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Showing papers in "Journal of Physics C: Solid State Physics in 1984"


Journal ArticleDOI
TL;DR: In this paper, the spin-orbit interaction Hamiltonian HSO = alpha ( sigma *k) was used to change the usual patterns of B-1-periodic oscillations; some oscillations are strongly suppressed due to the diminishing of the gaps between adjacent levels and new oscillations appear due to intersections of levels.
Abstract: Oscillatory effects in a strong magnetic field B and magnetic susceptibility are investigated, as applied to 2D systems, in which the twofold spin degeneracy is lifted by the spin-orbit-interaction Hamiltonian HSO= alpha ( sigma *k). nu . The term HSO is shown to change greatly the usual patterns of B-1-periodic oscillations; some oscillations are strongly suppressed due to the diminishing of the gaps between adjacent levels, and new oscillations appear due to intersections of levels.

2,390 citations


Journal ArticleDOI
TL;DR: In this article, closed nonlinear equations are derived for a self-consistent treatment of density propagation, self-diffusion and current relaxation in a classical monatomic fluid, and a simplified model is analyzed in detail.
Abstract: Closed nonlinear equations are derived for a self-consistent treatment of density propagation, self-diffusion and current relaxation in a classical monatomic fluid. The solution for a hard-sphere model system brings out a phase transition to a glass at the packing fraction 0.516. Approaching the transition from the glass side the particle mean-square displacement increases to a finite value. A simplified model is analysed in detail. Approaching the transition from the liquid side the diffusivity is predicted to decrease to zero with a power law with exponent 1.76 which the authors find to agree well with some experimental data. The low-frequency density spectrum is found to consist of two contributions; one is an elastic line of the frozen structure on the glass side, which then decays to a narrow diffusion broadened quasielastic peak on the fluid side; the other part is described by a dynamical scaling law and it yields in particular a spectrum diverging at the glass point with certain exponents.

817 citations


Journal ArticleDOI
TL;DR: A simplified version of the exact curved-wave theory of EXAFS is described in this article, where the simplifications arise from the angle-averaging process which is necessary when analysing data from polycrystalline or amorphous samples.
Abstract: A simplified version of the exact curved-wave theory of EXAFS is described. The simplifications arise from the angle-averaging process which is necessary when analysing data from polycrystalline or amorphous samples. Such an angle-averaging process is here performed analytically, resulting in a much simpler theoretical expression for the EXAFS function, but one which still treats the outgoing spherical wave exactly. Test runs show that such a theory is about a factor of forty faster in computation time than the original form of the curved-wave theory. Such rapid computation allows the authors routinely to use the curved-wave theory in structural analyses, rather than the plane-wave approximation which is limited to high photoelectron energies.

561 citations


Journal ArticleDOI
TL;DR: The detailed structure of porous Si (PS) layers formed in p-type wafers with resistivities 0.01-25 Omega cm has been investigated using reflectance, transmission, ellipsometry and photoluminescence techniques as discussed by the authors.
Abstract: The detailed structure of porous Si (PS) layers formed in p-type wafers with resistivities 0.01-25 Omega cm has been investigated using reflectance, transmission, ellipsometry and photoluminescence techniques. Marked differences were observed in the optical properties of PS formed in degenerate or non-degenerate Si and these results are correlated with the results of other techniques. The optical techniques together with effective medium modelling have been shown to be useful non-destructive methods for either assessment of PS density or detection of unsuspected phases. The degenerate PS layers consistently showed good retention of the single-crystal characteristics of the starting wafer, only c-Si and voids being detected. For these samples, good agreement was obtained between optical and gravimetric densities. However, the non-degenerate PS had much greater variability, with greater loss of crystallinity and significant incorporation of oxygen, due to partial oxidation having occurred on or immediately after anodisation. Oxide fractions have been determined both optically and gravimetrically, with up to 50% oxide being detected in some samples. Non-degenerate PS samples with high oxygen concentrations appeared to be in the form of a chemical mixture, SiOx, from interpretation of the optical constants. Photoluminescence measurements together with the other techniques indicated a complex mixture of phases in the latter samples-voids, alpha -Si:O (and/or alpha -Si:H), an unknown amorphous phase and silicon oxide. This complex structure probably contributes to the observed instability of thick non-degenerate PS layers when heated in UHV as part of the cleaning procedure prior to epitaxial growth, all degenerate samples being able to withstand heat treatment.

