Intrinsic Stress and Grain Alignment in Diamond Films

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9619520 Sheldon One problem with CVD deposition of diamond on many substrates is that the intrinsic stresses in the diamond film are larger than the stresses caused by the film/substrate thermal expansion mismatch, which causes the diamond film to spall off or the substrate to bow. Post- deposition annealing does not remove these intrinsic stresses. Recent work by the PI's group has determined that an intermediate annealing step, after significant grain impingement, but before a dense film was formed, can minimize intrinsic stress in the diamond film, and reduce the spallation. The intermediate annealing step alters the film microstructure in such a way to reduce stress evolution during subsequent diamond film growth. Preliminary electron microscopy studies (ex situ SEM and in situ TEM hot-stage experiments) indicate that contacting diamond grains rotate during annealing. A reasonable explanation for the observed stress reduction is that grain rotation results in better crystallographic alignment between adjacent grains. Subsequent growth on top of these grains can then form more stable grain boundary configurations that are less susceptible to the relaxation mechanisms that can induce intrinsic tensile stress. The proposed research would study the fundamentals of this phenomenon in order to optimize and control stress levels in diamond and other thin films. The research will be performed by a Focused Research Group consisting of the PI (CVD/thin films), and 2 co-PIs (a transmission electron microscopist/crystallographer and a physicist/Raman spectroscopist). %%% One problem with CVD deposition of diamond on many substrates is that the intrinsic stresses in the diamond film are larger than the stresses caused by the film/substrate thermal expansion mismatch, which causes the diamond film to spall off or the substrate to bow. Post- deposition annealing does not remove these intrinsic stresses. Recent work by the PI's group has determined that an intermediate annealing step, after significant grain impingement, but before a dense film was formed, can minimize intrinsic stress in the diamond film, and reduce the spallation. The proposed research would study the fundamentals of this phenomenon in order to optimize and control stress levels in diamond and other thin films. The research will be performed by a Focused Research Group consisting of the PI (CVD/thin films), and 2 co-PIs (a transmission electron microscopist/crystallographer and a physicist/Raman spectroscopist). ***