Resonance Photoemission Spectroscopic Study of Thermally Evaporated NiTiO₃ Thin Films

An ilmenite structure was maintained with better crystalline characteristics which were determined from structural examinations employing x-ray diffraction of thermally evaporated NiTiO₃ (NTO) thin films on Si (100) substrates. NiO₆ and TiO₆ octahedra are arranged in alternating layers in the lattice structure of NTO. Atomic force microscopy, which highlights the structure of the film surface, was used to assess the thin film microstructure and surface roughness. NTO preferentially absorbs ultraviolet radiation below 360 nm, visible light in the wavelength range from 420 nm to 540 nm and above 700 nm. NTO displays a band gap of 2.17 eV and exhibits direct band gap semiconductor characteristics. Corresponding to photon energy of 2.7 eV, 2.5 eV and 1.5 eV, NTO shows clear absorbance peaks at 448 nm, 502 nm and 743 nm, respectively. It is hypothesized that the peaks of NTO's visible light absorbance result mostly from the charge transfer transitions d → d of Ni inside its valence band. The films have been further characterized by x-ray photoemission spectroscopy and valence band spectroscopy, with a range of photonic energy resulting in the phenomenon of resonance photoemission spectroscopy (RPES) in accordance to find out the electronic spectra of NTO which eliminates the possibility of metal clusters in NTO films. The RPES spectra indicate that the Ti 3d (Ti³⁺ defect states) and O 2s are strongly hybridized. The magnetic hysteresis loop demonstrated that the NTO films may exhibit superparamagnetic behavior at 300 K. These characterization techniques help to understand its electronic and magnetic properties, which are important in photocatalytic devices.