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Georgia Tech science powers the technology behind TV and smartphone screens, thanks to breakthroughs in physics, chemistry, and materials science. Carlos Silva is adding to that legacy with his research into the next generation of semiconductors for electronic devices.
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Renay San Miguel: Hello and welcome to ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m Renay San Miguel.
(Football stadium sounds)
Renay San Miguel: The next time you watch sports on your flat screen TV, or on your smartphone, you can thank Georgia Tech scientists.
Not for the action on the field, but for the technology behind that screen. After all, not even a Nobel Prize-winning physicist can keep a quarterback from throwing an interception.
(Football stadium boos)
Renay San Miguel: Georgia Tech researchers in physics, chemistry, and materials sciences, have sparked winning advances over the years in photonics and optoelectronics, which involve the study of light. These are the sciences that bring you those crystal-clear images on large and small screens, specifically thanks to semiconductors called light-emitting diodes, or LEDs.
They are also the sciences that get the attention of Carlos Silva, professor in the School of Physics and in the School of Chemistry and Biochemistry. His research group is looking for the next generation of semiconductors, and looking at new advanced materials as a way to turn light into energy, and energy into light.
Carlos Silva: Yes, I think that Georgia Tech has been a leader in many technologies that are associated with optoelectronics, namely displays, solar cells, photovoltaics, detectors, and so on, in a very wide range of materials. The area of research that I'm involved in and that I know most about Georgia Tech involves so-called “organic” and “hybrid” optoelectronics.
Renay San Miguel: For our purposes, organic simply means molecules containing carbon, like carbon-based polymers or plastics. Their properties can be modified in specific ways to achieve specific effects. They are typically easier to process than inorganic materials. Hybrid means a combination of organic and inorganic materials. Typical semiconductors are complex inorganic materials, such as gallium arsenide, which Silva will mention later.
Carlos Silva: And so they are attractive because, being molecular materials, they can be tuned by chemical design, by chemical synthesis, and that's where there has been very world-leading activity here at Georgia Tech.
Renay San Miguel: Silva is searching for less expensive, more energy efficient, and more environmentally safe materials in the semiconductors that go into electronic devices.
Silva and his team are working to realize new applications that could include better and cheaper solar cells, wearable electronics, biomedical sensors inside our bodies, or spacesuit fabrics that can help astronauts monitor radiation as they explore a distant world.
Using lasers and spectroscopy – that is, using light to study matter -- Silva’s team studies what happens to certain particles when you overload them with energy – what are called excited states.
The excitement for Silva is that some of those applications have already resulted in cost benefits.
Carlos Silva: There has been a lot of interest in the last few years for photodetectors, ranging from specific wavelength, detect a specific color detectors, to solar cells, and there is now a renewed drive to achieve organic or plastic solar cells. The efficiencies of these devices have been creeping up to the point where now they're competitive with other technologies.
They’re cheap to produce or cheap to run. Really, the flexibility that the material platform provides is one of the main advantages in terms of spectral range, which colors are being absorbed by the material, and how that energy is being transformed to electrical power. It’s something that is, on the one hand, complex, on the other hand provides opportunities for new applications.
Renay San Miguel: By transforming that energy to power, Silva may open the door to a new class of semiconductor materials.
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Renay San Miguel: As mentioned earlier, photonics is the study of light; how it’s generated, detected, and manipulated. Optoelectronics is a subset of photonics in that it refers to light-emitting or detecting devices.
A lot of brainpower from Georgia Tech colleges and schools goes into developing the next generation of materials used in those disciplines.
Renay San Miguel: Your website, the lab website, says you and your researchers “think of our work as a linear combination of physical chemistry, condensed matter physics, materials physics, and materials chemistry.” Can you elaborate? What do these four disciplines allow you to do here?
Carlos Silva: Yes, well, one of the interesting aspects is that these disciplines are not, by any means, very well delineated. They are delineated in curricula, perhaps, in disciplinary listings in universities, but not in world-class research.
And so that is one of the aspects where, as you mentioned, Georgia Tech is extremely strong. In fact, I moved here one and a half years ago. One of the reasons why I wanted to move to Georgia Tech is because interdisciplinary and multidisciplinary research is not just allowed or tolerated or accepted, but it is a way of life at Georgia Tech. It's encouraged and this is a very important aspect in materials research. Materials research, materials sciences is a very multidisciplinary area where individual groups and individual expertise is part of a contribution for a broader outcome. And you really need to have different expertise, different groups with different techniques and backgrounds working together.
Our group has chemists, has physicists, has materials scientists working in conjunction in a way where everybody brings in a very specific expertise and interest and contributes to bigger objectives.
This is how our group operates. This is also how we pick our problems.
Renay San Miguel: That interest includes as we mentioned, so-called “excited states,” when particles are exposed to more energy than they’re used to. Light, heat, electricity, any kind of energy. How do materials change when their particles are in excited states? Silva’s group uses ultrafast spectroscopy and quantum optics – that’s how materials react to light on the subatomic level -- to understand the optical and electronic properties of semiconductor materials. Those include certain promising hybrid materials, meaning they are in part made of organic molecules.
Carlos Silva: Mainly the advantages of these materials stem from the fact that they are low-energy consumption in their production. And so the devices themselves are not fully but largely fabricated by low-energy methods.
The fact that they are molecular means that there's ample opportunity for tuning of their properties: color, the efficiency by which they absorb light, the way they absorb light. There's a lot of flexibility in chemical design.
Renay San Miguel: So when somebody goes to Best Buy and they see a monitor that says OLED organic light-emitting diodes, that's what we're talking about.
