Combinatorial Co-sputtering of Mg–Bi–O thin films: structural evolution and tunable optoelectronic properties

Abstract

Binary and ternary metal oxides offer diverse functionalities, enabling their use in photovoltaics, transparent conductors, water-splitting catalysts, and topological insulators. Despite this potential, many novel oxide systems remain underexplored for thin film solar energy applications. In this work, we present the first high-throughput investigation of magnesium bismuth oxide (Mg_xBi_yO_z) thin films using combinatorial co-sputtering across a wide compositional space. An integrated characterization workflow combining synchrotron-based grazing-incidence wide-angle X-ray scattering (GIWAXS) and spectroscopic ellipsometry is employed to systematically map their structural and optical properties. The as-deposited films are predominantly amorphous, with post-deposition annealing up to 450 °C revealing a strong correlation between the Mg : Bi ratio and crystallization behavior. These structural transitions directly influence the compositionally dependent absorption coefficients and band gaps across the visible spectral range This study establishes Mg_xBi_yO_z thin films as a compositionally versatile and optically tunable material system, and demonstrates the potential of combinatorial co-sputtering workflows to accelerate discovery and optimization in complex thin films.