12/4/2015 Fatima Farha, MechSE Communications
Written by Fatima Farha, MechSE Communications
van der Zande joined MechSE in August after completing a postdoc position in the Department of Mechanical Engineering at Columbia University, where he was also a fellow with the Energy Frontier Research Center. During his time there, he researched applications for a new class of 2D nanomaterial that has emerged in recent years. He used these new materials as molecular-scale building blocks to engineer ultra-small nanoelectromechanical systems and energy systems like ultra-thin solar cells.
van der Zande hopes these new materials will redefine how electronics can be used.
“Traditionally, electronics have existed on a silicon chip and can’t be moved or altered in any way. Right now, the research community is trying to find ways of changing how we interact with electronics. We are trying to engineer stretchable, flexible, and reconfigurable systems, which can fit on a curved surface, or be bent, or be put inside a liquid or biological environment while still functioning.”
Specifically, van der Zande’s focus at Illinois is to engineer devices from stacks of disparate 2D materials. The classic example of this is graphene, which is a single atom thick sheet of carbon.
“You can think of graphite as millions of graphene sheets stacked on top of each other, just like a stack of paper,” said van der Zande. “We like to pull out one of these sheets so we can manipulate it individually from the rest of the stack.”
In the last few years, scientists have discovered that there are actually hundreds of different 2D materials with slightly different chemistry but the same underlying structure. What makes this family of materials useful is that it contains all possible electrical properties found in traditional 3D materials; hexagonal boron nitride is an insulator, graphene is a conductor, and molybdenum disulfide is a semiconductor. These materials are also very stable, which makes them easier to work with. Just like paper, they can be stretched, folded, stacked, cut, torn, rippled, and vibrated. Yet, they are stronger than steel and can be manipulated without easily breaking—making them useful in many flexible technology applications.
“The trick is that we can stack these 2D materials on top of each other. By mixing and matching, we can re-engineer many traditional or 3D electronic, thermal, and mechanical systems down at ultra-small length scales, all while maintaining the useful mechanical properties of the monolayers.”
For van der Zande, his transition from 2D graphene membranes and one-dimensional carbon nanotubes—his focus during graduate school, to build tunable nanoelectromechanical systems—to several 2D nanomaterials wasn’t difficult. He said his work on carbon nanotubes and graphene showed him exactly how to manipulate these materials, so now, even if there are hundreds of similar materials, the fabrication process is the same.
“Using graphene and carbon nanotubes as a case study, we were able to figure out how to deal with this entire class of materials, and now I can take advantage of all that experience to interact with and build much more complicated structures,” he said.
However, one of the challenges he faces is the novice nature of the research itself. It is a relatively new area, so scientists have very few precedents upon which to model their work. But this also offers an opportunity to explore many avenues within the field.
For example, because these materials are so new, you can’t buy them at the store, and many of them cannot be grown yet. In order to start engineering these new systems, van der Zande has to start by growing them in his lab.
“We’re growing these materials and we’re figuring out what their properties are. At this stage, not much else has been done, which means it’s a wide open field where any question is fair game. But it also means if you want something done, you have to do it yourself.”
van der Zande considers the growth of 2D materials to be an important step for engineering applications.
“Right now, many groups are using a process of mechanical exfoliation to laboriously produce one prototype device at a time, often of only a few microns in size. Now that we can grow these materials, it is easy to scale up these early experiments to make millions of devices at a time.”
In the longer term, he hopes to integrate his experience with growth, nanomechanics and devices, to bring about new applications of 2D materials.
“I am still following my nose, discovering what new things can exist with these systems. Some of the applications we are pursuing for nano-electro-mechanical systems are obvious progressions from previous technologies, but others require understanding what is unique about these new systems—and that’s an exciting place to be. It is very much like being an explorer.”
van der Zande earned a BS in physics and mathematics in 2003 from the University of California at Santa Cruz, and an MS and PhD (in 2008 and 2011) in physics from Cornell University.