:84% It should be relevant to amorphous materials, obviously. 00:04:53.460 --> 00:04:56.180 align:middle line:84% Also, think about the breadth and depth. 00:04:56.180 --> 00:04:59.440 align:middle line:84% It should be something that I can cover within about 1.5-hour 00:04:59.440 --> 00:05:00.820 align:middle line:90% lecture time. 00:05:00.820 --> 00:05:01.320 align:middle line:90% OK? 00:05:01.320 --> 00:05:03.562 align:middle line:84% And also, it should have some scientific depth, 00:05:03.562 --> 00:05:05.520 align:middle line:84% so we can dig a little bit deeper into actually 00:05:05.520 --> 00:05:07.080 align:middle line:90% what happens. 00:05:07.080 --> 00:05:09.653 align:middle line:84% Now, I just want to give you some examples. 00:05:09.653 --> 00:05:11.820 align:middle line:84% I have been trying this for the last couple of times 00:05:11.820 --> 00:05:14.120 align:middle line:90% I offered this class. 00:05:14.120 --> 00:05:17.080 align:middle line:84% Back in 2021, we actually talked about how 00:05:17.080 --> 00:05:19.680 align:middle line:84% to apply deep learning into glass science, 00:05:19.680 --> 00:05:21.360 align:middle line:90% develop new glass materials. 00:05:21.360 --> 00:05:24.340 align:middle line:84% Now, in 2023, we actually have a far more interesting topic. 00:05:24.340 --> 00:05:28.140 align:middle line:84% Any of you have seen the TV series, Squid Games? 00:05:28.140 --> 00:05:30.320 align:middle line:90% AUDIENCE: Oh, yeah. 00:05:30.320 --> 00:05:32.060 align:middle line:84% JUEJUN HU: Anyway, there's one episode. 00:05:32.060 --> 00:05:33.920 align:middle line:84% There's actually one episode where they were actually 00:05:33.920 --> 00:05:34.545 align:middle line:90% talking about-- 00:05:34.545 --> 00:05:36.280 align:middle line:90% there's actually a glass bridge. 00:05:36.280 --> 00:05:38.000 align:middle line:84% And those participants of the Squid Game 00:05:38.000 --> 00:05:39.420 align:middle line:84% have to actually go across glass bridge. 00:05:39.420 --> 00:05:40.680 align:middle line:84% And it will break, depending on whether or not 00:05:40.680 --> 00:05:42.220 align:middle line:84% the glass is strengthened or not. 00:05:42.220 --> 00:05:42.905 align:middle line:90% OK? 00:05:42.905 --> 00:05:44.280 align:middle line:84% So we actually talked about that. 00:05:44.280 --> 00:05:46.155 align:middle line:84% In the end, we actually did some calculations 00:05:46.155 --> 00:05:49.040 align:middle line:84% to show that the scene they depicted-- it 00:05:49.040 --> 00:05:51.660 align:middle line:84% would only work in the very idealized scenario. 00:05:51.660 --> 00:05:53.395 align:middle line:90% Most likely, it doesn't work. 00:05:53.395 --> 00:05:56.020 align:middle line:84% The mechanical strength contrast between the strengthened glass 00:05:56.020 --> 00:05:58.580 align:middle line:84% and unstrengthened glass cannot provide what they are doing 00:05:58.580 --> 00:05:59.980 align:middle line:90% in the TV. 00:05:59.980 --> 00:06:01.980 align:middle line:84% So anyway, if you're interested, I 00:06:01.980 --> 00:06:04.860 align:middle line:84% can send those slides to you, if you want to explore 00:06:04.860 --> 00:06:06.120 align:middle line:90% what ideas you can propose. 00:06:06.120 --> 00:06:06.480 align:middle line:90% OK? 00:06:06.480 --> 00:06:09.063 align:middle line:84% So you can start thinking about it, and just send me an email. 00:06:09.063 --> 00:06:09.860 align:middle line:90% Very simple. 00:06:09.860 --> 00:06:11.440 align:middle line:84% What's the topic you want to look at? 00:06:11.440 --> 00:06:12.580 align:middle line:90% Specific points. 00:06:12.580 --> 00:06:14.530 align:middle line:90% OK? 00:06:14.530 --> 00:06:18.860 align:middle line:84% So I'm giving you here a few project examples. 00:06:18.860 --> 00:06:21.180 align:middle line:84% So for example, this topic can really 00:06:21.180 --> 00:06:22.400 align:middle line:90% come from your everyday life. 00:06:22.400 --> 00:06:28.080 align:middle line:84% For example, I read on the news about this here, the glass box. 00:06:28.080 --> 00:06:31.260 align:middle line:84% This is actually a glass box at the Willis Tower at Chicago. 00:06:31.260 --> 00:06:33.897 align:middle line:84% So Willis Tower used to be the tallest building in the world. 00:06:33.897 --> 00:06:36.480 align:middle line:84% If you go over to Chicago, you can actually take the elevator, 00:06:36.480 --> 00:06:38.260 align:middle line:84% go all the way up to the top floor. 00:06:38.260 --> 00:06:40.880 align:middle line:84% It gives you a very nice view of the skyline of Chicago. 00:06:40.880 --> 00:06:41.780 align:middle line:90% OK? 00:06:41.780 --> 00:06:44.260 align:middle line:84% What happens there is that at one point, 00:06:44.260 --> 00:06:46.140 align:middle line:84% this glass box, which allows you to actually 00:06:46.140 --> 00:06:50.160 align:middle line:84% stand on top of the building there, actually cracked. 00:06:50.160 --> 00:06:52.270 align:middle line:90% The bottom cracked. 00:06:52.270 --> 00:06:53.470 align:middle line:90% Scary, right? 00:06:53.470 --> 00:06:57.470 align:middle line:84% So now, the question is is that really safe? 00:06:57.470 --> 00:06:59.978 align:middle line:84% So you would essentially look into a little bit about how 00:06:59.978 --> 00:07:02.520 align:middle line:84% they actually strengthen the glass, what's the mechanism, why 00:07:02.520 --> 00:07:03.887 align:middle line:90% it actually cracks. 00:07:03.887 --> 00:07:05.470 align:middle line:84% You can also perform some calculations 00:07:05.470 --> 00:07:07.870 align:middle line:84% to figure out whether or not that's still safe. 00:07:07.870 --> 00:07:08.370 align:middle line:90% OK? 00:07:08.370 --> 00:07:12.230 align:middle line:84% Second example I'm listing there-- 00:07:12.230 --> 00:07:14.710 align:middle line:84% there's a paper that actually discovered a method 00:07:14.710 --> 00:07:18.990 align:middle line:84% to essentially use the laser to engrave optical structures 00:07:18.990 --> 00:07:21.030 align:middle line:90% onto your cell phone screen. 00:07:21.030 --> 00:07:24.930 align:middle line:84% So you can potentially create photonic circuits, for example, 00:07:24.930 --> 00:07:27.390 align:middle line:84% on top of your cell phone screen so that it's not just 00:07:27.390 --> 00:07:28.570 align:middle line:90% a passive glass cover. 00:07:28.570 --> 00:07:31.230 align:middle line:84% It can carry some active optical functionalities. 00:07:31.230 --> 00:07:34.790 align:middle line:84% Now, nobody has really figured out 00:07:34.790 --> 00:07:36.493 align:middle line:84% how that technology can be applied 00:07:36.493 --> 00:07:38.410 align:middle line:84% for-- what's an interesting application there. 00:07:38.410 --> 00:07:39.993 align:middle line:84% So if you have some interesting ideas, 00:07:39.993 --> 00:07:43.070 align:middle line:84% you may as well explore it and try 00:07:43.070 --> 00:07:45.790 align:middle line:84% to prove to yourself that this is something 00:07:45.790 --> 00:07:47.030 align:middle line:90% that's potentially viable. 00:07:47.030 --> 00:07:49.310 align:middle line:90% OK? 00:07:49.310 --> 00:07:54.230 align:middle line:84% Next one here-- starting 10 years ago, 00:07:54.230 --> 00:07:56.210 align:middle line:84% there has always been a rumor that iPhone 00:07:56.210 --> 00:07:59.330 align:middle line:84% is going to use liquid metal, basically, 00:07:59.330 --> 00:08:02.310 align:middle line:84% amorphous metal, for the iPhone casing, 00:08:02.310 --> 00:08:03.850 align:middle line:90% next generation iPhone casing. 00:08:03.850 --> 00:08:05.010 align:middle line:90% OK? 00:08:05.010 --> 00:08:06.970 align:middle line:90% That has never really come true. 00:08:06.970 --> 00:08:08.130 align:middle line:90% All right. 00:08:08.130 --> 00:08:11.050 align:middle line:84% The obvious reason, actually, is that this metallic glass, 00:08:11.050 --> 00:08:13.210 align:middle line:84% like most metal, tends to be too expensive. 00:08:13.210 --> 00:08:15.970 align:middle line:84% So it's economically not feasible. 00:08:15.970 --> 00:08:17.630 align:middle line:90% So you can explore that topic. 00:08:17.630 --> 00:08:21.410 align:middle line:84% For example, do some techno-economic analysis, 00:08:21.410 --> 00:08:24.550 align:middle line:84% figuring out if it's not applicable for iPhone, 00:08:24.550 --> 00:08:26.650 align:middle line:84% maybe for iWatch, would that be feasible? 00:08:26.650 --> 00:08:29.690 align:middle line:84% Would, again, the internal mechanical property potentially 00:08:29.690 --> 00:08:32.330 align:middle line:90% outweigh the much higher cost? 00:08:32.330 --> 00:08:33.090 align:middle line:90% OK? 00:08:33.090 --> 00:08:34.809 align:middle line:84% Or are there new processing technologies that are actually 00:08:34.809 --> 00:08:36.601 align:middle line:84% getting published over the past few years-- 00:08:36.601 --> 00:08:39.570 align:middle line:84% potentially allow much lower processing cost of these metals? 00:08:39.570 --> 00:08:41.010 align:middle line:90% OK? 00:08:41.010 --> 00:08:43.130 align:middle line:90% Now, last one. 00:08:43.130 --> 00:08:45.290 align:middle line:84% We are talking about smart windows. 00:08:45.290 --> 00:08:47.877 align:middle line:84% Smart windows essentially refers to essentially window 00:08:47.877 --> 00:08:49.460 align:middle line:84% glass materials that can automatically 00:08:49.460 --> 00:08:51.640 align:middle line:84% change light transmittance as a function of wavelength. 00:08:51.640 --> 00:08:52.140 align:middle line:90% OK? 00:08:52.140 --> 00:08:54.482 align:middle line:84% And there can be different modes they can operate. 00:08:54.482 --> 00:08:56.940 align:middle line:84% For example, they can allow visible light and most infrared 00:08:56.940 --> 00:08:59.400 align:middle line:84% light to transmit through in a cold day like today. 00:08:59.400 --> 00:09:01.420 align:middle line:84% So you actually warm up the house, OK? 00:09:01.420 --> 00:09:03.820 align:middle line:84% At night, you can essentially block the visible light 00:09:03.820 --> 00:09:06.260 align:middle line:90% transmission so it's dark. 00:09:06.260 --> 00:09:07.940 align:middle line:84% And then in the summer days, you may 00:09:07.940 --> 00:09:10.220 align:middle line:84% want to still let visible light transmit through, 00:09:10.220 --> 00:09:12.820 align:middle line:84% but completely reflect infrared radiation 00:09:12.820 --> 00:09:14.215 align:middle line:90% to keep the house cool. 00:09:14.215 --> 00:09:15.840 align:middle line:84% So the technology is already available. 00:09:15.840 --> 00:09:17.673 align:middle line:84% People have already published tons of papers 00:09:17.673 --> 00:09:20.712 align:middle line:84% on this topic over the past decade. 00:09:20.712 --> 00:09:22.420 align:middle line:84% I don't think I have really actually seen 00:09:22.420 --> 00:09:25.220 align:middle line:84% the commercial products of that already. 00:09:25.220 --> 00:09:25.720 align:middle line:90% OK? 00:09:25.720 --> 00:09:27.553 align:middle line:84% Now, I have to mention that I'm actually not 00:09:27.553 --> 00:09:29.240 align:middle line:84% an expert specific to that technology, 00:09:29.240 --> 00:09:30.700 align:middle line:90% so I don't know exactly why. 00:09:30.700 --> 00:09:31.840 align:middle line:90% So you can go and find out. 00:09:31.840 --> 00:09:34.580 align:middle line:84% Is that because there's some fundamental technology barrier 00:09:34.580 --> 00:09:37.100 align:middle line:84% in terms of reliability or maybe in terms of performance 00:09:37.100 --> 00:09:38.560 align:middle line:90% that make it not viable? 00:09:38.560 --> 00:09:40.360 align:middle line:84% Or is it because of economic reasons? 00:09:40.360 --> 00:09:43.020 align:middle line:84% There's just some manufacturing issues they cannot get rid of. 00:09:43.020 --> 00:09:43.800 align:middle line:90% Open topic, OK? 00:09:43.800 --> 00:09:46.857 align:middle line:84% So that's why I hope that through this project, 00:09:46.857 --> 00:09:48.940 align:middle line:84% you can gain some new insights about what happens. 00:09:48.940 --> 00:09:50.240 align:middle line:90% OK? 00:09:50.240 --> 00:09:53.820 align:middle line:84% Some more concrete examples about previous years' students, 00:09:53.820 --> 00:09:55.000 align:middle line:90% what they have done-- 00:09:55.000 --> 00:09:57.000 align:middle line:84% in the project proposal you're going to see, 00:09:57.000 --> 00:09:58.570 align:middle line:84% the example I put there, there are 00:09:58.570 --> 00:10:00.320 align:middle line:84% students looking into essentially modeling 00:10:00.320 --> 00:10:02.620 align:middle line:84% of the, essentially, breakage behavior of glasses. 00:10:02.620 --> 00:10:04.120 align:middle line:90% OK? 00:10:04.120 --> 00:10:07.160 align:middle line:84% Last year, one student actually used the breaker space 00:10:07.160 --> 00:10:10.860 align:middle line:84% to actually explore metallic nanoparticle precipitation 00:10:10.860 --> 00:10:12.480 align:middle line:84% when you're processing color glasses. 00:10:12.480 --> 00:10:13.897 align:middle line:84% There's actually a color mechanism 00:10:13.897 --> 00:10:16.080 align:middle line:84% for all of these color glasses, OK? 00:10:16.080 --> 00:10:19.080 align:middle line:84% People are also looking to essentially 3D printing of sugar 00:10:19.080 --> 00:10:21.753 align:middle line:90% glass, candy, hard candy. 00:10:21.753 --> 00:10:23.420 align:middle line:84% Hard candy is basically a kind of glass. 00:10:23.420 --> 00:10:23.800 align:middle line:90% OK? 00:10:23.800 --> 00:10:25.967 align:middle line:84% You can actually use a 3D printer to print all kinds 00:10:25.967 --> 00:10:26.660 align:middle line:90% of funny shapes. 00:10:26.660 --> 00:10:28.360 align:middle line:84% So they actually look into actually putting together a 3D 00:10:28.360 --> 00:10:28.860 align:middle line:90% printer. 00:10:28.860 --> 00:10:32.812 align:middle line:84% So there are lots of different things we can do, but as I said, 00:10:32.812 --> 00:10:34.520 align:middle line:84% when you have a project idea, we probably 00:10:34.520 --> 00:10:37.320 align:middle line:84% want to meet and discuss so we can actually 00:10:37.320 --> 00:10:39.840 align:middle line:84% make sure it's the right scope that you can complete 00:10:39.840 --> 00:10:43.000 align:middle line:84% within a semester while you also gain some new insights 00:10:43.000 --> 00:10:44.920 align:middle line:90% and have some fun. 00:10:44.920 --> 00:10:46.180 align:middle line:90% OK? 00:10:46.180 --> 00:10:48.740 align:middle line:90% Any questions about this? 00:10:48.740 --> 00:10:50.320 align:middle line:90% All right. 00:10:50.320 --> 00:10:50.820 align:middle line:90% No. 00:10:50.820 --> 00:10:52.020 align:middle line:84% Of course, I also want to mention 00:10:52.020 --> 00:10:53.820 align:middle line:84% that if you want to propose a project that actually involves 00:10:53.820 --> 00:10:56.200 align:middle line:84% some experiments, we'll cover all expenses for you. 00:10:56.200 --> 00:10:57.700 align:middle line:90% OK? 00:10:57.700 --> 00:11:00.980 align:middle line:84% There are lots of facilities you can get access to 00:11:00.980 --> 00:11:02.160 align:middle line:90% at the Breaker Space. 00:11:02.160 --> 00:11:06.020 align:middle line:84% I'm more than happy to connect you with Justin or Professor 00:11:06.020 --> 00:11:08.060 align:middle line:84% Grossman so that you have access to this space 00:11:08.060 --> 00:11:09.700 align:middle line:90% if you don't already have. 00:11:09.700 --> 00:11:11.500 align:middle line:84% If you need some assistance, potentially, I 00:11:11.500 --> 00:11:13.520 align:middle line:84% can also try to connect you, for example, 00:11:13.520 --> 00:11:14.860 align:middle line:84% with some experimental facilities on campus 00:11:14.860 --> 00:11:17.200 align:middle line:84% if you need to gain access to a specific piece of equipment. 00:11:17.200 --> 00:11:19.900 align:middle line:84% That's why I want to meet with you and discuss about the scope, 00:11:19.900 --> 00:11:23.180 align:middle line:84% ensure that I can be as helpful as possible. 00:11:23.180 --> 00:11:23.680 align:middle line:90% All right. 00:11:23.680 --> 00:11:25.878 align:middle line:84% So now, let's talk about amorphous materials. 00:11:25.878 --> 00:11:28.420 align:middle line:84% Now, you're also going to hear about this, another term here, 00:11:28.420 --> 00:11:29.420 align:middle line:90% glass. 00:11:29.420 --> 00:11:31.460 align:middle line:84% In fact, lots of people use glass 00:11:31.460 --> 00:11:33.980 align:middle line:84% and amorphous solid or amorphous materials pretty much 00:11:33.980 --> 00:11:34.900 align:middle line:90% synonymously. 00:11:34.900 --> 00:11:36.260 align:middle line:90% They're not exactly the same. 00:11:36.260 --> 00:11:36.860 align:middle line:90% OK? 00:11:36.860 --> 00:11:38.443 align:middle line:84% What I'm showing you here is basically 00:11:38.443 --> 00:11:42.140 align:middle line:84% a diagram that shows you how these different materials fall 00:11:42.140 --> 00:11:43.440 align:middle line:90% into different categories. 00:11:43.440 --> 00:11:44.670 align:middle line:90% OK? 00:11:44.670 --> 00:11:47.230 align:middle line:84% But before I give you a more scientifically 00:11:47.230 --> 00:11:51.390 align:middle line:84% rigorous definition of amorphous solids or glass, 00:11:51.390 --> 00:11:53.510 align:middle line:84% let's start with some descriptive terms. 00:11:53.510 --> 00:11:54.310 align:middle line:90% OK? 00:11:54.310 --> 00:12:00.790 align:middle line:84% So now, you can tell me some descriptive terms 00:12:00.790 --> 00:12:04.930 align:middle line:84% that you think should be associated with glass materials. 00:12:04.930 --> 00:12:05.710 align:middle line:90% OK? 00:12:05.710 --> 00:12:08.130 align:middle line:84% So for example, we can start with mechanical properties. 