272 citations


Journal ArticleDOI
TL;DR: In this paper, a transfer matrix method is used to study the variation with length scale L of the distribution PL(Jeff) of effective couplings in Ising spin glasses at zero temperature.
Abstract: A transfer matrix method is used to study the variation with length scale L of the distribution PL(Jeff) of effective couplings in Ising spin glasses at zero temperature. For a gaussian initial distribution the authors find in two dimensions J(L) identical to ( mod Jeff mod ) varies as L-1 nu / for 2

223 citations


Journal ArticleDOI
TL;DR: In this paper, a phenomenological renormalisation-group model is proposed for Ising-like spin glasses, where the model parameters are a typical interaction strength and a typical energy barrier for block spins.
Abstract: A phenomenological renormalisation-group model is proposed for Ising-like spin glasses. The model parameters are a typical interaction strength and a typical energy barrier for block spins. The energy barrier is found to be a function of length scale with the largest barrier at the correlation length. The system equilibration time varies at tau T varies as exp(V/T) or faster depending on dimensionality. For short times t< tau T the system is hysteretic and the noise spectrum is approximately 1/f. A two-level model with distributed level separations and barrier heights is derived.

190 citations


Journal ArticleDOI
H Asahina1, A Morita1
TL;DR: In this article, the frequency-dependent dielectric function of black phosphorus was calculated by using the band structure and wavefunctions obtained by the self-consistent pseudopotential calculation.
Abstract: First, the authors calculate the frequency-dependent dielectric function of black phosphorus by using the band structure and wavefunctions obtained by the self-consistent pseudopotential calculation. Then by using these results, they discuss the optical properties of black phosphorus such as KPS, UPS, plasmon frequency and reflectance in visible, VUV and soft X-ray regions. Experimental results for all these optical properties are explained consistently using the theoretical results.

181 citations


Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the infrared reflectivity spectra in KNbO3 is reported for the cubic, tetragonal and orthorhombic phases in a temperature range extending from 300 to 1200K.
Abstract: The temperature dependence of the infrared reflectivity spectra in KNbO3 is reported for the cubic, tetragonal and orthorhombic phases in a temperature range extending from 300 to 1200K. Spectra have been fitted with a model based on the factorised form of the dielectric function. The temperature dependence of the mode frequencies, the dampings and the oscillator strengths through the successive phase transitions is reported. The experimental data exhibit an unstable mode which decreases continuously in frequency upon cooling across the diverse transitions. The ionic effective charges, the spontaneous polarisation and the static dielectric constant are calculated from these data. All results are discussed in terms of a displacive/order-disorder crossover, which appears especially when the transition from the cubic to the tetragonal phase is approached. A particular phase transition mechanism is proposed, which leads to an understanding of the discrepancy between the experimental and the calculated values of the dielectric constant, the large damping of the soft mode, the incomplete softening of the unstable phonon and the special sequence of phase transitions.

181 citations


Journal ArticleDOI
TL;DR: In this article, the effect of random coordination percolation properties of the 3D Voronoi network and the body-centred cubic with second-nearest-neighbour bonding (BCC2) are calculated by Monte Carlo simulation and compared.
Abstract: To assess the effect of random coordination percolation properties of the three-dimensional (3D) Voronoi network and the body-centred cubic with second-nearest-neighbour bonding (BCC2) are calculated by Monte Carlo simulation and compared. The accessible fraction, backbone fraction and effective conductivity of the Voronoi network and regular networks are qualitatively the same. Moreover, when enough bonds are removed from the Voronoi network to make the average coordination match that of the BCC2 network the difference between the conductivities of the two networks is less than 0.002. Finite-size scaling theory is used to estimate percolation thresholds and critical exponents. The bond percolation thresholds of the Voronoi and BCC2 networks are 0.082 and 0.0991, whereas the site percolation thresholds are 0.145 and 0.169. The correlation length, backbone and conductivity exponents of the Voronoi network are v=0.88, beta '=1.06 and t=2.02, in good agreement with the values accepted for regular 3D networks. The effective conductivity of the network derived from a crude finite-element approximation to the Voronoi tessellation is only slightly different from that of the same network with the conductances redistributed at random.

