UNIVERSITY OF THE WITWATERSRAND, JOHANNESBURG

Prof Trevor Derry

Current Research Projects

1. Identification of the foreign atoms on diamond surfaces

  • Prof.T.E. Derry1, Dr.N.W. Makau1,2
  • 1Univ. of the Witwatersrand, 2Moi University, Kenya
  • Following on from recent XPS determinations of the O & H functional groups present on conventionally prepared diamond surfaces (with the CSIR), nuclear resonance studies of C atom transfer from the polishing lubricant were carried out at Wits, for all three low-index surfaces. It was suspected, and demonstrated using 13C labelled oil, that not only the hydrogen but also an outer monolayer of carbon is bonded from the oil. The work has been published but should be carried further.


2. Computation of the favoured surface locations of oxygen on diamond

  • Dr.N.W. Makau1, 2, Prof. C. Stampfl3, Prof.T.E. Derry1
  • 1Univ. of the Witwatersrand, 2Moi University, Kenya, 3Sydney University
  • To enable comparison with previous LEED, synchrotron X-ray and XPS work, density functional calculations have been carried out (with the Fritz Haber Institute and Sydney University) of work function, energy, and density of states for O & OH on various {111} surface sites, with and without (2x1) reconstruction. The agreement with experimental observations is good, e.g. in favouring a one-third monolayer O coverage, and reconstruction for zero coverage. Papers are currently in preparation.


3. Smoothness of conventionally prepared diamond surfaces

  • Prof.T.E. Derry 1, Dr.N.W. Makau1,2, Dr. N. van der Berg4
  • 1Univ. of the Witwatersrand, 2Moi University, Kenya, 4Pretoria University
  • Atomic Force Microscopy studies of polished surface planarity (with Pretoria University) were used to confirm that the manual final polishing stage which we have been using to produce the best mechanically prepared surfaces for research, does in fact show a measurable improvement in terms of RMS roughness and Fourier components. A paper is being processed.

4. Conversion of cubic to hexagonal boron nitride by ion irradiation

  • Prof.T.E. Derry 1, R. Machaka1,5, R. Erasmus1, Dr. D. Billing1
  • 1Univ. of the Witwatersrand, 5NMMU, Port Elizabeth
  • Following on from theoretical computer predictions in the Focus Area of Prof. J.E. Lowther, soft hexagonal BN slices were irradiated with MeV light ions and probed with Raman spectroscopy and electron diffraction. Evidence for the presence of the hard cubic BN phase in nanocrystalline form was found. The work is being published, and will be extended to heavier ions and other energies.

5. Characterization of the ion implantation damage in annealed diamond

  • Prof.T.E. Derry 1, E.K. Nshingabigwi 1,6, Dr.C. Levitt 1, Mr. M. Rebak1, Prof.J. Neethling 5
  • 1Univ. of the Witwatersrand, 5Nelson Mandela Metropolitan University, P.E., 6National Univ. of Rwanda,
  • It has formerly been shown (e.g. by Prins & Spits) that low damage levels, produced during the implantation doping of diamond as a semiconductor, anneal easily while high levels "graphitize" (above about 2x1015 ions cm-2). The difference in the defect types and their profiles, in the two cases, has never been directly observed, because of the difficulty in preparing specimens of this material for cross-section transmission electron microscopy. First they must be polished to ~40mm thickness, then implanted on edge and annealed, before final ion beam thinning to electron transparency. With the aid of the expertise at the NMMU, we have succeeded, revealing the damage distributions and opening the way to further studies by ourselves and others.

6. Diamond surface band-gap by Reflection Anisotropy Spectrometry

  • Prof. P. Chiaradia 7, Dr. G. Busetti 7, Dr. C. Goletti 7, Prof.T.E. Derry 1
  • 1Univ. of the Witwatersrand, 7Univ. of Roma-2, Italy
  • Surface reconstruction at diamond{111} causes the opening of a gap in the optical density of states, but the mechanism of this is still debated. Theoretical calculations require an exact measurement of the gap size, and this has now been achieved using the above technique at Roma-2 University. The value is 1.47 eV; a paper has been published in Europhysics Letters. A diamond that reconstructed into a single domain (2x1) was essential, and it interesting that the same specimen as was exploited by one of us (TED) in 1984 and in 1994 was used again. Further studies are underway.