00:12:08.130 --> 00:12:11.290 align:middle line:84% What do you think is the typical mechanical property of glass? 00:12:11.290 --> 00:12:11.790 align:middle line:90% Yes. 00:12:11.790 --> 00:12:12.710 align:middle line:90% AUDIENCE: Brittle. 00:12:12.710 --> 00:12:14.590 align:middle line:90% JUEJUN HU: Very good. 00:12:14.590 --> 00:12:16.830 align:middle line:90% Brittle. 00:12:16.830 --> 00:12:17.650 align:middle line:90% Anything else? 00:12:17.650 --> 00:12:20.830 align:middle line:90% 00:12:20.830 --> 00:12:22.970 align:middle line:90% [LAUGHS] It is brittle. 00:12:22.970 --> 00:12:24.470 align:middle line:84% Everybody think about it, all right? 00:12:24.470 --> 00:12:26.490 align:middle line:84% Maybe let's move away from mechanical properties. 00:12:26.490 --> 00:12:28.282 align:middle line:84% Let's think about maybe optical properties. 00:12:28.282 --> 00:12:30.710 align:middle line:90% 00:12:30.710 --> 00:12:32.750 align:middle line:84% AUDIENCE: It can vary from clear to opaque. 00:12:32.750 --> 00:12:33.750 align:middle line:90% JUEJUN HU: Very good. 00:12:33.750 --> 00:12:36.630 align:middle line:90% So clear. 00:12:36.630 --> 00:12:40.230 align:middle line:90% It can be opaque. 00:12:40.230 --> 00:12:41.790 align:middle line:90% OK. 00:12:41.790 --> 00:12:43.030 align:middle line:90% Electrical properties? 00:12:43.030 --> 00:12:47.610 align:middle line:90% 00:12:47.610 --> 00:12:48.890 align:middle line:90% AUDIENCE: Mostly insulating. 00:12:48.890 --> 00:12:49.765 align:middle line:90% JUEJUN HU: Very good. 00:12:49.765 --> 00:12:52.730 align:middle line:90% 00:12:52.730 --> 00:12:55.590 align:middle line:90% So insulating. 00:12:55.590 --> 00:12:56.090 align:middle line:90% Let's see. 00:12:56.090 --> 00:12:58.770 align:middle line:90% What else? 00:12:58.770 --> 00:13:01.970 align:middle line:90% Chemical properties. 00:13:01.970 --> 00:13:03.130 align:middle line:90% Reactive? 00:13:03.130 --> 00:13:03.783 align:middle line:90% Is it-- 00:13:03.783 --> 00:13:04.450 align:middle line:90% AUDIENCE: Inert. 00:13:04.450 --> 00:13:05.242 align:middle line:90% JUEJUN HU: --inert? 00:13:05.242 --> 00:13:07.010 align:middle line:90% OK. 00:13:07.010 --> 00:13:09.170 align:middle line:90% Soluble. 00:13:09.170 --> 00:13:10.250 align:middle line:90% Mostly inert. 00:13:10.250 --> 00:13:11.450 align:middle line:90% OK? 00:13:11.450 --> 00:13:12.070 align:middle line:90% All right. 00:13:12.070 --> 00:13:14.050 align:middle line:84% So we have a few descriptives here 00:13:14.050 --> 00:13:19.330 align:middle line:84% that capture what normally people will think glass is, OK? 00:13:19.330 --> 00:13:20.050 align:middle line:90% All right. 00:13:20.050 --> 00:13:21.258 align:middle line:90% So let's see if that's true. 00:13:21.258 --> 00:13:23.050 align:middle line:84% What I'll do next is then before I actually 00:13:23.050 --> 00:13:24.610 align:middle line:84% go into talking more specifically 00:13:24.610 --> 00:13:27.030 align:middle line:84% about the definition of glass and its properties, 00:13:27.030 --> 00:13:29.550 align:middle line:84% I'm going to show you a couple of YouTube videos. 00:13:29.550 --> 00:13:31.050 align:middle line:90% OK? 00:13:31.050 --> 00:13:33.850 align:middle line:84% So this YouTube video's from Corning. 00:13:33.850 --> 00:13:36.550 align:middle line:84% Disclaimer-- I do not own any stock of Corning, 00:13:36.550 --> 00:13:38.710 align:middle line:84% nor do I have any significant financial interest, 00:13:38.710 --> 00:13:40.500 align:middle line:84% but it's a premium glass company. 00:13:40.500 --> 00:13:43.300 align:middle line:84% And of course, lots of relevant glass technology 00:13:43.300 --> 00:13:44.220 align:middle line:90% comes from Corning. 00:13:44.220 --> 00:13:45.132 align:middle line:90% [VIDEO PLAYBACK] 00:13:45.132 --> 00:13:46.500 align:middle line:90% [MUSIC PLAYING] 00:13:46.500 --> 00:13:47.300 align:middle line:90% - Pop quiz. 00:13:47.300 --> 00:13:49.940 align:middle line:84% If you were able to look back on the present from deep 00:13:49.940 --> 00:13:53.540 align:middle line:84% in the future, what age would you say we're living in? 00:13:53.540 --> 00:13:55.260 align:middle line:90% - Is this a trick question? 00:13:55.260 --> 00:13:57.520 align:middle line:84% I mean, I want to say Information Age, 00:13:57.520 --> 00:13:59.420 align:middle line:90% but it seems too obvious. 00:13:59.420 --> 00:14:00.865 align:middle line:90% Can I say more than one age? 00:14:00.865 --> 00:14:02.740 align:middle line:84% - Yeah, I think it is safe to say that we are 00:14:02.740 --> 00:14:05.160 align:middle line:90% living in more than one age. 00:14:05.160 --> 00:14:06.420 align:middle line:90% [BLOOP] 00:14:06.420 --> 00:14:08.140 align:middle line:84% From the beginning of humanity, we've 00:14:08.140 --> 00:14:10.900 align:middle line:84% seen prevailing technologies marked with milestones-- 00:14:10.900 --> 00:14:14.460 align:middle line:84% the Stone Age, the Bronze Age, the Iron Age-- all occurring 00:14:14.460 --> 00:14:16.420 align:middle line:90% many thousands of years ago. 00:14:16.420 --> 00:14:19.600 align:middle line:84% Man's mastery of these materials has defined us, 00:14:19.600 --> 00:14:22.020 align:middle line:84% but by that metric, the last couple of hundred years 00:14:22.020 --> 00:14:26.180 align:middle line:84% have seen a flurry of ages-- the Steam Age, the Industrial 00:14:26.180 --> 00:14:29.620 align:middle line:84% Age, the Atomic Age, the Television Age, the Space 00:14:29.620 --> 00:14:31.400 align:middle line:90% Age, to name but a few. 00:14:31.400 --> 00:14:32.700 align:middle line:90% [RADIO CHATTER] 00:14:32.700 --> 00:14:35.660 align:middle line:84% But those are not the answers I was looking for. 00:14:35.660 --> 00:14:36.580 align:middle line:90% - Is that a clue? 00:14:36.580 --> 00:14:37.920 align:middle line:90% - Yes, it is. 00:14:37.920 --> 00:14:41.780 align:middle line:84% I think that this age could be classified as the Glass Age. 00:14:41.780 --> 00:14:44.590 align:middle line:90% [MUSIC PLAYING] 00:14:44.590 --> 00:14:45.405 align:middle line:90% 00:14:45.405 --> 00:14:46.780 align:middle line:84% - That's not what I was thinking. 00:14:46.780 --> 00:14:47.600 align:middle line:90% - I know. 00:14:47.600 --> 00:14:49.180 align:middle line:84% - So how are we in the Glass Age? 00:14:49.180 --> 00:14:50.763 align:middle line:84% - Well, let me put it to you this way. 00:14:50.763 --> 00:14:54.360 align:middle line:84% Can you imagine a world without glass? 00:14:54.360 --> 00:14:55.860 align:middle line:84% - Now, I don't want a cheeky answer. 00:14:55.860 --> 00:14:57.360 align:middle line:84% I want you to really think about it. 00:14:57.360 --> 00:15:00.120 align:middle line:90% [MUSIC PLAYING] 00:15:00.120 --> 00:15:00.940 align:middle line:90% - OK, no. 00:15:00.940 --> 00:15:02.940 align:middle line:84% I can't imagine a world without glass. 00:15:02.940 --> 00:15:03.800 align:middle line:90% - Exactly. 00:15:03.800 --> 00:15:06.620 align:middle line:84% Glass is really quite extraordinary. 00:15:06.620 --> 00:15:08.560 align:middle line:84% Without it, many of our major accomplishments 00:15:08.560 --> 00:15:10.100 align:middle line:90% would never have happened. 00:15:10.100 --> 00:15:12.780 align:middle line:84% Glass has a deep and complex history. 00:15:12.780 --> 00:15:15.440 align:middle line:84% And as a material, it has properties and characteristics 00:15:15.440 --> 00:15:17.940 align:middle line:84% that we are only just beginning to understand. 00:15:17.940 --> 00:15:21.580 align:middle line:84% We look right through it and think of it one-dimensionally. 00:15:21.580 --> 00:15:24.360 align:middle line:84% Most of us think of glass as a fragile, brittle thing 00:15:24.360 --> 00:15:26.640 align:middle line:84% that, if not handled correctly, will 00:15:26.640 --> 00:15:29.240 align:middle line:90% break in a spectacular fashion. 00:15:29.240 --> 00:15:31.520 align:middle line:84% - So you're going to break that to make a point? 00:15:31.520 --> 00:15:32.480 align:middle line:90% - Indeed. 00:15:32.480 --> 00:15:33.340 align:middle line:90% - Can I help? 00:15:33.340 --> 00:15:35.764 align:middle line:90% - Yes, you can. 00:15:35.764 --> 00:15:37.210 align:middle line:90% [CRACK] 00:15:37.210 --> 00:15:38.660 align:middle line:90% 00:15:38.660 --> 00:15:39.600 align:middle line:90% And it's true. 00:15:39.600 --> 00:15:42.280 align:middle line:84% Our everyday common variety of glass is brittle, 00:15:42.280 --> 00:15:44.320 align:middle line:84% but it doesn't have to be that way. 00:15:44.320 --> 00:15:46.220 align:middle line:84% Glass has already altered our lives 00:15:46.220 --> 00:15:50.140 align:middle line:84% and is behaving in ways that is totally unexpected. 00:15:50.140 --> 00:15:51.340 align:middle line:90% - Got it. 00:15:51.340 --> 00:15:54.380 align:middle line:84% - Let's start with a history of glass. 00:15:54.380 --> 00:15:56.000 align:middle line:90% - I think I can handle that. 00:15:56.000 --> 00:15:57.380 align:middle line:90% [MUSIC PLAYING] 00:15:57.380 --> 00:15:59.180 align:middle line:84% Glass as we know it is most commonly 00:15:59.180 --> 00:16:02.620 align:middle line:84% made of silica, the primary ingredient of beach sand. 00:16:02.620 --> 00:16:05.160 align:middle line:84% Mix silica with a couple of other key ingredients, 00:16:05.160 --> 00:16:07.200 align:middle line:84% heat it all up till it melts, and bang. 00:16:07.200 --> 00:16:08.580 align:middle line:90% You've got glass. 00:16:08.580 --> 00:16:11.160 align:middle line:84% Humans have been making glass since ancient times, 00:16:11.160 --> 00:16:15.500 align:middle line:84% starting with beads, vessels, and ceremonial accoutrements. 00:16:15.500 --> 00:16:18.300 align:middle line:84% Glass-making techniques spread out from Mesopotamia, 00:16:18.300 --> 00:16:21.060 align:middle line:84% culture to culture, changing in incremental ways for much 00:16:21.060 --> 00:16:23.420 align:middle line:90% of the last 4,500 years or so. 00:16:23.420 --> 00:16:25.860 align:middle line:84% The Romans even had glass windows in their important 00:16:25.860 --> 00:16:29.500 align:middle line:84% buildings as early as the 1st century AD. 00:16:29.500 --> 00:16:31.600 align:middle line:84% Glassblowing was discovered around that time. 00:16:31.600 --> 00:16:33.860 align:middle line:84% And soon, inexpensive and ubiquitous glass 00:16:33.860 --> 00:16:36.240 align:middle line:84% became one of the hallmarks of the Roman Empire. 00:16:36.240 --> 00:16:37.190 align:middle line:90% [CHATTER] 00:16:37.190 --> 00:16:39.030 align:middle line:84% But no period has seen such growth 00:16:39.030 --> 00:16:41.050 align:middle line:84% in the development of glass technologies 00:16:41.050 --> 00:16:43.270 align:middle line:90% as in the last 150 years. 00:16:43.270 --> 00:16:45.550 align:middle line:84% We've been able to unlock the secrets of glass 00:16:45.550 --> 00:16:48.690 align:middle line:84% in ways that would have seemed like magic to our forebears. 00:16:48.690 --> 00:16:49.510 align:middle line:90% [MUSIC PLAYING] 00:16:49.510 --> 00:16:50.510 align:middle line:90% - Nice. 00:16:50.510 --> 00:16:51.130 align:middle line:90% - Thanks. 00:16:51.130 --> 00:16:54.310 align:middle line:84% - So tell me what's so special about the last 150 years. 00:16:54.310 --> 00:16:55.710 align:middle line:90% - Well, several things. 00:16:55.710 --> 00:16:59.030 align:middle line:84% In that period, technology evolved at an exponential rate. 00:16:59.030 --> 00:17:01.230 align:middle line:84% With that came tools and processes 00:17:01.230 --> 00:17:05.030 align:middle line:84% that enabled advancement across all material sciences. 00:17:05.030 --> 00:17:08.410 align:middle line:84% The leader in glass material science was, and still is, 00:17:08.410 --> 00:17:11.069 align:middle line:84% an upstate New York glass company that started out 00:17:11.069 --> 00:17:13.030 align:middle line:90% in the mid-1800s-- 00:17:13.030 --> 00:17:14.869 align:middle line:90% Corning Incorporated. 00:17:14.869 --> 00:17:17.470 align:middle line:84% One of their first products was a toughened glass lens 00:17:17.470 --> 00:17:19.190 align:middle line:84% for railroad signal lanterns that 00:17:19.190 --> 00:17:21.910 align:middle line:84% offered two radical improvements over any other lens 00:17:21.910 --> 00:17:22.990 align:middle line:90% of that time. 00:17:22.990 --> 00:17:25.170 align:middle line:84% It could be produced in a consistent color, 00:17:25.170 --> 00:17:26.950 align:middle line:84% and more importantly, it didn't break 00:17:26.950 --> 00:17:29.470 align:middle line:90% when rain hit the hot glass. 00:17:29.470 --> 00:17:31.390 align:middle line:84% This helped save lives by bringing down 00:17:31.390 --> 00:17:32.610 align:middle line:90% the number of train wrecks. 00:17:32.610 --> 00:17:37.010 align:middle line:84% But it also set a course for 160 years of innovation in glass. 00:17:37.010 --> 00:17:40.250 align:middle line:84% Of course, everybody knows about Corningware and Pyrex products, 00:17:40.250 --> 00:17:41.090 align:middle line:90% too. 00:17:41.090 --> 00:17:42.650 align:middle line:84% Those innovations came from Corning 00:17:42.650 --> 00:17:44.790 align:middle line:84% during the early part of the last century. 00:17:44.790 --> 00:17:46.790 align:middle line:84% - You know, I have tons of this in my kitchen. 00:17:46.790 --> 00:17:49.350 align:middle line:84% - Mm-hmm, but Corning no longer makes kitchenware. 00:17:49.350 --> 00:17:51.810 align:middle line:84% They've innovated way beyond that. 00:17:51.810 --> 00:17:52.910 align:middle line:90% Let's take a look. 00:17:52.910 --> 00:17:55.790 align:middle line:90% [MUSIC PLAYING] 00:17:55.790 --> 00:17:59.610 align:middle line:90% 00:17:59.610 --> 00:18:00.950 align:middle line:90% We'll start with this. 00:18:00.950 --> 00:18:02.690 align:middle line:90% - Ah, optical fiber. 00:18:02.690 --> 00:18:04.530 align:middle line:90% - Right, optical fiber. 00:18:04.530 --> 00:18:06.970 align:middle line:84% This does two things, both astonishing. 00:18:06.970 --> 00:18:08.510 align:middle line:90% The first one is this. 00:18:08.510 --> 00:18:11.310 align:middle line:90% [MUSIC PLAYING] 00:18:11.310 --> 00:18:11.810 align:middle line:90% 00:18:11.810 --> 00:18:14.530 align:middle line:84% - That right there is pure glass, 00:18:14.530 --> 00:18:18.150 align:middle line:84% a glass strand inside the cable, tightly wound around a pencil, 00:18:18.150 --> 00:18:18.650 align:middle line:90% And. 00:18:18.650 --> 00:18:20.370 align:middle line:90% Yet not breaking. 00:18:20.370 --> 00:18:23.750 align:middle line:84% When you stop and think about it, that is a mind-bender. 00:18:23.750 --> 00:18:25.250 align:middle line:90% OK, what's the second thing? 00:18:25.250 --> 00:18:27.590 align:middle line:84% - Well, it's the way the light moves through the glass. 00:18:27.590 --> 00:18:29.370 align:middle line:84% When the glass is bent this way, you'd 00:18:29.370 --> 00:18:32.450 align:middle line:84% expect light to leak out and get weaker and corrupt the data 00:18:32.450 --> 00:18:33.570 align:middle line:90% that it carries. 00:18:33.570 --> 00:18:34.970 align:middle line:90% But that's not happening. 00:18:34.970 --> 00:18:37.350 align:middle line:84% Nearly all the light entering this optical fiber 00:18:37.350 --> 00:18:38.910 align:middle line:90% is coming out the other end. 00:18:38.910 --> 00:18:41.330 align:middle line:90% - So it has a low attenuation? 00:18:41.330 --> 00:18:42.610 align:middle line:90% - Yeah, exactly. 00:18:42.610 --> 00:18:43.950 align:middle line:90% Very low. 00:18:43.950 --> 00:18:46.870 align:middle line:84% In the late 1960s, Corning figured out how to limit 00:18:46.870 --> 00:18:48.990 align:middle line:84% the attenuation, or loss of light, 00:18:48.990 --> 00:18:52.530 align:middle line:84% as it travels through fiber, even when that fiber is bent. 00:18:52.530 --> 00:18:53.110 align:middle line:90% - Nice. 00:18:53.110 --> 00:18:55.510 align:middle line:84% - This discovery led to the practical use of fiber 00:18:55.510 --> 00:18:58.110 align:middle line:84% as a medium for voice and data communications over great 00:18:58.110 --> 00:19:01.170 align:middle line:84% distances, ushering in an era of low-cost, 00:19:01.170 --> 00:19:03.630 align:middle line:84% high-bandwidth communications, and ultimately, 00:19:03.630 --> 00:19:05.590 align:middle line:90% the internet as we know it. 00:19:05.590 --> 00:19:06.110 align:middle line:90% - Wow. 00:19:06.110 --> 00:19:09.910 align:middle line:84% So just how much data can these optical fibers carry? 00:19:09.910 --> 00:19:11.550 align:middle line:84% - This video playing back right here 00:19:11.550 --> 00:19:15.430 align:middle line:84% is sucking in data at around 20 gigabits per second. 00:19:15.430 --> 00:19:17.650 align:middle line:90% - That is a lot of data. 00:19:17.650 --> 00:19:21.070 align:middle line:84% - Yeah, this is ultra high definition raw video, but even 00:19:21.070 --> 00:19:24.830 align:middle line:84% in this case, the optical fiber is not anywhere near capacity. 00:19:24.830 --> 00:19:29.150 align:middle line:84% The bottlenecks are here and here, not here. 00:19:29.150 --> 00:19:32.070 align:middle line:84% The practical limit of data transport over optical fiber 00:19:32.070 --> 00:19:33.200 align:middle line:90% keeps increasing. 00:19:33.200 --> 00:19:36.200 align:middle line:84% Using today's technology, it's possible to transport 00:19:36.200 --> 00:19:39.960 align:middle line:84% more than a million gigabits per second, about a petabit. 00:19:39.960 --> 00:19:44.080 align:middle line:84% That would be like downloading 17,000 high definition movies 00:19:44.080 --> 00:19:46.640 align:middle line:90% from Netflix in a single second. 00:19:46.640 --> 00:19:47.700 align:middle line:90% - That's amazing. 00:19:47.700 --> 00:19:49.440 align:middle line:90% OK, tell me about this stuff. 