Far infrared absorption by acoustic phonons in titanium dioxide nanopowders

TL;DR

This study investigates far infrared absorption in TiO2 nanopowders, linking observed spectral features to acoustic phonon modes and highlighting quantum effects and surface charge contributions.

Contribution

It provides experimental evidence of acoustic phonon absorption in TiO2 nanoparticles and introduces a quantum mechanical perspective to explain the observed absorption intensities.

Findings

Absorption peaks match predicted dipolar acoustic phonon frequencies.

Continuum elastic theory cannot fully explain absorption intensities.

Surface charge layers likely contribute to absorption mechanisms.

Abstract

We report spectral features of far infrared electromagnetic radiation absorption in anatase TiO2 nanopowders which we attribute to absorption by acoustic phonon modes of nanoparticles. The frequency of peak excess absorption above the background level corresponds to the predicted frequency of the dipolar acoustic phonon from continuum elastic theory. The intensity of the absorption cannot be accounted for in a continuum elastic dielectric description of the nanoparticle material. Quantum mechanical scale dependent effects must be considered. The absorption cross section is estimated from a simple mechanical phenomenological model. The results are in plausible agreement with the absorption being due to a sparse layer of charge on the nanoparticle surface.