Showing papers in "Journal of Physics C: Solid State Physics in 1985"
TL;DR: In this article, the authors present a systematic approach to the derivation of empirical potential parameters for binary oxides; they also consider their modification for use in mixed oxide systems, and discuss successful applications of the potentials to the calculation of perfect lattice properties.
Abstract: The authors present a systematic approach to the derivation of empirical potential parameters for binary oxides; they also consider their modification for use in mixed oxide systems. Shell-model potentials are used but, unlike the case of the alkali halides within which polarisability and short-range interaction parameters can be transferred, modifications must be introduced when transferring potential parameters between different oxides. The anion polarisability varies with structure and with the nature of the host cation, and changes in cation coordination are reflected in the short-range repulsive cation-anion interaction. Parameters are derived for a range of oxides, and trends in these parameters are discussed. They discuss successful applications of the potentials to the calculation of perfect lattice properties. Equal success is enjoyed when defect and surface properties are considered; in particular the models correctly predict the activation energies for dopant diffusion in NiO, and to a large extent model the surface rumpling of MgO.
1,035 citations
TL;DR: In this article, the supercell method was used for the energy and the dipole tensor of ionic point defects in periodically repeating geometry, where the point defects carry a net charge, so that the Coulomb energy is divergent.
Abstract: The energy, the elastic dipole tensor and the entropy of point defects in ionic crystals are usually calculated by the Mott-Littleton approach, which treats a single defect in an infinite crystal. The authors suggest that there may be advantages, particularly for the dipole tensor and the entropy, in performing the calculations in periodically repeating geometry. They examine how this 'supercell' method can be used for the energy and the dipole tensor, paying attention to the problem that for charged defects the repeating unit carries a net charge, so that the Coulomb energy is divergent. They test the supercell method on a number of both charged and uncharged defects, and show that the results for the energy and dipole tensor are in close agreement with those obtained by the conventional approach.
433 citations
TL;DR: In this article, a review of the available experimental and theoretical understanding on the structure and electronic properties of grain boundaries in semiconducting materials is presented, where high-resolution electron microscope images of interfaces are interpreted within the framework of the structural unit model of grain boundary, and the electronic properties are discussed with relation to the popular symmetric Schottky barrier model for charge trapping and potential barrier formation.
Abstract: This review presents the available experimental and theoretical understanding on the structure and electronic properties of grain boundaries in semiconducting materials. High-resolution electron microscope images of interfaces are interpreted within the framework of the structural unit model of grain boundaries, and the electronic properties of the grain boundaries discussed with relation to the popular symmetric Schottky barrier model for charge trapping and potential barrier formation. It is shown that these models give some limited understanding of the physical processes that occur at grain boundaries in elemental semiconductors, but that in compound semiconducting materials the effects of non-stoichiometry at the boundary regions must also be considered. Segregation of impurity and dopant species to the boundaries can have significant influence on their electrical properties, and the question of what structural or chemical features are responsible for the observed properties is posed. Diffusion at semiconductor grain boundaries is also discussed, and finally the electrical properties of zinc oxide varistor material are presented in the light of the models of carrier interactions with grain boundaries.
431 citations
TL;DR: In this paper, the authors present a quantitative model for the magnetic equation of state of nearly or weakly ferromagnetic metals at low temperatures which includes corrections to conventional Stoner theory arising from enhanced fluctuations in the local magnetisation.
Abstract: The authors present a quantitative model for the magnetic equation of state of nearly or weakly ferromagnetic metals at low temperatures which includes corrections to conventional Stoner theory arising from enhanced fluctuations in the local magnetisation. The model takes account of both longitudinal and transverse fluctuations in terms of four physically transparent parameters which may be determined independently from the equation of state in the T=0 limit and from inelastic neutron scattering, or calculated directly from a semi-empirical band structure model near the Fermi level fitted for example to experimental Fermi surface areas. For parameters of the same order of magnitude as those recently determined in the weakly spin-polarised metal Ni3Al, the model yields approximately a quadratic temperature dependence of the spontaneous magnetisation over a wide range well below the Curie temperature (Tc), a nearly linear inverse susceptibility well above Tc, and nearly linear magnetic isotherms (Arrott plots) at high magnetic fields. These results are qualitatively consistent with the behaviour observed in many magnetic metals near the ferromagnetic instability at low temperatures. For Ni3Al the model yields good quantitative agreement with experiment for the magnitude of the Curie temperature Tc, for the ratio peff/p0 of the high- to low-temperature effective magnetic moments, and for the coefficient of the quadratic (T2) variation of the magnetisation with temperature well below Tc, without the use of any free adjustable parameters. Finally the authors show that the model also provides a good quantitative description of the paramagnetic susceptibility and transition temperature of the more complex magnetic system MnSi, the only other unsaturated magnetic metal for which all of the microscopic parameters are well known.
