Three-dimensional mapping of stresses in plastically deformed diamond using micro-Raman and photoluminescence spectroscopy

The extreme mechanical properties of diamond have made it the material of choice for many industrial applications, ranging from cutting and grinding to wire-drawing dies. A detailed knowledge of its mechanical properties, also at high temperature, is thus of importance. Micro-Raman and photoluminescence (PL) spectroscopy were used to map the three-dimensional (3D) stress distribution surrounding a plastic impression made in a synthetic, type Ib single crystal diamond. The impression was created on a (100) face of the crystal with an Si(3)N(4) impressor at 1400 C using the so-called soft impressor technique. The diamond Raman peak was mapped at room temperature at the surface and at fixed intervals of 10 mu m below the surface using a motorised X-Y stage. The depth (Z)-resolution was limited to 10 mu m by means of a confocal pinhole. Using data from the Raman peak position, a 3D map of the stress contours surrounding the impression was generated, while the Raman width data yielded a map of the plastic deformation volume. The surface stress map shows a cross-shaped rosette pattern that corresponds very closely with micrographs imaging the pile-up on the surface due to dislocation movement. The "arms" of the pattern are in compression (similar to 1.5 GPa), while the center of the impression is in tension (similar to 1 GPa). The deformation map shows a radially symmetric area of deformation centered on the impression, with the maximum degree of deformation at the center. The stress contours compare favorably with the resolved shear stress contours calculated for diamond. PL intensity maps of the zero phonon line (ZPL) associated with the [N-V](-) defect center at 1.945 eV provide images of the extent of vacancy formation and movement during the impression process. Data concerning the position and width of the ZPL correspond well with the Raman results. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3531548]