Episode 17: Hybrid material replaces doping in bandgap engineering

In this podcast episode, MRS Bulletin’s Laura Leay interviews Sathvik Iyengar, a PhD candidate at Rice University, about the development of a hybrid material called “glaphene.” A hybrid of graphene and two-dimensional (2D) silica glass, glaphene is a semiconductor with a bandgap of ~4 eV. More importantly, Iyengar and colleagues introduce a new method of bandgap engineering using hybrid materials instead of doping, which opens new possibilities for producing electronic components. This work was published in a recent issue of Advanced Materials. 

Transcript

LAURA LEAY: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on hot topics in materials research. My name is Laura Leay. Our research often surprises us; there is a history of surprising, accidental discoveries. Glaphene is a new material that combines graphene with 2D silica glass to arrive at something with properties that are drastically different to its components.

SATHVIK IYENGAR: Most of the questions we ask are how can we mix unconventional materials’ properties together so that we can come up with hybrid application. It just opens doors to so much more materials design. This project in particular was actually quite accidental. We were trying to recreate a system that’s just a vertical stack, you know, a layered stack of graphene – that is a 2D sheet of graphite – and 2D silica glass. So we just wanted to make a 2D layer vertical stack of two different materials which was done in our lab almost ten years ago.

LAURA LEAY: That was Sathvik Iyengar, a PhD candidate at Rice University and lead author of the study. When he was first trying to recreate this vertical stack, an unusual signal in the Raman spectrum was noticed, something that didn’t correspond to either the graphene or the silica. Working with a multidisciplinary team, the signal was traced to electronic cloud redistribution at the interface between the two components. This electronic proximity effect promotes interlayer hybridization.

SATHVIK IYENGAR: Since we’re talking about 2D materials, they’re typically bonded by weak van der Waals forces and they end up with van der Waals gaps between them. These gaps are anywhere between 1 Å to 1 nm depending on how you synthesize these structures and what these structures are. So it’s a very narrow, tiny gap and typically in that gap you have certain electron orbitals that can poke out of plane. They’re just mathematical wave functions that tell you there’s a chance that these electrons can occupy those spaces in the gaps. And when these orbitals of one layer interact with orbitals of the layer on top, you actually have some sort of interaction – that’s the electronic proximity effect, given that they are within proximity of each other and these electrons are talking.  

LAURA LEAY: The work involved spectroscopy, microscopy, and ab initio calculations. The calculations explained how the material vibrated when illuminated with the Raman laser so that the source of the unusual signal in the Raman spectrum could be identified and it enabled the team to refine the experimental work by fine-tuning the characterization and synthesis parameters. The synthesis relies on a slightly unconventional method. Instead of the usual vapor deposition commonly used to produce 2D materials, the team used a liquid precursor inflow module.

SATHVIK IYENGAR: We attached a sort of methodology to inflow liquid precursors into the tube or the chamber where the reactions happen. With the simultaneous control of liquid as well as wafer precursors that gives us freedom to choose or shift gears when it comes to what reaction is going on inside the furnace. The graphene grows first, which is pretty standard in the literature and in industry now. You start with something that’s a copper substrate – a metal substrate – and then it offers this catalytic support. But then, our set-up really kicks in after that and a liquid precursor called tetraethyl orthosilicate – TEOS for short – it acts as a hybrid silica as well as carbon source. And that’s what we flow in next. And without the liquid precursor inflow module we really would not be able to control the flow of this TEOS.

LAURA LEAY: The resultant structure is also a little unusual. Although you would expect the silica to be glassy, it exhibited a disordered crystalline structure, effectively borrowing structure from the graphene. The resultant new material is a semiconductor with a bandgap of around 4 eV. This new method of bandgap engineering using hybrid materials instead of doping opens up new possibilities for producing electronic components. In addition, if a flexible substrate can be used, the glaphene could be used to create flexible, bendable components for electronic devices. This work was published in a recent issue of Advanced Materials. My name is Laura Leay from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on X, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.