Dr Christopher Latham
Research Associate
Email: christopher.latham@surrey.ac.uk
Phone: Work: 01483 68 2582
Room no: 31 AZ 02
Further information
Publications
Journal articles
- . (2012) 'Electron microscopy of nuclear graphite: A modelling approach'. Journal of Physics: Conference Series, 371
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(2010) 'Comment on "increase in specific heat and possible hindered rotation of interstitial C2 molecules in neutron-irradiated graphite"'. Physical Review B - Condensed Matter and Materials Physics, 82 (5)Full text is available at: http://epubs.surrey.ac.uk/741005/
Abstract
Iwata and Watanabe's model for the observed low-temperature specific heat of neutron-irradiated graphite assumes that self-interstitial atoms exist as clusters of nearly free C2 molecules. We suggest that their hypothesis is not supported by other experiments and theory, including our own calculations. Not only is it inconsistent with the long-known kinetics of interstitial prismatic dislocation loop formation, density-functional theory shows that the di-interstitial is covalently bonded to the host crystal. In such calculations no prior assumptions are made about the nature of the bonding, covalent or otherwise. © 2010 The American Physical Society.
- . (2008) 'The di-interstitial in graphite'. Journal of Physics Condensed Matter, 20 (39)
- . (2008) 'Effect of the dipole-dipole interaction of particles in an active medium on the character of superradiation'. SP MAIK Nauka/Interperiodica Plasma Physics Reports, 34 (7), pp. 555-561.
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(2008) 'Effect of dipole-dipole interactions between atoms in an active medium'. Optical Society of America Journal of the Optical Society of America B: Optical Physics, 25 (3), pp. 458-462.Full text is available at: http://epubs.surrey.ac.uk/741156/
Abstract
On the basis of the results of numerical modeling, it is shown that dipole–dipole interactions among atoms in the active medium strongly influences the character of the associated superradiation. The main effect is to make the nuclear subsystem behave chaotically. Its strength increases with the atom density and leads to the suppression of distant collective correlations and superradiation. Near correlations between the atoms are established, causing a confinement effect: a shielding of radiation in the active medium.
- . (2006) 'A pseudopotential density functional theory study of native defects and boron impurities in FeAl'. Institute of Physics Journal of Physics: Condensed Matter, 18 (39), pp. 8859-8876.
- . (2006) 'Electronic structure calculations for substitutional copper and monovacancies in silicon'. Institute of Physics Physica Scripta: an international journal for experimental and theoretical physics, 2006 (T126), pp. 61-64.
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(2005) 'Passivation of copper in silicon by hydrogen'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 72 (23) Article number 235205 Full text is available at: http://epubs.surrey.ac.uk/741004/
Abstract
The structures and energies of model defects consisting of copper and hydrogen in silicon are calculated using the AIMPRO local-spin-density functional method. For isolated copper atoms, the lowest energy location is at the interstitial site with Td symmetry. Substitutional copper atoms are found to adopt a configuration with D2d symmetry. We conclude that the symmetry is lowered from Td due to the Jahn-Teller effect. Interstitial hydrogen atoms are found to bind strongly to substitutional copper atoms with an energy that is more than the difference in formation energy over the interstitial site for Cu. The resulting complex has C2v symmetry in the −2 charge state where the H atom is situated about 1.54 Å away from the Cu atom in a [100] direction. In other charge states the symmetry of the defect is lowered to Cs or C1. A second hydrogen atom can bind to this complex with nearly the same energy as the first. Two structures are found for copper dihydride complexes that have nearly equal energies; one with C2 symmetry, and the other with Cs symmetry. The binding energy for a third hydrogen atom is slightly more than for the first. Calculated electronic levels for the model defects relative to one another are found to be in fair to good agreement with experimental data, except for the copper-dihydride complex. The copper trihydride complex has no deep levels in the bandgap, according to our calculations.
- . (2003) 'Calculated properties of nitrogen-vacancy complexes in beryllium- and magnesium-doped GaN'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 68 (20) Article number 205209
- . (2003) 'The structures and properties of tetrafluoromethane, hexafluoroethane, and octafluoropropane using the aimpro density functional program'. Elsevier Journal of Fluorine Chemistry, 121 (2), pp. 193-199.
