Smitha Vasudevan

Confinement, Transport Gap, and Valley Polarization in Graphene from Two Parallel Decorated Line Defects

Quantum transport calculations show that a transport gap approximately E(g) = 2ħv(F)/W can be engineered in graphene using two parallel transport barriers, separated by W, extended along the zigzag direction. The barriers, modeled by chemically decorated observed line defects, create confinement and resonance bands tracing the bands in zigzag nanoribbons. The resonance bands terminate at the dimensional crossover, where the states become boundary-localized, leaving the transport gap. The structure also allows for nearly perfect valley polarization.

Controlling transistor threshold voltages using molecular dipoles

We develop a theoretical model for how organic molecules can control the electronic and transport properties of an underlying transistor channel to whose surface they are chemically bonded. The influence arises from a combination of long-ranged dipolar electrostatics due to the molecular head-groups, as well as short-ranged charge transfer and interfacial dipole driven by equilibrium band-alignment between the molecular backbone and the reconstructed semiconductor surface atoms.

Modeling Electrostatic and Quantum Detection of Molecules

We describe two different modes for electronically detecting an adsorbed molecule using a nanoscale transistor. The attachment of an ionic molecular target shifts the threshold voltage through modulation of the depletion layer electrostatics. A stronger bonding between the molecule and the channel, involving actual overlap of their quantum mechanical wavefunctions, leads to scattering by the molecular traps that creates characteristic fingerprints when scanned with a backgate. We describe a theoretical approach to model these transport characteristics.