 So Kurt mentioned a wide range of applications where materials by design are important. I want to show you something, a snapshot of some of the programs that are underway in my group, focused mostly around what I'm going to call hybrid materials. These in this particular case, because there's many types of hybrid materials, are typically inorganic, glassy type materials with an inorganic component as well as an organic component. And they are ubiquitously used in a wide range of technologies. Every one of you are sitting here with some of these materials in your pocket right at the moment if you have a cell phone with a microelectronic device in it because they're used as dielectric layers in the back end structures of a device. But they can be used in many other applications as you can see here from touchscreens to organic thin film transistor structures, organic photovoltaic devices all the way through to anti-reflection coatings for solar technologies. So these are the typical applications of these, the kind of materials that I'm going to talk about today. Very often they can be made very inexpensively. Materials by design now has to involve a component of cost and manufacturability. And so being able to use roll-to-roll processing, or as I'll mention a little bit later, new forms of atmospheric plasma deposition, so depositing these kind of films in-air at room temperature with a plasma process is very important. I'm going to make mention of one other type of hybrid material in the talk today, and that is some of the soft tissues that actually exist in our bodies. Because in some ways these are hybrid-like materials, particularly the top layers of your skin. And I'll show you some of the work that we're doing there, treating these as hybrid systems. Part of the focus of our work has been the thermomechanical properties of these types of materials and how they connect to the underlying molecular structure. And I'll show you an example of how we can make that bridge in our studies. Very often these materials, here's a hybrid film over here, it could be in any one of these applications, is either processed in relatively harsh environments or it operates in harsh environments. And so there might be environmental species, stresses in the film, incoming high-energy photons from the solar spectrum. And the synergistic effect of all these stressing parameters is very important in terms of determining the degradation, the reliability, the adhesion, the cohesion and even things like the stiffness of these layers. So this is a complex interaction that we seek to understand. So probably the most important work we've done over the years in this area, this is over many years now starting initially in the microelectronics area, has been to show how you can quantify some of these properties. So for example, how do you measure adhesion or cohesion in a thin organic photovoltaic device structure? It turns out that up until recently that had never been done. And using techniques that we have developed years ago and that are now standard in the microelectronics industry, we can reliably measure things like the cohesion in the middle of a bulk heterojunction layer in an organic photovoltaic device. And you can see the numbers here are somewhere around about one and a half joules per meter squared, which just to calibrate you is hellish low. The chairs that you're sitting on have legs of steel which have fracture energies, the same kind of energy here, same units of perhaps 20 or 30,000 joules per meter squared. So we're expecting to take this material with a cohesion that is incredibly low and have it operate reliably in a terrestrial environment. Similar numbers we're measuring for other PV technologies like SIGs. Again, the numbers are relatively low and so it's really critical in these technologies to design the materials to have better thermomechanical properties. We're also interested in the rate at which interfaces separate or the rate at which defects evolve and we can measure those down. You can see here down to 10 to the minus 10 to 10 to the minus 12 meters per second. So that's sub-amstrone per second. The horizontal axis here is the applied load. The vertical axis is the rate at which these defects are evolving and you can see that as the loads increase, so the rate at which the interface separates increases in the dark. But if you actually illuminate the sample while you're doing the measurement, it turns out that arriving photons coming through these layers actually accelerate the rate at which bonds cleaves and interfaces separate. So this interaction between photons, between environmental species, temperature and mechanical loads all give rise to the evolution of these kinds of defects which control the reliability of these structures. So that's a little bit of the background, hybrid layers in nanoscience and biotechnologies. Of course, like most faculty, I don't do any of this work. I just get the pleasure of standing here and telling you about it and I'll acknowledge here many of my group members that will have contributed to the work that I will talk to you about today working in these different areas. Also like many Stanford faculty, I interact very significantly with many other research groups, not just at Stanford but also in industry. In fact, many of the materials that we look at in our studies over the years come from collaborators. We make some materials as I'll show you ourselves, but we work very extensively with industry and I think this is really a hallmark of one of the things that we do very well at Stanford