148 citations


Journal ArticleDOI
TL;DR: In this article, the influence of pressure on the OD stretching modes and the lattice vibrational frequencies is discussed, and it is estimated that the pressure compresses the O-O bond lengths on average about 5 pm GPa-1 in the Ih, II, III, IX, V and VI types of ice.
Abstract: The Raman spectra of various forms of ice Ih, II, III, IX, V and VI of H2O, D2O, H218O and small percentages of HOD in both D2O and H2O have been recorded in their true regions of stability. The high-pressure low-temperature Raman cell used for this work is described. The influence of pressure on the OH and OD stretching modes and the lattice vibrational frequencies is discussed. It is estimated that the pressure compresses the O-O bond lengths on average about 5 pm GPa-1 in the Ih, II, III and V types of ice. An attempt is made to correlate the available spectroscopic and crystallographic data for the various forms of ice in order to make assignments of the Raman- and infrared-active lattice vibrational spectra.

126 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that a complete set of localised Wannier functions which form a representation of the magnetic translation group in two dimensions can be constructed if and only if the sub-band carries no Hall current.
Abstract: It is shown that a complete set of localised Wannier functions which form a representation of the magnetic translation group in two dimensions can be constructed if and only if the sub-band carries no Hall current.

Book ChapterDOI
TL;DR: In this paper, the authors present a review on the Thomas-Fermi statistical theory at nonzero temperature and a brief survey of the original Hohenberg-Kohn theorem at elevated temperatures.
Abstract: Publisher Summary The chapter presents a study on the foundations, achievements, and limitations of density functional methods. Because these methods have their origins in the description of the charge clouds in atoms as a degenerate inhomogeneous electron gas by Thomas and Fermi, the chapter presents a review on the Thomas–Fermi statistical theory. The chapter also discusses Dirac's extension to include exchange. Because the foundations of density functional theory at elevated temperatures are discussed, the chapter includes a brief survey of Thomas–Fermi theory at nonzero temperature. After several of the basic concepts of modern density functional theory, the Hohenberg–Kohn theorem and its principal extensions are discussed. This theorem formally completes the original Thomas–Fermi theory by showing that the ground state of a many-electron system is indeed a unique functional of its electron density. The chapter presents a formal discussion on extensions of the original Hohenberg–Kohn theorem to include (1) spin and relativistic effects and (2) elevated temperatures. In the treatment of calculational procedures, the chapter presents the relation of Slater's transition-state method to density functional theory of excited states. After a justification of single-particle equations, the calculational procedures deals exclusively with local density approximations; therefore a short account of approximate ways in which local density approximations can be transcended is presented. Applications of density functional theory to solids are discussed, the former treating some problems, which fall within the scope of linear response theory.

