Structure and thermal stability of δ-Bi2O3 thin films deposited by reactive sputtering

Nanocrystalline delta-Bi2O3 thin films have been deposited onto Si (100) and quartz substrates by reactive sputtering. The structural characteristics and thermal stability of the thin films have been investigated by x-ray diffraction and Raman spectra. It was found that the delta-Bi2O3 thin films could exist stably below 200 degrees C and undergo a phase transition sequence delta -> ss -> alpha with increasing annealing temperature beyond 200 degrees C. These phase transitions were further confirmed by optical constant and optical band gap studies.