337 citations
TL;DR: In this paper, a discussion of the experimental results concerning defect creation (versus the energy of irradiation, temperature, doping concentration, nature of the material, crystalline orientation) and annealing was conducted and it was concluded that the defects produced in n-and p-type GaAs by electron irradiation consist in a distribution of vacancy-interstitial pairs in the As sublattice.
Abstract: From a discussion of the experimental results concerning defect creation (versus the energy of irradiation, temperature, doping concentration, nature of the material, crystalline orientation) and annealing (versus doping concentration, carrier injection), it is concluded that the defects produced in n- and p-type GaAs by electron irradiation consist in a distribution of vacancy-interstitial pairs in the As sublattice. The vacancy-interstitial pairs in the Ga sublattice recombine immediately after their creation. The mobility of the As interstitial, which can be induced by hole injection in the case of irradiation with high fluxes, explains the formation of antisites AsGa by exchange with donor impurities on Ga sites and of few complexes following irradiations at high fluences. The existence of several types of pairs explains the occurrence of the numerous electron and hole traps observed. The electrical and optical characteristics of the electron traps are consistent with the existence of a strong-electron-lattice coupling which can be evaluated semiquantitatively.
331 citations
TL;DR: In this paper, the concept of normalised Stevens operators O'kq is extended to k=3 and 5 where numerical coefficients relating both sets of operators are given. And the transformation matrices for the normalised operators can be read in a straightforward way from the expressions for the conventional operators.
Abstract: Extensions of the conventional Stevens operators Okq to negative values of q and their transformation properties are reviewed and reconsidered. Transformation matrices with k=1 to 6 and -k
285 citations
TL;DR: In this article, a generalised, dilute, infinite-ranged Ising spin-glass model is introduced and studied as a function of the concentration p and temperature T. The phase diagram is investigated and paramagnetic (P), ferromagnetic (F), spin glass (SG) and mixed (M) phases are identified.
Abstract: A generalised, dilute, infinite-ranged Ising spin-glass model is introduced and studied as a function of the concentration p and temperature T. The phase diagram is investigated and paramagnetic (P), ferromagnetic (F), spin glass (SG) and mixed (M) phases, meeting at a multicritical point (p*,T*), are identified. The P/F and P/SG phase boundaries are derived, and the F/M and M/SG boundaries are calculated close to (p*,T*). The condition for having a re-entrant spin-glass transition is derived. In non-zero magnetic field a p-dependent A-T instability line is obtained. The authors apply their results to the insulator EuxSr1-xS, it is predicted to exhibit re-entrant behaviour.
267 citations
TL;DR: A survey of the recent progress on the properties of transition-metal impurities in the most common III-V compounds GaAs, InP and GaP is presented in this paper, where a summary of experimental techniques available for identifying deep centers and/or locating deep levels in the band gap is given.
Abstract: A survey of the recent progress on the properties of transition-metal impurities in the most common III-V compounds GaAs, InP and GaP is presented. A summary of experimental techniques available for identifying deep centers and/or locating deep levels in the band gap is given. The author concentrates on 3d isolated impurities, giving the known energy levels of Fe-group substitutional impurities in the three compounds. Complexes involving these impurities are also considered. In addition, 4d, 5d and rare earth impurities are briefly discussed.
191 citations
TL;DR: In this paper, the authors demonstrate that it is possible to observe diffuse scattering that originates in the abrupt change of density at a crystal surface and that such a discontinuity gives rise, in general, to rods of scattering in reciprocal space which are most intense close to the Bragg peaks tau and are well defined for sufficiently smooth surfaces.
