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Publication details for Prof Brian TannerTanner, B.K., Garagorri, J., Gorostegui-Colinas, E., Elizalde, M.R. Allen, D.M., McNally, P.J., Wittge, J., Ehlers, C. & Danilewsky, A.N. (2016). X-ray asterism and the structure of cracks from indentations in silicon. Journal of Applied Crystallography 49(1): 250-259.
- Publication type: Journal Article
- ISSN/ISBN: 0021-8898, 1600-5767
- DOI: 10.1107/S1600576715024620
- Further publication details on publisher web site
- Durham Research Online (DRO) - may include full text
Author(s) from Durham
AbstractThe asterism observed in white radiation X-ray diffraction images (topographs) of extended cracks in silicon is investigated and found to be associated with material that is close to breakout and surrounded by extensive cracking. It is a measure of the mechanical damage occurring when the fracture planes do not follow the low-index cleavage planes associated with the crystal structure. It is not related to a propensity for some cracked wafers to shatter during subsequent high-temperature processing. There is no correlation between crack morphology and alignment of an indenter with respect to the orientation of a silicon wafer, the cracks being generated from the apices of the indenter and having threefold symmetry for Berkovich indents and fourfold symmetry for Vickers indents. X-ray diffraction imaging (XRDI) of indents does not reveal this underlying symmetry and the images exhibit a very substantial degree of variation in their extent. This arises because the XRDI contrast is sensitive to the long-range strain field around the indent and breakout reduces the extent of this long-range strain field. Breakout is also detected in the loss of symmetry in the short-range strain field imaged by scanning micro-Raman spectroscopy. Weak fourfold symmetric features at the extremes of the images, and lying along <110> directions, are discussed in the context of slip generated below the room-temperature indents. Scanning electron microscopy imaging of the region around an indent during focused ion beam milling has permitted the three-dimensional reconstruction of the crack morphology. The surface-breaking Palmqvist cracks are found to be directly connected to the median subsurface cracks, and the presence of extensive lateral cracks is a prerequisite for material breakout at indenter loads above 200 mN. The overall crack shape agrees with that predicted from simulation
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