Studying local variations in the Seebeck coefficient of materials is important for understanding and optimizing their thermoelectric properties, yet most thermoelectric measurements are global over a whole device or material, thus overlooking spatial divergences in the signal and the role of local variation and internal structure. Such variations can be caused by local defects, metallic contacts or interfaces that often substantially influence thermoelectric properties, especially in two dimensional materials. Here, we demonstrate scanning thermal gate microscopy, a non-destructive method to obtain high resolution 2-dimensional maps of the thermovoltage, to study graphene samples. We demonstrate the efficiency of this newly developed method by measuring local Seebeck coefficient in a graphene ribbon and in a junction between single-layer and bilayer graphene.

On-chip temperature sensing on a micro- to nanometer scale is becoming more desirable as the complexity of nanodevices keeps increasing and their downscaling continues. The continuation of this trend makes thermal probing and management more and more challenging. This highlights the need for scalable and reliable temperature sensors, which have the potential to be incorporated into current and future device structures. Here, it is shown that U-shaped graphene stripes consisting of one wide and one narrow leg form a single material thermocouple that can function as a self-powering temperature sensor. It is found that the graphene thermocouples increase in sensitivity with a decrease in leg width, due to a change in the Seebeck coefficient, which is in agreement with previous findings and report a maximum sensitivity of ΔS ≈ 39 μV K⁻¹.