is to interact with industry. And so please for me and for any of the other faculty that you hear talking in the next couple of days, if there's interest from you or your companies, please contact us because we're good at interacting with industry. This is just a little snapshot of what I'm going to say now. I want to show you an example of materials by design where we can actually do molecular modeling, design materials, and then actually go out and make them and probe their properties. I'm really excited about this new technique of atmospheric plasma deposition that we've been developing over the last number of years, show you what we're doing there. I'll talk a little bit about some hybrid materials in organic photovoltaic systems and then end by telling you something about yourself, or at least your skin. This is a molecular dynamic simulation that we've undertaken in my group to compute the structure of an organic containing silicate glassy material. This could be used for anything from a anti-reflection coding through to a dielectric layer. The gray atoms over here are little carbon links, so these are like little carbon reinforcing elements in an otherwise normal silicate matrix. Also the yellow atoms here are silicon, so silicon-oxygen bonding. We can compute these structures very accurately. We do not build them. We don't take precursors and connect them together. We actually put precursors into a box of any type, not just these materials, and we allow them to react, and then through a simulated annealing process, we bring them down to room temperature and confirm that we have accurately computed the structure. We can do that not just for the molecular structure, but we can even include nanoscale porosity. We actually use a templating process here where we put organic molecules into the simulation and then just like you do in real processing, we volatize them once we've vitrified the glass. So we can compute these materials very accurately. And we can then do experiments in the computer to predict properties. So here's one of the properties that you're often very interested in from a technological point of view. That is the stiffness of the material. This controls everything from wear properties to cohesion properties to the ability to integrate with high yield these materials. So just to give you an example of this, here are two different precursors that we've used in our simulations. They've both got this little carbon bridge. One of them has got a methyl group. So it's inherently less connected when you form a glass. And so by computing the initial structure, we can actually predict then the properties, the stiffness of these materials as a function of how condensed the materials are. Condensed is something that chemists like a lot because it's something that's relevant in the lab when you're making these materials. What the condensation degree is, how many bonds have formed between the precursors. From a modeling point of view, a better metric is the connectivity. So each silicon atom can at most be connected to four other silicon atoms through a little oxygen bridge. The full connectivity here would then be specified by one. You can see that the precursor with the methyl group is inherently more, is less stiff, sorry it's this blue line over here, than the one that doesn't have the methyl group because it's connected more. And we can compute that. When we plot it as a function of the connectivity, you can see all the data lines up on the same line. These open symbols over here are actual experimental materials. So we can then go and make materials and confirm that the stiffness that we're predicting is right. Fracture properties, cohesion, adhesion are a lot more complicated to compute because fracture doesn't happen as a plane through this glassy network. The crack will actually seek out a path, the weakest path through this glassy network that involves failing the most number of weak bonds and the least number of strong bonds. So we have to compute this and my student came up with a very clever method to do this. It's computationally very expensive to try and do this in a simulation that contains hundreds of thousands of atoms. So he actually uses a graph theory approach where we actually take the computed network converted into a graph and then use mathematical graph theory approaches to actually ask what's the min cut through this glass that would involve breaking the least number of strong bonds and the most number of weak bonds. And so we can compute this path. And from this we can compute then the number of bonds you need to break to separate the material and from that we can compute the fracture energy. And when we take our simulation results and we compare them to experimental results from many, many papers in the literature we can compute that very well. So this is a really good example of where you can compute molecular structure and you can actually predict properties and you can verify that. So this means now you can search for new materials. And so in this simulation here you can see we've taken a whole range of different precursors, formed the glass structure and said which one gives us the stiffest glass? And it turned out that this 135 benzene precursor, which if you think about it is a little precursor, it's very stiff, it's got these stiff connections to the silicon atoms, formed a very stiff glass way above the normal scaling that we would see. So we then went to our synthetic chemistry friends and had them actually make precursors and we made the glass. And here are the experimental