Oral: Direct Phonon Dispersion Measurement from an Array of Wurtzite InP Nanowires via meV-Resolved Grazing-Incidence Inelastic X-ray Scattering

Probing the lattice dynamics of nanowires (NWs) or other nanostructures presents a formidable experimental challenge due to their intrinsically low sample volume. In this study, we show that by growing an almost perfectly aligned 2D hexagonal comb-like array of nanowires using state-of-the-art nanofabrication methods [1,2] and combining this with meV-resolution grazing incidence inelastic x-ray scattering (GI-IXS) at a 4^th generation synchrotron source (ESRF, France) we can perform the first direct measurement of the phonon dispersion from a system of NWs.



As a prototypical nanowire system, we study the wurtzite phase of InP, of great interest for photovoltaic applications and only experimentally stable in nanostructured form. We determine a mixture of acoustic and optical phonon dispersion relations along the Γ-K-M and Γ-M directions which show remarkable agreement with our theoretical predictions from ab-initio lattice dynamics simulations of the wurtzite InP phase.



This work serves as a demonstration study, opening the door for exploring lattice dynamics in a vast array of technologically relevant nanostructured materials. This represents a significant milestone in the study of phonon-assisted processes in nanostructures, establishing an experimental framework for investigating dynamic phenomena within nanostructure arrays such as soft-mode driven phase transitions, thermal conductivity, elasticity, superconductivity, charge-density wave formation to list only a few.