00:19:49.440 --> 00:19:51.980 align:middle line:84% - Well, obviously it's an optical fiber as well, 00:19:51.980 --> 00:19:54.120 align:middle line:84% but instead of sending light through one end 00:19:54.120 --> 00:19:55.880 align:middle line:84% and out the other, it emits light 00:19:55.880 --> 00:19:57.840 align:middle line:90% throughout its entire length. 00:19:57.840 --> 00:19:58.800 align:middle line:90% - Cool. 00:19:58.800 --> 00:20:00.320 align:middle line:90% What's it good for? 00:20:00.320 --> 00:20:02.760 align:middle line:90% - I have no idea. 00:20:02.760 --> 00:20:06.560 align:middle line:84% OK, so I was able to seriously bend a strand of glass. 00:20:06.560 --> 00:20:08.720 align:middle line:84% Didn't break, but what do you think 00:20:08.720 --> 00:20:12.380 align:middle line:84% is going to happen when I try to bend a pane of glass? 00:20:12.380 --> 00:20:13.000 align:middle line:90% - Uh-- 00:20:13.000 --> 00:20:14.560 align:middle line:90% - Rhetorical question. 00:20:14.560 --> 00:20:15.420 align:middle line:90% Check this out. 00:20:15.420 --> 00:20:18.420 align:middle line:90% [MUSIC PLAYING] 00:20:18.420 --> 00:20:20.920 align:middle line:90% 00:20:20.920 --> 00:20:23.920 align:middle line:90% [CRACK, SHATTERING] 00:20:23.920 --> 00:20:25.920 align:middle line:90% 00:20:25.920 --> 00:20:28.080 align:middle line:84% - That doesn't look like it went very well. 00:20:28.080 --> 00:20:30.520 align:middle line:84% - Well, that was soda lime glass, the normal stuff 00:20:30.520 --> 00:20:32.420 align:middle line:90% we see around us every day. 00:20:32.420 --> 00:20:34.240 align:middle line:90% But watch what happens next. 00:20:34.240 --> 00:20:35.200 align:middle line:90% [MUSIC PLAYING] 00:20:35.200 --> 00:20:35.700 align:middle line:90% - This? 00:20:35.700 --> 00:20:38.860 align:middle line:90% This is glass, too. 00:20:38.860 --> 00:20:44.500 align:middle line:84% It's called Willow glass, also made by Corning. 00:20:44.500 --> 00:20:45.880 align:middle line:90% And it's flexible. 00:20:45.880 --> 00:20:48.180 align:middle line:90% - No way. 00:20:48.180 --> 00:20:50.740 align:middle line:90% I cannot believe that is glass. 00:20:50.740 --> 00:20:52.060 align:middle line:90% - Well, it is. 00:20:52.060 --> 00:20:53.940 align:middle line:90% There's no trickery here. 00:20:53.940 --> 00:20:57.740 align:middle line:84% This is glass, but it's as flexible as paper. 00:20:57.740 --> 00:20:59.800 align:middle line:84% - So what kind of applications does that have? 00:20:59.800 --> 00:21:01.600 align:middle line:84% - Well, that's where it gets really cool. 00:21:01.600 --> 00:21:03.020 align:middle line:90% Check this out. 00:21:03.020 --> 00:21:03.840 align:middle line:90% - All right. 00:21:03.840 --> 00:21:07.032 align:middle line:84% This looks like a piece of stainless steel. 00:21:07.032 --> 00:21:07.740 align:middle line:90% And what is this? 00:21:07.740 --> 00:21:11.400 align:middle line:84% Willow glass bonded to one side as a scratch-resistant coating? 00:21:11.400 --> 00:21:11.900 align:middle line:90% - Yep. 00:21:11.900 --> 00:21:13.560 align:middle line:90% - OK, but tell me this. 00:21:13.560 --> 00:21:17.180 align:middle line:84% How is the Willow glass anywhere near as durable as stainless? 00:21:17.180 --> 00:21:18.940 align:middle line:90% - Well, that's a good question. 00:21:18.940 --> 00:21:19.800 align:middle line:90% Watch this. 00:21:19.800 --> 00:21:22.740 align:middle line:90% [MUSIC PLAYING] 00:21:22.740 --> 00:21:24.204 align:middle line:90% 00:21:24.204 --> 00:21:27.132 align:middle line:90% [BUZZING] 00:21:27.132 --> 00:21:29.572 align:middle line:90% 00:21:29.572 --> 00:21:32.490 align:middle line:90% [MUSIC PLAYING] 00:21:32.490 --> 00:21:32.990 align:middle line:90% 00:21:32.990 --> 00:21:34.570 align:middle line:90% - That is amazing. 00:21:34.570 --> 00:21:38.550 align:middle line:84% I cannot believe that the blade did not shatter the glass. 00:21:38.550 --> 00:21:39.510 align:middle line:90% - It didn't. 00:21:39.510 --> 00:21:41.170 align:middle line:90% And that's just half the story. 00:21:41.170 --> 00:21:43.930 align:middle line:90% [MUSIC PLAYING] 00:21:43.930 --> 00:21:46.190 align:middle line:90% 00:21:46.190 --> 00:21:47.870 align:middle line:84% - All right, so what are we doing? 00:21:47.870 --> 00:21:48.690 align:middle line:90% - Give me that. 00:21:48.690 --> 00:21:49.270 align:middle line:90% - OK. 00:21:49.270 --> 00:21:50.210 align:middle line:90% - Take this. 00:21:50.210 --> 00:21:51.950 align:middle line:90% [MUSIC PLAYING] 00:21:51.950 --> 00:21:52.893 align:middle line:90% - This is heavy, man. 00:21:52.893 --> 00:21:54.310 align:middle line:84% What do you want me to do with it? 00:21:54.310 --> 00:21:57.310 align:middle line:84% - I want you to drop that right on that piece of stainless steel 00:21:57.310 --> 00:21:59.110 align:middle line:90% with the Willow glass on it. 00:21:59.110 --> 00:21:59.710 align:middle line:90% - Seriously? 00:21:59.710 --> 00:22:00.830 align:middle line:90% - Let's see what happens. 00:22:00.830 --> 00:22:03.030 align:middle line:90% - Here we go. 00:22:03.030 --> 00:22:05.744 align:middle line:90% 3, 2, 1. 00:22:05.744 --> 00:22:07.106 align:middle line:90% [PING] 00:22:07.106 --> 00:22:08.470 align:middle line:90% 00:22:08.470 --> 00:22:09.610 align:middle line:90% No way. 00:22:09.610 --> 00:22:11.590 align:middle line:90% [MUSIC PLAYING] 00:22:11.590 --> 00:22:14.010 align:middle line:84% - It dented it, but it didn't break the glass. 00:22:14.010 --> 00:22:15.370 align:middle line:90% - That is insane. 00:22:15.370 --> 00:22:18.590 align:middle line:84% - And you can attach this to just about any solid surface. 00:22:18.590 --> 00:22:21.910 align:middle line:84% - Bendy, flexible, durable glass-- impressive, 00:22:21.910 --> 00:22:24.630 align:middle line:84% and characteristics you wouldn't normally associate with glass, 00:22:24.630 --> 00:22:25.130 align:middle line:90% right? 00:22:25.130 --> 00:22:26.630 align:middle line:90% - Right. 00:22:26.630 --> 00:22:28.550 align:middle line:84% I like this new Glass Age we're in. 00:22:28.550 --> 00:22:31.535 align:middle line:90% [MUSIC PLAYING] 00:22:31.535 --> 00:22:42.490 align:middle line:90% 00:22:42.490 --> 00:22:43.750 align:middle line:90% - Let's switch gears. 00:22:43.750 --> 00:22:45.642 align:middle line:84% Your smartphone-- you hold it in your hand, 00:22:45.642 --> 00:22:48.350 align:middle line:84% you put it to your ear, you keep it in your pocket or your purse. 00:22:48.350 --> 00:22:50.130 align:middle line:84% It's a great everyday use of glass 00:22:50.130 --> 00:22:51.810 align:middle line:90% that you might not think about. 00:22:51.810 --> 00:22:52.790 align:middle line:90% - Till it breaks. 00:22:52.790 --> 00:22:53.630 align:middle line:90% - Until it breaks. 00:22:53.630 --> 00:22:56.182 align:middle line:84% I myself have shattered over a dozen of these, 00:22:56.182 --> 00:22:57.890 align:middle line:84% but you might have noticed over the years 00:22:57.890 --> 00:23:00.610 align:middle line:84% that the display on your phone has been getting harder 00:23:00.610 --> 00:23:01.570 align:middle line:90% to break. 00:23:01.570 --> 00:23:05.200 align:middle line:90% Let's go back a few years. 00:23:05.200 --> 00:23:06.660 align:middle line:90% [JINGLING] 00:23:06.660 --> 00:23:07.160 align:middle line:90% 00:23:07.160 --> 00:23:09.130 align:middle line:90% [SCRAPING] 00:23:09.130 --> 00:23:12.150 align:middle line:84% If you've done that to your standard 2008 phone, 00:23:12.150 --> 00:23:13.510 align:middle line:90% that's what would have happened. 00:23:13.510 --> 00:23:14.155 align:middle line:90% - Not pretty. 00:23:14.155 --> 00:23:14.655 align:middle line:90% - No. 00:23:14.655 --> 00:23:16.030 align:middle line:84% And that could easily happen just 00:23:16.030 --> 00:23:18.350 align:middle line:84% by keeping your keys and your phone in the same pocket. 00:23:18.350 --> 00:23:20.530 align:middle line:84% And if you then dropped that phone, 00:23:20.530 --> 00:23:23.810 align:middle line:84% well, the probability of the phone breaking was high. 00:23:23.810 --> 00:23:24.610 align:middle line:90% - How high? 00:23:24.610 --> 00:23:25.430 align:middle line:90% - Very high. 00:23:25.430 --> 00:23:27.588 align:middle line:90% Let me show you. 00:23:27.588 --> 00:23:29.130 align:middle line:84% - Aren't you going to drop the phone? 00:23:29.130 --> 00:23:30.270 align:middle line:90% - Well, sort of. 00:23:30.270 --> 00:23:31.687 align:middle line:84% Instead of dropping the phone, I'm 00:23:31.687 --> 00:23:34.090 align:middle line:84% going to drop something on the phone-- this steel ball. 00:23:34.090 --> 00:23:35.230 align:middle line:90% - For consistency's sake? 00:23:35.230 --> 00:23:35.870 align:middle line:90% - Exactly. 00:23:35.870 --> 00:23:39.310 align:middle line:84% In this way, my phone drops exactly the same way 00:23:39.310 --> 00:23:40.870 align:middle line:90% every single time. 00:23:40.870 --> 00:23:41.690 align:middle line:90% Here we go. 00:23:41.690 --> 00:23:43.310 align:middle line:90% 3, 2, 1. 00:23:43.310 --> 00:23:45.218 align:middle line:90% [THUD] 00:23:45.218 --> 00:23:45.718 align:middle line:90% 00:23:45.718 --> 00:23:48.110 align:middle line:90% [MUSIC PLAYING] 00:23:48.110 --> 00:23:50.150 align:middle line:90% Oh. 00:23:50.150 --> 00:23:52.490 align:middle line:84% - I've seen you do that so many times in real life. 00:23:52.490 --> 00:23:56.150 align:middle line:84% - [SIGHS] Me, too, but that was then. 00:23:56.150 --> 00:23:57.250 align:middle line:90% This is now. 00:23:57.250 --> 00:23:59.285 align:middle line:84% Thanks to Corning, we have Gorilla Glass. 00:23:59.285 --> 00:24:01.410 align:middle line:84% - I'm pretty sure that's what I've got on my phone. 00:24:01.410 --> 00:24:03.130 align:middle line:84% - And it's on this phone as well. 00:24:03.130 --> 00:24:05.490 align:middle line:84% I'm about to do the same test a second time. 00:24:05.490 --> 00:24:06.370 align:middle line:90% Check this out. 00:24:06.370 --> 00:24:08.230 align:middle line:90% [MUSIC PLAYING] 00:24:08.230 --> 00:24:09.190 align:middle line:90% - No scratch. 00:24:09.190 --> 00:24:10.250 align:middle line:90% - Not at all. 00:24:10.250 --> 00:24:13.670 align:middle line:90% Now, same drop test. 00:24:13.670 --> 00:24:14.430 align:middle line:90% Ready? 00:24:14.430 --> 00:24:14.930 align:middle line:90% - Yeah. 00:24:14.930 --> 00:24:17.090 align:middle line:90% - 3, 2, 1. 00:24:17.090 --> 00:24:19.070 align:middle line:90% [THUD, CLATTERING] 00:24:19.070 --> 00:24:23.030 align:middle line:90% 00:24:23.030 --> 00:24:23.790 align:middle line:90% - Wow. 00:24:23.790 --> 00:24:25.617 align:middle line:84% What a difference a few years can make. 00:24:25.617 --> 00:24:28.200 align:middle line:84% - Actually, Corning came up with this method for strengthening 00:24:28.200 --> 00:24:29.680 align:middle line:90% glass long ago. 00:24:29.680 --> 00:24:32.200 align:middle line:84% Gorilla Glass evolved from that process and today 00:24:32.200 --> 00:24:35.400 align:middle line:84% is found on all the best small devices, like this. 00:24:35.400 --> 00:24:38.400 align:middle line:84% It's beginning to find its way onto larger-format displays, 00:24:38.400 --> 00:24:38.900 align:middle line:90% too. 00:24:38.900 --> 00:24:41.600 align:middle line:90% [MUSIC PLAYING] 00:24:41.600 --> 00:24:43.620 align:middle line:90% - Now, it's not unbreakable. 00:24:43.620 --> 00:24:46.080 align:middle line:84% If you set out to break it, you will, 00:24:46.080 --> 00:24:49.100 align:middle line:84% but as Corning figures out ways to unlock more secrets of glass, 00:24:49.100 --> 00:24:51.340 align:middle line:84% it will continue to get more resilient. 00:24:51.340 --> 00:24:54.560 align:middle line:84% It may even get to a state where devices such as these 00:24:54.560 --> 00:24:56.400 align:middle line:90% simply don't break anymore. 00:24:56.400 --> 00:24:58.080 align:middle line:84% Oh, and by the way, Corning has just 00:24:58.080 --> 00:25:01.580 align:middle line:84% come out with a new and improved version of Gorilla Glass. 00:25:01.580 --> 00:25:02.080 align:middle line:90% - Really? 00:25:02.080 --> 00:25:02.720 align:middle line:90% - Yeah. 00:25:02.720 --> 00:25:05.080 align:middle line:90% Let's go deeper. 00:25:05.080 --> 00:25:06.400 align:middle line:90% Watch this. 00:25:06.400 --> 00:25:07.360 align:middle line:90% - Hot stuff. 00:25:07.360 --> 00:25:08.120 align:middle line:90% - Yeah. 00:25:08.120 --> 00:25:11.300 align:middle line:84% This hot stuff is your basic, everyday, soda lime glass. 00:25:11.300 --> 00:25:13.000 align:middle line:84% There's nothing remarkable about it 00:25:13.000 --> 00:25:15.880 align:middle line:84% except that it's white-hot and molten. 00:25:15.880 --> 00:25:16.420 align:middle line:90% There we go. 00:25:16.420 --> 00:25:18.660 align:middle line:84% And I'm going to drop it in cold water. 00:25:18.660 --> 00:25:20.680 align:middle line:84% It's called a Prince Rupert drop. 00:25:20.680 --> 00:25:21.780 align:middle line:90% - Who's Prince Rupert? 00:25:21.780 --> 00:25:23.700 align:middle line:90% - Some Bavarian from the 1600s. 00:25:23.700 --> 00:25:24.720 align:middle line:90% He came up with this. 00:25:24.720 --> 00:25:27.720 align:middle line:90% [MUSIC PLAYING] 00:25:27.720 --> 00:25:31.220 align:middle line:90% 00:25:31.220 --> 00:25:34.740 align:middle line:84% OK, so there's a few things going on here. 00:25:34.740 --> 00:25:38.800 align:middle line:84% The cold water rapidly cools the exterior surface of the glass, 00:25:38.800 --> 00:25:40.940 align:middle line:90% hardening it almost immediately. 00:25:40.940 --> 00:25:44.440 align:middle line:84% The interior, still molten, cools more slowly. 00:25:44.440 --> 00:25:47.540 align:middle line:84% As it cools, it contracts and attempts to pull the surface 00:25:47.540 --> 00:25:50.940 align:middle line:84% in with it, but it can't-- well, not very much. 00:25:50.940 --> 00:25:52.640 align:middle line:84% The surface has already hardened, 00:25:52.640 --> 00:25:55.580 align:middle line:84% so it gets pulled in only a little, compressing it, 00:25:55.580 --> 00:25:59.140 align:middle line:84% while also creating an internal layer that remains forever 00:25:59.140 --> 00:26:00.280 align:middle line:90% under tension. 00:26:00.280 --> 00:26:01.220 align:middle line:90% [WHISTLING] 00:26:01.220 --> 00:26:02.980 align:middle line:84% It is this action that gives the glass 00:26:02.980 --> 00:26:05.000 align:middle line:90% its uncharacteristic strength. 00:26:05.000 --> 00:26:07.240 align:middle line:90% We call it compressive strength. 00:26:07.240 --> 00:26:08.445 align:middle line:90% - Hmm. 00:26:08.445 --> 00:26:09.820 align:middle line:84% It sounds like the same principle 00:26:09.820 --> 00:26:13.120 align:middle line:84% as how an arch provides strength in structural engineering. 00:26:13.120 --> 00:26:14.128 align:middle line:90% - Yes, kind of. 00:26:14.128 --> 00:26:15.920 align:middle line:84% Now, Jamie, I'm going to ask for your help. 00:26:15.920 --> 00:26:18.960 align:middle line:84% We're going to attempt to destroy this Prince Rupert drop. 00:26:18.960 --> 00:26:22.060 align:middle line:84% I just want you to tip that hammer past its center point. 00:26:22.060 --> 00:26:23.430 align:middle line:90% Go ahead. 00:26:23.430 --> 00:26:24.879 align:middle line:90% [CLUNK] 00:26:24.879 --> 00:26:25.845 align:middle line:90% 00:26:25.845 --> 00:26:28.743 align:middle line:90% [MUSIC PLAYING] 00:26:28.743 --> 00:26:29.710 align:middle line:90% 00:26:29.710 --> 00:26:31.570 align:middle line:84% - I feel like we've been swindled. 00:26:31.570 --> 00:26:32.650 align:middle line:90% - Swindled not. 00:26:32.650 --> 00:26:36.970 align:middle line:84% We have just experienced the power of compressive strength. 00:26:36.970 --> 00:26:39.010 align:middle line:84% It does, however, have an Achilles heel. 00:26:39.010 --> 00:26:42.470 align:middle line:84% Take those nippers right there, and nip 00:26:42.470 --> 00:26:45.972 align:middle line:84% the backside of the tail of this Prince Rupert drop, 00:26:45.972 --> 00:26:46.930 align:middle line:90% and watch what happens. 00:26:46.930 --> 00:26:47.370 align:middle line:90% Wait, wait, wait. 00:26:47.370 --> 00:26:48.470 align:middle line:90% Cue the high-speed camera. 00:26:48.470 --> 00:26:49.530 align:middle line:90% OK, here we go. 00:26:49.530 --> 00:26:52.760 align:middle line:90% 00:26:52.760 --> 00:26:53.670 align:middle line:90% [SNAP] 00:26:53.670 --> 00:26:55.105 align:middle line:90% Whoa! 00:26:55.105 --> 00:26:58.075 align:middle line:90% [SNAP] 00:26:58.075 --> 00:27:00.055 align:middle line:90% 00:27:00.055 --> 00:27:02.035 align:middle line:90% [LAUGHS] 00:27:02.035 --> 00:27:03.030 align:middle line:90% 00:27:03.030 --> 00:27:07.070 align:middle line:84% That was even cooler than I thought it would be. 00:27:07.070 --> 00:27:09.630 align:middle line:84% That is what happens when you release the stress 00:27:09.630 --> 00:27:11.370 align:middle line:90% in compressive strength glass. 00:27:11.370 --> 00:27:12.710 align:middle line:90% The whole thing shatters. 00:27:12.710 --> 00:27:13.810 align:middle line:90% - Spectacularly. 00:27:13.810 --> 00:27:15.930 align:middle line:84% - Yes, well, at least in that example, it was. 00:27:15.930 --> 00:27:17.710 align:middle line:84% That's because the stress was so great 00:27:17.710 --> 00:27:20.618 align:middle line:84% between the outer compressive layer and the inner tension 00:27:20.618 --> 00:27:21.410 align:middle line:90% inattention layer-- 00:27:21.410 --> 00:27:24.650 align:middle line:84% - --that when released, it was a catastrophic result. 00:27:24.650 --> 00:27:27.510 align:middle line:90% [SNAP] 00:27:27.510 --> 00:27:28.010 align:middle line:90% 00:27:28.010 --> 00:27:30.890 align:middle line:90% [MUSIC PLAYING] 00:27:30.890 --> 00:27:33.070 align:middle line:90% - This is Gorilla Glass. 00:27:33.070 --> 00:27:35.930 align:middle line:84% It has been refined over time, but like all Gorilla Glass 00:27:35.930 --> 00:27:39.650 align:middle line:84% variants that came before it, it is compressive strength glass, 00:27:39.650 --> 00:27:42.210 align:middle line:84% but it's not made in the same way as we just demonstrated, 00:27:42.210 --> 00:27:43.470 align:middle line:90% the rapid cooling method. 