Nano-mechanical and condensed phase characterization of cylindrical magnetron sputtered self-assembled TiN nano-hill coating

Abstract

TiN nano-layered thin films were synthesized using an indigenously built cylindrical magnetron sputtering (CMS) apparatus at varying nitrogen flow rates ranging between 5 and 45 sccm at a constant deposition pressure of 9.5 × 10⁻² mbar. Grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), laser Raman spectroscopy (LRS), and nano-indentation studies were performed to characterize these as-deposited films. Unlike conventional sputtering, CMS grown films exhibited Stranski–Krastanov (SK) growth with self-assembled nano-hill architecture. The growth of nano-hills is attributed to the shadowing effect of oblique incident flux arising from cylindrical shaped cathode. Additional relaxation based on inverse Hall–Petch formalism brings about indentation induced buckling of nano-hills leading to softening of the TiN films. Higher hill heights at lower nitrogen flow led to increased friction and wear as they are crushed under the applied load generating debris. In contrast, the shorter nano-hills at high nitrogen flow tend to buckle rather than collapse under indenter load resulting in reduced friction. Coefficient of friction value is further influenced by the angle between nano-hill arrays, growth orientation, and indenter sliding directions. Raman spectroscopy data shows the appearance of high wave number anti-symmetric A + O mode for films synthesized at higher argon or nitrogen concentrations.