Atomic-Scale Mapping of Thermoelectric Power on Graphene: Role of Defects and Boundaries

Abstract

This is the first report on the spatial distribution of thermoelectric response due to electron scattering effect at defects and boundaries in graphene. It provides a rare glimpse of thermal-electrical energy conversion process at an unprecedented atomic level. Microscopic thermoelectric measurements are usually carried out with a technique developed by Philip Kim et al., where a local heater made of a metal line produces a temperature difference ΔT between the two ends of a sample, which gives rise to a thermoelectric voltage V th measured by electrodes defined by standard electron beam lithography and nanofabrication process. The thermopower is obtained as the ratio of V th to ΔT across a sample. This method however lacks the spatial resolution for probing the variations of thermoelectric properties across a sample surface which can be the key for revealing the inhomogeneities and defect scattering effects in thermoelectric materials. Here an alternate method is applied to measure the thermoelectric power with an STM technique where a thermovoltage arises from a temperature gradient between the STM tip and the sample. Due to the strong dependence of thermovoltage on th