Seminar "Studies of Two-dimensional Materials using Electrons: Reflectivity, Tunneling and Transport"

Wednesday 13 December 2017 14:15 - 15:15
K457, Dep of Physics
Published 2017-12-06 11:32 by Anneli Löfgren

Seminar by Prof Randall Feenstra, Dept. Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA.

Randall Feenstra has pioneered a number of the methods used for Scanning Tunneling Spectroscopy of semiconductors and is also using low energy electron microscopy (which is found at MAX IV). He has recently applied these methods for 2D materials with significant success, one aim is to do TFETs.   

Abstract: Studies are described of two-dimensional (2D) materials, including graphene, hexagonal boron nitride and transitional metal dichalcogenides such as MoS2. Electrons are used as a probe of the materials, utilizing both low-energy electron microscopy (LEEM) and low-temperature scanning tunneling microscopy (LT-STM). LEEM probes electron states that reside 5 – 20 eV above the Fermi energy, including in particular interlayer states that have plane-wave character between the planes of 2D material. Such states are shown to provide a quantitative measure of the number of 2D layers, as well as providing information on their detailed structural arrangement. LT-STM provides an atomic-scale view of defects in the layers, and through spectroscopic measurements it also yields the band gaps of the materials and band offsets between neighboring layers. We find in particular the occurrence of localized electron states associated with the moiré pattern that forms when one layer of a 2D material is placed on another layer with different lattice constant. The end goal of our materials studies is for the fabrication of interlayer tunneling field-effect transistors (TFETs). Simulations of such structures yield current magnitudes that are useful for application in beyond-CMOS devices. Experimental progress in fabricating interlayer TFETs will be discussed.

Work performed in collaboration with P. Mende, S. de la Barrera, J. Li, Q. Gao, M. Widom (CMU), Y.-C. Lin, J. A. Robinson (Penn State), Y. Nie, K. Cho (Univ. Texas Dallas), A. Ismach, R Ruoff (Univ. Texas Austin), Y. Pan, S. Fölsch (Paul Drude Inst.), and supported in part by the Center for Low Energy Systems Technology (LEAST), one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.