Bismuth oxide is an excellent candidate material for optoelectronic applications. It is a versatile, crystalline material with a large energy bandgap, high optical transmittance and semiconducting properties. These characteristics make bismuth oxide thin films suitable for atmospheric sensors, humidity sensors, and optoelectronics.
There are several techniques to produce bismuth oxide thin films. Physical vapor deposition (PVD) and thermal oxidation in air are two methods. Both have advantages and disadvantages.
PVD techniques include pulsed laser deposition of bismuth targets and thermal vacuum evaporation of bismuth trioxide powder. Thermal oxidation in air can be performed in two stages, each lasting for one hour. This process can generate an under-layer of bismuth, as well as internally remnant un-oxidized bismuth. The second oxidation step requires the bismuth film to be heated to 270degC.
Thin films made from bismuth oxide can exhibit high resistance. They are also useful in temperature-sensitive electronic circuits. For example, their resistance to water vapor is very sensitive. Their sensitivity is also highly dependent on the nature of the substrate.
X-ray diffraction (XRD) spectra show that bismuth oxide thin films can be polycrystalline or polymorphic. By changing the deposition method, it is possible to produce films with complex structures. In addition, it is possible to tailor the films by varying the temperature.
AFM can be used to examine the grain distribution of bismuth oxide thin films. An anomalous dispersion pattern can be observed in the bismuth oxide films.
In addition to its structural and morphological features, bismuth oxide thin films have a high refractive index. When deposited on conductive substrates, they display Megaohms resistance.