00:27:43.470 --> 00:27:43.970 align:middle line:90% No. 00:27:43.970 --> 00:27:47.050 align:middle line:84% Instead, Corning uses an ion exchange process. 00:27:47.050 --> 00:27:49.410 align:middle line:84% To break it down simply, the surface ion 00:27:49.410 --> 00:27:51.930 align:middle line:84% particles that naturally form during the manufacture 00:27:51.930 --> 00:27:54.790 align:middle line:84% are replaced with larger ion particles. 00:27:54.790 --> 00:27:57.010 align:middle line:84% Once exchanged, the larger ion particles 00:27:57.010 --> 00:27:59.130 align:middle line:84% create the same sort of inward pressure 00:27:59.130 --> 00:28:01.270 align:middle line:84% that we see on the Prince Rupert drop. 00:28:01.270 --> 00:28:04.810 align:middle line:84% And with this method, they are able to control and manage 00:28:04.810 --> 00:28:06.408 align:middle line:90% the resulting tension. 00:28:06.408 --> 00:28:08.450 align:middle line:84% - I think what you're saying with this process is 00:28:08.450 --> 00:28:10.410 align:middle line:84% that they're able to tune strength in the glass 00:28:10.410 --> 00:28:13.843 align:middle line:84% by dialing in the right balance between compression and tension? 00:28:13.843 --> 00:28:15.510 align:middle line:84% - Yeah, that's a great way of saying it. 00:28:15.510 --> 00:28:18.010 align:middle line:84% That, and also, by adding in a few other tricks 00:28:18.010 --> 00:28:20.690 align:middle line:84% that change the molecular structure of the glass. 00:28:20.690 --> 00:28:24.470 align:middle line:84% Corning is steadily moving forward towards the Holy Grail. 00:28:24.470 --> 00:28:27.450 align:middle line:84% - Thin, unbreakable glass for our mobile devices? 00:28:27.450 --> 00:28:31.530 align:middle line:84% - Well, maybe not unbreakable, but yes, thin and very tough. 00:28:31.530 --> 00:28:34.270 align:middle line:84% And by the way, the applications for this tough glass 00:28:34.270 --> 00:28:36.750 align:middle line:90% go well beyond mobile devices. 00:28:36.750 --> 00:28:37.730 align:middle line:90% Let's go over this way. 00:28:37.730 --> 00:28:39.150 align:middle line:90% [MUSIC PLAYING] 00:28:39.150 --> 00:28:41.630 align:middle line:84% - Behold, the common automobile windshield 00:28:41.630 --> 00:28:43.870 align:middle line:84% made from regular soda lime glass. 00:28:43.870 --> 00:28:46.470 align:middle line:84% It's quite strong because it's very thick, 00:28:46.470 --> 00:28:48.430 align:middle line:84% and it's laminated, which means it's 00:28:48.430 --> 00:28:50.870 align:middle line:84% two pieces of glass bonded together using 00:28:50.870 --> 00:28:52.170 align:middle line:90% resin in the middle. 00:28:52.170 --> 00:28:53.970 align:middle line:90% And the resin does two things. 00:28:53.970 --> 00:28:56.950 align:middle line:84% It gives it added strength, and it holds the glass together 00:28:56.950 --> 00:28:57.690 align:middle line:90% on impact. 00:28:57.690 --> 00:29:00.490 align:middle line:84% You've probably seen broken windshields before. 00:29:00.490 --> 00:29:03.990 align:middle line:84% Lots of crazy cracked glass, but still mostly held together 00:29:03.990 --> 00:29:05.350 align:middle line:90% in the shape of a windshield. 00:29:05.350 --> 00:29:06.290 align:middle line:90% - Like this. 00:29:06.290 --> 00:29:08.790 align:middle line:90% [CRUNCHING] 00:29:08.790 --> 00:29:09.910 align:middle line:90% That's pretty cool. 00:29:09.910 --> 00:29:11.130 align:middle line:90% - Yes, it is. 00:29:11.130 --> 00:29:14.270 align:middle line:84% Windshields have been made of laminated glass for the last 100 00:29:14.270 --> 00:29:16.250 align:middle line:84% years, and they've served us well. 00:29:16.250 --> 00:29:18.210 align:middle line:90% But there is a big drawback. 00:29:18.210 --> 00:29:19.960 align:middle line:84% - I think I know what you're going to say. 00:29:19.960 --> 00:29:20.860 align:middle line:90% It's heavy. 00:29:20.860 --> 00:29:22.820 align:middle line:90% - Yes, very heavy. 00:29:22.820 --> 00:29:25.200 align:middle line:84% And as we strive for more energy-efficient cars 00:29:25.200 --> 00:29:26.960 align:middle line:84% and trucks, the weight of all that glass 00:29:26.960 --> 00:29:28.660 align:middle line:90% can be a bit of a problem. 00:29:28.660 --> 00:29:31.320 align:middle line:84% - I have a feeling you're about to show an alternative. 00:29:31.320 --> 00:29:32.080 align:middle line:90% - Yes. 00:29:32.080 --> 00:29:33.060 align:middle line:90% Take a look at this. 00:29:33.060 --> 00:29:35.910 align:middle line:90% [MUSIC PLAYING] 00:29:35.910 --> 00:29:37.980 align:middle line:84% Now, this is also a laminate windshield, 00:29:37.980 --> 00:29:40.100 align:middle line:84% but it's not one you'd find in production. 00:29:40.100 --> 00:29:42.640 align:middle line:84% It's experimental, which is great because we're 00:29:42.640 --> 00:29:44.260 align:middle line:90% going to experiment with it. 00:29:44.260 --> 00:29:47.683 align:middle line:84% It has regular soda lime glass on its outside surface and resin 00:29:47.683 --> 00:29:49.100 align:middle line:84% in the center, like the other one, 00:29:49.100 --> 00:29:53.240 align:middle line:84% but this windshield has Gorilla Glass on the inside surface. 00:29:53.240 --> 00:29:53.840 align:middle line:90% - Sweet. 00:29:53.840 --> 00:29:54.960 align:middle line:90% It looks thinner. 00:29:54.960 --> 00:29:57.060 align:middle line:84% - Yes, it is, and a lot lighter, too. 00:29:57.060 --> 00:29:59.420 align:middle line:84% In fact, just by changing the one laminate, 00:29:59.420 --> 00:30:01.780 align:middle line:84% the overall weight is reduced by about 1/3. 00:30:01.780 --> 00:30:04.040 align:middle line:90% In a car, that adds up fast. 00:30:04.040 --> 00:30:05.140 align:middle line:90% - Thinner, lighter. 00:30:05.140 --> 00:30:08.240 align:middle line:84% And let me guess, it's just as strong as windshield A. 00:30:08.240 --> 00:30:09.300 align:middle line:90% - Well, maybe. 00:30:09.300 --> 00:30:10.260 align:middle line:90% Let's find out. 00:30:10.260 --> 00:30:11.022 align:middle line:90% - Oh, goody. 00:30:11.022 --> 00:30:11.980 align:middle line:90% - OK, wait, wait, wait. 00:30:11.980 --> 00:30:12.460 align:middle line:90% No, no, no, no. 00:30:12.460 --> 00:30:13.860 align:middle line:84% You don't need the sledgehammer for this one. 00:30:13.860 --> 00:30:14.880 align:middle line:90% Put that down. 00:30:14.880 --> 00:30:17.460 align:middle line:84% Instead, you're going to shoot this windshield with an air 00:30:17.460 --> 00:30:18.700 align:middle line:90% cannon. 00:30:18.700 --> 00:30:20.072 align:middle line:90% - Cool. 00:30:20.072 --> 00:30:21.280 align:middle line:90% - Now, don't get too excited. 00:30:21.280 --> 00:30:22.940 align:middle line:84% We're going to have to mount this, tie it down 00:30:22.940 --> 00:30:23.880 align:middle line:90% so it doesn't wobble. 00:30:23.880 --> 00:30:26.660 align:middle line:84% And we're going to simulate a pebble hitting this windshield 00:30:26.660 --> 00:30:28.125 align:middle line:90% at a super high speed. 00:30:28.125 --> 00:30:29.000 align:middle line:90% - Good enough for me. 00:30:29.000 --> 00:30:30.240 align:middle line:90% When do I start shooting? 00:30:30.240 --> 00:30:33.080 align:middle line:84% - Well, before we shoot the Gorilla Glass laminate, 00:30:33.080 --> 00:30:35.220 align:middle line:84% let's shoot the regular soda lime laminate, 00:30:35.220 --> 00:30:37.040 align:middle line:90% windshield A. This way. 00:30:37.040 --> 00:30:39.620 align:middle line:90% 00:30:39.620 --> 00:30:41.580 align:middle line:90% All right, here we go. 00:30:41.580 --> 00:30:42.420 align:middle line:90% Perfect. 00:30:42.420 --> 00:30:43.600 align:middle line:90% You want to do the honors? 00:30:43.600 --> 00:30:44.100 align:middle line:90% - Sure. 00:30:44.100 --> 00:30:44.892 align:middle line:90% - I'll count it in. 00:30:44.892 --> 00:30:46.880 align:middle line:90% 3, 2, 1, go. 00:30:46.880 --> 00:30:48.040 align:middle line:90% [SHATTERING] 00:30:48.040 --> 00:30:48.540 align:middle line:90% - Whoa. 00:30:48.540 --> 00:30:51.040 align:middle line:84% - [CHUCKLES] That was a lot of damage. 00:30:51.040 --> 00:30:52.680 align:middle line:84% - Can we see that in slow motion? 00:30:52.680 --> 00:30:54.300 align:middle line:84% - The ball bearing hits the windshield 00:30:54.300 --> 00:30:57.260 align:middle line:90% at around 120 miles per hour. 00:30:57.260 --> 00:31:00.100 align:middle line:84% This could be a stone flicked up by another car. 00:31:00.100 --> 00:31:02.200 align:middle line:84% It penetrates the exterior glass. 00:31:02.200 --> 00:31:03.560 align:middle line:90% It stretches the resin. 00:31:03.560 --> 00:31:05.980 align:middle line:84% It's slowed down a bit, but it still 00:31:05.980 --> 00:31:08.840 align:middle line:84% has momentum to break the interior glass layer, 00:31:08.840 --> 00:31:11.780 align:middle line:84% causing small fragments of glass to spray 00:31:11.780 --> 00:31:13.840 align:middle line:84% out through the interior of the car. 00:31:13.840 --> 00:31:15.550 align:middle line:90% [MUSIC PLAYING] 00:31:15.550 --> 00:31:17.270 align:middle line:90% - Not good. 00:31:17.270 --> 00:31:19.450 align:middle line:90% - So let's try windshield B. 00:31:19.450 --> 00:31:21.390 align:middle line:90% [WHOOSHING] 00:31:21.390 --> 00:31:22.350 align:middle line:90% 00:31:22.350 --> 00:31:25.050 align:middle line:84% The Gorilla Glass didn't appear to break. 00:31:25.050 --> 00:31:27.170 align:middle line:90% The foil is intact. 00:31:27.170 --> 00:31:28.910 align:middle line:90% - Let's see it in slow-mo. 00:31:28.910 --> 00:31:30.870 align:middle line:84% - The ball bearing hits the windshield 00:31:30.870 --> 00:31:34.030 align:middle line:84% at around 120 miles per hour, just as before. 00:31:34.030 --> 00:31:37.070 align:middle line:84% It goes through the front layer of soda lime glass, 00:31:37.070 --> 00:31:40.790 align:middle line:84% stretches the resin, but doesn't have enough energy 00:31:40.790 --> 00:31:42.590 align:middle line:90% to break the Gorilla Glass. 00:31:42.590 --> 00:31:44.090 align:middle line:90% It's not bulletproof. 00:31:44.090 --> 00:31:46.250 align:middle line:84% I'm pretty sure if we turned up the velocity, 00:31:46.250 --> 00:31:50.230 align:middle line:84% we'd breach the gorilla layer 2, but in this test, and all things 00:31:50.230 --> 00:31:54.270 align:middle line:84% being equal, it performed a lot better than the thicker, heavier 00:31:54.270 --> 00:31:56.070 align:middle line:90% soda lime laminate windshield. 00:31:56.070 --> 00:31:57.290 align:middle line:90% That's impressive. 00:31:57.290 --> 00:31:58.310 align:middle line:90% [MUSIC PLAYING] 00:31:58.310 --> 00:32:01.030 align:middle line:84% What we're seeing here is compressive strength 00:32:01.030 --> 00:32:02.970 align:middle line:90% at its finest moment. 00:32:02.970 --> 00:32:05.750 align:middle line:90% [MUSIC PLAYING] 00:32:05.750 --> 00:32:09.230 align:middle line:84% - OK, so it's lighter, thinner, and stronger. 00:32:09.230 --> 00:32:10.210 align:middle line:90% That's pretty good. 00:32:10.210 --> 00:32:11.270 align:middle line:90% - Yes, it is. 00:32:11.270 --> 00:32:12.770 align:middle line:90% - Can I get this on my car? 00:32:12.770 --> 00:32:15.163 align:middle line:90% - Not today, but soon, I hope. 00:32:15.163 --> 00:32:15.830 align:middle line:90% Come on, though. 00:32:15.830 --> 00:32:18.038 align:middle line:84% After living through the Iron Age and the Bronze Age, 00:32:18.038 --> 00:32:20.010 align:middle line:90% you could wait a little longer. 00:32:20.010 --> 00:32:22.970 align:middle line:84% Actually, when you think about it, the application for this 00:32:22.970 --> 00:32:25.770 align:middle line:84% goes way beyond the car, doesn't it? 00:32:25.770 --> 00:32:27.130 align:middle line:90% Ah, yes. 00:32:27.130 --> 00:32:29.650 align:middle line:84% Feels good to be in the Glass Age. 00:32:29.650 --> 00:32:31.482 align:middle line:90% Come on. 00:32:31.482 --> 00:32:32.190 align:middle line:90% - Don't touch me. 00:32:32.190 --> 00:32:32.690 align:middle line:90% - Sorry. 00:32:32.690 --> 00:32:34.650 align:middle line:90% [END PLAYBACK] 00:32:34.650 --> 00:32:39.810 align:middle line:84% JUEJUN HU: OK, so now, what I actually have here-- 00:32:39.810 --> 00:32:41.970 align:middle line:84% I actually have brought with me a few pieces 00:32:41.970 --> 00:32:45.970 align:middle line:84% of Willow glass, which is the type of glass they mentioned 00:32:45.970 --> 00:32:48.030 align:middle line:90% that's actually flexible. 00:32:48.030 --> 00:32:49.450 align:middle line:90% It's actually a flexible sheet. 00:32:49.450 --> 00:32:53.330 align:middle line:90% I'm going to pass it around. 00:32:53.330 --> 00:32:54.670 align:middle line:90% It does break. 00:32:54.670 --> 00:32:57.810 align:middle line:84% Actually, it's stronger if you bend it one way than the other. 00:32:57.810 --> 00:32:59.750 align:middle line:84% I cannot really tell which side is which, 00:32:59.750 --> 00:33:03.050 align:middle line:84% but you can play around a little bit with it. 00:33:03.050 --> 00:33:04.890 align:middle line:84% Don't worry about it if you break it. 00:33:04.890 --> 00:33:07.770 align:middle line:90% Just don't hurt yourself, OK? 00:33:07.770 --> 00:33:09.410 align:middle line:90% I also have a thin sheet here. 00:33:09.410 --> 00:33:11.430 align:middle line:84% It's a bit easier to demonstrate how it bends. 00:33:11.430 --> 00:33:19.030 align:middle line:90% 00:33:19.030 --> 00:33:23.590 align:middle line:84% You can clearly see it does flex quite a lot. 00:33:23.590 --> 00:33:25.850 align:middle line:90% AUDIENCE: I don't [INAUDIBLE]. 00:33:25.850 --> 00:33:27.870 align:middle line:90% is too much. 00:33:27.870 --> 00:33:29.262 align:middle line:90% [WOBBLING SOUND] 00:33:29.262 --> 00:33:29.762 align:middle line:90% 00:33:29.762 --> 00:33:31.654 align:middle line:90% [LAUGHTER] 00:33:31.654 --> 00:33:33.450 align:middle line:90% 00:33:33.450 --> 00:33:33.950 align:middle line:90% - Good? 00:33:33.950 --> 00:33:34.490 align:middle line:90% OK. 00:33:34.490 --> 00:33:37.110 align:middle line:90% 00:33:37.110 --> 00:33:37.770 align:middle line:90% All right. 00:33:37.770 --> 00:33:39.230 align:middle line:90% AUDIENCE: Sounds pretty good. 00:33:39.230 --> 00:33:42.670 align:middle line:84% JUEJUN HU: Now, I also want to mention that this Willow glass-- 00:33:42.670 --> 00:33:45.630 align:middle line:84% it's actually developed more than a decade ago. 00:33:45.630 --> 00:33:48.550 align:middle line:84% It has a thickness of about 160 microns. 00:33:48.550 --> 00:33:52.550 align:middle line:84% So it's about the thickness of a thick sheet of paper. 00:33:52.550 --> 00:33:55.150 align:middle line:84% State-of-the-art, ultra-thin glass-- 00:33:55.150 --> 00:33:58.030 align:middle line:84% they can get down to a thickness of about 30 microns, 00:33:58.030 --> 00:34:01.070 align:middle line:84% which is less than 1/3 of a thin sheet of paper. 00:34:01.070 --> 00:34:05.150 align:middle line:84% And those glasses-- they do flex, just 00:34:05.150 --> 00:34:06.590 align:middle line:90% like a piece of paper. 00:34:06.590 --> 00:34:08.590 align:middle line:84% In fact, I had the opportunity to actually visit 00:34:08.590 --> 00:34:10.710 align:middle line:84% one of the large glass plants that 00:34:10.710 --> 00:34:13.679 align:middle line:84% actually produce this kind of ultra thin glass sheets. 00:34:13.679 --> 00:34:17.040 align:middle line:84% They have a width of about 8 meters. 00:34:17.040 --> 00:34:19.159 align:middle line:90% They are transported on rollers. 00:34:19.159 --> 00:34:23.092 align:middle line:84% And they almost fly on the rollers because it's so thin, 00:34:23.092 --> 00:34:24.800 align:middle line:84% and has such a little weight, and they're 00:34:24.800 --> 00:34:26.020 align:middle line:90% mechanically flexible. 00:34:26.020 --> 00:34:28.478 align:middle line:84% So it's quite amazing to see how this glass is continuously 00:34:28.478 --> 00:34:30.880 align:middle line:84% being made on the big rollers that come out. 00:34:30.880 --> 00:34:31.880 align:middle line:90% OK? 00:34:31.880 --> 00:34:33.900 align:middle line:84% OK, so that's about mechanical properties. 00:34:33.900 --> 00:34:36.060 align:middle line:84% So as the video already mentioned, 00:34:36.060 --> 00:34:39.000 align:middle line:84% you can already see properties that you normally would not 00:34:39.000 --> 00:34:40.460 align:middle line:90% associate with glass, OK? 00:34:40.460 --> 00:34:43.920 align:middle line:84% Glasses can be flexible, bendable as well. 00:34:43.920 --> 00:34:46.520 align:middle line:84% Now, what about some other properties? 00:34:46.520 --> 00:34:48.882 align:middle line:84% Let's start by looking at optical properties. 00:34:48.882 --> 00:34:51.340 align:middle line:84% You have already mentioned that glasses can be transparent. 00:34:51.340 --> 00:34:53.159 align:middle line:90% They can also be opaque. 00:34:53.159 --> 00:34:55.120 align:middle line:84% Just to make the point, I also have with me 00:34:55.120 --> 00:34:57.705 align:middle line:90% here a piece of glass. 00:34:57.705 --> 00:34:58.580 align:middle line:90% Don't break this one. 00:34:58.580 --> 00:35:01.280 align:middle line:84% This one-- the mechanical property is not that good, OK? 00:35:01.280 --> 00:35:04.020 align:middle line:90% But I will pass it around. 00:35:04.020 --> 00:35:06.960 align:middle line:84% This is actually a chalcogenide glass. 00:35:06.960 --> 00:35:08.000 align:middle line:90% Instead of oxygen, It. 00:35:08.000 --> 00:35:09.860 align:middle line:90% Actually has sulfur in it. 00:35:09.860 --> 00:35:11.100 align:middle line:90% OK? 00:35:11.100 --> 00:35:12.080 align:middle line:90% It's completely opaque. 