Carlos Silva: That is one example.
And a lot of the important conceptual development in the field that leads to these devices stems from work at Georgia Tech and largely led by the Center for Organic Photonics and Electronics.
Renay San Miguel: That center, known by its acronym COPE, is part of Georgia Tech’s STAMI, or the Center for the Science and Technology of Advanced Materials and Interfaces. Silva is COPE’s co-director. Its members study what happens when certain liquids, foams, gels, liquid crystals, and other substances are subjected to stimuli like electricity, light, heat, or chemicals.
Imagine artificial retinas made of semiconducting polymers that connect to your eye’s neurons, and improve vision. A host of applications like that, ranging from health and medicine to engineering and manufacturing, could result from the Silva group’s research.
Carlos Silva: There are non-traditional applications. For example, organic materials, particularly polymers, being plastic means that they have mechanical advantages that traditional materials may not have. So people talk about wearable electronics and flexible electronics and printable electronics.
And these are all opportunities that these materials provide.
Renay San Miguel: A major telephone, a smartphone maker just came out with a screen that folds. Are we talking about that kind of technology going in there?
Carlos Silva: That is one of the platforms that is certainly amenable to these technologies. And my understanding is that organic materials are used in some of these applications.
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Renay San Miguel: Professors love metaphors, and so do students, because usually, they make it easier to understand complex scientific concepts.
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Renay San Miguel: For Silva, a dancing metaphor comes in handy to explain unusual behavior that could lead to more powerful and versatile semiconductors.
Silva uses dance to talk about hybrid organic–inorganic perovskites, or HIOPs. These are layered mixes of organic and inorganic materials with intriguing electrical properties and can be cheaply made at low temperatures.
Remember those excited states we talked about earlier? When you add energy to an electron, the electron jumps to a new energy level in the atom. The space it left is called an electron hole. That hole, believe it or not, becomes the dance partner, if you will, of the original electron. They join forces to become a new particle called an exciton.
This is where the dance really kicks in.
Silva says the excitons can leave their atoms and dance with excitons from other atoms. You can have many electrons and many holes dancing in a very close-knit choreography.
Carlos Silva: They dance very closely and very precisely together in this environment that is very noisy. So these lattice, these semiconductors are very different from traditional semiconductors in that way.
You can think of them as opposed to a very calm beach. It's a very, very noisy earthquake in Mexico City. And that would be the comparison between these materials and let's say a gallium arsenide semiconductor. And in spite of that, the energy by which the electrons in the holes interact in the multi-particle way is much higher than you find, for example, in gallium arsenide.
Carlos Silva: So very strong electronic correlations, in spite of the fact that they're dancing on an earthquake.
Renay San Miguel: I'm kind of picturing two couples doing a beautiful slow waltz or a couple doing a beautiful slow waltz while everybody's doing a polka and the chicken dance and everything around them.
Carlos Silva: Yes, imagine a group of 10 salsa dancers doing a perfect choreography in an earthquake, as opposed to a polka dancer or, let's get more extreme, let's say body slamming—
[laughter]
—on a very tranquil surface.
Renay San Miguel: Absolutely, punk rock bands playing, throwing themselves at each other.
But here are these couples just slowly gyrating in the middle.
Carlos Silva: Yes.
Renay San Miguel: Why does it matter that these excitons are dancing calmly to their own tune in the midst of all that chaos? That’s the part that excites Silva, because it can mean a faster conversion to energy than is possible with traditional semiconductors.
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Renay San Miguel: When you were a little kid, were you dissecting frogs when everybody else was going no? Or were you like… Did you have a chemistry set? Was there something that your folks saw in you as a kid? Yeah, he’s heading in that direction.
Carlos Silva: Well, I don't know that they knew what direction I was heading in, but they certainly recognized that I was highly inquisitive. I did things that would be highly experimental.
For example, I ate a scorpion once because that was an experiment.
Renay San Miguel: Eating a scorpion as an experiment? You could say that. Yeah.
Carlos Silva: I dissected a live wire once with scissors because that was an experiment.
There were signs in my childhood that were pointing to kind of the scientific method.
Renay San Miguel: I would imagine. But maybe experiment on something else besides your own body.
Carlos Silva: Yes.
Renay San Miguel: Did you get sick from eating a scorpion?
Carlos Silva: No, it turns out I did not. I tell my son… My son really loves Spiderman, and I said that I'm probably a scorpion man.
Renay San Miguel: What is it that that drives you to come to work every day and not see it as work and see it as I'm researching something that could really help humanity?
Carlos Silva: I'm absolutely fascinated by the applications and the context of the applications. That is a very important driving force.
I'm also fascinated by the process of doing science. I have never ceased to be excited about the process of doing science. Just being able to put the two together is really what I would say is a privilege as a scientist and the scientists at Georgia Tech. So I'm definitely very much an experimentalist, and I get just joy out of just doing experiments. That is something that I always have enjoyed, and I enjoyed doing experiments that have a real context in both a scientific problem and being part of the puzzle to come up with new technologies. So all of that is so exciting. And that's really what I think I will never stop being excited about.
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Renay San Miguel: The American Physical Society elected Carlos Silva one of its 2019 Fellows, for his work using ultrafast lasers s optoelectronics research.
I thank Carlos Silva for his time, and encourage you to check out his lab’s website at ww2-dot-chemistry-dot-gatech-dot-edu-slash-silva.
Siyan Zhou, a former research associate with the School of Psychology, composed our theme music.
If you like ScienceMatters, please subscribe. We’re on Apple Music and Soundcloud.
This is ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m RSM. Thank you for listening.
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