No abstract

Single-point diamond turning of monocrystalline semiconductors is an important field of research within brittle materials machining. Monocrystalline silicon samples with a (100) orientation have been diamond turned under different cutting conditions (feed rate and depth of cut). Micro-Raman spectroscopy and atomic force microscopy have been used to assess structural alterations and surface finish of the samples diamond turned under ductile and brittle modes. It was found that silicon undergoes a phase transformation when machined in the ductile mode. This phase transformation is evidenced by the creation of an amorphous surface layer after machining which has been probed by Raman scattering. Compressive residual stresses are estimated for the machined surface and it is observed that they decrease with an increase in the feed rate and depth of cut. This behaviour has been attributed to the formation of subsurface cracks when the feed rate is higher than or equal to 2.5 μm/rev. The surface roughness was observed to vary with the feed rate and the depth of cut. An increase in the surface roughness was influenced by microcrack formation when the feed rate reached 5.0 μm/rev. Furthermore, a high-pressure phase transformation induced by the tool/material interaction and responsible for the ductile response of this typical brittle material is discussed based upon the presented Raman spectra. The application of this machining technology finds use for a wide range of high quality components, for example the creation of a micrometre-range channel for microfluidic devices as well as microlenses used in the infrared spectrum range.

Structural disorder and strain effects in ductile-regime single-point-diamond-turned gallium arsenide monocrystalline samples were probed by Raman scattering. The positive frequency shift of the longitudinal and transverse optical phonons observed in the machined samples indicate a residual compressive stress of about 1.5 GPa. This residual strain was attributed to the hysteresis of phase transformation generated by the high pressure imposed by the cutting tool tip during the machining process. The broadening of the Raman peaks indicate a high degree of structural disorder in the GaAs lattice. Moreover, the Raman spectrum of annealed samples, after machining, shows a less disordered but still misoriented matrix. In addition, it was found that crystalline arsenic formed into the surface vicinity.

Single-point diamond turning tests were carried out in two different [001]-oriented semiconductors, InSb and Si single crystals. The analysis of the conditions in which the machining is in ductile or brittle mode indicates that the plasticity presented by semiconductor crystals during micromachining can be correlated to the value of the transition pressure. It is shown that the ductility presented by different semiconductor single crystals is inversely related to the transition pressure value of the material.