Highly oriented as-grown beta-phase bismuth oxide for optical MEMS

Reactive sputtering of bismuth has been used to form highly oriented beta-phase Bi₂O₃ thin films at 120 °C. Notably, the films consist of nearly vertical ~ 50 nm diameter nano-filaments of highly aligned β phase pure bismuth oxide. The optical characteristics of the films include a direct optical bandgap of 3.95 eV at 300 K and nearly negligible optical absorption in the wavelength range from 500 to 3000 nm. Nanoindentation experiments show that the mechanical characteristics of the films include reduced modulus and hardness values of 90 and 4.5 GPa, respectively. As fabricated, the films exhibit tensile stress which in combination with a relatively high refractive index value in the range of 2.4–2.5 makes the realized Bi₂O₃ films structurally and optically suitable for fabrication of optical microelectromechanical (MEMS) devices with applications in the visible to mid-infrared wavelength region, such as MEMS-based Fabry–Pérot microspectrometers, which is demonstrated through simulations. Graphical Abstract: (Figure presented.)