Imaging charge density fluctuations in graphene using Coulomb blockade spectroscopy

TL;DR

This study employs Coulomb blockade spectroscopy with STM to visualize and analyze local charge density fluctuations in graphene, revealing electron and hole puddles with a characteristic size of about 20 nm.

Contribution

It introduces a novel method combining STM and Coulomb blockade spectroscopy to directly image charge puddles in graphene.

Findings

Charge puddles have a characteristic length scale of ~20 nm.

Theoretical calculations agree with measured puddle sizes.

Charge density fluctuations are visualized at the nanoscale.

Abstract

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.