Quaternary sputtered TiAlSiN coatings were investigated for their high temperature structural stability, surface morphology, mechanical behaviors, surface chemical bonding states, solar absorptance and thermal emittance for possible solar selective surface applications. The TiAlSiN films were synthesized, via unbalanced magnetron sputtered technology, on AISI M2 steel substrate and annealed at 500 °C - 800 °C temperature range. SEM micrographs show nanocomposite-like structure with amorphous grain boundaries. Nanoindentation analyses indicate a decrease of hardness, plastic deformation and constant yield strength for the coatings. XPS analysis show mixed Ti, Al and Si nitride and oxide as main coating components but at 800 °C the top layer of the coatings is clearly composed of only Ti and Al oxides. Synchrotron radiation XRD (SR-XRD) results indicate various Ti, Al and Si nitride and oxide phases, for the above annealing temperature range with a phase change occurring with the Fe component of the substrate. UV–Vis spectroscopy, FTIR spectroscopy studies determined a high solar selectivity, s of 24.6 for the sample annealed at 600 °C. Overall results show good structural and morphological stability of these coatings at temperatures up to 800 °C with a very good solar selectivity for real world applications

Transition metal nitride Ti _x M _1−x−y N _y (M = Al or AlSi) based thin films are evaluated as solar selective surfaces by correlating their spectral selective features with their crystal structure and chemical bonding state including mechanical strength.

The optical frequency response and changes to the dielectric and optical parameters due to annealing temperature variation (200–500 °C) of sol–gel derived CuCoO_x thin film coatings were investigated. The optical constants such as absorption coefficient, band-gaps, Urbach energy, complex refractive index, complex dielectric constants, optical dispersion parameters, and energy loss functions were determined from reflectance data analysis recorded in the ultraviolet to near-infrared (190–2200 nm) range. The absorption coefficient and the broadening of absorption edge (steepness parameter), energy band-gaps, Urbach energy, loss tangent and energy loss functions decreased with the increase in annealing temperatures. The refractive index displayed normal dispersion behaviors at higher frequency with the maximum value at a temperature of 500 °C. First-principles simulations, density functional theory (DFT+U) as implemented in the Cambridge Serial Total Energy Package (CASTEP), based on a cluster structure of Cu_0.5Co_2.5O₄ system, optimized the crystalline structure and calculated the electronic structure of the framework. The calculated density of states (DOS) and associated absorption coefficient and dielectric constant results reasonably support the experimental findings.