The Intersection of Electrical Engineering and Materials Design
A Q&A with professor Adrienne Stiff-Roberts about Duke ECE's Nanoelectronic Materials and Devices research
1. Can you tell us a bit about your research interests, and what goes on in your lab at Duke?
My research interests are in thin film deposition of hybrid materials for optoelectronic devices, meaning I’m interested in making devices based on the interaction of light and matter.
optoelectronics: (äp-tō-i-lek-ˈträ-niks) a branch of electronics that deals with electronic devices for emitting, modulating, transmitting, and sensing light
There are some everyday applications that you might be familiar with—things like light-emitting diodes (LEDs) that are used for lighting, and in consumer products like televisions. Solar cells are used to convert sunlight into electricity. Photodetectors that sense light and lasers are other important applications. The materials that I’m interested in using to make these devices are hybrid materials, meaning they’re made of organic and inorganic materials.
Inorganic materials are things like semiconductors, that are very good at conducting charge and offer a high level of control. Organic materials are things like plastics, which have properties like flexibility and transparency. Combining the two is interesting because of the properties you then get in the final device. But it’s very challenging, because the two are inherently different.
Sometimes people wonder why you would want to put plastic in something that is used to make these devices, because plastics are typically thought of as insulators—but there’s a very special class of organic materials that have a configuration of carbon bonds that allow them to behave as semiconductors.
So, how do you make a thin film of this hybrid material so you can turn it into one of these devices? That’s the work we do in my group—we develop a novel type of thin-film deposition technique that enables control over these hybrid materials. I’m interested in using my deposition technique, RIR-MAPLE, to deposit such hybrid materials. One specific example is the class of materials known as hybrid perovskites, especially those with a large organic component.
RIR-MAPLE: Resonant Infrared Matrix-Assisted Pulsed Laser Evaporation, developed by Duke professor Adrienne Stiff-Roberts over the past decade.
2. Why is your research important? How will it advance the field?
In general, when we talk about hybrid devices that are based on the interaction of light and matter, one reason they’re important is because of the types of future systems they could enable. Think about your smartphone or your tablet—it’s full of these optoelectronic devices. You have a display that’s emitting an image, that’s based on some type of optoelectronic device. These are based on traditional semiconductor materials. If you can make the device hybrid, though, there’s the possibility that you could have devices that are flexible, or transparent, or more transportable, or deployed in our everyday lives in fundamentally different ways. They might be integrated into clothing and other fabrics or building materials. They could open up fundamentally different types of systems.
One material I’m working with right now, that I’m very excited about, is hybrid perovskites. Hybrid perovskites are cool because they have a crystalline structure–an inorganic crystalline framework that fits organic molecules inside of it. That’s important because when we know exactly where all the atoms are that make up a material, we can make predictions about how the material will behave and we can better describe its behavior—which means we can design and fabricate better devices because we understand the materials so well.
“When we know exactly where all the atoms are that make up a material, we can make predictions about how the material will behave and we can better describe its behavior—which means we can design and fabricate better devices.”
Adrienne Stiff-roberts, Jeffrey N. Vinik Professor of Electrical and Computer Engineering
Hybrid perovskites are exciting because of their potential to improve the efficiency of solar cells. To give you a frame of reference—silicon solar cells were first demonstrated in 1954, and from that time to today, these single devices reach around 25 percent efficiency, more or less. We’re losing 75 percent of that energy from the sun. These hybrid perovskite solar cells were first demonstrated around 2009, and they’re already up to that same 25 percent efficiency. When you think about the development of that technology, it’s extremely exciting that these materials could give us more efficient conversion of solar energy to electricity—that would obviously have a big impact on reducing carbon emissions.
3. What makes Duke strong in the area of materials?
Its strength really is that it’s multidisciplinary. You can find materials research in ECE, in BME, in chemistry, physics—materials touch a lot. After all, whatever you want to make, you have to make it out of something! And in order to have that product work well, you first have to understand the materials.
multidisciplinary: (məltēˈdisəpləˌnerē) combining or involving several academic disciplines or professional specializations in an approach to a topic or problem.
As you can imagine, the organic materials that I’ve been talking about are something that chemists often study, and the inorganic materials, especially semiconductors, are something that electrical engineers like to study. Having people interested in different aspects of these materials is inherently multidisciplinary, and the problems we face today, more and more often, demand that we bring these different areas together to solve them.
4. Can you give me an example of how this kind of collaboration plays out in your own work?
I’m working in a center called CHOISE—the Center for Hybrid Organic-Inorganic Semiconductors for Energy. This is a DoE Energy Frontier Research Center led by the National Renewable Energy Lab (NREL). I belong to that project along with two other engineers from Duke—David Mitzi and Volker Blum—and others from the University of Utah, UNC Chapel Hill, and other organizations. We’re looking at hybrid materials like perovskites, trying to understand those materials as their own semiconductor technology.
When we talk about semiconductor technology, the one we’re familiar with is silicon. But what if you had a semiconductor technology that was hybrid organic-inorganic? What are all the different devices we could make from it, to control electrons, photons, or spin?
That’s what the center is about. And it’s a huge, multifaceted problem: how do you make the materials? How do you characterize the materials to understand what they do? How do you model the materials so you can make predictions? What kinds of device demonstrations can you do to show that they are meaningful? All of that is very broad and spans chemistry, physics, electrical engineering and materials science. My part is answering the question, “How do we make thin films of these materials and what special properties does a particular technique give to the materials as a result?”
5. For students who share your interest in materials and want to learn and study more, when would one apply to ECE versus the University Program in Materials Science?
It’s really about how a student views themselves, and how they want to present themselves. When you’re thinking about graduate education, particularly at the master’s level, there are a few things I think you should think about. One is, what is your own background and what is the goal for this degree? Do you want to do a deep dive into material that you learned as an undergraduate? Do you want to change direction or change your field to broaden your perspective? Or do you want to be able to precisely tailor your curriculum? Each of those, I think, has a different path.
If you’re interested in materials, ECE is a good fit for master’s education, particularly if you’re especially interested in electronic and photonic materials. Or, if you want to supplement your studies of materials with things that are relevant to ECE because of their applications. Maybe you want to learn more about computer engineering or semiconductor devices, or circuits—photonic materials directly relevant to communication systems or computer systems. Then, ECE makes a lot of sense. And at Duke, the ECE master’s degree is flexible so you can augment ECE training with electives in other departments that are materials-related.
As far as the University Program in Materials Science, for which I am the director of graduate studies, it makes a lot of sense to take that route if you want a strong foundation in materials science and engineering—maybe because you’re coming from a different field. And there, you have the ability to do research with faculty in the eight participating departments. There’s a common curriculum, but you can diversify in terms of the research you do.