Optical and thermal properties of BeO thin films prepared by reactive ionized-cluster beam technique

Preparation of BeO thin films is successfully achieved by the reactive ionized-cluster beam technique developed by the authors. Transparent BeO films with the c-axis preferential orientation which is peculiar to a hexagonal structure are obtained on glass substrates, and single-crystal epitaxial films are formed on sapphire substrates at low substrate temperatures up to 400 °C. Optical and thermal transport properties of films are investigated in detail. A strong reststrahlen reflection peak is observed in the vicinity of wavelength 13.5 μm, from which the frequencies of the transverse and longitudinal vibration modes are determined. Anisotropic lattice thermal conductivities parallel and perpendicular to the c axis of the films are measured, and the values of κ∥ph ?2.6 W/cm deg and κ⊥ph ?0.6 W/cm deg at 300 K are obtained. It is also shown that the thermal conductivities of BeO films are proportional to T−2 below Debye temperature ϑD?1053 K of this material.