Optical properties of surface-tunable NiO films depending on oxygen pressure, growth temperature, and growth duration

Nanostructures based on thin oxide films have a number of applications. In this work, we report the physical and optical properties of a wide range of NiO thin film nanostructures. These films were fabricated using thermal oxidation of a Ni substrate with different oxygen partial pressures, growth temperatures, and growth durations. SEM observations of NiO films evaporated in static air to 200 sccm O-2 partial pressure conditions show the evolution of the microstructure from initially coarse islands or particles to well-formed NiO thin films combined with neighboring structures. The root-mean-square crystallite sizes from AFM measurements were 50.769 nm and 137.66 nm for temperatures of 620 degrees C and 730 degrees C and durations of 4 and 6 h, respectively. X-ray diffraction was performed to understand the microstructure of the two-dimensional NiO thin films in more detail. Photoluminescence (PL) spectra of the NiO films reveal that the both the PL intensity and energy vary with respect to oxygen pressure, temperature, and duration. The mechanisms for the different observed microstructures and the optical transitions in the NiO thin films are considered.