Acoustic cavities in 2D heterostructures.

Two-dimensional (2D) materials offer unique opportunities in engineering the ultrafast spatiotemporal response of composite nanomechanical structures. In this work, we report on high frequency, high quality factor (Q) 2D acoustic cavities operating in the 50-600 GHz frequency (f) range with f × Q up to 1 × 10. Monolayer steps and material interfaces expand cavity functionality, as demonstrated by building adjacent cavities that are isolated or strongly-coupled, as well as a frequency comb generator in MoS/h-BN systems.

High-pressure nuclear inelastic scattering with backscattering monochromatization.

The capability to perform high-pressure low-temperature nuclear inelastic scattering on Te and Sb with a sapphire backscattering monochromator is presented. This technique was applied to measure nuclear inelastic scattering in TeO at pressures up to 10 GPa and temperatures down to 25 K. The evaluated partial Te densities of phonon states were compared with theoretical calculations and with Raman scattering measured under the same conditions.

Antisite Pairs Suppress the Thermal Conductivity of BAs.

BAs was predicted to have an unusually high thermal conductivity with a room temperature value of 2000  W m^{-1} K^{-1}, comparable to that of diamond. However, the experimentally measured thermal conductivity of BAs single crystals is still lower than this value. To identify the origin of this large inconsistency, we investigate the lattice structure and potential defects in BAs single crystals at the atomic scale using aberration-corrected scanning transmission electron microscopy (STEM).