00:35:12.080 --> 00:35:13.580 align:middle line:84% You will not be able to see through it. 00:35:13.580 --> 00:35:14.980 align:middle line:84% But later on in the semester, we are 00:35:14.980 --> 00:35:17.188 align:middle line:84% going to see is that this glass material is actually, 00:35:17.188 --> 00:35:18.940 align:middle line:84% despite being opaque in visible, it's 00:35:18.940 --> 00:35:21.620 align:middle line:84% actually very transparent if you go to an infrared wavelength 00:35:21.620 --> 00:35:22.120 align:middle line:90% range. 00:35:22.120 --> 00:35:24.360 align:middle line:84% You can actually see through it with infrared camera. 00:35:24.360 --> 00:35:26.068 align:middle line:84% In fact, people use these kind of glasses 00:35:26.068 --> 00:35:29.220 align:middle line:84% to make lenses for infrared cameras. 00:35:29.220 --> 00:35:31.078 align:middle line:90% OK? 00:35:31.078 --> 00:35:32.620 align:middle line:84% And by the way, on that point, I also 00:35:32.620 --> 00:35:33.995 align:middle line:84% have to mention that when we talk 00:35:33.995 --> 00:35:37.260 align:middle line:84% about the definition of glass, Corning primarily 00:35:37.260 --> 00:35:40.800 align:middle line:84% focus on silicate glasses, the glasses made of SiO2. 00:35:40.800 --> 00:35:41.340 align:middle line:90% OK? 00:35:41.340 --> 00:35:43.132 align:middle line:84% So that's why they have been talking about, 00:35:43.132 --> 00:35:45.440 align:middle line:84% essentially, only silicate glass materials. 00:35:45.440 --> 00:35:47.478 align:middle line:84% But glasses is a much broader family. 00:35:47.478 --> 00:35:50.020 align:middle line:84% It also includes things like chalcogenide, which doesn't even 00:35:50.020 --> 00:35:52.198 align:middle line:90% contain oxygen. OK? 00:35:52.198 --> 00:35:53.740 align:middle line:84% Later on in the semester, we're going 00:35:53.740 --> 00:35:55.282 align:middle line:84% to talk about the structural origins, 00:35:55.282 --> 00:35:57.120 align:middle line:84% why some glasses, like silicate glasses, 00:35:57.120 --> 00:35:59.980 align:middle line:84% they stay forever, billions of years, doesn't crystallize, 00:35:59.980 --> 00:36:02.020 align:middle line:84% versus for these kind of glass materials, 00:36:02.020 --> 00:36:04.380 align:middle line:84% they crystallize in a matter of a few hours. 00:36:04.380 --> 00:36:05.500 align:middle line:90% OK? 00:36:05.500 --> 00:36:06.000 align:middle line:90% All right. 00:36:06.000 --> 00:36:08.280 align:middle line:84% So that's for mechanical optical properties. 00:36:08.280 --> 00:36:10.510 align:middle line:84% Now, we'll do electrical properties. 00:36:10.510 --> 00:36:13.190 align:middle line:84% You mentioned about most glass materials are insulating. 00:36:13.190 --> 00:36:15.145 align:middle line:84% There are actually some counterexamples here, 00:36:15.145 --> 00:36:16.270 align:middle line:90% what I'm going to show you. 00:36:16.270 --> 00:36:17.870 align:middle line:90% This piece is all glass. 00:36:17.870 --> 00:36:21.210 align:middle line:84% It looks like a sheet of metal, but this is a metallic glass. 00:36:21.210 --> 00:36:23.393 align:middle line:90% It's actually amorphous metal. 00:36:23.393 --> 00:36:24.810 align:middle line:84% In terms of electrical properties, 00:36:24.810 --> 00:36:26.560 align:middle line:84% it behaves pretty much like regular metal. 00:36:26.560 --> 00:36:29.750 align:middle line:90% It's electrically conducting. 00:36:29.750 --> 00:36:33.190 align:middle line:84% People mostly use it for their interesting mechanical and 00:36:33.190 --> 00:36:35.950 align:middle line:84% magnetic properties, which we are going to talk about later. 00:36:35.950 --> 00:36:37.450 align:middle line:90% OK? 00:36:37.450 --> 00:36:41.983 align:middle line:84% Now, there are also glass materials, even oxide glasses, 00:36:41.983 --> 00:36:44.150 align:middle line:84% you can also make electrically conductive by putting 00:36:44.150 --> 00:36:47.430 align:middle line:84% in mobile ions so that they can essentially transport current, 00:36:47.430 --> 00:36:47.930 align:middle line:90% OK? 00:36:47.930 --> 00:36:50.110 align:middle line:84% And those glasses are actually very important when 00:36:50.110 --> 00:36:51.890 align:middle line:84% it comes to, essentially, solid-state batteries, 00:36:51.890 --> 00:36:52.410 align:middle line:90% for example. 00:36:52.410 --> 00:36:55.230 align:middle line:84% They are used as electrolytes or as electrodes. 00:36:55.230 --> 00:36:56.990 align:middle line:90% OK? 00:36:56.990 --> 00:36:59.690 align:middle line:84% Chemical properties-- most glass materials-- 00:36:59.690 --> 00:37:00.675 align:middle line:90% they are pretty inert. 00:37:00.675 --> 00:37:02.550 align:middle line:84% That's why we don't have to replace our glass 00:37:02.550 --> 00:37:03.910 align:middle line:90% window every year, OK? 00:37:03.910 --> 00:37:06.110 align:middle line:84% However, people have actually come up 00:37:06.110 --> 00:37:09.850 align:middle line:90% with actually soluble glass. 00:37:09.850 --> 00:37:13.490 align:middle line:84% Now, you may wonder, why do I want soluble glasses? 00:37:13.490 --> 00:37:16.370 align:middle line:84% They are actually called bioactive glasses. 00:37:16.370 --> 00:37:18.650 align:middle line:84% They are used in a lot of tissue engineering. 00:37:18.650 --> 00:37:22.330 align:middle line:84% So for example, if someone has a broken bone, 00:37:22.330 --> 00:37:26.610 align:middle line:84% conventional, essentially, bone fills-- 00:37:26.610 --> 00:37:28.990 align:middle line:84% essentially, they are not biodegradable. 00:37:28.990 --> 00:37:30.670 align:middle line:84% You have to actually take them out, OK? 00:37:30.670 --> 00:37:33.210 align:middle line:90% So that's another surgery. 00:37:33.210 --> 00:37:35.930 align:middle line:84% If it's bioactive glasses, they can actually slowly 00:37:35.930 --> 00:37:38.010 align:middle line:90% dissolve in the body fluids. 00:37:38.010 --> 00:37:38.650 align:middle line:90% OK? 00:37:38.650 --> 00:37:40.810 align:middle line:84% And in the process, people have also 00:37:40.810 --> 00:37:43.970 align:middle line:84% engineered its microstructure so that you can actually 00:37:43.970 --> 00:37:47.210 align:middle line:84% essentially form micropores inside that selectively leech 00:37:47.210 --> 00:37:49.735 align:middle line:84% out in body fluids so that bone tissue can actually 00:37:49.735 --> 00:37:51.610 align:middle line:84% grow in those pores, and eventually, fill out 00:37:51.610 --> 00:37:52.790 align:middle line:90% the entire system there. 00:37:52.790 --> 00:37:53.610 align:middle line:90% OK? 00:37:53.610 --> 00:37:56.210 align:middle line:84% So they are actually very useful for these kind 00:37:56.210 --> 00:37:58.650 align:middle line:90% of medical applications. 00:37:58.650 --> 00:38:01.650 align:middle line:84% Now, last descriptive term that you have not mentioned here 00:38:01.650 --> 00:38:02.970 align:middle line:90% is actually man-made. 00:38:02.970 --> 00:38:06.590 align:middle line:84% Now, you may think that glasses actually are man-made materials. 00:38:06.590 --> 00:38:09.550 align:middle line:84% Turns out there are also lots of natural glasses as well. 00:38:09.550 --> 00:38:11.290 align:middle line:90% What I have here-- a few pieces. 00:38:11.290 --> 00:38:12.870 align:middle line:90% This one is obsidian. 00:38:12.870 --> 00:38:15.390 align:middle line:84% This is a little obsidian arrowhead. 00:38:15.390 --> 00:38:17.490 align:middle line:84% You can see that's actually translucent glass. 00:38:17.490 --> 00:38:19.210 align:middle line:84% It comes from volcanic activities. 00:38:19.210 --> 00:38:20.830 align:middle line:84% It's basically, what happens when you have lava. 00:38:20.830 --> 00:38:22.330 align:middle line:84% It actually cools down very quickly. 00:38:22.330 --> 00:38:23.890 align:middle line:84% It does not have time to crystallize. 00:38:23.890 --> 00:38:25.750 align:middle line:90% It becomes amorphous material. 00:38:25.750 --> 00:38:27.470 align:middle line:90% This one is tektite. 00:38:27.470 --> 00:38:29.630 align:middle line:90% It comes from a meteor's impact. 00:38:29.630 --> 00:38:31.130 align:middle line:84% Again, if a meteor's coming in here, 00:38:31.130 --> 00:38:32.710 align:middle line:84% high temperature, melt the mineral, 00:38:32.710 --> 00:38:34.950 align:middle line:84% quickly cools down, that's what you get. 00:38:34.950 --> 00:38:36.530 align:middle line:84% Same thing with lightning strike. 00:38:36.530 --> 00:38:38.170 align:middle line:84% You need lots of energy to melt it. 00:38:38.170 --> 00:38:39.630 align:middle line:90% This one is fulgurite. 00:38:39.630 --> 00:38:42.730 align:middle line:84% So these are all naturally forming glasses. 00:38:42.730 --> 00:38:43.230 align:middle line:90% OK? 00:38:43.230 --> 00:38:47.570 align:middle line:90% 00:38:47.570 --> 00:38:48.990 align:middle line:90% Doesn't look like glass. 00:38:48.990 --> 00:38:51.330 align:middle line:84% The obsidian looks a bit more like glass. 00:38:51.330 --> 00:38:54.510 align:middle line:90% It's more translucent. 00:38:54.510 --> 00:38:58.550 align:middle line:84% And in fact, you'll find it not just on Earth. 00:38:58.550 --> 00:39:03.150 align:middle line:84% You can actually find it even on the moons of Jupiter or comets 00:39:03.150 --> 00:39:03.730 align:middle line:90% everywhere. 00:39:03.730 --> 00:39:04.440 align:middle line:90% OK? 00:39:04.440 --> 00:39:06.140 align:middle line:84% So glasses are really ubiquitous. 00:39:06.140 --> 00:39:07.280 align:middle line:90% They are everywhere. 00:39:07.280 --> 00:39:11.880 align:middle line:84% Now, comes back in terms of application of glasses. 00:39:11.880 --> 00:39:15.840 align:middle line:84% Human beings have started to use glass actually way 00:39:15.840 --> 00:39:18.160 align:middle line:90% before we have written history. 00:39:18.160 --> 00:39:19.880 align:middle line:90% Talking about Stone Age. 00:39:19.880 --> 00:39:23.720 align:middle line:84% One question is what is the stone people used 00:39:23.720 --> 00:39:26.000 align:middle line:90% to actually make those tools? 00:39:26.000 --> 00:39:31.400 align:middle line:84% Turns out the stones they used are mostly either glassy 00:39:31.400 --> 00:39:34.060 align:middle line:84% or it's called a cryptocrystalline. 00:39:34.060 --> 00:39:41.000 align:middle line:90% 00:39:41.000 --> 00:39:45.800 align:middle line:84% So this word is used to describe minerals that has very, very 00:39:45.800 --> 00:39:47.560 align:middle line:90% small fine grains. 00:39:47.560 --> 00:39:49.680 align:middle line:84% In a lot of cases, it's actually a mixture 00:39:49.680 --> 00:39:52.340 align:middle line:84% of amorphous matrix with crystalline precipitates, OK? 00:39:52.340 --> 00:39:55.840 align:middle line:84% So mechanically, they actually behave like glass, 00:39:55.840 --> 00:39:57.440 align:middle line:90% amorphous materials. 00:39:57.440 --> 00:39:59.160 align:middle line:84% Later on, we're actually going to talk 00:39:59.160 --> 00:40:00.820 align:middle line:90% about fractography of glass. 00:40:00.820 --> 00:40:02.740 align:middle line:84% Glass actually break, or they fracture, 00:40:02.740 --> 00:40:04.660 align:middle line:90% in very specific manners. 00:40:04.660 --> 00:40:07.120 align:middle line:84% So if you know how they actually behave when you break, 00:40:07.120 --> 00:40:08.160 align:middle line:90% you can control it. 00:40:08.160 --> 00:40:09.820 align:middle line:84% And that's actually how our ancestors 00:40:09.820 --> 00:40:13.820 align:middle line:84% were able to make all these tools with very high quality. 00:40:13.820 --> 00:40:19.140 align:middle line:84% One fine example of these kinds glass tools or stone tools 00:40:19.140 --> 00:40:21.500 align:middle line:90% people were able to make-- 00:40:21.500 --> 00:40:24.460 align:middle line:84% let's think about Aztecs in Mesoamerica. 00:40:24.460 --> 00:40:24.960 align:middle line:90% OK? 00:40:24.960 --> 00:40:26.585 align:middle line:84% You may have read in history books that 00:40:26.585 --> 00:40:29.220 align:middle line:84% Aztecs-- they live in the Stone Age, they use stone tools, OK? 00:40:29.220 --> 00:40:31.420 align:middle line:84% This does not mean that they don't 00:40:31.420 --> 00:40:32.840 align:middle line:90% know how to make use of metal. 00:40:32.840 --> 00:40:34.600 align:middle line:84% They can actually make bronze tools, 00:40:34.600 --> 00:40:38.220 align:middle line:84% but they choose to stick with stone tools. 00:40:38.220 --> 00:40:39.203 align:middle line:90% Why? 00:40:39.203 --> 00:40:40.620 align:middle line:84% They actually used obsidian, which 00:40:40.620 --> 00:40:42.120 align:middle line:84% is the thing I passed around over there. 00:40:42.120 --> 00:40:44.453 align:middle line:84% They used obsidian to actually make these different kind 00:40:44.453 --> 00:40:45.420 align:middle line:90% of tools there. 00:40:45.420 --> 00:40:46.820 align:middle line:84% They have mastered the technology 00:40:46.820 --> 00:40:50.520 align:middle line:84% to actually process obsidian so that actually, for example, 00:40:50.520 --> 00:40:51.920 align:middle line:90% they can make knives. 00:40:51.920 --> 00:40:52.940 align:middle line:90% They are far more sharp. 00:40:52.940 --> 00:40:54.980 align:middle line:84% Or blades-- far sharper compared to what 00:40:54.980 --> 00:40:56.660 align:middle line:90% you can make using metal. 00:40:56.660 --> 00:40:57.540 align:middle line:90% OK? 00:40:57.540 --> 00:40:59.560 align:middle line:84% So that's why people have actually commented. 00:40:59.560 --> 00:41:03.270 align:middle line:84% I have quoted some people, quoted here. 00:41:03.270 --> 00:41:05.870 align:middle line:84% "Obsidian is capable of producing an edge sharper 00:41:05.870 --> 00:41:08.310 align:middle line:84% than high quality steel razor blades. 00:41:08.310 --> 00:41:11.370 align:middle line:84% What need could there be for a replacement material? 00:41:11.370 --> 00:41:15.350 align:middle line:84% The Aztecs didn't develop the use of metal because they simply 00:41:15.350 --> 00:41:17.510 align:middle line:90% couldn't see beyond obsidian." 00:41:17.510 --> 00:41:19.710 align:middle line:84% Because it's so good, they basically 00:41:19.710 --> 00:41:23.030 align:middle line:84% just did not actually develop metal further. 00:41:23.030 --> 00:41:24.390 align:middle line:90% OK? 00:41:24.390 --> 00:41:26.310 align:middle line:84% What I'm showing on this plot here-- 00:41:26.310 --> 00:41:29.310 align:middle line:84% actually, basically, what this Aztec warrior is holding 00:41:29.310 --> 00:41:31.862 align:middle line:84% is actually a saw made of obsidian. 00:41:31.862 --> 00:41:34.070 align:middle line:84% Now, it doesn't look like a normal saw, you will see, 00:41:34.070 --> 00:41:35.110 align:middle line:90% made of metal. 00:41:35.110 --> 00:41:37.570 align:middle line:84% It basically has this big wooden shaft. 00:41:37.570 --> 00:41:40.697 align:middle line:84% And then you have pieces of very sharp blades made of obsidian 00:41:40.697 --> 00:41:41.530 align:middle line:90% put it on there, OK? 00:41:41.530 --> 00:41:43.730 align:middle line:84% The reason they constructed it that way, 00:41:43.730 --> 00:41:46.270 align:middle line:84% rather than a monolithic piece of big obsidian, 00:41:46.270 --> 00:41:49.510 align:middle line:84% is because obsidian, despite that it can be very sharp, just 00:41:49.510 --> 00:41:51.310 align:middle line:90% has one Achilles heel. 00:41:51.310 --> 00:41:52.250 align:middle line:90% It's brittle. 00:41:52.250 --> 00:41:52.750 align:middle line:90% OK? 00:41:52.750 --> 00:41:54.550 align:middle line:90% So it tends to break. 00:41:54.550 --> 00:41:58.130 align:middle line:84% So if you have a one big piece, if it cracks, 00:41:58.130 --> 00:42:00.110 align:middle line:90% then you lose the whole thing. 00:42:00.110 --> 00:42:01.910 align:middle line:84% But if you have these individual pieces, 00:42:01.910 --> 00:42:03.890 align:middle line:90% you can always replace it. 00:42:03.890 --> 00:42:06.370 align:middle line:84% So that's the technology they have developed. 00:42:06.370 --> 00:42:09.170 align:middle line:84% It's actually purely based on glass. 00:42:09.170 --> 00:42:12.930 align:middle line:84% Now, let's fast-forward to today. 00:42:12.930 --> 00:42:14.930 align:middle line:84% Glasses are really amorphous materials 00:42:14.930 --> 00:42:16.550 align:middle line:90% that are really ubiquitous, OK? 00:42:16.550 --> 00:42:18.590 align:middle line:84% If you think about the phone in your pocket, 00:42:18.590 --> 00:42:20.250 align:middle line:84% there are tons of things that actually 00:42:20.250 --> 00:42:21.550 align:middle line:90% make use of these materials. 00:42:21.550 --> 00:42:24.410 align:middle line:84% You have the glass cover, all the camera lenses 00:42:24.410 --> 00:42:25.910 align:middle line:90% using optical properties. 00:42:25.910 --> 00:42:28.250 align:middle line:84% You have the thin film display, where 00:42:28.250 --> 00:42:31.370 align:middle line:84% from both the materials used to make transistors 00:42:31.370 --> 00:42:33.570 align:middle line:84% to the display itself, it's all amorphous. 00:42:33.570 --> 00:42:36.290 align:middle line:84% You always involve amorphous materials, one or the other. 00:42:36.290 --> 00:42:38.430 align:middle line:84% Or dielectric materials and packaging materials-- 00:42:38.430 --> 00:42:40.210 align:middle line:90% they are mostly amorphous, OK? 00:42:40.210 --> 00:42:43.850 align:middle line:84% And finally, there are also some potential emerging applications 00:42:43.850 --> 00:42:46.910 align:middle line:84% people may one day also apply to consumer electronic devices, 00:42:46.910 --> 00:42:49.710 align:middle line:84% such as metallic glasses, new phase change memories, 00:42:49.710 --> 00:42:50.713 align:middle line:90% solid-state batteries. 