Incomplete screening by epitaxial graphene on the Si face of 6H–SiC(0001)

Abstract

A biased scanning tunneling microscope (STM) tip is used to study the ability of carriers in graphene to screen external electrostatic fields by monitoring the effect of tunneling-junction width on the position of image potential-derived surface states. These states are unusually sensitive to local electric fields due to the STM tip in both single layer and bilayer epitaxial graphene. This is attributed to the incomplete screening of applied fields in epitaxial graphene on SiC(0001). Our observations imply that charged impurity scattering is likely to be a dominant factor in the transport properties of epitaxial graphene on SiC.

Superatom orbitals of C60on Ag(111): Two-photon photoemission and scanning tunneling spectroscopy

“…These graphene image potential levels have been predicted to exhibit a unique double Rydberg series, 36 and this has been confirmed experimentally 37 and exploited as a local transport probe of epitaxial graphene. 38 These levels are of potential interest because their weak binding leads to heightened sensitivity to the local electrostatics, thus opening the possibility for modulating electronic properties. This would, however, require tuning these levels to near the Fermi level, for instance, by endohedral doping of C 60 .…”

Multiple coexisting intercalation structures of sodium in epitaxial graphene-SiC interfaces

“…Because the n = 1 peak position of epitaxial graphene is sensitive to different tip states due to poor screening in the graphene sheet, 25 it is important to keep track of the tip state. We collected the STS data for intercalation structures SiC/Na/G, SiC/Na/G/G and SLG simultaneously (i.e., with the same tip state) for use as an internal reference (in contrast to usual STS studies in which the substrate Fermi level is the most useful reference).…”

“…Different layers can be easily distinguished by the reduction in substrateinduced corrugation in the bilayer and by the systematic energy differences in IPS's in STS. 25 By choosing a lower annealing temperature (1000…”

“…These states arise outside of a surface due to polarization of surface charge 22 and have recently been connected with the formation of interlayer states in graphite 23,24 and used to understand screening and doping effects in epitaxial graphene in SiC(0001). 25 Changes in work function because of doping are often visible as corresponding shifts in the energy of IPS's 26 and demonstrate doping effects in sodium-intercalated epitaxial graphene. Most importantly, STS results have been connected with work-function changes calculated from first principles that unambiguously distinguish the different locations of Na in the intercalation structures.…”

Electronic transition from graphite to graphene via controlled movement of the top layer with scanning tunneling microscopy

“…Assuming the sample is stationary, this process indirectly probes its density of states (DOS). 27 A second interaction is also taking place, though, in which the tip bias induces an image charge in the grounded sample, resulting in an electrostatic attraction that increases with the bias. We have found that in some materials, such as graphite 28 and freestanding graphene, 29 this attraction can result in physical movement of the sample, convoluting and often eclipsing any DOS measurement.…”