Thermal laser evaporation of elemental metal sources in oxygen

Abstract

Thermal laser epitaxy (TLE) is a novel film growth technique capable of fabricating ultrapure films of many material systems. For growing oxide films with TLE, the impact of source oxidation on the evaporation rate is a central issue, which, however, has not yet been explored systematically. Here, we report a systematic, experimental study of the role of source oxidation on source evaporation at various oxygen pressures and source temperatures in TLE. The volatility of the oxidized metal sources affects the source evaporation rate. When the oxidized metal source is more volatile than the metal, the source evaporation rate increases with the oxygen supply. In a strongly oxidizing environment, stable oxides with lower volatility tend to form and decrease the evaporation rate of the source. Increasing the laser power—and thereby the source temperature—tends to prevent the formation of stable oxides. At even higher source temperatures, the metal vapor pressure can dominate the oxide vapor pressure even in a high oxygen pressure atmosphere. A power-law relation between deposition rate and oxidizing gas pressure is found in case the formation and evaporation of volatile oxides of the elemental source material dominates the total evaporation process. The exponent of this law is a measure of the relevance of source oxidation for the evaporation of the source.