Measuring strain in polycrystalline CVD diamond films

Three-dimensional reciprocal-space mapping was performed to determine the true microstrain: that is, the distribution of strain within individual grains: and to calculate the precise lattice parameters and deviation from near-perfect samples. In order to accomplish this, Bragg reflections from individual grains were isolated (Fewster P F 1997 Crit. Rev. Solid State Mater. Sci. 22 69-110; Golshan M, Fewster P F, Andrew N L, Kidd P, Moore M and Butler J E 2001 J. Phys. D: Appl. Phys. 34 A44-6). This was achieved by increasing the 2θ resolution and by reducing the axial divergence of the beam, resulting in a smaller probe and partially eliminating the effect of projection on to the diffraction plane along the perpendicular direction. A suitable divergence was achieved by using two pairs of slits, placed after the monochromator and before the detector, respectively. The incident beam size was reduced to 50 μm2 to ensure that only a small part of the sample was illuminated. The experiments were carried out at Daresbury Laboratory, Stations 16.3 (Collins S P, Cernik R J, Fell B, Tang C C, Harris N W, Miller M C and Oszlanyi G 1998 J. Synchrotron Radiat. 5 1263-9) and at ESRF, ID10B. The results obtained from three different grades of CVD diamond films were compared. Nitrogen incorporated in one diamond during growth appeared to relieve the strain and give a sharper texture to the film