Condensed Matter Seminar Series

Tuning Electrical and Optical Properties of 2D Atomic Crystals

A.K.M. Newaz

Vanderbilt University

Thursday January 24,  11:30 am,  Room 298,  Physics Building

Abstract: Two-dimensional (2D) atomic crystals are recently discovered materials that are only atoms thick, and yet can span laterally over millimeters. The diverse family of such materials includes graphene, a semimetal with massless relativistic charge carriers, and monolayer molybdenum disulfide (MoS2), a direct band gap semiconductor with strong spin-orbit interaction. Since every atom in these materials belongs to the surface, their physical properties are greatly affected by the immediate microenvironment. In my talk, I will demonstrate the wide tunability of the electrical and optical properties of both graphene and MoS2 and discuss some novel device applications.

In the first part of the talk, I will demonstrate the use of graphene field effect transistors (FETs) in sensing different physical parameters of nanometer-thick interfacial liquid volumes. I will demonstrate sensing of local liquid dielectric constant, mass flow velocity – with sensitivity 70nL/min, and ion concentration with sensitivity as low as 40 nM. I will also show that charge carrier scattering in graphene can be efficiently suppressed by placing graphene into a liquid environment. Overall, our results highlight the usefulness of graphene FETs for applications in ultra-precise fluidic sensing and as a potential replacement for silicon in next generation transistors.

In the second part of my talk, I will focus on mononalyer MoS2 and demonstrate that its optical properties, fluorescence quantum yield and transparency, can be tuned via electrical gating. In particular, we have observed a hundredfold modulation of excitonic photoluminescence from MoS2 at room temperature by varying the electric fields within ±1.7 MV/cm. Our findings demonstrate that MoS2 is the thinnest possible electroactive material and suggest the possibility of diverse applications ranging from nanoscale electro-optical modulators to quantum computing based on the spin degree of freedom.