00:42:50.713 --> 00:42:52.130 align:middle line:84% And we are going to talk about all 00:42:52.130 --> 00:42:54.710 align:middle line:84% of these different applications in the lecture here, OK? 00:42:54.710 --> 00:42:58.310 align:middle line:84% So we'll be covering structural, chemical, 00:42:58.310 --> 00:43:01.710 align:middle line:84% optical, electrical, transport properties, everything 00:43:01.710 --> 00:43:03.150 align:middle line:90% about glass materials. 00:43:03.150 --> 00:43:04.950 align:middle line:90% OK? 00:43:04.950 --> 00:43:05.530 align:middle line:90% All right. 00:43:05.530 --> 00:43:09.070 align:middle line:84% Now, finally, this comes back about the definition 00:43:09.070 --> 00:43:12.710 align:middle line:90% of glass and amorphous solids. 00:43:12.710 --> 00:43:16.650 align:middle line:84% I want to show you this little, basically, screenshot. 00:43:16.650 --> 00:43:18.190 align:middle line:90% I quote from a paper there. 00:43:18.190 --> 00:43:22.255 align:middle line:84% Well, this paper was published in 2017, just eight years ago, 00:43:22.255 --> 00:43:23.630 align:middle line:84% where people were actually trying 00:43:23.630 --> 00:43:25.510 align:middle line:84% to actually give a glass material a more 00:43:25.510 --> 00:43:26.990 align:middle line:90% rigorous definition. 00:43:26.990 --> 00:43:28.538 align:middle line:84% So what you see here is that this 00:43:28.538 --> 00:43:30.830 align:middle line:84% is a topic that still has quite some controversy there. 00:43:30.830 --> 00:43:32.913 align:middle line:84% People have not really converged into a consensus, 00:43:32.913 --> 00:43:34.810 align:middle line:90% even just 10 years ago. 00:43:34.810 --> 00:43:36.070 align:middle line:90% OK? 00:43:36.070 --> 00:43:37.990 align:middle line:90% It can be pretty complicated. 00:43:37.990 --> 00:43:40.470 align:middle line:90% You don't have to memorize it. 00:43:40.470 --> 00:43:41.450 align:middle line:90% What I want to do-- 00:43:41.450 --> 00:43:43.510 align:middle line:84% I will give you actually a working definition 00:43:43.510 --> 00:43:46.243 align:middle line:84% of glass, which is generally accepted by most glass 00:43:46.243 --> 00:43:47.410 align:middle line:90% scientists around the world. 00:43:47.410 --> 00:43:48.910 align:middle line:90% OK? 00:43:48.910 --> 00:43:49.570 align:middle line:90% All right. 00:43:49.570 --> 00:43:52.990 align:middle line:90% So here you go. 00:43:52.990 --> 00:43:55.690 align:middle line:84% So let's go back to this plot here. 00:43:55.690 --> 00:43:58.760 align:middle line:84% This big circle represents all the solid matter, OK? 00:43:58.760 --> 00:44:02.840 align:middle line:84% Within it, it's our amorphous solids. 00:44:02.840 --> 00:44:04.840 align:middle line:90% Now, not all the glasses-- 00:44:04.840 --> 00:44:08.040 align:middle line:84% sorry, not all amorphous solids are glasses. 00:44:08.040 --> 00:44:08.680 align:middle line:90% OK? 00:44:08.680 --> 00:44:13.360 align:middle line:84% Amorphous solids refer to a solid material that's metastable 00:44:13.360 --> 00:44:16.240 align:middle line:84% and lacks long-range atomic order. 00:44:16.240 --> 00:44:18.940 align:middle line:84% Now, in order for an amorphous solid to qualify as a glass, 00:44:18.940 --> 00:44:20.640 align:middle line:84% there's actually additional criteria. 00:44:20.640 --> 00:44:24.400 align:middle line:84% It needs to exhibit a glass transition. 00:44:24.400 --> 00:44:27.800 align:middle line:84% Not all amorphous solids exhibit glass transition. 00:44:27.800 --> 00:44:30.240 align:middle line:84% A lot of the metal oxides-- they can be amorphous, 00:44:30.240 --> 00:44:32.700 align:middle line:84% but they do not exhibit glass transition. 00:44:32.700 --> 00:44:34.672 align:middle line:90% OK? 00:44:34.672 --> 00:44:36.880 align:middle line:84% We're going to talk about some examples, for example, 00:44:36.880 --> 00:44:38.560 align:middle line:90% like amorphous silicon. 00:44:38.560 --> 00:44:40.820 align:middle line:84% It's amorphous, but normally, people normally 00:44:40.820 --> 00:44:42.320 align:middle line:84% don't consider it as a glass, but it 00:44:42.320 --> 00:44:46.360 align:middle line:84% has very important application in the electronic semiconductor 00:44:46.360 --> 00:44:46.860 align:middle line:90% field. 00:44:46.860 --> 00:44:48.240 align:middle line:90% OK? 00:44:48.240 --> 00:44:50.600 align:middle line:84% Now, within that big circle of glass, 00:44:50.600 --> 00:44:53.800 align:middle line:84% we have a much smaller circle of silicate glass. 00:44:53.800 --> 00:44:57.670 align:middle line:84% This is what's referred to as glass in the video from Corning, 00:44:57.670 --> 00:44:59.420 align:middle line:84% but it's really only talking about glasses 00:44:59.420 --> 00:45:01.880 align:middle line:84% based on SiO2 as a key backbone material. 00:45:01.880 --> 00:45:02.860 align:middle line:90% OK? 00:45:02.860 --> 00:45:05.340 align:middle line:84% We are going to see a lot more varieties of glass materials 00:45:05.340 --> 00:45:07.620 align:middle line:84% beyond just a very simple circuit. 00:45:07.620 --> 00:45:10.280 align:middle line:84% And finally, the glass as we know it every day-- 00:45:10.280 --> 00:45:12.860 align:middle line:84% this typically refers to so-called soda lime glass. 00:45:12.860 --> 00:45:16.460 align:middle line:84% It's one subgroup of silicate glass. 00:45:16.460 --> 00:45:19.736 align:middle line:90% OK. 00:45:19.736 --> 00:45:22.680 align:middle line:84% So now, let's actually take a look at the definition here. 00:45:22.680 --> 00:45:23.260 align:middle line:90% OK? 00:45:23.260 --> 00:45:25.980 align:middle line:84% So for the definition, there are essentially a few key words 00:45:25.980 --> 00:45:26.620 align:middle line:90% here. 00:45:26.620 --> 00:45:28.000 align:middle line:90% You need to be a full glass. 00:45:28.000 --> 00:45:29.620 align:middle line:90% You need to be metastable. 00:45:29.620 --> 00:45:31.780 align:middle line:84% You need to lack long-range order. 00:45:31.780 --> 00:45:34.060 align:middle line:84% It also needs to exhibit glass transition. 00:45:34.060 --> 00:45:36.393 align:middle line:84% We're going to take a look at that three attributes, OK? 00:45:36.393 --> 00:45:39.700 align:middle line:84% So first of all, let's start with metastable. 00:45:39.700 --> 00:45:42.180 align:middle line:84% So metastable can be illustrated by this plot here, 00:45:42.180 --> 00:45:43.847 align:middle line:84% where I'm showing you, essentially, this 00:45:43.847 --> 00:45:45.340 align:middle line:84% is basically a free energy of glass 00:45:45.340 --> 00:45:48.180 align:middle line:90% as a function of the structure. 00:45:48.180 --> 00:45:49.660 align:middle line:84% Now, as you probably already know, 00:45:49.660 --> 00:45:51.980 align:middle line:84% the thermodynamically stable state of a material 00:45:51.980 --> 00:45:53.950 align:middle line:90% is its crystalline state. 00:45:53.950 --> 00:45:55.690 align:middle line:84% So because it's thermodynamically stable, 00:45:55.690 --> 00:45:57.390 align:middle line:84% it means that on this plot here, it 00:45:57.390 --> 00:46:01.270 align:middle line:84% must be a global minimum in terms of energy. 00:46:01.270 --> 00:46:04.050 align:middle line:84% Glasses, on the other hand-- it is metastable. 00:46:04.050 --> 00:46:06.950 align:middle line:84% So it means that it resides in a basin that 00:46:06.950 --> 00:46:09.470 align:middle line:90% represents a local minimum. 00:46:09.470 --> 00:46:11.470 align:middle line:84% And this local minimum is separated 00:46:11.470 --> 00:46:14.410 align:middle line:84% from the global minimum by some energy barrier. 00:46:14.410 --> 00:46:17.510 align:middle line:90% 00:46:17.510 --> 00:46:19.350 align:middle line:84% So the height of this energy barrier 00:46:19.350 --> 00:46:21.710 align:middle line:84% actually dictates whether or not the glassy state 00:46:21.710 --> 00:46:23.950 align:middle line:90% is actually stable, OK? 00:46:23.950 --> 00:46:28.230 align:middle line:84% A glass is metastable means that with appropriate stimulus, 00:46:28.230 --> 00:46:30.710 align:middle line:84% it can always overcome this barrier 00:46:30.710 --> 00:46:34.190 align:middle line:84% and relax towards the thermodynamically stable state. 00:46:34.190 --> 00:46:36.790 align:middle line:90% This is called crystallization. 00:46:36.790 --> 00:46:38.270 align:middle line:90% OK? 00:46:38.270 --> 00:46:40.490 align:middle line:84% Now, some glasses-- this process can take forever, 00:46:40.490 --> 00:46:41.418 align:middle line:90% like silicates. 00:46:41.418 --> 00:46:43.210 align:middle line:84% Some glasses-- this can be very, very fast. 00:46:43.210 --> 00:46:45.085 align:middle line:84% It all depends on the height of this barrier. 00:46:45.085 --> 00:46:47.990 align:middle line:84% You can also expedite this process by essentially giving it 00:46:47.990 --> 00:46:49.022 align:middle line:90% some energy, OK? 00:46:49.022 --> 00:46:50.730 align:middle line:84% You nudge the glass network a little bit, 00:46:50.730 --> 00:46:52.690 align:middle line:84% for example, by simply heating it up. 00:46:52.690 --> 00:46:54.750 align:middle line:84% If all the atoms have more thermal energy, 00:46:54.750 --> 00:46:56.625 align:middle line:84% then you will be able to actually crystallize 00:46:56.625 --> 00:46:57.570 align:middle line:90% a lot faster. 00:46:57.570 --> 00:46:58.250 align:middle line:90% OK? 00:46:58.250 --> 00:47:00.167 align:middle line:84% Again, we are going to talk about the kinetics 00:47:00.167 --> 00:47:02.810 align:middle line:84% of crystallization later on in the semester, OK? 00:47:02.810 --> 00:47:06.610 align:middle line:84% But for now, you need to know that all the amorphous solids 00:47:06.610 --> 00:47:08.330 align:middle line:84% and glasses as well-- they always 00:47:08.330 --> 00:47:12.570 align:middle line:84% have to be residing in this local metastable state. 00:47:12.570 --> 00:47:14.930 align:middle line:90% OK? 00:47:14.930 --> 00:47:19.890 align:middle line:84% Next attribute-- no long-range atomic order. 00:47:19.890 --> 00:47:23.290 align:middle line:84% So you have seen this in 3091, but what I'm trying to represent 00:47:23.290 --> 00:47:26.050 align:middle line:84% here is a fictitious 2D compound. 00:47:26.050 --> 00:47:29.290 align:middle line:84% It's some kind of atom, A, combined with oxygen, A2O3. 00:47:29.290 --> 00:47:29.790 align:middle line:90% OK? 00:47:29.790 --> 00:47:35.290 align:middle line:84% So A is basically plus 3, has a plus 3 valence state. 00:47:35.290 --> 00:47:39.730 align:middle line:84% We can imagine that a plausible crystal structure for this A2O3 00:47:39.730 --> 00:47:42.570 align:middle line:84% crystal is this 2-dimensional solid, 00:47:42.570 --> 00:47:45.410 align:middle line:84% where each of the A atoms here, these black dots, 00:47:45.410 --> 00:47:47.530 align:middle line:90% connect to 3 oxygen atoms. 00:47:47.530 --> 00:47:52.630 align:middle line:84% And 1 oxygen atom connects to 2 A atoms here, OK? 00:47:52.630 --> 00:47:55.750 align:middle line:84% Now, we say that for this crystal, 00:47:55.750 --> 00:47:58.750 align:middle line:84% it exhibits a long-range atomic order. 00:47:58.750 --> 00:47:59.708 align:middle line:90% What do I mean by that? 00:47:59.708 --> 00:48:01.458 align:middle line:84% It's that suppose you know the orientation 00:48:01.458 --> 00:48:02.590 align:middle line:90% of this single crystal. 00:48:02.590 --> 00:48:05.590 align:middle line:84% And you know the location of one atom here. 00:48:05.590 --> 00:48:09.430 align:middle line:84% Then you'll be able to predict the specific coordinates 00:48:09.430 --> 00:48:13.350 align:middle line:84% of all the other atoms in this big single crystal 00:48:13.350 --> 00:48:14.330 align:middle line:90% instantaneously. 00:48:14.330 --> 00:48:14.830 align:middle line:90% OK? 00:48:14.830 --> 00:48:17.510 align:middle line:84% So you have this kind of spatial periodicity 00:48:17.510 --> 00:48:21.990 align:middle line:84% that's preserved over macroscopic distances. 00:48:21.990 --> 00:48:26.190 align:middle line:84% On the other hand, if you look at its amorphous counterpart, 00:48:26.190 --> 00:48:28.170 align:middle line:84% the short-range order is still preserved, OK? 00:48:28.170 --> 00:48:29.967 align:middle line:84% When I talk about short-range order, 00:48:29.967 --> 00:48:32.050 align:middle line:84% I basically talk about local chemical environment. 00:48:32.050 --> 00:48:32.310 align:middle line:90% OK? 00:48:32.310 --> 00:48:34.643 align:middle line:84% So if you look at, for example, this amorphous structure 00:48:34.643 --> 00:48:38.230 align:middle line:84% here, look at A atom, it is still connected to 3 oxygen 00:48:38.230 --> 00:48:39.790 align:middle line:90% atoms there, OK? 00:48:39.790 --> 00:48:43.350 align:middle line:84% Each oxygen atom is still connected to 2 A atoms. 00:48:43.350 --> 00:48:46.190 align:middle line:84% So the basic structural unit to form this network here 00:48:46.190 --> 00:48:50.420 align:middle line:84% is basically this AO3 little cluster here. 00:48:50.420 --> 00:48:55.200 align:middle line:84% It stays exactly the same as in the case of an A2O3 crystal. 00:48:55.200 --> 00:48:59.240 align:middle line:84% However, what is changing here is 00:48:59.240 --> 00:49:03.200 align:middle line:84% the bond length between the atoms, and so it's bond angle. 00:49:03.200 --> 00:49:04.380 align:middle line:90% Mostly, the bond angle. 00:49:04.380 --> 00:49:07.120 align:middle line:84% The bond length usually changes to a very, very small extent. 00:49:07.120 --> 00:49:11.400 align:middle line:84% Most of the time, it's just bond angle difference. 00:49:11.400 --> 00:49:13.840 align:middle line:84% Now, because of the variation of the bond angle, 00:49:13.840 --> 00:49:16.480 align:middle line:84% this structural disorder will accumulate 00:49:16.480 --> 00:49:20.240 align:middle line:84% as you move from one structural unit to another one. 00:49:20.240 --> 00:49:23.380 align:middle line:84% So after passing through a few atomic interspacing, 00:49:23.380 --> 00:49:27.960 align:middle line:84% you quickly lose track of the orientation of your network 00:49:27.960 --> 00:49:28.500 align:middle line:90% there. 00:49:28.500 --> 00:49:29.000 align:middle line:90% OK? 00:49:29.000 --> 00:49:33.440 align:middle line:84% And that's where you essentially get this continuous network 00:49:33.440 --> 00:49:35.662 align:middle line:90% of an amorphous solid. 00:49:35.662 --> 00:49:37.120 align:middle line:84% So that's why sometimes, people are 00:49:37.120 --> 00:49:41.320 align:middle line:84% saying that if you are working in this amorphous glass network, 00:49:41.320 --> 00:49:43.640 align:middle line:84% you are working with an odometer, 00:49:43.640 --> 00:49:45.280 align:middle line:90% but without [INAUDIBLE]. 00:49:45.280 --> 00:49:48.220 align:middle line:84% Odometer means that the bond length still pretty much keeps 00:49:48.220 --> 00:49:52.340 align:middle line:84% constant, but the orientation of this structural unit 00:49:52.340 --> 00:49:55.020 align:middle line:84% becomes essentially random across the solid material. 00:49:55.020 --> 00:49:58.212 align:middle line:90% OK? 00:49:58.212 --> 00:50:02.900 align:middle line:84% So one immediate consequence of this inherent structure disorder 00:50:02.900 --> 00:50:06.420 align:middle line:84% in glass network is that it actually lacks-- 00:50:06.420 --> 00:50:08.300 align:middle line:84% it's perfectly symmetric, and therefore, it's 00:50:08.300 --> 00:50:10.160 align:middle line:90% usually isotropic. 00:50:10.160 --> 00:50:10.660 align:middle line:90% OK? 00:50:10.660 --> 00:50:14.700 align:middle line:84% So unless you apply a specific external stimuli, 00:50:14.700 --> 00:50:18.080 align:middle line:84% most glass solids essentially exhibit isotropic properties. 00:50:18.080 --> 00:50:20.380 align:middle line:84% Its property does not depend on orientation. 00:50:20.380 --> 00:50:21.740 align:middle line:90% OK? 00:50:21.740 --> 00:50:22.240 align:middle line:90% OK. 00:50:22.240 --> 00:50:26.460 align:middle line:84% So this picture, this glass, or these inorganic 00:50:26.460 --> 00:50:31.940 align:middle line:84% glasses-- they consist of this random network of atoms. 00:50:31.940 --> 00:50:34.340 align:middle line:84% This is called a Zachariasen's random network theory, 00:50:34.340 --> 00:50:36.580 align:middle line:84% first formulated by the scientist Zachariasen back 00:50:36.580 --> 00:50:37.560 align:middle line:90% in the 1930s. 00:50:37.560 --> 00:50:38.060 align:middle line:90% OK? 00:50:38.060 --> 00:50:42.700 align:middle line:84% This is a structural model that applies to inorganic glasses. 00:50:42.700 --> 00:50:43.780 align:middle line:90% OK? 00:50:43.780 --> 00:50:46.300 align:middle line:84% For metallic glasses, there's actually 00:50:46.300 --> 00:50:47.730 align:middle line:90% a different structural model. 00:50:47.730 --> 00:50:49.272 align:middle line:84% Later on in the semester, we're going 00:50:49.272 --> 00:50:51.775 align:middle line:84% to discuss about structural model of amorphous metals, OK? 00:50:51.775 --> 00:50:53.150 align:middle line:84% But this applies to, essentially, 00:50:53.150 --> 00:50:57.390 align:middle line:84% all the other inorganic glasses, OK? 00:50:57.390 --> 00:50:57.890 align:middle line:90% All right. 00:50:57.890 --> 00:51:02.150 align:middle line:84% So just to take a closer look at the structural property 00:51:02.150 --> 00:51:04.310 align:middle line:84% of the glass material here, the most common way 00:51:04.310 --> 00:51:06.643 align:middle line:84% we use to actually characterize the structure of a solid 00:51:06.643 --> 00:51:08.470 align:middle line:90% is the X-ray diffraction. 00:51:08.470 --> 00:51:11.430 align:middle line:84% So what I'm comparing here is X-ray diffraction spectra 00:51:11.430 --> 00:51:13.470 align:middle line:84% of three different kinds of solid materials. 00:51:13.470 --> 00:51:16.550 align:middle line:84% On top, you have basically silica glass, vitreous. 00:51:16.550 --> 00:51:18.130 align:middle line:84% Vitreous essentially means amorphous. 