SYNCHROTRON X-RAY STUDIES OF STRAIN IN (100)-ORIENTED HIGH-PRESSURE HIGH-TEMPERATURE (HP-HT) SYNTHETIC DIAMONDS

The wavelength tunability and high intensity of a dedicated synchrotro n X-ray source were extensively used in four-azimuth double-crystal di ffraction experiments to study synthetic diamonds with (001) polished faces. These had major growth sectors of {001} and {111} type and some minor sectors of {110} and {113}. Many series of topographs (up to 80 per sample) in symmetric Bragg reflection geometry mere recorded. Som e of the common features frequently present in synthetic diamonds, nam ely metallic cylindrical inclusions as well as the growth sectors and growth sector boundaries, were the subject of this study. The presence of any source of strain in the crystal map seriously affect its perfo rmance in applications: mechanical (tools), optical (IR windows) or el ectronic (radiation detectors). X-Ray ''pinhole'' rocking curve measur ements as well as detailed analysis of the topographic records yielded interesting new results concerning the state Of the lattice in close proximity to each inclusion and inside growth sectors of the minor for ms of {113} and {110} type. The axisymmetric strain field caused by th e embedded body of each cylindrical caused by the embedded body of eac h cylindrical inclusion was recorded as a symmetrically compressed lat tice. The lattice parameter of the I smaller (by 7 ppm) than that of t he surrounding major growth sectors. More importantly, it Is recorded and reported here for the first time that in addition to lattice param eter differences there exists significant lattice bending (radius R = 7.5 m) inside the minor sectors that is created by the compressive act ion of the surrounding major {001} and {111} growth sectors. Previous experiments have been unable to record this component of stress in syn thetic diamonds either because of an inappropriate choice of diffracti on geometry or because of incompleteness of the experimental procedure s.