- . (2003) 'Calculated properties of point defects in Be-doped GaN'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 67 (20) Article number 205206
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(2003) 'Calculated properties of point defects in Be-doped GaN'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 67 (20) Article number 205206 Full text is available at: http://epubs.surrey.ac.uk/741006/
Abstract
The properties of several point defects in hexagonal gallium nitride that can compensate beryllium shallow acceptors (BeGa) are calculated using the AIMPRO method based on local density functional theory. BeGa itself is predicted to have local vibrational modes (LVM’s) very similar to magnesium acceptors. The highest frequency is about 663cm-1. Consistent with other recent studies, we find that interstitial beryllium double donors and single-donor beryllium split interstitial pairs at gallium sites are very likely causes of compensation. The calculations predict that the split interstitial pairs possess three main LVM’s at about 1041, 789, and 738cm-1. Of these, the highest is very close to the experimental observation in Be-doped GaN. Although an oxygen donor at the nearest-neighboring site to a beryllium acceptor (BeGa-ON) is also a prime suspect among defects that are possibly responsible for compensation, its highest frequency is calculated to be about 699cm-1 and hence is not related in any way to the observed center. Another mode for this defect is estimated to be about 523cm-1 and is localized on the ON atom. These two vibrations of BeGa-ON are thus equivalent to those for the isolated substitutional centers perturbed by the presence of their impurity partners.
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(2001) 'Density functional calculations of carbon doping in III-V compound semiconductors'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 63 (15) Article number 155202 Full text is available at: http://epubs.surrey.ac.uk/741008/
Abstract
This article reports the results of investigations based on local-density-functional theory into the relative formation energies for single substitutional carbon atoms in nine III-V compound semiconductors. The calculations are performed using a supercell formalism derived from the AIMPRO real-space cluster method. Only a very slight trend is discernible down the periodic table. When a metal atom is replaced with carbon, it is energetically least favorable in the phosphides, very marginally lower energy in the arsenides, and ≈0.5–0.7 eV lower in the antimonides. The situation is approximately reversed when a P, As, or Sb atom is substituted by a C atom: for the In compounds the energy is ≈0.4–0.8 eV higher than for the Al and Ga compounds.
- . (2001) 'Density-functional calculations of carbon doping in III-V compound semiconductors'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 63 (15) Article number 155202
- . (2000) 'Small aggregates of interstitials and models for platelets in diamond'. Institute of Physics Journal of Physics: Condensed Matter, 12 (49), pp. 10257-10261.
- . (2000) 'Structures, energetics and electronic properties of complex III–V semiconductor systems'. WILEY-VCH Verlag Physica Status Solidi B: Basic Solid State Physics, 217 (1), pp. 473-511.
- . (1999) 'Mechanism for dicarbon defect formation in AlAs and GaAs'. Physica B: Condensed Matter, 273–274, pp. 784-787.
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(1999) 'Density-functional calculations of carbon diffusion in GaAs'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 60 (22), pp. 15117-15122.Full text is available at: http://epubs.surrey.ac.uk/741010/
Abstract
Self-consistent-charge density-functional tight-binding (SCC-DFTB) calculations have been performed to survey the potential-energy surface for a single interstitial carbon atom introduced into GaAs. The results provided a possible model for the diffusion of carbon through GaAs with an activation energy of less than 1 eV. The carbon atom moves via split-interstitial and bond-centered configurations. Subsequently, the energetics of the model reaction were refined using a fully self-consistent density-functional method, AIMPRO. These calculations were found to be in good agreement with the more approximate SCC-DFTB results. Experimental studies have also found an activation energy of ∼1 eV for carbon migration in heavily doped material.
- . (1999) 'Raman scattering observations and ab initio models of dicarbon complexes in AlAs'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 60 (8), pp. 5447-5455.
- . (1998) 'Di-carbon complexes in AlAs and GaAs'. WILEY-VCH Verlag Physica Status Solidi B: Basic Solid State Physics, 210 (2), pp. 869-872.
- . (1998) 'Nitrogen-hydrogen defects in GaP'. WILEY-VCH Verlag Physica Status Solidi B: Basic Solid State Physics, 210 (2), pp. 321-326.
- . (1998) 'Quantitative density-functional study of nested fullerenes'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 57 (21), pp. 13339-13342.
- . (1998) 'Nitrogen doping in purely sp2 bonded forms of carbon'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 57 (2), pp. R661-R665.
- . (1997) 'Carbon atoms catalyse fullerene growth'. Taylor and Francis Fullerene Science and Technology, 5 (4), pp. 727-745.
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(1997) 'Di-carbon defects in annealed highly carbon doped GaAs'. The American Physical Society Physical Review Letters, 78 (1), pp. 74-77.Full text is available at: http://epubs.surrey.ac.uk/741011/
Abstract
Formation of bonded dicarbon C-C centers is deduced from the observation of Raman lines at 1742, 1708, and 1674 cm-1 in GaAs codoped with 12C and 13C after annealing at 850 °C with concomitant loss of vibrational scattering from CAs. The frequencies agree with results of ab initio theory for a C-C split interstitial (deep donor) formed by the trapping of a mobile interstitial C (displaced CAs) atom by an undisplaced CAs acceptor. Other mechanisms of carrier loss are inferred since a weaker Raman triplet is detected at 1859, 1824, and 1788 cm-1 from a different C-C complex.
- . (1996) 'Autocatalysis during fullerene growth'. American Association for the Advancement of Science Science, 272 (5258), pp. 87-89.