Abstract: X-ray measurements performed on a variety of materials demonstrate that it is possible to observe diffuse scattering that originates in the abrupt change of density at a crystal surface. Such a discontinuity gives rise, in general, to rods of scattering in reciprocal space which are most intense close to the Bragg peaks tau and are well defined for sufficiently smooth surfaces. For wave-vector transfer Q= tau +q the q-dependence of the intensity of scattering gives information on the topographic structure of the crystal surface. Experimental results on crystals of GaAs and KTaO3, with surfaces prepared in various ways, were obtained using conventional X-ray techniques with a rotating anode source and can be described by a continuum model of the surface. There are discrepancies between the predictions of the models and the experimental results and these suggest that further experiments are needed to achieve a more complete understanding.
149 citations
TL;DR: In this paper, the E(k/sub-) band structure of 1T-TaS2 and 2H-TaSe2 at temperatures where commensurate CDWS are well developed is investigated.
Abstract: Angle-resolved photoemission spectroscopy (ARPES) measurements of the E(k/sub ///) band structure are reported for 1T-TaS2 and 2H-TaSe2 at temperatures where commensurate CDWS are well developed. Empirical tight-binding calculations of the band structure in the presence of the experimentally known CDW superlattice are also reported. In the case of the square root 13* square root 13 CDW in 1T-TaS2, experiment and theory both reveal a gross distortion of the band structure, in which the Ta-derived d band collapses into three sub-band manifolds separated by gaps. The thirteenth electron is predicted to reside in a conduction band only 50 meV wide, where it is susceptible to a Mott-Anderson transition. In the case of 2H-TaSe2, additional peaks are seen in the ARPES data in the presence of the CDW, but the effects are too weak to distinguish between a band-structure distortion and weak Umklapp associated with the 3*3 superlattice. Calculated densities of states, decomposed according to the inequivalent atomic sites, are presented.
136 citations
TL;DR: The scaling laws derived by Grinstein (1976) for the random-field Ising model (RFIM) are rederived on the assumption that the transition is second order and that the critical behaviour is controlled by a zero-temperature fixed point as discussed by the authors.
Abstract: The scaling laws derived by Grinstein (1976) for the random-field Ising model (RFIM) are rederived on the assumption that the transition is second order and that the critical behaviour is controlled by a zero-temperature fixed point The scaling laws involve three independent exponents nu , eta and gamma , the last appearing in a modified hyperscaling relation, 2- alpha =(d-y) nu It is argued that such hyperscaling modifications are a general feature of phase transitions controlled by zero-temperature fixed points Explicit evaluation of the RFIM exponents in d=2+ epsilon dimensions, yields, to order epsilon , 1/ nu = epsilon , eta =1- epsilon /2 and y=1+ epsilon /2 The exponent nu is different from that of the pure model in (d-y) dimensions implying that no exact 'dimensional reduction' is possible near two dimensions
TL;DR: In this paper, the authors argue that many phenomena associated with metal/nonmetal interfaces and similar situations with a large dielectric constant mismatch can be understood in terms of the image interactions due to charges in the nonmetal.
Abstract: The authors argue that many phenomena associated with metal/nonmetal interfaces and similar situations with a large dielectric constant mismatch can be understood in terms of the image interactions due to charges in the nonmetal. The effects are additional to the traditional interactions, and are especially significant when no reactions between the phases occur. The image-charge concept allows one to rationalise much apparently unrelated information concerning: (a) the systematics of wetting and nonwetting of oxides by liquid metals; (b) the systematics of strong metal-support interaction in catalysis; (c) the spatial variation of stoichiometry in oxides grown on metals; (d) the dependence on thickness of the observed changes in the wetting by water of oxide grown on silicon; (e) some features of radiation-enhanced adhesion; and (f) a number of correlations of behaviour with nonmetal properties in which the precise choice of metal is not critical.
TL;DR: In this article, the authors studied the electrical properties of a GaAs/AlxGa1-xAs modulation doped heterostructure where there are parallel competing conduction paths in the 2D gas at the interface and in the undepleted AlxGa 1 -xAs.
