The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
J.p.f. Sellschop - One of the best experts on this subject based on the ideXlab platform.
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The effect of light on positron annihilation in Natural Diamond
Applied Surface Science, 1997Co-Authors: R.w.n. Nilen, U. Lauff, Simon Henry Connell, Hermann Stoll, A. Siegle, H. Schneider, P. Castellaz, J. Kraft, Krish Bharuth-ram, J.p.f. SellschopAbstract:The age-momentum correlation (AMOC) technique of positron annihilation spectroscopy has been used to study a gamma-irradiated Natural Diamond sample. A light-induced reversible change in both the intensity and the lifetime of the trapped positron component in Diamond was observed. No signal attributable to positronium was detected in the measurements, supporting the view that positronium formation does not occur in Diamond. The measurements demonstrate the sensitivity of positron annihilation to optically active centers in Diamond.
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channeling radiation of electrons in Natural Diamond crystals and their coherence and occupation lengths
Physical Review B, 1996Co-Authors: H Genz, J.p.f. Sellschop, L Groening, P Hoffmannstascheck, A Richter, M Hofer, J Hormes, U Nething, C Toepffer, M WeberAbstract:Measurements have been performed at the superconducting Darmstadt electron linear accelerator (S-DALINAC) to investigate systematically channeling radiation produced by bombarding Natural Diamond crystals with thicknesses of 13, 20, 30, and 55 \ensuremath{\mu}m with electrons at 5.2 and 9.0 MeV. Planar channeling from the (110) and (111) planes was studied for a variety of transitions with respect to their energy, intensity, and linewidth. Axial channeling from the $〈110〉$ axis could be detected as well. It was found that the intensity increases as a function of the crystal thickness, and values up to 7.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ photons/esr could be obtained, which is the highest intensity at low electron energies achieved so far. The intensity increases with electron energy as ${\ensuremath{\gamma}}^{\frac{5}{2}}$. The $\frac{1}{e}$ occupation length deduced from the photon yield as a function of the crystal thickness was found to be ${l}_{\mathrm{occ}}\ensuremath{\approx}29 \mathrm{and} 85$ \ensuremath{\mu}m for planar and for axial channeling, respectively. These values are by far the largest ever observed. Comparison with a quantum mechanical theory of channeling radiation exhibits fairly good agreement for the intensity and linewidth provided that contributions caused by electronic scattering and Bloch wave broadening, which actually are largest for Diamond, are properly taken into account. It turns out that multiple scattering dominates in the planar case and single scattering for the axial channeling. The coherence length could be deduced to be of the order of 0.7 \ensuremath{\mu}m, which is about a factor of 2 larger than observed before in silicon.
S Khasawinah - One of the best experts on this subject based on the ideXlab platform.
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forced diffusion of impurities in Natural Diamond and polycrystalline Diamond films
Journal of Applied Physics, 1995Co-Authors: G Popovici, Mark A. Prelas, T Sung, S Khasawinah, R G WilsonAbstract:A method is proposed for the determination of the state of an impurity (donor, acceptor, or deep level) in semiconductor lattice. To demonstrate the method boron was diffused into type Ia Natural Diamond under a dc electric field. The concentration and diffusion profiles of boron were affected by the applied field. Boron diffuses as a negative ion since it is an acceptor shallow enough to be partially ionized at the temperature of diffusion. The drift velocity of boron ions at the temperature of diffusion was also estimated. The diffusion of lithium and oxygen from a Li2CO3 source in chemical vapor deposited Diamond films was performed under bias at 1000 °C in an argon atmosphere. After diffusion, the concentrations of Li, O, and H in the Diamond films were found to be around (3–4)×1019 cm−3. No dependence of these concentrations on the applied bias was observed. It was found that the diffusion of Li goes primarily through grain boundaries, which may explain why it does not depend on the applied voltage. ...