- . (1996) 'The theory of CVD diamond growth'. Diamond and Related Materials, 5 (3–5), pp. 236-241.
- . (1996) 'Cooperative polarization in ice Ih and the unusual strength of the hydrogen-bond'. Elsevier Chemical Physics Letters, 249 (5–6), pp. 485-490.
- . (1996) 'Energetics of fullerene isomer transformation'. Elsevier Synthetic Metals, 77 (1–3), pp. 165-168.
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(1996) 'On the graphitization of diamond surfaces: The importance of twins'. Diamond and Related Materials, 5 (1), pp. 102-107.Full text is available at: http://epubs.surrey.ac.uk/745034/
Abstract
Ab initio total energy calculations reported recently (M.I. Heggie, C.D. Latham, R. Jones and P.R. Briddon, Phys. Rev. B, 50 (1994) 5937) revealed that the tetrahedrally bonded icosahedral C molecule decomposed spontaneously into two concentric fullerenes (C and C). This C molecule belongs to a series of structures that may be viewed as the diamond analogues of fullerenes (L. Zeger and E. Kaxiras, Phys. Rev. Lett., 70 (1993) 2920). Since these molecules can be seen to be effectively a heavily twinned molecular diamond, their stability is important in the context of investigating the diamond {111} surface where a twin emerges. We present ab initio self-consistent calculations on a rather small CH molecule representing the core of a twin intersecting two diamond {111} surfaces, and compare the results with those obtained with a non-self-consistent density-functional based tight-binding method. Since the latter is also capable of handling larger and periodic models in a molecular dynamics relaxation, we use it to study the graphitization effect as a function of temperature. We find nearly the same ground state for the small molecule which is clearly due to a graphitization, and find strong surface graphitization for a model of 128 carbon atoms at elevated temperatures. At 2700 K the top layer of this periodic model delaminates completely.
- . (1995) 'Hypothetical C100 molecule and diamond-graphite interface: unstable and metastable states of carbon'. Elsevier Diamond and Related Materials, 4 (4), pp. 528-531.
- . (1994) 'The energetics of hydrogenic reactions at diamond surfaces calculated by a local spin-density functional theoretical method'. Elsevier Diamond and Related Materials, 3 (11–12), pp. 1370-1374.
- . (1994) 'Instability of tetrahedral bonding for the C100 molecule'. Physical Review B: Condensed Matter and Materials Physics, 50 (9), pp. 5937-5940.
- . (1993) 'Ab initio energetics of CVD growth reactions on the three low-index surfaces of diamond'. Elsevier Diamond and Related Materials, 2 (12), pp. 1493-1499.
- . (1992) 'Stable and metastable states of C60H: buckminsterfullerene monohydride'. Elsevier Chemical Physics Letters, 196 (3-4), pp. 311-316.
- . (1992) 'Ab initio calculations of the structure and dynamics of C60 and C60 3-'. Taylor and Francis Philosophical Magazine Letters: structure and properties of condensed matter, 65 (6), pp. 291-298.
- . (1992) 'Molecular-diffusion of oxygen and water in crystalline and amorphous silica'. Taylor and Francis Philosophical Magazine B, 65 (3), pp. 463-471.
Conference papers
- . (1997) 'LDF calculations on large fullerenes and onions'. Pennington, NJ : The Electrochemical Society Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, Montreal, Canada: Fullerenes: Chemistry, Physics, and New Directions IX 4, pp. 1141-1150.
- . (1995) 'Local density functional modeling of diamond growth and graphitization'. Pennington, NJ : Electrochemical Society Diamond Materials, Reno, Nevada: Fourth International Symposium on Diamond Materials 4, pp. 643-648.
- . (1995) 'Local density functional modelling of the Stone-Wales transformation in fullerenes'. Pennington, NJ : The Electrochemical Society Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, Reno, Nevada: Fullerenes: Chemistry, Physics, and New Directions VII 2, pp. 1218-1223.
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(1992) 'Calculations of energy barriers to CVD diamond growth'. Bellingham : SPIE Diamond Optics V, San Diego: Diamond Optics V 1759, pp. 135-144.doi: 10.1117/12.130768
- . (1992) 'Stability of the hypothetical superhard carbon metal H-6'. Institute of Metals Proceedings of the second European conference on advanced material and processes, Cambridge: 531, pp. 368-370.
Book chapters
- . (2011) 'The atomic-, nano-, and meso-scale origins of graphite’s response to energetic particles'. in Bichoutskaia E (ed.) Computational nanoscience Cambridge : The Royal Society of Chemistry 4 Article number 12 , pp. 378-414.
- . (2000) 'Effective doping in novel sp² bonded carbon allotropes'. in Riedel R (ed.) Handbook of Ceramic Hard Materials Weinheim, Germany : WILEY-VCH Verlag GmbH , pp. 271-285.