Characterisation of electron irradiated boron-doped diamond

Various boron-doped polycrystalline chemical vapour deposition (CVD) and single crystal high pressure-high temperature (HPHT) diamonds of different doping levels have been investigated by transmission electron microscopy (TEM) electron irradiation and subsequent study by low-temperature photoluminescence spectroscopy in a Renishaw microspectrometer. Several new optical centres have been discovered that have only been seen in irradiated B-doped diamonds that are evidently closely related, with zero phonon lines at 635.7, 651.2 and 666.0 nm. UV laser irradiation causes inter-centre conversion. In the presence of the 666.0-nm centre, the 635.7-nm centre grows enormously at the expense of the 666.0-nm centre at temperatures above 100 K and the initial relative intensities of these centres determine the details of the temperature dependence. Other unrelated centres are also normally obtained with zero phonon lines at 506.0, 648.0 and 732 ran. The 648.0-mn centre evidently has an associated local mode. Polycrystalline CVD samples of B-doped diamond were examined at DTC Maidenhead to measure the free and boron-bound excitons of the samples and surface maps of the intensity were created. These quantitative results show that the boron level varies from grain to grain by up to 10 times presumably as a result of facet orientation on each crystallite. This detail corresponds exactly with the contrast shown under a scanning electron microscope (SEM) under low beam currents; however, after a long exposure to the electron beam the contrast in the SEM changes to show much larger structures that are believed to be related to grain clusters with a common growth direction (while the exciton map remains constant). (C) 2002 Elsevier Science B.V. All rights reserved.