  Local variations in the Seebeck coefficient in low-dimensional
materials-based nanostructures and devices play a major role in their
thermoelectric performance. Unfortunately, currently most thermoelectric
measurements probe the aggregate characteristics of the device as a whole,
failing to observe the effects of the local variations and internal structure.
Such variations can be caused by local defects, geometry, electrical contacts
or interfaces and often substantially influence thermoelectric properties, most
profoundly in two-dimensional (2D) materials. Here, we use Scanning Thermal
Gate Microscopy (STGM), a non-invasive method not requiring an electrical
contact between the nanoscale tip and the probed sample, to obtain nanoscale
resolution 2D maps of the thermovoltage in graphene samples. We investigate a
junction formed between single-layer and bilayer graphene and identify the
impact of internal strain and Fermi level pinning by the contacts using a
deconvolution method to directly map the local Seebeck coefficient. The new
approach paves the way for an in-depth understanding of thermoelectric
behaviour and phenomena in 2D materials nanostructures and devices.