Book ChapterDOI
Alexander Wokaun1
TL;DR: In this article, a study on surface-enhanced electromagnetic processes is presented, and the theoretical expression for the enhancement is analyzed and represented as a product of a purely geometrical "lightning-rod" factor and an electromagnetic factor representing the local field enhancement because of particle plasmon resonances.
Abstract: Publisher Summary The chapter presents a study on surface- enhanced electromagnetic processes. The chapter discusses evidence that an electromagnetic mechanism involving localized surface plasmons provides a very important contribution to the enhancement. Experiments on surface second harmonic generation, as well as on enhanced one- and two-photon absorption by adsorbed dyes, are described. They emphasize the generality of the phenomenon and provide further strong support for the electromagnetic model. Characteristic observations in surface-enhanced Raman scattering (SERS) experiments are reviewed. It was established that preparation of a microscopically rough surface was a necessary prerequisite for observing SERS. The metals silver and gold proved to be most efficient in providing the Raman enhancement. Along with the experimental investigations, a variety of theoretical models were proposed to explain the effect, which are included in this chapter. The electromagnetic model, which forms the basis for the subsequent discussion, is described, with the main emphasis on the physical origin of the effect. Strong experimental evidence in support of the electromagnetic mechanism is presented. The theoretical expression for the enhancement is analyzed and represented as a product of a purely geometrical “lightning-rod’’ factor and an electromagnetic factor representing the local field enhancement because of particle plasmon resonances.

Journal ArticleDOI
TL;DR: In this paper, the coherent diffuse quasielastic neutron scattering from single crystals of three fluorite compounds PbF2, SrCl2 and CaF2 was investigated, and the diffuse intensity indicates that dynamic correlations exist between the defective anions in the fast-ion phase.
Abstract: Some materials with the fluorite structures show a pronounced specific heat anomaly well below their melting temperature. This anomaly is a consequence of lattice disorder and is associated with the onset of fast-ion conduction. This paper presents the results of a series of experiments in which the coherent diffuse quasielastic neutron scattering from single crystals of three such fluorite compounds PbF2, SrCl2 and CaF2, was investigated. The diffuse scattering intensity, and its energy width, increases with temperature into the fast-ion phase, and when integrated over energy transfer the intensity exhibits a characteristic variation with scattering vector, falling on an anisotropic shell in reciprocal space and peaking in certain directions. The diffuse intensity indicates that dynamic correlations exist between the defective anions in the fast-ion-phase. A model of short-lived clusters comprising anion Frenkel interstitials, anion vacancies and relaxed anions has been developed which satisfactorily accounts for the distribution of intensity.

Journal ArticleDOI
TL;DR: In this paper, a theoretical investigation of the possible occurrence of surface modes in semi-infinite ferroelectric materials is made, and three different approaches are used: (1) a microscopic pseudo-spin theory based on the Ising model in a transverse field, (2) a macroscopic Landau theory in which surface effects can be introduced phenomenologically, and (3) a polariton model appropriate to the very long wavelength region.
Abstract: A theoretical investigation is made of the possible occurrence of surface modes in semi-infinite ferroelectric materials. Three different approaches are used: (1) a microscopic pseudo-spin theory based on the Ising model in a transverse field, (2) a macroscopic Landau theory in which surface effects can be introduced phenomenologically, and (3) a polariton model appropriate to the very long wavelength region. Existence conditions and dispersion relations are deduced for the localised surface modes, which are predicted by all three methods. The results are illustrated by means of numerical examples. Methods (1) and (2) are found to give rise to similar results in certain limits, and the authors are able to establish a formal relationship between the two approaches. The applicability of the theoretical models to real ferroelectrics is discussed, and some experimental techniques by which the surface modes might be detected are suggested.

Journal ArticleDOI
TL;DR: In this paper, the radial Dirac equations for an electron in a potential with a magnetic component are derived and the solutions to these equations, when expanded to lowest order in 1/c2 (c is the velocity of light), thus treat spin-orbit coupling and spin-polarisation effects on an equal footing.
Abstract: Relativistic spin-polarised scattering theory is discussed and the relevant radial Dirac equations for an electron in a potential with a magnetic component are derived. The solutions to these equations, when expanded to lowest order in 1/c2 (c is the velocity of light), thus treat spin-orbit coupling and spin-polarisation effects on an equal footing. By matching to free-particle solutions at the boundary of the potential, expressions for the scattering amplitudes are given. The authors perform explicit calculations for the example of an electron scattering from a single Pt atom in an external magnetic field. The interpretation of the results gives a clear and useful picture of the interplay between spin-orbit coupling and spin polarisation. A scattering analogue to a generalised 'Zeeman effect' is described.