Abstract: Presents the results of a study of the electrical properties of a GaAs/AlxGa1-xAs modulation doped heterostructure where there are parallel competing conduction paths in the 2D gas at the GaAs/AlxGa1-xAs interface and in the undepleted AlxGa1-xAs. The authors show that the presence of these two paths introduces a magnetic field dependence into the measured resistivity and Hall coefficient of the heterostructure. This magnetic field dependence is analysed in order to determine the carrier densities and mobilities in the separate layers. This analysis is then used to investigate the effects of illumination on the heterojunction and to explain partially the temperature dependence of the properties of the heterojunction.
TL;DR: In this article, the effect of the 4f level on the magnetic properties of the valence bands has been investigated in terms of the mixing mechanism between 4f and the 4F states and it is shown that the calculated effective 4F level becomes shallower than the level observed by XPS measurements.
Abstract: Unusual magnetic properties in CeSb and CeBi are interpreted in terms of the mixing mechanism between the 4f state and the valence bands. To explain the magnetic properties quantitatively the effective 4f level should be considered, which is a virtual concept introduced to interpret the higher-order effects of the p-f mixing. The calculated effective 4f level becomes shallower than the level observed by the XPS measurements.
TL;DR: In this paper, a high-pressure X-ray scattering study has revealed that the compressible molecular crystal SnI4 gradually transforms from the crystalline to the amorphous state, this process being accompanied by a remarkable decrease in electrical resistivity induced by the pressure.
Abstract: A high-pressure X-ray scattering study has revealed that the compressible molecular crystal SnI4 gradually transforms from the crystalline to the amorphous state, this process being accompanied by a remarkable decrease in electrical resistivity induced by the pressure. Taken together with the Raman scattering study described in the following paper, this indicates that the amorphous structure attained above about 20 GPa is formed by dimerised SnI4 tetrahedral molecules packing randomly and densely.
TL;DR: Using magnetic translation symmetry, the Hall conductance of an isolated magnetic band in units of e2/h was shown to satisfy the Diophantine equation p sigma +qm=1, where p and q are relatively prime integers giving the number of flux quanta per unit cell area, phi =p/q, and m is an integer.
Abstract: Using magnetic translation symmetry, the Hall conductance of an isolated magnetic band in units of e2/h is shown to satisfy the Diophantine equation p sigma +qm=1, where p and q are relatively prime integers giving the number of flux quanta per unit cell area, phi =p/q, and m is an integer. This equation holds for a general periodic Schrodinger Hamiltonian with an arbitrary magnetic field and is a direct consequence of the q-fold degeneracy of magnetic bands. Extension to general real phi gives the equation phi sigma H- rho =integer with sigma H the Hall conductance and rho the number of electrons per unit cell, from which sigma H is uniquely determined once rho , phi and the gap structure are given.
TL;DR: In this article, it is shown that the presence of higher frequency relaxations for components of the same dipole degrades this property by extending the memory into the timescale of relaxation, thus giving a non-debye behaviour which can be expected to occur in all practical dielectric materials.
Abstract: Debye relaxation behaviour is unique in the sense that all memory of excitation is instantaneously lost. It is shown that the presence of higher-frequency relaxations for components of the same dipole degrades this property by extending the memory into the timescale of relaxation, thus giving a nonDebye behaviour which can be expected to occur in all practical dielectric materials. In this case it is not possible, as has been suggested, that knowledge of the polarisation or of the depolarisation current at a single time is sufficient, alone, to define the relaxation behaviour of the system for all subsequent times. Furthermore the Guo and Guo experiment (1983) is shown to be incapable of discriminating between this picture of sequential relaxation and the alternative possibility of an ensemble of independent relaxations.
TL;DR: In this paper, non-linear integral equations describing the thermodynamic properties of the multichannel Kondo problem are derived on the basis of the exact solution of the Kondo Problem.
Abstract: Non-linear integral equations describing the thermodynamic properties of the multichannel Kondo problem are derived on the basis of the exact solution. Certain analytical results are obtained.
TL;DR: In this article, the authors present a systematic formulation of the conduction band Hamiltonian in the presence of a magnetic field by an invariant expansion and by expressing the coefficients of this expansion in terms of the band parameters of an extended Kane model.
