2, University of Oxford, Oxford, , United Kingdom
As the power density increases in ever shrinking electronics, high research efforts are focusing on transforming this heat into electricity with the use of high figure of merit thermoelectric materials and exploiting thermoelectric phenomena is data storage such as in phase change memories. While two-dimensional and Van-der-Waals bound materials are progressively being considered for their ground-breaking physical properties, nanoscale measurement methods of thermoelectric systems are lagging behind, hindering the understanding of local thermoelectric phenomena on nanoscale. In this report, we present a novel microscopy technique, Scanning Thermal Gate Microscopy (SThGM) which enables mapping Seebeck coefficient with nanoscale (20-50 nm) spatial resolution.
Our method is based on Scanning thermal microscopy (SThM) which is an AFM technique using a heated sensor tip to locally probe thermal conductance of a sample. SThGM uses the nanoscale heating capabilities of the SThM tip in order to create a local temperature rise with sharp gradient in a probed device. This gradient creates a thermovoltage which can be directly measured at the device terminals and that is proportional to the Seebeck coefficient of the material under the tip and the temperature gradient created. As the nanoscale temperature distribution created by the SThM is well characterised, the SThGM allows to provide both the nanoscale map of the Seebeck coefficient distribution and quantitatively evaluate its magnitude.
The results of nanoscale thermoelectric maps of three different samples: standard thermoelectric thin films, 2D materials heterostructures and graphene nanoconstrictions are discussed. SThGM allows to explore novel thermoelectric phenomena and to open possibilities for investigations and development of more efficient electronic and thermoelectric devices.