TEM Observation of Thermoelectric Cooling in a Bismuth Telluride and Bismuth-Antimony Telluride Nanoscale Heterojunction*

Thermoelectrics have a wide variety of applications, but their efficiency must be improved before they become economical for non-niche applications. We demonstrate cooling in thermoelectric heterojunctions constructed from 2D flakes of exfoliated bismuth telluride and bismuth-antimony telluride using a new transmission electron microscopy (TEM)-based technique: plasmon energy expansion thermometry (PEET). PEET measures temperature by measuring the sample material’s bulk plasmon energy. The plasmon energy is related to the electron density, which in turn is related to temperature via the material’s coefficient of thermal expansion. Because the plasmon peaks in bismuth telluride and bismuth-antimony telluride are too broad to be precisely located, we evaporate indium nanoparticles near the heterojunction to serve as local nano-thermometers. Measuring the nanoparticles’ temperature as a function of the junction current, we have observed heterojunction cooling by 30⁰C. With better ohmic contacts and improved device geometry, we hope to increase the thermoelectric efficiency of these 2D devices relative to their bulk 3D counterparts.