Abstract: The authors present a systematic formulation of the conduction band Hamiltonian in the presence of a magnetic field by an invariant expansion and by expressing the coefficients of this expansion in terms of the band parameters of an extended Kane model. This Hamiltonian can be used to describe non-parabolicity effects such as dipole-allowed spin-flip and higher-harmonic cyclotron resonance transitions and their angular dependence, and the magnetic-field dependence of the cyclotron mass and g-factor.
TL;DR: In this paper, the authors examined and obtained analytic expressions for the basic nonlinear excitations in a monoatomic chain with cubic and quartic interatomic potentials and verified their stability under collision.
Abstract: The authors have examined and obtained analytic expressions for the basic nonlinear excitations in a monoatomic chain with cubic and quartic interatomic potentials and verified their stability under collision. They determined bounds on the potential parameters for which kink, breather, envelope and dark solitons exist. The kink and the envelope of a soliton are determined in the long-wavelength approximation, while the oscillations of the carrier in the envelope soliton are treated exactly. The introduction of second-neighbour interactions (SNI) changes drastically the character of the solutions. Kinks are supersonic if the dispersive term is positive and subsonic if it is negative. In a cubic potential the envelope solitons are asymmetric (there is a net displacement). There is a switch from a kink to a symmetric envelope as the potential parameters are changed; these parameters also determine the regions for which plane waves are unstable. The above excitations can be created by using arbitrary initial conditions which, however, have a net displacement for kinks and the correct Fourier components for an envelope soliton. The asymmetric envelope solitons explain earlier computer simulations using as initial conditions optical gaussian pulses.
TL;DR: In this article, it is suggested that small aggregates of these intrinsic defects should alternately be considered as the complexes giving the donor properties, and it has been established that these treatments also lead to the generation of self-interstitials.
Abstract: There is a long-standing view that small aggregates of oxygen impurities in silicon produced by heat treatments at 450 degrees C are the defects that act as thermal donors. Recently it has been established that these treatments also lead to the generation of self-interstitials. It is now suggested that small aggregates of these intrinsic defects should alternately be considered as the complexes giving the donor properties.
TL;DR: In this article, the specific energy loss of a relativistic electron beam and the probability of excitation of surface and bulk modes in a semi-infinite medium are calculated.
Abstract: The interaction of a relativistic electron beam, travelling parallel to the surface of a semi-infinite medium, is analysed. The specific energy loss of the beam and the probability of excitation of surface and bulk modes in the medium are calculated. Beams both external and internal with the medium are considered, and the predictions are compared with well known non-retarded limits. A detailed analysis of the expressions derived is provided for electron beams interacting with specific dielectric materials. The effects of retardation are seen to be large, particularly for beam energy losses in regions where the real part of the dielectric constant is large. The retarded excitation probability is typically about 10-30% larger than the non-retarded result, for electron energies greater than about 100 keV. The image force is calculated for an external beam, and the radiative de-excitation of the medium is also analysed.
TL;DR: In this article, the structure of a concentrated aqueous solution of LiCl has been investigated by neutron diffraction and it was concluded that structural features characteristic of both the molten salt and the dilute solution coexist in concentrated solution and that each Li+ ion is surrounded, on average, by three water molecules and three chloride ions.
Abstract: The structure of a concentrated aqueous solution of LiCl has been investigated by neutron diffraction. The methods of first- and second-order differences were used. It is concluded that structural features characteristic of both the molten salt and the dilute solution coexist in concentrated solution and that each Li+ ion is surrounded, on average, by three water molecules and three chloride ions.
TL;DR: In this article, the physical basis and experimental techniques of inelastic electron tunnelling spectroscopy are described, and a discussion of the essential features of quantitative theory shows how to set about detailed analysis of spectra.
Abstract: The authors describe the physical basis and experimental techniques of inelastic electron tunnelling spectroscopy. A discussion of the essential features of quantitative theory shows how to set about detailed analysis of spectra. The power and versatility of the technique are illustrated by accounts of a variety of applications, and suggestions are made about the directions in which the field will develop.