results, here's our computed result over here. This by the way takes a process of fragmentation into account. Turns out when you actually really make these materials some of these precursors fragment and you have to figure that out with NMR. But then when you run the simulation you can see that we get an experimental result that's consistent. So this is really cool because we've made a super stiff glass with a precursor that we would not otherwise have thought about. So that's an example of using materials by design. The reason for this is this hyperconnectivity, this is sort of a hyperconnected hybrid molecular materials where normally silicon can only be connected to four other silicons but with this very stiff precursor we can actually connect it to five. Okay, so that's a little example there. How do we make these materials? We make them with CBD processing, we make them with Sol-gel processing, but we can also make them with atmospheric plasma deposition. So atmospheric plasma, this is actually one of our plasma heads over here. This is the plasma and you can see it's depositing onto somebody's hand. So you can do this deposition on your own hand if you so choose. Most people don't choose to do that but you could do this. It's low temperature, it's kind of cool. At Halloween it's really cool because you can walk around the lab with this kind of ghost-like plasma right in air. Now we've made some developments on the system which involve more complex precursor delivery systems. It turns out that if you make a higher temperature precursor delivery system you have access to precursors that have higher molecular weights and therefore higher boiling temperatures and therefore are less volatile. So if you just try and do this at room temperature then you wouldn't be able to volatize these precursors. So we've developed a really cool high temperature system where we can volatize very carefully these precursors and we can do it with more than one precursor so we can feed in multiple precursors and do deposition of a wide range of materials that were otherwise inaccessible. So not to go through all the details here, just again to give you a snapshot. These are coatings here deposited on plastic at room temperature, very high transparencies above 98% and you can see these are the kind of hybrid films I was just talking about. They're molecular hybrids, a little bit of organic component, a silicate component but you can see here that we get very good properties. We get extremely high stiffnesses, as high as dense silica and we get very good adhesion way above what you would get with commercial sol-gel processing. So we're very excited about this method and we're currently looking at ways of making graded coatings. So less stiff coatings on the plastic, much harder coatings on top. But we've also been interested in making other types of materials like transparent conducting oxides, zinc oxide for example. And here's an example of a study that's just completed, it's just going to be published. Again, I'm really excited about this. This is depositing a zinc oxide film in air with plasma at room temperature on plastics. Okay, that's cool. 98% transparency in these films as you can see over here. If we change the processing conditions, then you can see the transparency drops off. So there's a whole range of parameters that we can control here. This is the feed rate of the precursors, the kind of gases that we're flowing into the plasma system and the plasma power itself. Which of course, fundamentally affects the reaction kinetics of many of these different reactions that are occurring. And you can see here in probing around, without using any dopants. So zero dopants here, we can get down to very low resistivities for these films that there's a position over here. And we're working now on using some dopants to actually pull this down even further. So I think this is a very exciting possibility for these types of materials. Okay, let me say a little bit now about some of hybrid materials in organic photovoltaic systems. This is a program we have looking at inverted organic photovoltaic devices that are formed in a roll to roll process on pet substrates. So this is a collaboration that we have with Frederick Krebs University of Denmark. This is the structure over here. Here's the flexible pet, ITO, and then the bulk hetra junction layer, and then a conducting polymer p.pss layer. Now it turns out this is a strongly hydrophobic layer, being an organic layer. And this is a solution processed, aqueous solution processed conducting polymer. And so this does not wet easily the surface, and turns out to result in very poor adhesion. Now I already showed you that the cohesion of these bulk hetra junction layers themselves are very low. So this number here is even lower, and when we began to probe round, you can see here that depending on the composition of this bulk hetra junction layer, here this is all polymer, and here this is all fullerene. You can see how the adhesion of this top interface now drops from 1.6, which of course is low, to almost nothing when you get to the pure fullerene. And the problem with all of this is that if you look at the efficiency of these devices, they peak right where this adhesion value drops to virtually nothing. Now we're gonna go and take these things and put them in the sun and hope that they last for what, 10 minutes? Because that's about all you're gonna get. So this has to be addressed. This is not a unique problem, and I'm not a naysayer for this technology. I'm just saying that we have to address