Mid- and far-infrared optical characterization of monoclinic HfO2 nanoparticles and evidence of localized surface phonon polaritons

Abstract

Monoclinic HfO2 nanoparticles (9 - 45 nm) are synthesized using a sol-gel method and optically characterized using transmission- and angle-dependent reflection spectroscopy in the mid- to far-infrared. A detailed HfO2 identification of the infrared-active phonon modes is presented; consistent with previously reported thin film values, and in excellent agreement with density functional perturbation theory calculations. An anomaly is observed in both reflection and transmission measurements, at 556 cm-1 that is not attributed to the optical phonon modes. Numerical models indicate that this measured anomaly is in the spectral region of a localized surface phonon polariton mode. The results of this work suggest that HfO2 nanoparticles could enable new mid- and far-infrared materials and devices with engineered optical properties.