Journal ArticleDOI
TL;DR: In this article, the diffusion coefficient of oxygen in silicon has been studied in the temperature range 650 to 1050 degrees C using the techniques of chemical etching, IR absorption applied to the 9 mu m band (4.2K), and small-angle neutron scattering (SANS).
Abstract: The precipitation of oxygen in silicon has been studied in the temperature range 650 to 1050 degrees C using the techniques of chemical etching, IR absorption applied to the 9 mu m band (4.2K), and small-angle neutron scattering (SANS). The IR data and etch pit counts, relating to the number densities of precipitate particles, have been fitted to Ham's theoretical model for the diffusion limited growth of randomly distributed particles. Full allowance is made for the increase in size of the precipitates with increasing time and good agreement is found over the complete period starting from zero time. Values of the diffusion coefficient of oxygen so determined are in excellent agreement with other data obtained by different methods, including SANS measurements at 750 degrees C described in the present work. The combined data give D=0.11 exp(-2.51 eV/kT) cm2s-1. The SANS data also indicate that the precipitates are not spherical in shape after a short initial period, and they show that the initial concentration of particles nucleated decreases with annealing time. The solid solubility cs(T) is determined at each temperature and compared with previous measurements. The authors conclude that the best combination of results leads to cs(T)=2.6*1022 exp(-1.4 eV/kT) down to 850 degrees C. At lower temperatures cs decreases more slowly with decreasing temperature, indicating a possible change in the structure or the form of the precipitated SiO2 phase.

Journal ArticleDOI
TL;DR: In this paper, the effect of X-irradiation on the absorption spectra of pure and impurity (Cu, Mn, Ni, Eu)-doped LiNbO3 has been systematically investigated.
Abstract: The effect of X-irradiation on the absorption spectra of pure and impurity (Cu, Mn, Ni, Eu)-doped LiNbO3 has been systematically investigated. Three main bands with peaks at 1.6, 2.5 and 3.2 eV have been observed in pure crystals or Mn-, Ni- and Eu-doped crystals after low-temperature (10K) irradiation. For the Cu-doped samples, a competition is apparent between the production of these bands and the conversion of Cu2+ (1.2 eV band) into Cu+ (3.1 eV band). From this information and the thermal annealing behaviour of optical bands together with a comparison with the EPR data of Schirmer and Von der Linde (1978), the following assignment of optical bands has been made: the 1.6 eV band to polaron (Nb4+) states; the 2.5 and 3.2 eV bands to holes trapped at Li vacancies or other lattice defects. The reduction treatments induce a broad absorption made up of two main bands at 2.6 and 3.2 eV. Optical bleaching experiments at 10K, turn these bands into the same 1.6 eV (polaron) band of irradiated crystals. For Mn- and Cu-doped samples those treatments induce, as a first stage, the reduction of Mn3+ and Cu2+ which is then followed by the formation of the same bands of pure crystals. These results have led us to associate both bands with F centres (2.6 eV) and F+ centres (3.2 eV).

Journal ArticleDOI
TL;DR: To assess the effects of random coordination, the percolation and conduction properties of the Voronoi network and of its closest kin among regular networks, the triangular network, are calculated and compared by means of Monte Carlo simulations.
Abstract: The network generated from a Voronoi tessellation of space is a natural prototype for topologically random networks. To assess the effects of random coordination, the percolation and conduction properties of the Voronoi network and of its closest kin among regular networks, the triangular network, are calculated and compared by means of Monte Carlo simulations.

Journal ArticleDOI
TL;DR: In this article, a simple approximation from first principles is proposed for the determination of the local distortion around an impurity atom in a host lattice, which is calculated for various impurities in GaAs and GaP and is found to be in accordance with the experimentally known systems.
Abstract: It is shown that modified overlap interaction, covalent interaction and polar energy introduced by Harrison (1980, 1981) allows the nearest-neighbour spacing in semiconductors to be determined accurately. It is also shown that the force constants of the diamond and zincblende structure semiconductors result from the same covalent and overlap interactions, and are obtained in terms of Herman-Skillman atomic potentials in accordance with experiment. A simple approximation from first principles is proposed for the determination of the local distortion around an impurity atom in a host lattice. The local distortion is calculated for various impurities in GaAs and GaP and is found to be in accordance with the experimentally known systems.