these kind of thermo-mechanical reliability issues early on in the design stage. And so we have a number of programs looking at a number of different strategies that involve everything from how the layer thicknesses affect thermo-mechanical properties to the composition of the bulk hetra junction there, the tethers that are on the fullerene, the type of conducting polymer, the molecular weight of the conducting polymer, turns out to make an enormous effect on not only efficiency, but also on cohesion. Whether the molecules are intercalated or not makes another difference. And other material science things that we can do here to manipulate the structure. This is just a little example showing that in fact when we look at the intercalation of these fullerenes with the polymers, when they do intercalate for this system here, you can see that we get this enormous increase in cohesion. We have other studies underway where we're playing with the molecular weight and we can bring these numbers all the way up to 16 to 20 joules per meter squared. So this is entirely satisfactory for making a reliable technology. This is the last little section here that I'll spend a couple of minutes on is our skin, an example of another hybrid material which is exposed to solar radiation. And so I've had a program looking at soft tissues for many years now. And as our photovoltaics programs emerged, I eventually thought, well, why don't we do some of the same experiments that we do on solar materials exposed to terrestrial environments on human skin and see what happens, see whether we can predict damage that might occur. So this is a result of a study that was published recently in the Proceedings of the National Academy where we were looking particularly at the very top layer of your skin. So when I look at you, I'm mostly looking at your stratum corneum. It's about 15 microns in thickness. It is composed of these corneasite cells. They do not have a nucleus at this point. So they've moved up through the dermal and epidermal layers into the stratum corneum. It takes about two to three weeks for them to move through the cell and then disclimate from the surface. The intercellular boundaries are formed by lipids and also very strong protein connections called corneodesma zones indicated by these little areas over here. So the very important enzymatic reaction that happens in your stratum corneum that basically degrades these corneodesma zones and allows these cells to exfoliate. So what happens when you expose the structure to UVA and UVB light? Well, what happens is that the cohesion of these layers in the stratum corneum decreases very significantly. So in this study over here, we're measuring, we're quantifying, joules per meter squared, same kind of adhesion energy that we talked about earlier on as a function of increasing dosage, UVB dosage. And you can see there's this dramatic decrease. So the stratum corneum is becoming weaker. Now we do lots of other studies to figure out what's happening to the lipids and the proteins and whether bond cleavage is happening and how the mobility of the lipids are being affected. But the net effect in terms of the strength of this vital barrier is that it decreases significantly. At the same time, if we measure the stresses that develop in the stratum corneum when we dry them in different environments, this is stress over here. They actually increase with increasing UV exposure. So the stresses in your skin go up and the resistance to failure goes down. So guess what happens? What happens is that the propensity for cracking and damage can be modeled. Now again, I'm not telling you any of the details here, but you can actually precisely model the role of increasing UV exposure on whether your skin will break. Anything above this line over here, this is the normalized driving force for damage, indicates that the skin will fail. Anything below this means that it won't fail. And so this number over here is about one and a bit day in full Florida sun is when we predict your stratum corneum will begin to break. And this is consistent with what's actually observed clinically. So it turns out that these biomechanical measures of the properties of the stratum corneum are very sensitive to things like exposures. So in our recent work here, we've been looking at new ways of protecting ourselves from the sun. And one idea we have is to make a sunscreen that basically lasts for about two weeks. So if you're going on vacation, you apply the sunscreen only once. It doesn't come off because it irreversibly petitions into the lipids in your stratum corneum and provides protection for two weeks. And here are some of the areas that we're working on. One is to refunctionalize some of the nanoparticles that are typically used in sunscreen so that they petition irreversibly into the lipid structure. The other is that we're looking at a number of UV absorbing molecules that do something similar. If you think this is far-fetched and that the FDA is going to get all upset about it, just bear in mind that in most of the skin science area, all the moisturizing treatments that we lull our cells up with every day, there's no FDA oversight. If you go to a tattoo parlor and have tattoos, you don't have FDA inspectors there either. So we think this is a viable way actually to provide longer term protection through some innovative irreversible screens that- We're gonna have to wrap up. Yeah, and in fact, I'm right at the end. So with that, this gives you a view of a number of things that we've been looking at. Thank you for your attention.