High-resolution measurement of SiO2 surface potential using scanning Kelvin-probe microscopy*

It is now widely recognized that the dominant contribution to disorder in SiO$_2$-supported graphene is due to scattering from charged impurities. These charged impurities give rise to a conductivity which is linear in carrier density, and create electron-hole puddles in graphene. The screened potential variation produced in graphene has been imaged using scanning tunneling microscopy/spectroscopy (STM/STS) by spatially mapping the variation in the Dirac point, revealing a length scale of ~20 nm for the charge puddles. However, there is a substantial gap in resolution between the STM measurements and previous measurements with much greater potential sensitivity but limited spatial resolution. Here we attempt to bridge this gap using scanning Kelvin-probe microscopy (SKPM) of SiO$_2$ in ultrahigh vacuum. Our measurement takes advantage of the high spatial resolution allowed by UHV non-contact AFM while maintaining UHV control of the sample environment.\\[4pt] [1] Y. Zhang et al., Nature Physics 5, 722 (2009)\\[0pt] [2] J. Martin et al., Nature Physics 4, 144 (2008)