TL;DR: In this paper, the dielectric permittivity and loss of 1-cyanoadamantane have been measured under isothermal conditions in the frequency range, 100-2*105 Hz and the temperature range, 80-350K in the glassy crystal, supercooled (metastable) and stable (disordered) crystals and partially ordered crystalline states.
Abstract: The dielectric permittivity and loss of 1-cyanoadamantane have been measured under isothermal conditions in the frequency range, 100-2*105 Hz and the temperature range, 80-350K in the glassy crystal, supercooled (metastable) and stable (disordered) crystals and partially ordered crystalline states. Two relaxation regions were observed, one above the glass-like transition temperature (170K) and the other below it. (The latter finding is contrary to the observations of Amoureux et al., for which reasons are given.) The characteristics of the two relaxations are remarkably similar to those found in other isotropic and anisotropic glasses and glassy crystals. The implications of this similarity for concepts of the glass transition and configurational states are pointed out. The static permittivity of 1-cyanoadamantane shows that it is only partially disordered even at high temperatures and that its disorder-order transformation occurs over a wide temperature range. Isothermal measurements in this range show no time dependence of the ordering process.
TL;DR: In this paper, it was shown that the current distribution within the two-dimensional Hall potential distribution is strongly inhomogeneous and has no similarity with the calculated distribution for an ideal system.
Abstract: Measurements of the Hall potential distribution in quantum Hall effect experiments lead to the conclusion that the current distribution within the two-dimensional system is strongly inhomogeneous and has no similarity with the calculated distribution for an ideal system.
TL;DR: In this article, a compilation of data that concern the point defect parameters in LiF is presented, and it is shown that the entropy scales with the enthalpy (h) for the following processes: Schottky formation, free cation migration and (re) orientation of the 'Mg2+cation vacancy' dipole.
Abstract: A compilation of data that concern the point defect parameters in LiF is presented. It is shown that the entropy (s) scales with the enthalpy (h) for the following processes: Schottky formation, free cation migration and (re) orientation of the 'Mg2+-cation vacancy' dipole. The ratio s/h is governed only by well known macroscopic properties of the bulk solid. Furthermore, the ratio of the defect volume and the defect energy is discussed.
TL;DR: In this article, a two-dimensional interacting electron gas in a strong perpendicular magnetic field with an integral number of fully occupied Landau levels was considered and an expression for the spin-dependent response function of this system has been derived in a Hartree-Fock approximation.
Abstract: The authors consider a two-dimensional interacting electron gas in a strong perpendicular magnetic field with an integral number of fully occupied Landau levels. An expression for the spin-dependent response function of this system has been derived in a Hartree-Fock approximation. Numerical results for the static polarisability have been obtained for one, two and three full Landau levels. Dispersion relations for the collective excitations of the system have been determined by locating poles in the response functions. Some conclusions are made concerning the reliability of the approximation by referring to the low-field limit.
TL;DR: In this article, the one-dimensional Hubbard model bounded by infinitely high potential walls is exactly diagonalized by Bethe-Yang ansatz techniques and the surface energy is studied for the half-filled band and in the Fermi gas limit.
Abstract: The one-dimensional Hubbard model bounded by infinitely high potential walls is exactly diagonalised by Bethe-Yang ansatz techniques. The 'surface' energy is studied for the half-filled band and in the Fermi gas limit. The analysis starts with a solution of a more general model in which the particles also interact with their mirror-image sites. In the linear band limit the states of this system become the Bethe eigenstates of the Kondo model at zero coupling.
TL;DR: From magnetic susceptibility and hysteresis loop measurements on the cubic perovskite Sr2FeNbO6, it was shown that a spin glass transition does exist in this compound which has a non-frustrated lattice, and only antiferromagnetic interactions.
Abstract: From magnetic susceptibility and hysteresis loop measurements on the cubic perovskite Sr2FeNbO6, it is shown that a spin glass transition does exist in this compound which has a non-frustrated lattice, and only antiferromagnetic interactions. This experimental results allows the authors to conclude that lattice frustration is not an essential feature for the spin glass transition in antiferromagnetic insulators. Moreover, it is argued that short-range atomic correlations, which modify the magnetic phase diagrams of the diluted compounds, make this spin glass transition possible.