Using scanning tunneling microscopy, we have imaged local charge density fluctuations in monolayer graphene. By placing a small gold nanoparticle on the end of the STM tip, a charge sensor is created. By raster scanning the tip over the surface and using Coulomb blockade spectroscopy, we map the local charge on the graphene. We observe a series of electron and hole doped puddles with a characteristic length scale of about 20 nm. Theoretical calculations for the correlation length of the puddles based on the number of impurities are in agreement with our measurements.
@article{arxiv.1012.0374,
title = {Imaging charge density fluctuations in graphene using Coulomb blockade spectroscopy},
author = {A. Deshpande and W. Bao and H. Zhang and Z. Zhao and C. N. Lau and B. J. LeRoy},
journal= {arXiv preprint arXiv:1012.0374},
year = {2015}
}