Dielectric function of LaAlO3 from 0.8 to 6 eV between 77 and 700 K

Abstract

The authors used spectroscopic ellipsometry to determine the dielectric function and the refractive index of LaAlO3 as a function of photon energy from 0.8 to 6 eV between 77 and 700 K. The ellipsometric angles were acquired over a broad range of incidence angles with a computer-controlled Berek waveplate compensator and with zone-averaging of the adjustable polarizer. The data were corrected for surface effects, such as surface roughness or adsorbed overlayers. The authors report Tauc–Lorentz model parameters for LaAlO3 at 300 K. After annealing in UHV for 20 h, the surface layer thickness decreased from 15 Å to less than 1 Å. They speculate that the anneal causes surface modifications, such as the evaporation of adsorbed molecular layers (hydrocarbons or water) or surface vacancies, and that surface diffusion leads to a reduction of surface roughness. They have also measured the temperature-dependence of the refractive index at 1.96 eV between 77 and 700 K and given a theoretical explanation of its origin.