Published in J. Vac. Sci. Technol. B 34, 04J106 (2016).
Thickness characterization of atomically-thin WSe2 on epitaxial graphene by
low-energy electron reflectivity oscillations
Sergio C. de la Barrera,1 Yu-Chuan Lin,2 Sarah Eichfeld,2 Joshua A. Robinson,2 Qin
Gao,1 Michael Widom,1 and Randall M. Feenstra1
1Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
2Department of Materials Science and Engineering and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802 USA
Abstract
In this work, low-energy electron microscopy is employed to probe structural as well
as electronic information in few-layer WSe2 on epitaxial graphene on SiC. The emergence
of unoccupied states in the WSe2–graphene heterostructures are studied using
spectroscopic low-energy electron reflectivity. Reflectivity minima corresponding to
specific WSe2 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 WSe22 electron reflectivity. This method allows for
unambiguous counting of WSe22 layers, and furthermore may be applied to other 2D
transition metal dichalcogenide materials.
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