Amorphous phase stability of NbTiAlSiN_X high-entropy films

In this study, high-entropy films with the composition of NbTiAlSiN_X were prepared by a reactive direct current (DC) magnetron sputtering technique, with different nitrogen flow rates (0, 4 and 8 ml·min⁻¹). The microstructures and properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), nano-indenter and spectrophotometer. All of the as-deposited NbTiAlSiN_X films are shown to have an amorphous structure, and the films exhibit high thermal stability up to 700 °C. The maximum hardness and modulus values of the films reach 20.5 GPa (4 ml·min⁻¹) and 206.8 GPa (0 ml·min⁻¹), respectively. The films exhibit high absorption of the solar energy in the wavelength of 0.3–2.5 μm, which indicates that NbTiAlSiN_X nitride film is a potential candidate solar selective absorbing coating for high-temperature photo-thermal conversion in the concentrated solar power project.