Electron-Transparent Thermoelectric Coolers Demonstrated with Nanoparticle and Condensation Thermometry

More efficient thermoelectric devices would revolutionize refrigeration and energy production, and low-dimensional thermoelectric materials are predicted to be more efficient than their bulk counterparts. But nanoscale thermoelectric devices generate thermal gradients on length scales that are too small to resolve with traditional thermometry methods. Here we fabricate, using single-crystal bismuth telluride (Bi₂Te₃) and antimony/bismuth telluride (Sb_2-BiTe₃) flakes exfoliated from commercially available bulk materials, functional thermoelectric coolers (TECs) that are only 100 nm thick. These devices are the smallest TECs ever demonstrated by a factor of 10⁴. After depositing indium nanoparticles to serve as nanothermometers, we measure the heating and cooling produced by the devices with plasmon energy expansion thermometry (PEET), a high-spatial-resolution, transmission electron microscopy (TEM)-based thermometry technique, demonstrating a ΔT = -21 ± 4 K from room temperature. We also establish proof-of-concept for condensation thermometry, a quantitative temperature-change mapping technique with a spatial precision of ≲300 nm.