Sequentially PARMS-coated sub-nanometric film stacks for UV applications

We present a comparative study of two types of materials with tunable artificial refractive indices that were obtained by sequentially coating sub-nanometric film stacks of Ta 2 O 5 /SiO 2 and Nb 2 O 5 /SiO 2 . These sub-nanometric film stacks were fabricated using Plasma-Assisted Reactive Magnetron Sputtering and simultaneous co-sputtering of two targets. The thickness of individual sub-layers was controlled by the turntable rotation speed, and the ratio between the two materials was determined by the power applied to the respective targets. We show that these materials with tunable refractive indices present an interesting alternative to classical high-refractive-index materials for UV applications. However, the achievable bandgap is not as large as classical materials like HfO 2 , and the lower the bandgap of the high-refractive-index material, the lower the bandgap of the nanolaminate at a given refractive index.