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diffusion of boron lithium oxygen hydrogen and nitrogen in type iia Natural Diamond
Journal of Applied Physics, 1995Co-Authors: G Popovici, Mark A. Prelas, T Sung, R G Wilson, S KhasawinahAbstract:Diffusion of boron, lithium, nitrogen, oxygen, and hydrogen into type IIa Natural Diamond was studied. The diffusion was performed in two steps. First, diffusion of Li and oxygen was performed in nitrogen atmosphere at 860 °C for one hour. The sample was then placed in a hot filament chemical vapor deposition (CVD) growth reactor and diffusion was performed for two hours in hydrogen atmosphere from a boron solid source placed on the surface of the sample. The condition of diffusion were those used routinely during CVD growth. After diffusion, the concentration of Li was of the order of 2×1016 cm−3 at the depth of 0.5 micrometer, and oxygen, nitrogen, and boron were found to be in the range (1–4)×1020 cm−3 at the same depth. The diffusion of hydrogen under conditions specific to CVD growth has also been studied for the first time and was found to be quite strong.
Peter Oelhafen - One of the best experts on this subject based on the ideXlab platform.
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Valence band spectroscopy of reconstructed (100) and (111) Natural Diamond
Diamond and Related Materials, 1995Co-Authors: G. Francz, Peter OelhafenAbstract:Abstract The electronic structures of Natural Diamond type IIb single crystals of orientations (100) and (111) were investigated by core level and valence band photoelectron spectroscopy. The samples were measured at room temperature, and then heated in situ up to 955 °C. On annealing, a distinct decrease in oxygen contamination at the surface was observed; simultaneously additional electronic states near the valence band maxima appeared. These additional states can be interpreted as surface states of the reconstructed Diamond (in both the (100) and (111) orientations). The data obtained are compared with other carbon phases, such as graphite and Diamond films prepared by chemical vapour deposition.
Shin-ichi Shikata - One of the best experts on this subject based on the ideXlab platform.
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Defects in synthesized and Natural Diamond probed by positron annihilation
Journal of Physics Condensed Matter, 1999Co-Authors: Akira Uedono, N. Morishita, Shigeo Tanigawa, Hiroaki Itoh, S. Fujii, Shin-ichi ShikataAbstract:Defects in synthesized and Natural Diamond were studied using the positron annihilation technique.\nFor a synthesized type IIa specimen, the lifetime of positrons annihilating from the free state was\ndetermined to be 98.7 ps. For a synthesized type Ib specimen, the effects of the annihilation of\npositrons trapped by open spaces introduced by substitutional nitrogen atoms on the positron\nparameters were discussed. After electron irradiation, the species of the major vacancy-type defects\nwas identified to be a neutral and/or negatively charged monovacancy. For Natural type IIa and IIb\nspecimens, the annihilation mode of positrons trapped by vacancy clusters was observed. For the\nNatural type IIb specimen, the temperature dependence of the trapping rate of the vacancy clusters\nwas explained assuming that these clusters act as compensators for acceptor impurities (boron).
P L Diggle - One of the best experts on this subject based on the ideXlab platform.
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point defects and interstitial climb of 90 partial dislocations in brown type iia Natural Diamond
Acta Materialia, 2020Co-Authors: F H J Laidlaw, D. Fisher, Richard Beanland, P L DiggleAbstract:Abstract Multiple electron microscopy techniques have been used to study a brown type IIa Natural Diamond. Electron backscatter diffraction shows evidence of plastic deformation in the form of slip bands, while cathodoluminescence reveals a network of low-angle grain boundaries, also observed in transmission electron microscopy together with long straight dislocations and dislocation dipoles. Aberration-corrected scanning transmission electron microscopy shows interstitial absorption on the 90° partial of both dissociated dislocations and Z-type faulted vacancy dipoles, forming structures similar to that observed in other fcc materials. The observations indicate an interstitial concentration of 1017 to 1019 cm−3 and calculations of point defect concentrations produced by plastic deformation show that this can be produced by strains of the order of 1%. Brown coloration in Diamond has been previously attributed to vacancies and vacancy clusters with concentrations around 1018 cm−3, which suggests that roughly equal numbers of interstitials and vacancies are generated in Diamond via plastic deformation. Atomic resolution images of Z-type faulted dipoles allowed a stacking fault energy of 472 ± 38 mJ m−2 to be determined.