Journal ArticleDOI
TL;DR: In this paper, a low-dose proton and helium-implanted silicon was studied by deep-level transient spectroscopy and the defect was tentatively identified as a vacancy-hydrogen complex or a hydrogen atom in a single interstitial site.
Abstract: Low-dose proton- and helium-implanted silicon was studied by deep-level transient spectroscopy. By comparing the spectra as well as the defect level concentration profiles, five electron traps and one hole trap (after proton implantation at room temperature) and one dominant electron trap (after proton implantation at 80K) were identified to be hydrogen-related. Two of the hydrogen-related defect levels produced at room temperature represent different charge states of the same defect with a structure probably containing two hydrogen atoms. The electron trap produced by proton implantation at 80K is a donor level located at about Ec-0.2 eV. The defect is tentatively identified as a vacancy-hydrogen complex or a hydrogen atom in a single interstitial site and anneals out before reaching room temperature.

Journal ArticleDOI
TL;DR: In this article, the compression curves of CeSb and LaSb were measured up to 25 GPa by X-ray diffraction in a diamond anvil cell and the relative volume reductions were equal in the pressure range investigated.
Abstract: The compression curves of CeSb and LaSb were measured up to 25 GPa by X-ray diffraction in a diamond anvil cell. For the two compounds the relative volume reductions are equal in the pressure range investigated. Below 11 GPa, CeSb and LaSb maintain the NaCl-type structure. Then there occurs a crystallographic phase transition. In both compounds, the high-pressure phases show similar diffraction patterns which can be indexed in a tetragonal structure (Ce or La:0, 0, 0; Sb: 1/2, 1/2, 1/2; space group P4/mmm). This structure is highly anisotropic with c/a approximately=0.82. The bulk moduli of CeSb and LaSb are equal and so a small negative electronic contribution in CeSb may be inferred. Comparison of CeAs with CeSb (or LaSb) shows an additional contribution to the bulk moduli in antimony compounds which could come from an increase of the covalent bonding.

Journal ArticleDOI
TL;DR: In this paper, a qualitative physical mechanism is proposed for the power-law response of luminescent decay in solids and a simple model involving either one or two sets of such trapping centres can explain most of the observed features of transient response under short excitation.
Abstract: A review of experimental data on the time dependence of luminescent decay in solids shows very few examples of the classically expected exponential dependence and none of the bimolecular law. The prevailing long-term time dependence obeys power laws in time with exponents between -1 and -2. It is suggested that the widely applicable power-law dependence is the result of many-body interactions dominating the dynamics of charge release from trapping centres. A simple model involving either one or two sets of such trapping centres can explain most of the observed features of transient response under short excitation. A qualitative physical mechanism is proposed for the power-law response.

Journal ArticleDOI
TL;DR: In this paper, an exact expression for the moments of the resistance of a 1D chain of atoms (RN) is obtained for positive integer N and analytically continue this result to all N and use this to calculate (ln R) and the density of states.
Abstract: An exact expression for the moments of the resistance of a 1D chain of atoms (RN) is obtained for positive integer N. The authors show how to analytically continue this result to all N and use this to calculate (ln R) and the density of states. They compare results for the localisation length with direct simulation work using a program generated by MacKinnon and derive some analytic results from their formulae.

Journal ArticleDOI
William Hayes1, M J Kane1, O Salminen1, R L Wood1, S P Doherty1 
TL;DR: In this article, a triplet state with a very large fine-structure splitting was found to contribute to the 2.8 eV luminescence band in quartz using magnetic resonance (ODMR).
Abstract: The well known 2.8 eV luminescence band in quartz has been studied using optically detected magnetic resonance (ODMR). A triplet state with a very large fine-structure splitting is found to contribute to the emission. The principle axes of the triplet are identified. The possibility that the luminescence originates in the decay of a self-trapped exciton involving a transient oxygen Frenkel pair is discussed.

