Molecular beam epitaxy of Sr5Au2O8 thin films

Abstract

The synthesis of complex transition metal oxides using molecular beam epitaxy is well established with the exception of gold. Overcoming the oxophobicity of gold is a mandatory step towards an entire new section of complex transition metal oxides. Here, we show that ${\mathrm{Sr}}_{5}{\mathrm{Au}}_{2}{\mathrm{O}}_{8}$ thin films can be epitaxially grown onto ${\mathrm{SrTiO}}_{3}$ substrates using a high-efficiency radio-frequency-operated atomic oxygen source as an oxidizing agent. Stoichiometric atomic beam fluxes of strontium and gold were controlled by electron-impact emission spectroscopy. ${\mathrm{Sr}}_{5}{\mathrm{Au}}_{2}{\mathrm{O}}_{8}$ thin films were grown at temperatures between 627 and 653 ${}^{\ensuremath{\circ}}\mathrm{C}$. Owing to the sensitivity of ${\mathrm{Sr}}_{5}{\mathrm{Au}}_{2}{\mathrm{O}}_{8}$ thin films to environmental agents, e.g., water and ${\mathrm{CO}}_{2}$, we capped them with a 300-nm layer of Se or a 200-nm layer of Au.