Subsurface deformation of germanium in ultra-precision cutting: characterization of micro-Raman spectroscopy

Abstract

Germanium is widely used for infrared components and high-speed transistors. Ultra-precision single-point diamond turning (SPDT) can be employed to achieve its nanometric surface, while subsurface damage has a significant influence on surface integrity due to its brittle feature. This study investigated its subsurface deformation after SPDT. A characterization model of micro-Raman spectroscopy was established with the aim to characterize the subsurface deformation, including phase transformation and residual stress, where the transformation from single crystal structure to amorphous structure is dominant. A spectral fitting method was utilized to analyze the variation of subsurface deformation in various machining parameters. The degenerated single crystal Raman peak was widened due to anisotropic stress. It was discovered that the turning operation at a moderately low spindle speed and tool feed rate reduces phase transformation and residual stress based on the value of Raman ratio and Raman shift. These findings provided significant basis for the manufacturing process of optical components with good surface integrity.