STM Graphene Spectra (IMAGE) DOE/Lawrence Berkeley National Laboratory Caption These STM electron tunneling spectra were obtained at the same physical location on a graphene surface held at different gate voltages. The vertical scale gives a measure of the energy-dependent graphene electron density of states; the different curves result from the different applied gate voltages. Changing the gate voltage allows the density of charge carriers in the graphene to be controllably varied. The red arrows indicate the measured tunnel current signal that occurs when electrons tunnel from the STM tip to the graphene Dirac point, a minimum in the graphene density of states. Credit Lawrence Berkeley National Laboratory Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.