TiN and TiNxOy thin films share many properties such as electrical and optical properties. In this work, a comparison is conducted between TiN (with and without annealing at 400 °C in air and vacuum) and TiNxOy thin films deposited by using RF magnetron sputtering with the same pure titanium target, Argon (Ar) flow rate, nitrogen flow rates, and deposition time on stainless steel substrates. In the case of TiNxOy thin film, oxygen was pumped in addition. The optical properties of the thin films were characterized by spectrophotometer, and Fourier transform infrared spectroscopy (FTIR). The morphology, topography, and structure were studied by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). The results show that both thin films have metal-like behavior with some similarities in phases, structure, and microstructure and differences in optical absorbance. It is shown that the absorbance of TiN (after vacuum-annealing) and TiNxOy have close absorbance percentages at the visible range of light with an unstable profile, while after air-annealing the optical absorbance of TiN exceeds that of TiNxOy. This work introduces annealed TiN thin films as a candidate solar selective absorber at high-temperature applications alternatively to TiNxOy.
Understanding the microstructure evolution of metal thin films on various substrates is essential for developing thin films that need specific requirements. The microstructure of thin films has been identified to be related to the mobility of the adatoms during growth. Recently, the theory of non-classical crystallisation of thin films has been introduced to explain the structure formation in chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes. Much work has been conducted on CVD deposited thin films, while little data appears on PVD techniques. The effect of substrate material on the microstructure of the deposited nickel-titanium (NiTi) thin film and its optical absorbance is studied in this work. Three different substrates with identified surface conditions were used to deposit thin films of NiTi in the same chamber under the same processing conditions. The NiTi thin film was deposited using radio frequency (RF) PVD sputtering process on stainless steel (SS), aluminium (Al) and copper (Cu) substrates. The results were analysed in view of state of art structure models and mechanisms. The microstructure was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical absorbance was measured by spectrophotometery. The results have shown that the structure and morphology of the grown films have varied in all conditions. Amorphous structures were obtained for Al and Cu substrates, while crystalline structures were obtained for the stainless-steel substrate at the same sputtering conditions.
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