Probing the Dynamic Fluctuations of Bismuth Nanoparticles by Thermovoltage Measurements

Metal and semiconductor nanoparticles (NPs) with a characteristic diameter of 1 nm or less undergo structural and shape fluctuations at elevated temperatures that affect their catalytic and optical properties. Individual bismuth nanoparticles (BiNPs) have been shown to undergo spontaneous phase transitions already at room temperatures due to their shallow potential landscape. To further explore these fluctuations, we perform STM-based thermovoltage measurements of individual ∼5 nm BiNPs. We show an excellent agreement between the measured thermovoltage statistics and a theoretical model that considers the large quantum confinement in these particles and the high anisotropy of the effective mass tensor of their charge carriers. Based on this we conclude that the potential energy surface of these particles is sufficiently shallow to enable random structural sampling of their entire configurational space at room temperature. The results also show that for certain crystalline orientations large Seebeck values, >600 μV/K, can be achieved making BiNPs a promising material for thermoelectric (TE) applications.