Work Function Variations in Twisted Graphene Layers
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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By combining optical imaging, Raman spectroscopy, kelvin probe force microscopy KFPM, and photoemission electron microscopy PEEM, we show that graphenes layer orientation, as well as layer thickness, measurably changes the surface potential Phi. Detailed mapping of variable-thickness, rotationally-faulted graphene films allows us to correlate Phi with specific morphological features. Using KPFM and PEEM we measure Delta Phi up to 39 mV for layers with different twist angles, while Delta Phi ranges from 36-129 mV for different layer thicknesses. The surface potential between different twist angles or layer thicknesses is measured at the KPFM instrument resolution of 200 nm. The PEEM measured work function of 4.4 eV for graphene is consistent with doping levels on the order of 1012cm-2. We find that F scales linearly with Raman G-peak wavenumber shift slope 22.2 mVcm-1 for all layers and twist angles, which is consistent with doping-dependent changes to graphenes Fermi energy in the high doping limit. Our results here emphasize that layer orientation is equally important as layer thickness when designing multilayer two-dimensional systems where surface potential is considered.
- Physical Chemistry