00:51:18.130 --> 00:51:18.630 align:middle line:90% OK? 00:51:18.630 --> 00:51:20.310 align:middle line:90% So it's amorphous silica. 00:51:20.310 --> 00:51:22.550 align:middle line:90% Here this is cristobalite. 00:51:22.550 --> 00:51:25.150 align:middle line:84% Basically, this is the crystalline counterpart of SiO2. 00:51:25.150 --> 00:51:25.990 align:middle line:90% All right? 00:51:25.990 --> 00:51:27.590 align:middle line:84% At the bottom, you have silica gel. 00:51:27.590 --> 00:51:32.110 align:middle line:84% Silica gel basically consists of many small, tiny nanoparticles 00:51:32.110 --> 00:51:33.530 align:middle line:90% of amorphous silica. 00:51:33.530 --> 00:51:36.310 align:middle line:84% They are stacked together, but there is actually an air gap 00:51:36.310 --> 00:51:36.810 align:middle line:90% in-between. 00:51:36.810 --> 00:51:39.470 align:middle line:84% There's nano voids in-between those amorphous solids. 00:51:39.470 --> 00:51:39.970 align:middle line:90% OK? 00:51:39.970 --> 00:51:42.178 align:middle line:84% So if you look at, actually, the following structure, 00:51:42.178 --> 00:51:44.250 align:middle line:84% you see that silica gel and amorphous silica-- 00:51:44.250 --> 00:51:45.370 align:middle line:90% they are pretty similar. 00:51:45.370 --> 00:51:48.210 align:middle line:84% You have this broad bump there, the difference 00:51:48.210 --> 00:51:49.770 align:middle line:84% being that for silica gel, there's 00:51:49.770 --> 00:51:54.010 align:middle line:84% also this rising scattering intensity as you 00:51:54.010 --> 00:51:57.010 align:middle line:84% go to a small diffraction angle, OK? 00:51:57.010 --> 00:52:00.410 align:middle line:84% So if you think about the Bragg's law, 00:52:00.410 --> 00:52:12.490 align:middle line:84% which basically says that lambda equals to 2d sine theta-- 00:52:12.490 --> 00:52:16.910 align:middle line:84% so if the wavelength is fixed in one particular experiment here, 00:52:16.910 --> 00:52:18.430 align:middle line:84% if you have small diffraction angle, 00:52:18.430 --> 00:52:20.090 align:middle line:84% essentially, what that means is you're 00:52:20.090 --> 00:52:24.330 align:middle line:84% looking at spacing that's actually larger. 00:52:24.330 --> 00:52:24.850 align:middle line:90% OK? 00:52:24.850 --> 00:52:26.450 align:middle line:84% So in fact, what we are seeing here-- 00:52:26.450 --> 00:52:28.290 align:middle line:84% this is called low angle scattering. 00:52:28.290 --> 00:52:30.410 align:middle line:84% Low angle scattering usually is indicative 00:52:30.410 --> 00:52:33.450 align:middle line:84% that there are actually nano voids inside a solid material. 00:52:33.450 --> 00:52:34.010 align:middle line:90% OK? 00:52:34.010 --> 00:52:36.770 align:middle line:84% Those nano voids have a characteristic length scale 00:52:36.770 --> 00:52:38.950 align:middle line:84% much larger than inter-atomic spacing. 00:52:38.950 --> 00:52:41.210 align:middle line:84% That's why the diffraction peak tends 00:52:41.210 --> 00:52:44.110 align:middle line:84% to appear at a much smaller diffraction angle. 00:52:44.110 --> 00:52:47.310 align:middle line:90% 00:52:47.310 --> 00:52:49.990 align:middle line:84% So it's basically a nanoporous material. 00:52:49.990 --> 00:52:52.710 align:middle line:84% Now, the fact that for amorphous glass, 00:52:52.710 --> 00:52:54.990 align:middle line:84% there's no such low angle scattering 00:52:54.990 --> 00:52:58.910 align:middle line:84% indicates that there's no nano voids, 00:52:58.910 --> 00:53:01.410 align:middle line:84% or glass solids is not nanoporous. 00:53:01.410 --> 00:53:03.470 align:middle line:90% It's a continuous network. 00:53:03.470 --> 00:53:05.390 align:middle line:84% That's what I mean by continuous, OK? 00:53:05.390 --> 00:53:13.190 align:middle line:90% 00:53:13.190 --> 00:53:13.770 align:middle line:90% OK. 00:53:13.770 --> 00:53:17.710 align:middle line:84% Next, we can compare this diffraction spectra 00:53:17.710 --> 00:53:21.030 align:middle line:84% with the crystalline cristobalite. 00:53:21.030 --> 00:53:21.667 align:middle line:90% OK? 00:53:21.667 --> 00:53:23.750 align:middle line:84% So if it's crystalline material-- you have already 00:53:23.750 --> 00:53:25.917 align:middle line:84% learned about X-ray diffraction from other glasses-- 00:53:25.917 --> 00:53:28.030 align:middle line:84% you're going to see a set of peaks 00:53:28.030 --> 00:53:31.007 align:middle line:84% that correspond to specific lattice spacing, OK? 00:53:31.007 --> 00:53:33.590 align:middle line:84% You probably have also learned about this, called the Scherrer 00:53:33.590 --> 00:53:34.870 align:middle line:90% equation. 00:53:34.870 --> 00:53:37.470 align:middle line:84% So Scherrer equation allows you to actually predict 00:53:37.470 --> 00:53:40.510 align:middle line:84% the size of the crystalline grid by looking 00:53:40.510 --> 00:53:43.080 align:middle line:84% at the full width half maximum of these X-ray diffraction 00:53:43.080 --> 00:53:44.200 align:middle line:90% peaks. 00:53:44.200 --> 00:53:47.160 align:middle line:84% So you can actually apply this Scherrer equation 00:53:47.160 --> 00:53:50.700 align:middle line:84% onto this very broad diffraction peak of amorphous glass there. 00:53:50.700 --> 00:53:53.000 align:middle line:84% If you go ahead and do the calculation, 00:53:53.000 --> 00:53:56.520 align:middle line:84% you will find out that the "crystalline grain," 00:53:56.520 --> 00:54:00.280 align:middle line:84% with a quotation mark, or the order region, 00:54:00.280 --> 00:54:04.840 align:middle line:84% has a dimension of about less than 8 Angstrom. 00:54:04.840 --> 00:54:07.680 align:middle line:84% Now, if you look at the unit cell size of a cristobalite, 00:54:07.680 --> 00:54:10.400 align:middle line:90% it's about 7 Angstrom. 00:54:10.400 --> 00:54:14.360 align:middle line:84% So what that tells you is that the whole concept 00:54:14.360 --> 00:54:17.160 align:middle line:84% of crystalline grain is completely 00:54:17.160 --> 00:54:20.840 align:middle line:84% inapplicable for amorphous materials. 00:54:20.840 --> 00:54:23.480 align:middle line:84% Sometimes, you may hear people saying that amorphous solid 00:54:23.480 --> 00:54:25.595 align:middle line:84% is basically like a limit of nanocrystal material. 00:54:25.595 --> 00:54:27.220 align:middle line:84% If you have a nanocrystalline material, 00:54:27.220 --> 00:54:28.920 align:middle line:84% you made the grain very, very small. 00:54:28.920 --> 00:54:30.220 align:middle line:90% You then get amorphous solids. 00:54:30.220 --> 00:54:30.720 align:middle line:90% OK? 00:54:30.720 --> 00:54:33.760 align:middle line:84% What we're trying to argue is that that concept 00:54:33.760 --> 00:54:40.820 align:middle line:84% is at least flawed because all the regions inside glass 00:54:40.820 --> 00:54:43.060 align:middle line:84% material simply does not go beyond even just 00:54:43.060 --> 00:54:45.660 align:middle line:90% a couple atomic spacing. 00:54:45.660 --> 00:54:46.380 align:middle line:90% OK? 00:54:46.380 --> 00:54:48.940 align:middle line:84% So glasses-- you should not treat it 00:54:48.940 --> 00:54:51.820 align:middle line:84% as a collection of very small crystals. 00:54:51.820 --> 00:54:55.360 align:middle line:84% It's just a continuous amorphous network. 00:54:55.360 --> 00:54:57.940 align:middle line:90% 00:54:57.940 --> 00:54:58.440 align:middle line:90% All right. 00:54:58.440 --> 00:55:00.580 align:middle line:84% So in this slide, I've shown you, essentially, 00:55:00.580 --> 00:55:03.780 align:middle line:84% qualitative analysis of actually differential fracture. 00:55:03.780 --> 00:55:06.660 align:middle line:84% We want to go a bit more quantitative. 00:55:06.660 --> 00:55:09.420 align:middle line:84% And that's what scientists have done, actually, back in-- this 00:55:09.420 --> 00:55:11.363 align:middle line:90% is almost 60 years ago. 00:55:11.363 --> 00:55:13.780 align:middle line:84% At the time, they didn't have advanced computer simulation 00:55:13.780 --> 00:55:14.280 align:middle line:90% tools. 00:55:14.280 --> 00:55:15.905 align:middle line:84% So what they can do-- they can actually 00:55:15.905 --> 00:55:19.120 align:middle line:84% construct the atomic model of glass by stick model. 00:55:19.120 --> 00:55:20.520 align:middle line:90% Literally stick model. 00:55:20.520 --> 00:55:23.020 align:middle line:84% They actually use balls and sticks, put it together, OK? 00:55:23.020 --> 00:55:25.000 align:middle line:84% So they follow Zachariasen's model. 00:55:25.000 --> 00:55:27.700 align:middle line:84% They constructed this actual model. 00:55:27.700 --> 00:55:30.140 align:middle line:84% And then from that, they can then calculate, essentially, 00:55:30.140 --> 00:55:32.685 align:middle line:84% a structure factor, and therefore, the, 00:55:32.685 --> 00:55:34.060 align:middle line:84% in this case, radial distribution 00:55:34.060 --> 00:55:35.280 align:middle line:90% function of glass materials. 00:55:35.280 --> 00:55:37.060 align:middle line:84% We're going to talk about this radial distribution function 00:55:37.060 --> 00:55:38.382 align:middle line:90% in the next few slides, OK? 00:55:38.382 --> 00:55:40.840 align:middle line:84% It's basically a parameter that characterizes the structure 00:55:40.840 --> 00:55:42.720 align:middle line:90% of this network here. 00:55:42.720 --> 00:55:45.560 align:middle line:84% But long story short, if you look at the comparison 00:55:45.560 --> 00:55:47.440 align:middle line:84% here, on top, you get the experimentally 00:55:47.440 --> 00:55:50.880 align:middle line:84% measured radial distribution function from actual diffraction 00:55:50.880 --> 00:55:53.000 align:middle line:84% spectra-- actually, differential spectra of glass. 00:55:53.000 --> 00:55:57.480 align:middle line:84% At the bottom, this is the model, the radial distribution 00:55:57.480 --> 00:56:01.560 align:middle line:84% function from this ball and stick network. 00:56:01.560 --> 00:56:03.600 align:middle line:84% You see this striking similarity there 00:56:03.600 --> 00:56:07.120 align:middle line:84% that again indicates that this, Zachariasen's random network 00:56:07.120 --> 00:56:10.720 align:middle line:84% model, gives you a very precise description of the glass 00:56:10.720 --> 00:56:12.280 align:middle line:90% structure there. 00:56:12.280 --> 00:56:13.920 align:middle line:90% OK? 00:56:13.920 --> 00:56:14.800 align:middle line:90% All right. 00:56:14.800 --> 00:56:18.480 align:middle line:84% Now, finally, I want to mention that seeing is believing. 00:56:18.480 --> 00:56:23.660 align:middle line:84% If you fast forward to just about 10 years ago, now, 00:56:23.660 --> 00:56:26.080 align:middle line:84% people have state-of-the-art electron microscopy that can 00:56:26.080 --> 00:56:27.700 align:middle line:90% actually resolve single atoms. 00:56:27.700 --> 00:56:30.000 align:middle line:84% So we will now be able to actually directly visualize 00:56:30.000 --> 00:56:32.240 align:middle line:84% the network structure inside glass. 00:56:32.240 --> 00:56:33.160 align:middle line:90% OK? 00:56:33.160 --> 00:56:36.720 align:middle line:84% So the story behind it is that this is actually 00:56:36.720 --> 00:56:37.920 align:middle line:90% a group in Cornell. 00:56:37.920 --> 00:56:40.250 align:middle line:84% They were actually looking at some samples, some carbon 00:56:40.250 --> 00:56:41.210 align:middle line:90% samples. 00:56:41.210 --> 00:56:43.210 align:middle line:84% Then the grad student actually working on this 00:56:43.210 --> 00:56:44.918 align:middle line:84% noticed that there was actually something 00:56:44.918 --> 00:56:47.150 align:middle line:84% that looked like impurity on the sample 00:56:47.150 --> 00:56:49.730 align:middle line:84% here she's looking at [? NT ?] here, OK? 00:56:49.730 --> 00:56:51.650 align:middle line:84% Instead of just simply discounting it 00:56:51.650 --> 00:56:53.870 align:middle line:84% as just this is contamination of the sample, 00:56:53.870 --> 00:56:56.370 align:middle line:84% she actually dug a little bit deeper, did some analysis, 00:56:56.370 --> 00:56:59.050 align:middle line:84% and found out that what she has there is actually 00:56:59.050 --> 00:57:02.950 align:middle line:90% a bilayer silica glass. 00:57:02.950 --> 00:57:03.450 align:middle line:90% OK? 00:57:03.450 --> 00:57:06.145 align:middle line:84% Now, to explain what bilayer silica glass looks like, 00:57:06.145 --> 00:57:07.770 align:middle line:84% we have to take a look at, essentially, 00:57:07.770 --> 00:57:09.990 align:middle line:84% the basic structural unit of silica glass. 00:57:09.990 --> 00:57:12.240 align:middle line:84% If you think about, for example, quartz crystal, which 00:57:12.240 --> 00:57:15.130 align:middle line:84% is basically crystalline SiO2, the basic structural unit 00:57:15.130 --> 00:57:20.258 align:middle line:84% is this S, silicon, O4, SiO4, tetrahedra. 00:57:20.258 --> 00:57:21.550 align:middle line:90% You have silicon in the center. 00:57:21.550 --> 00:57:24.570 align:middle line:84% You have 4 oxygen atoms on the sides. 00:57:24.570 --> 00:57:26.890 align:middle line:84% They can then connect together to form 00:57:26.890 --> 00:57:28.370 align:middle line:90% the three-dimensional network. 00:57:28.370 --> 00:57:31.990 align:middle line:84% Now, in the case of a 2D silica glass, 00:57:31.990 --> 00:57:35.370 align:middle line:84% what you have here is essentially 2 of these 00:57:35.370 --> 00:57:36.410 align:middle line:90% tetrahedra. 00:57:36.410 --> 00:57:38.988 align:middle line:84% They share one corner, and they connect 00:57:38.988 --> 00:57:40.530 align:middle line:84% to each other [INAUDIBLE] vertically. 00:57:40.530 --> 00:57:41.030 align:middle line:90% OK? 00:57:41.030 --> 00:57:44.772 align:middle line:84% So now, if you look from on top, they're actually aligned. 00:57:44.772 --> 00:57:47.230 align:middle line:84% So if you look on top, what you see here will be basically, 00:57:47.230 --> 00:57:51.470 align:middle line:90% you have 3 oxygen and 1 silicon. 00:57:51.470 --> 00:57:51.990 align:middle line:90% OK? 00:57:51.990 --> 00:57:54.270 align:middle line:84% Then these units can connect to each other 00:57:54.270 --> 00:57:56.210 align:middle line:84% to form, basically, a two-dimensional network. 00:57:56.210 --> 00:57:58.710 align:middle line:84% That's what's called a bilayer silica glass. 00:57:58.710 --> 00:57:59.470 align:middle line:90% OK? 00:57:59.470 --> 00:58:01.710 align:middle line:84% So that's what I'm trying to show here, how, 00:58:01.710 --> 00:58:05.670 align:middle line:84% if you look from on top, you get a 2D projection of this silicon 00:58:05.670 --> 00:58:09.250 align:middle line:84% oxygen triangle here, which looks very similar, by the way, 00:58:09.250 --> 00:58:13.450 align:middle line:84% to the fictitious 2D model I had mentioned about this A2O3 glass. 00:58:13.450 --> 00:58:18.350 align:middle line:84% They look quite similar there from 2D projection perspective. 00:58:18.350 --> 00:58:19.150 align:middle line:90% All right. 00:58:19.150 --> 00:58:20.830 align:middle line:84% Now, what I'm showing you here-- this 00:58:20.830 --> 00:58:24.430 align:middle line:84% is the actual image of this bilayer silica, OK? 00:58:24.430 --> 00:58:26.750 align:middle line:84% Left-hand side-- this is actually crystalline region. 00:58:26.750 --> 00:58:31.150 align:middle line:84% Right-hand side is actually the amorphous region. 00:58:31.150 --> 00:58:33.870 align:middle line:84% And they were able to verify that the structure they actually 00:58:33.870 --> 00:58:36.800 align:middle line:84% observed under [? TN ?] agrees perfectly 00:58:36.800 --> 00:58:41.280 align:middle line:84% with what Zachariasen had predicted almost 100 years ago. 00:58:41.280 --> 00:58:41.820 align:middle line:90% OK? 00:58:41.820 --> 00:58:45.440 align:middle line:84% So this gives you a very strong belief that seeing is believing. 00:58:45.440 --> 00:58:49.440 align:middle line:84% Now, you can verify this theory with high confidence. 00:58:49.440 --> 00:58:54.080 align:middle line:84% And beyond that, turns out they also get into the Guinness World 00:58:54.080 --> 00:58:55.600 align:middle line:90% Record book. 00:58:55.600 --> 00:58:59.640 align:middle line:84% It's basically the thinnest glass you can ever make. 00:58:59.640 --> 00:59:01.880 align:middle line:84% And unlike other world records-- you have probably 00:59:01.880 --> 00:59:04.060 align:middle line:84% heard about people breaking the world record once in a while-- 00:59:04.060 --> 00:59:05.685 align:middle line:84% this is one of the world records that's 00:59:05.685 --> 00:59:08.340 align:middle line:84% going to stay forever because this is really the thinnest 00:59:08.340 --> 00:59:09.340 align:middle line:90% glass you can ever make. 00:59:09.340 --> 00:59:12.920 align:middle line:84% You can't make anything that's thinner than that, OK? 00:59:12.920 --> 00:59:14.040 align:middle line:90% OK. 00:59:14.040 --> 00:59:17.400 align:middle line:84% So we still have about 10 minutes. 00:59:17.400 --> 00:59:20.240 align:middle line:84% Now, let's go to the last point here-- 00:59:20.240 --> 00:59:21.880 align:middle line:90% essentially, glass transition. 00:59:21.880 --> 00:59:24.900 align:middle line:84% So for amorphous solids, it needs to be metastable. 00:59:24.900 --> 00:59:26.940 align:middle line:90% It needs to exhibit this-- 00:59:26.940 --> 00:59:29.100 align:middle line:84% it needs to lack this long-range structure order. 00:59:29.100 --> 00:59:29.880 align:middle line:90% OK? 00:59:29.880 --> 00:59:31.260 align:middle line:90% So that's for amorphous solids. 00:59:31.260 --> 00:59:34.500 align:middle line:84% In order for an amorphous solid to qualify as glass, 00:59:34.500 --> 00:59:37.100 align:middle line:84% it also needs to exhibit this very important property here. 00:59:37.100 --> 00:59:39.820 align:middle line:84% It needs to exhibit a glass transition. 