Depositing one layer of atoms at a time can result in materials that greatly improve fuel cells, batteries and other devices. In this research, scientists precisely added chromium to iron oxides to control the electronic and optical properties. The result was a highly ordered thin film of chromium ferrite (Fe2CrO4). Chromium ferrite becomes more electrically conductive by absorbing light. The material could be useful for vital solar processes, such as water splitting to make hydrogen for fuel, coolants and more.