Determining phonon transport properties of bismuth telluride thin films with extremely small grain size using nanoindentation and 3ω method


 The phonon transport properties of Bi2Te3 thin films with extremely small grain size (3.4 nm) is investigated in this study using radio-frequency magnetron sputtering. The films exhibited an average group velocity of 2083 m/s and lattice thermal conductivity of 0.42 W/(m∙K), as determined by nanoindentation and 3ω method, respectively. The phonon mean free path (MFP) was 0.49 nm, determined from the group velocity and lattice thermal conductivity. The lattice thermal conductivity decreased to 35% for single-crystal Bi2Te3 owing to the decrease in the phonon MFP, whereas the group velocity hardly changed in the region of extremely small grain size.