Thickness characterization of atomically-thin WSe$_2$ on epitaxial graphene by low-energy electron reflectivity oscillations

TL;DR

This study uses low-energy electron microscopy and spectroscopy to analyze the layer structure and electronic states of atomically-thin WSe$_2$ on epitaxial graphene, revealing layer-dependent unoccupied states and developing a theoretical explanation.

Contribution

It introduces a spectroscopic method to determine layer number and electronic states in WSe$_2$ heterostructures, supported by a developed theoretical model.

Findings

Reflectivity minima indicate layer number in WSe$_2$

Unoccupied states are localized between layers

Theoretical model explains reflectivity features

Abstract

In this work, low-energy electron microscopy is employed to probe structural as well as electronic information in few-layer WSe$_2$ on epitaxial graphene on SiC. The emergence of unoccupied states in the WSe$_2$--graphene heterostructures are studied using spectroscopic low-energy electron reflectivity. Reflectivity minima corresponding to specific WSe$_2$ states that are localized between the monolayers of each vertical heterostructure are shown to reveal the number of layers for each point on the surface. A theory for the origin of these states is developed and utilized to explain the experimentally observed featured in the WSe$_2$ electron reflectivity.