Journal ArticleDOI
TL;DR: In this paper, a unified theory of the electrical current produced by electron hopping between localised states is presented, and the electron mobility in a multiquantum well structure is investigated.
Abstract: Presents a unifying theory of the electrical current produced by electron hopping between localised states. In this framework, the authors investigate the electron mobility in a multiquantum well structure. Finally, they compare the theoretical results with those experimentally obtained on a series of GaAs-GaxAl1-xAs superlattices.

Journal ArticleDOI
TL;DR: In this paper, a closed set of equations for the spin glass mean-field theory in terms of a local magnetisation on long timescales and a distribution of gradually frozen local fields were derived.
Abstract: From a variational principle the authors derive a closed set of equations for the spin glass mean-field theory in terms of a local magnetisation on long timescales and a distribution of gradually frozen local fields. These equations are useful for deriving general relations and they find that the frozen field obeys a Langevin equation. Numerical solutions of the equations are obtained at T=0. The local field distribution shows a linear behaviour for small fields.

Journal ArticleDOI
TL;DR: In this article, the defect-induced one-phonon infrared absorption in natural diamond can be divided into a number of overlapping components, and the computational method of extracting the spectral shapes of these contributions is described.
Abstract: The defect-induced one-phonon infrared absorption in natural diamond can be divided into a number of overlapping components. The computational method of extracting the spectral shapes of these contributions is described. The A and B components are associated with nitrogen defects. The A defect is a pair of substitutional nitrogen atoms and the B defect is currently considered to be an agglomerate containing four nitrogen atoms. The C spectrum is associated with the singly substituted nitrogen atom and is characteristic of synthetic diamonds. The D spectrum has been observed only in diamonds which also contain B defects, and for this reason is also considered to be a defect which contains nitrogen. Some studies have been carried out on the thermal stability of the A, B and D defects during heat treatment in the range 2100-2800 degrees C under a pressure of 9.5 GPa. A possible nitrogen aggregation sequence is suggested to describe the observations.

Journal ArticleDOI
TL;DR: In this article, high-resolution luminescence studies from individual dislocations and related defects in ZnSe and InP performed in a transmission electron microscope were performed in the presence of complex dislocation tangles.
Abstract: Results are presented of high-resolution luminescence studies from individual dislocations and related defects in ZnSe and InP performed in a transmission electron microscope. In the case of ZnSe unusual luminescence bands (Y at 2.60 eV and S at 2.52 eV) originally observed in photoluminescence studies are attributed to dislocations. In some instances, complete quenching of the excitonic transitions was observed to correlate with the presence of Y emission from complex dislocation tangles. In the case of individual screw dislocations this quenching of the exciton luminescence was found to be variable; for example reduction of the exciton signal was not always observed. For InP, donor-exciton-related transitions were quenched at individual screw dislocations. Donor-acceptor pair/free-to-bound and deep level (band C) transitions were unaffected. For the case of InP, unlike ZnSe, no dislocation-related luminescence was observed within the system detection limit (0.7-4.0 eV).

Journal ArticleDOI
TL;DR: In this paper, the authors have calculated self-consistent total energy surface for hydrogen present interstitially as H+, H0 and H2 in crystalline silicon and diamond.
Abstract: The authors have calculated self-consistent total-energy surface for hydrogen present interstitially as H+, H0 and H2 in crystalline silicon and diamond. The dissimilarities of the two materials are more evident than their similarities, for they show molecular hydrogen to be the stable form in silicon, and atomic hydrogen to be the stable form in diamond in the absence of impurities. The energy surfaces for H0 and H+ are complex, with minima too small to trap the atoms when zero-point energy is taken into account. They discuss their results in relation to other theories and to the normal and anomalous muonium ( mu +e-) experiments.