Abstract
The defects and subsurface damages induced by crystal growth and micro/nano-machining have a significant impact on the functional performance of machined products. Raman spectroscopy is an efficient, powerful, and non-destructive testing method to characterize these defects and subsurface damages. This paper aims to review the fundamentals and applications of Raman spectroscopy on the characterization of defects and subsurface damages in micro/nano-machining. Firstly, the principle and several critical parameters (such as penetration depth, laser spot size, and so on) involved in the Raman characterization are introduced. Then, the mechanism of Raman spectroscopy for detection of defects and subsurface damages is discussed. The Raman spectroscopy characterization of semiconductor materials’ stacking faults, phase transformation, and residual stress in micro/nano-machining is discussed in detail. Identification and characterization of phase transformation and stacking faults for Si and SiC is feasible using the information of new Raman bands. Based on the Raman band position shift and Raman intensity ratio, Raman spectroscopy can be used to quantitatively calculate the residual stress and the thickness of the subsurface damage layer of semiconductor materials. The Tip-Enhanced Raman Spectroscopy (TERS) technique is helpful to dramatically enhance the Raman scattering signal at weak damages and it is considered as a promising research field.
Highlights
During mico/nano-machining and crystal growth, various defects and damages in crystals occur inevitably, including microstructure change, residual strain, dislocation, phase transformation, and so on [1]
Many non-destructive methods have been applied to measure and characterize these defects and subsurface damages: the X-ray diffraction technique was adopted by Bismayer et al [9] to quantitatively determine the residual stress of grinded single crystal silicon
(2) For the photoluminescence technique, it is mainly applied for the detection of microdefects and dislocations, the residual stress detection and phase transformation characterization is hardly feasible
Summary
During mico/nano-machining (such as micro/nano cutting, micro/nano milling, micro/nano grinding, etc.) and crystal growth, various defects and damages in crystals occur inevitably, including microstructure change, residual strain, dislocation, phase transformation, and so on [1]. Many non-destructive methods have been applied to measure and characterize these defects and subsurface damages: the X-ray diffraction technique was adopted by Bismayer et al [9] to quantitatively determine the residual stress of grinded single crystal silicon. The Raman vibration spectra of materials is significantly influenced by microstructural changes, impurities, residual stress, and so on, which leads to changes in the number of scattering molecules, phonon frequency, breakdown of Raman selection rules and other effects [18] These defects and subsurface damages induced by crystal growth and micro/nano-machining can be characterized using Raman information, namely, band position, band position shift, full width at half maximum (FWHM), and intensity. The Raman spectroscopy technique is an efficient, powerful, sample preparation friendly, and non-destructive testing method to characterize these defects and subsurface damages [19]. Based on the calculated laser penetration depth, laser wavelength should be carefully selected during Raman spectroscopy characterization, especially for the micro/nano-scale sensitive surface/subsurface tests
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