00:59:39.820 --> 00:59:41.480 align:middle line:84% To explain what glass transition is, 00:59:41.480 --> 00:59:44.500 align:middle line:84% let's first take a look at the crystalline counterpart, OK? 00:59:44.500 --> 00:59:47.420 align:middle line:84% So if you have crystalline material, what 00:59:47.420 --> 00:59:49.980 align:middle line:84% I'm plotting here-- vertical axis 00:59:49.980 --> 00:59:53.260 align:middle line:84% is some macroscopic thermodynamic parameter. 00:59:53.260 --> 00:59:54.420 align:middle line:90% It can be volume. 00:59:54.420 --> 00:59:56.060 align:middle line:90% It can be enthalpy. 00:59:56.060 --> 00:59:58.900 align:middle line:84% And what I'm showing here is how that macroscopic thermal 00:59:58.900 --> 01:00:03.820 align:middle line:84% parameter varies as a function of a temperature. 01:00:03.820 --> 01:00:06.420 align:middle line:84% If it's crystalline material, and assume 01:00:06.420 --> 01:00:08.660 align:middle line:84% you keep everything in thermal equilibrium, which 01:00:08.660 --> 01:00:12.020 align:middle line:84% means that you have to essentially heat up or cool down 01:00:12.020 --> 01:00:15.600 align:middle line:84% indefinitely slow, then everything stays in equilibrium, 01:00:15.600 --> 01:00:18.100 align:middle line:84% and you get the plot like this, which you probably have seen 01:00:18.100 --> 01:00:19.620 align:middle line:90% in your thermodynamics class. 01:00:19.620 --> 01:00:22.480 align:middle line:84% Your crystalline material-- you heat it up slowly. 01:00:22.480 --> 01:00:23.620 align:middle line:90% You get to melting point. 01:00:23.620 --> 01:00:25.000 align:middle line:90% You get liquid. 01:00:25.000 --> 01:00:25.620 align:middle line:90% OK? 01:00:25.620 --> 01:00:26.480 align:middle line:90% Vice versa. 01:00:26.480 --> 01:00:27.200 align:middle line:90% You have liquid. 01:00:27.200 --> 01:00:28.540 align:middle line:90% You start to cool it down. 01:00:28.540 --> 01:00:30.340 align:middle line:84% As soon as you hit the melting point, 01:00:30.340 --> 01:00:33.800 align:middle line:84% you then go and transform into crystalline state. 01:00:33.800 --> 01:00:34.640 align:middle line:90% OK? 01:00:34.640 --> 01:00:36.960 align:middle line:84% There's a discontinuity there for this kind 01:00:36.960 --> 01:00:39.140 align:middle line:90% of an extensive parameter, OK? 01:00:39.140 --> 01:00:41.160 align:middle line:84% It indicates, essentially, there's 01:00:41.160 --> 01:00:43.940 align:middle line:84% a volume change between the solid and the liquid state 01:00:43.940 --> 01:00:46.180 align:middle line:84% or an enthalpy change, which gives you latent heat. 01:00:46.180 --> 01:00:46.680 align:middle line:90% OK? 01:00:46.680 --> 01:00:50.320 align:middle line:84% So those are the characteristics of this first order solid liquid 01:00:50.320 --> 01:00:51.320 align:middle line:90% phase transition. 01:00:51.320 --> 01:00:52.560 align:middle line:90% OK? 01:00:52.560 --> 01:00:55.000 align:middle line:84% Now, in order to form glass, you have 01:00:55.000 --> 01:00:58.760 align:middle line:84% to go to an irreversible process. 01:00:58.760 --> 01:01:01.880 align:middle line:84% You have to cool down this liquid sufficiently fast. 01:01:01.880 --> 01:01:05.640 align:middle line:84% So you actually avoid crystallization. 01:01:05.640 --> 01:01:08.920 align:middle line:84% So now, starting from the melt, if you cool down quick enough 01:01:08.920 --> 01:01:11.840 align:middle line:84% so that kinetically, you don't allow this liquid 01:01:11.840 --> 01:01:15.198 align:middle line:84% to actually nucleate and grow, then 01:01:15.198 --> 01:01:17.240 align:middle line:84% what you end up getting here is then going to be, 01:01:17.240 --> 01:01:19.840 align:middle line:90% basically, a supercooled liquid. 01:01:19.840 --> 01:01:22.560 align:middle line:84% And if you continue to cool down, 01:01:22.560 --> 01:01:26.480 align:middle line:84% this supercooled liquid then transitions into glass, 01:01:26.480 --> 01:01:28.640 align:middle line:84% if you can suppress crystallization. 01:01:28.640 --> 01:01:32.210 align:middle line:90% 01:01:32.210 --> 01:01:37.770 align:middle line:84% In-between here, this line-- this is the line that 01:01:37.770 --> 01:01:39.490 align:middle line:90% indicates glass, OK? 01:01:39.490 --> 01:01:43.010 align:middle line:84% Here, this is basically a supercooled liquid. 01:01:43.010 --> 01:01:45.330 align:middle line:84% In-between, there's this region here 01:01:45.330 --> 01:01:48.810 align:middle line:84% that's called glass transition, where the slope of this line 01:01:48.810 --> 01:01:49.970 align:middle line:90% actually changes. 01:01:49.970 --> 01:01:50.770 align:middle line:90% OK? 01:01:50.770 --> 01:01:52.930 align:middle line:90% Gradually changes. 01:01:52.930 --> 01:01:56.070 align:middle line:84% This is called a glass transition. 01:01:56.070 --> 01:01:58.930 align:middle line:90% 01:01:58.930 --> 01:02:01.430 align:middle line:84% Now, a few important features about this glass transition. 01:02:01.430 --> 01:02:05.450 align:middle line:84% First of all, you see that this is a continuous change. 01:02:05.450 --> 01:02:09.690 align:middle line:84% Unlike melting or solidification, 01:02:09.690 --> 01:02:11.450 align:middle line:84% in a crystalline solid, you don't 01:02:11.450 --> 01:02:16.870 align:middle line:84% see a sudden jump of the extensive parameters, OK? 01:02:16.870 --> 01:02:19.890 align:middle line:90% 01:02:19.890 --> 01:02:22.570 align:middle line:84% So it's a continuous transformation. 01:02:22.570 --> 01:02:27.210 align:middle line:84% Essentially, liquid transitions into solid smoothly 01:02:27.210 --> 01:02:29.590 align:middle line:90% or continuously. 01:02:29.590 --> 01:02:31.870 align:middle line:84% However, one thing I want to emphasize-- 01:02:31.870 --> 01:02:34.178 align:middle line:84% this is really important-- is that despite the glass 01:02:34.178 --> 01:02:36.470 align:middle line:84% and liquid-- they are connected together continuously-- 01:02:36.470 --> 01:02:38.970 align:middle line:90% glasses is different. 01:02:38.970 --> 01:02:43.950 align:middle line:84% They are fundamentally different from liquids. 01:02:43.950 --> 01:02:44.655 align:middle line:90% OK? 01:02:44.655 --> 01:02:47.030 align:middle line:84% Again, sometimes, you may hear people saying that glasses 01:02:47.030 --> 01:02:49.310 align:middle line:90% are basically frozen liquids. 01:02:49.310 --> 01:02:51.470 align:middle line:84% That's actually not quite true because if you 01:02:51.470 --> 01:02:53.390 align:middle line:84% look at the property of glass, they 01:02:53.390 --> 01:02:56.150 align:middle line:84% are basically different from liquid. 01:02:56.150 --> 01:02:59.010 align:middle line:84% Now, simply put, think about the slope of this line. 01:02:59.010 --> 01:03:00.630 align:middle line:90% What is the slope of this line? 01:03:00.630 --> 01:03:02.570 align:middle line:84% It depends on what the vertical axis is. 01:03:02.570 --> 01:03:06.222 align:middle line:84% If it's volume, it's basically a thermal expansion coefficient, 01:03:06.222 --> 01:03:07.930 align:middle line:84% volumetric thermal expansion coefficient. 01:03:07.930 --> 01:03:11.930 align:middle line:84% If it's an enthalpy, it's basically a heat capacity. 01:03:11.930 --> 01:03:14.750 align:middle line:90% 01:03:14.750 --> 01:03:17.350 align:middle line:84% So the thermal expansion coefficient essentially 01:03:17.350 --> 01:03:18.950 align:middle line:90% relates to a glass structure. 01:03:18.950 --> 01:03:21.670 align:middle line:84% The heat capacity relates to the degree of freedom 01:03:21.670 --> 01:03:25.510 align:middle line:84% the atoms can actually access in the solid state. 01:03:25.510 --> 01:03:28.920 align:middle line:84% So the fact that glass has a different heat 01:03:28.920 --> 01:03:32.640 align:middle line:84% capacity and volumetric thermal expansion coefficient compared 01:03:32.640 --> 01:03:36.360 align:middle line:84% to liquids means that fundamentally, glassy state 01:03:36.360 --> 01:03:38.380 align:middle line:90% is different from liquid state. 01:03:38.380 --> 01:03:41.880 align:middle line:84% You cannot just treat them as the same. 01:03:41.880 --> 01:03:44.860 align:middle line:84% So the glass transition, despite being continuous, 01:03:44.860 --> 01:03:47.460 align:middle line:90% is a real structure transition. 01:03:47.460 --> 01:03:54.240 align:middle line:90% 01:03:54.240 --> 01:03:55.360 align:middle line:90% OK? 01:03:55.360 --> 01:03:58.120 align:middle line:84% Again, later, we are going into more details about what's 01:03:58.120 --> 01:04:01.440 align:middle line:84% your macroscopic and thermodynamic origin 01:04:01.440 --> 01:04:04.863 align:middle line:84% of the glass transition, but for now, you just 01:04:04.863 --> 01:04:06.280 align:middle line:84% need to know that essentially, you 01:04:06.280 --> 01:04:08.040 align:middle line:84% have to go through this smoothly region 01:04:08.040 --> 01:04:10.623 align:middle line:84% there that indicates that you are converting from liquid state 01:04:10.623 --> 01:04:11.760 align:middle line:90% to the glassy state. 01:04:11.760 --> 01:04:14.438 align:middle line:84% And one useful concept I also want to introduce here 01:04:14.438 --> 01:04:15.980 align:middle line:84% is so-called fictive temperature, OK? 01:04:15.980 --> 01:04:20.040 align:middle line:84% So fictive temperature-- you can define it on this plot 01:04:20.040 --> 01:04:22.320 align:middle line:84% here by simply extending the glass 01:04:22.320 --> 01:04:25.880 align:middle line:84% line and the supercooled liquid line. 01:04:25.880 --> 01:04:27.320 align:middle line:84% Because they have different slope, 01:04:27.320 --> 01:04:29.340 align:middle line:84% they must cross over at some point. 01:04:29.340 --> 01:04:31.440 align:middle line:84% The crossover point corresponds to a temperature. 01:04:31.440 --> 01:04:34.380 align:middle line:84% This is what we call the fictive temperature. 01:04:34.380 --> 01:04:41.100 align:middle line:90% 01:04:41.100 --> 01:04:43.220 align:middle line:84% Now, a couple of points about fictive temperature. 01:04:43.220 --> 01:04:44.620 align:middle line:84% First thing is that you probably have 01:04:44.620 --> 01:04:46.220 align:middle line:84% heard about another temperature called 01:04:46.220 --> 01:04:50.100 align:middle line:84% glass transition temperature, TG. 01:04:50.100 --> 01:04:54.200 align:middle line:84% So fictive temperature is close to glass transition temperature, 01:04:54.200 --> 01:04:56.415 align:middle line:84% but they're not exactly the same. 01:04:56.415 --> 01:04:58.040 align:middle line:84% We'll talk about that definition later. 01:04:58.040 --> 01:04:59.380 align:middle line:90% OK? 01:04:59.380 --> 01:05:02.140 align:middle line:84% Fictive temperature, despite being a temperature, 01:05:02.140 --> 01:05:06.660 align:middle line:84% is actually usually used to characterize glass structure. 01:05:06.660 --> 01:05:08.980 align:middle line:84% Later on, you will see that this is actually 01:05:08.980 --> 01:05:13.797 align:middle line:84% treated as a structure parameter, here, OK? 01:05:13.797 --> 01:05:16.380 align:middle line:84% Different glass structures have different fictive temperature, 01:05:16.380 --> 01:05:18.732 align:middle line:90% all right? 01:05:18.732 --> 01:05:23.580 align:middle line:84% OK, just to prove my point here that different structures have 01:05:23.580 --> 01:05:27.260 align:middle line:84% different fictive temperature, quite obviously, if you start 01:05:27.260 --> 01:05:29.760 align:middle line:84% to cool down glass, for example, at different cooling rates, 01:05:29.760 --> 01:05:32.200 align:middle line:84% turns out you end up with different glassy states. 01:05:32.200 --> 01:05:34.880 align:middle line:84% If you cool down at a faster cooling rate, 01:05:34.880 --> 01:05:37.560 align:middle line:84% this glass line is going to deviate 01:05:37.560 --> 01:05:40.740 align:middle line:84% from the supercooled liquid line at an earlier point. 01:05:40.740 --> 01:05:45.680 align:middle line:84% So you initiate glass transition actually sooner. 01:05:45.680 --> 01:05:49.880 align:middle line:84% And the resulting glass also has different thermodynamic 01:05:49.880 --> 01:05:51.700 align:middle line:84% properties that depend on cooling rate. 01:05:51.700 --> 01:05:55.440 align:middle line:84% On this plot here, we'll see that typically, 01:05:55.440 --> 01:05:58.280 align:middle line:84% if you cool down faster, you tend to get glasses 01:05:58.280 --> 01:05:59.300 align:middle line:90% with lower density. 01:05:59.300 --> 01:06:03.320 align:middle line:90% 01:06:03.320 --> 01:06:05.380 align:middle line:84% There are exceptions, but most glasses, 01:06:05.380 --> 01:06:09.200 align:middle line:84% if you cool down faster, you tend to get lower density. 01:06:09.200 --> 01:06:14.880 align:middle line:84% Also, if you cool down faster, you always get a glassy state 01:06:14.880 --> 01:06:17.040 align:middle line:90% with higher enthalpy, always. 01:06:17.040 --> 01:06:18.400 align:middle line:90% There's no exception. 01:06:18.400 --> 01:06:19.040 align:middle line:90% OK? 01:06:19.040 --> 01:06:21.020 align:middle line:84% So if the vertical axis is enthalpy, 01:06:21.020 --> 01:06:22.700 align:middle line:90% then this plot always holds. 01:06:22.700 --> 01:06:26.210 align:middle line:84% If it's volume, they're actual volume anomaly, in some glasses. 01:06:26.210 --> 01:06:30.130 align:middle line:90% 01:06:30.130 --> 01:06:31.765 align:middle line:84% So now, obviously, if you start to try 01:06:31.765 --> 01:06:33.890 align:middle line:84% to plot with the fictive temperature of these three 01:06:33.890 --> 01:06:37.010 align:middle line:84% different lines here, you draw your extension. 01:06:37.010 --> 01:06:39.690 align:middle line:84% What you'll find out almost immediately 01:06:39.690 --> 01:06:44.448 align:middle line:84% is that for the three glasses, glass 3 01:06:44.448 --> 01:06:46.490 align:middle line:84% with highest cooling rate should have the highest 01:06:46.490 --> 01:06:48.610 align:middle line:90% fictive temperature. 01:06:48.610 --> 01:06:51.410 align:middle line:84% So the higher the cooling rate, the higher the fictive 01:06:51.410 --> 01:06:53.693 align:middle line:90% temperature. 01:06:53.693 --> 01:06:55.610 align:middle line:84% And this is exactly because of this dependence 01:06:55.610 --> 01:06:57.830 align:middle line:84% of fictive temperature on the processing condition 01:06:57.830 --> 01:07:00.290 align:middle line:84% that people are actually using fictive temperature as a way 01:07:00.290 --> 01:07:02.010 align:middle line:90% to quantify glass structure. 01:07:02.010 --> 01:07:02.682 align:middle line:90% OK? 01:07:02.682 --> 01:07:04.890 align:middle line:84% So later on, again, we're going to talk about models, 01:07:04.890 --> 01:07:07.530 align:middle line:84% how this can actually be used to quantitatively, for example, 01:07:07.530 --> 01:07:10.090 align:middle line:84% predict glass relaxation that depends on structure. 01:07:10.090 --> 01:07:10.630 align:middle line:90% OK? 01:07:10.630 --> 01:07:13.530 align:middle line:90% 01:07:13.530 --> 01:07:14.170 align:middle line:90% All right. 01:07:14.170 --> 01:07:18.210 align:middle line:84% Now, I also want to show you some peculiar behavior 01:07:18.210 --> 01:07:19.570 align:middle line:90% of the glass transition here. 01:07:19.570 --> 01:07:22.530 align:middle line:84% I've shown you how this line looks when you actually 01:07:22.530 --> 01:07:24.430 align:middle line:84% try to cool down the supercooled liquid. 01:07:24.430 --> 01:07:27.150 align:middle line:84% Now, what happens if you try to reheat it up? 01:07:27.150 --> 01:07:29.230 align:middle line:84% In a crystalline material, because it's 01:07:29.230 --> 01:07:32.230 align:middle line:84% a reversible process, if you do it slowly, 01:07:32.230 --> 01:07:35.910 align:middle line:84% whether heating or cooling, it always traces the same line. 01:07:35.910 --> 01:07:40.830 align:middle line:84% But for amorphous solids, its property actually 01:07:40.830 --> 01:07:44.870 align:middle line:90% depends on the thermal history. 01:07:44.870 --> 01:07:48.590 align:middle line:84% So depending on whether you're cooling it down or heating it 01:07:48.590 --> 01:07:52.133 align:middle line:84% up, this line actually goes in different trajectories. 01:07:52.133 --> 01:07:53.550 align:middle line:84% So if you heat it up, most likely, 01:07:53.550 --> 01:07:55.630 align:middle line:84% we're going to see something like this. 01:07:55.630 --> 01:07:58.870 align:middle line:84% It goes down, and then goes back up. 01:07:58.870 --> 01:07:59.670 align:middle line:90% OK? 01:07:59.670 --> 01:08:02.030 align:middle line:84% That's actually a sign of relaxation 01:08:02.030 --> 01:08:04.470 align:middle line:84% during the glass transition regime. 01:08:04.470 --> 01:08:06.470 align:middle line:84% And again, later in this semester, 01:08:06.470 --> 01:08:09.070 align:middle line:84% I'm going to give you a quantitative model that 01:08:09.070 --> 01:08:13.290 align:middle line:84% allows you to predict these kind of curves in glass materials. 01:08:13.290 --> 01:08:13.790 align:middle line:90% OK? 01:08:13.790 --> 01:08:16.310 align:middle line:90% 01:08:16.310 --> 01:08:18.550 align:middle line:90% All right. 01:08:18.550 --> 01:08:21.240 align:middle line:84% We are running out of time here, so I'll actually 01:08:21.240 --> 01:08:22.520 align:middle line:90% conclude this lecture. 01:08:22.520 --> 01:08:24.939 align:middle line:90% Any last-minute questions? 01:08:24.939 --> 01:08:28.399 align:middle line:90% 01:08:28.399 --> 01:08:30.120 align:middle line:90% All good? 01:08:30.120 --> 01:08:33.359 align:middle line:90% Crystal clear, not amorphous? 01:08:33.359 --> 01:08:34.939 align:middle line:90% All right, that's it. 01:08:34.939 --> 01:08:38.530 align:middle line:84% Thank you, and I will see you on Wednesday. 01:08:38.530 --> 01:09:21.000 align:middle line:90%