Surface Potential and Thin Film Quality of Low Work Function Metals on Epitaxial Graphene
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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Metal films deposited on graphene are known to influence its electronic properties, but little is known about graphenes interactions with very low work function rare earth metals. Here we report on the work functions of a wide range of metals deposited on n-type epitaxial graphene EG as measured by Kelvin Probe Force Microscopy KPFM. We compare the behaviors of rare earth metals Pr, Eu, Er, Yb, and Y with commonly used noble metals Cr, Cu, Rh, Ni, Au, and Pt. The rare earth films oxidize rapidly, and exhibit unique behaviors when on graphene. We find that the measured work function of the low work function group is consistently higher than predicted, unlike the noble metals, which is likely due to rapid oxidation during measurement. Some of the low work function metals interact with graphene for example, Eu exhibits bonding anomalies along the metal-graphene perimeter. We observe no correlation between metal work function and photovoltage, implying the metal-graphene interface properties are a more determinant factor. Yb emerges as the best choice for future applications requiring a low-work function electrical contact on graphene. Yb films have the strongest photovoltage response and maintains a relatively low surface roughness, similar to approx.5 nm, despite sensitivity to oxidation.
- Electrooptical and Optoelectronic Devices