Showing papers on "Charge density published in 1976"
TL;DR: In this paper, the suppression by electric fields of longitudinal resistivity anomalies at 145 and 59 K in the compound Nb${\mathrm{Se}}_{3} was reported, and attributed the observed suppression to Zener breakdown across extremely small gaps introduced by the presence of charge density waves.
Abstract: We report the suppression by electric fields of longitudinal resistivity anomalies at 145 and 59 K in the compound Nb${\mathrm{Se}}_{3}$. Sample resistance was determined by conventional four-probe dc measurement as well as with short current pulses. We attribute the observed suppression to Zener breakdown across extremely small gaps introduced by the presence of charge density waves.
342 citations
TL;DR: In this paper, the electronic structure of a jellium-Si interface was calculated using a Jellium density corresponding to Al and self-consistent Si pseudopotentials.
Abstract: The electronic structure of a jellium-Si interface is calculated using a jellium density corresponding to Al and self-consistent Si pseudopotentials. Local densities of states and charge densities are used to study states near the interface. At the Si surface, a high density of extra states is found in the energy range of the Si fundamental gap. These states are bulklike in jellium and decay into Si with a high concentration of charge in the dangling-bond free-surface-like Si state. Truly localized interface states are also found but at lower energies. The calculated barrier height is in excellent agreement with recent experimental results.
314 citations
TL;DR: In this article, the authors proposed a valence density multipole model for pseudoatoms restricted to single exponential radial functions, which can be used for determination of static charge physical properties and aspects of chemical bonding.
Abstract: The one-electron density function for a group of atoms within the asymmetric region of a unit cell is represented by a finite multipole expansion of the charge density about each atomic center. Each atomic expansion is called a pseudoatom. If the pseudoatom charge density is effectively rigid with nuclear motion, then the model may be used for a static charge density analysis of X-ray diffraction data. A valence density multipole model for pseudoatoms is restricted to single exponential radial functions. The representation is rotationally invariant. The model may be used for determination of static charge physical properties as well as aspects of chemical bonding. These results can be a critical test of the X-ray diffraction experiment for the determination of electron density distributions. The pseudoatoms discussed are primarily intended for crystals comprised of first and second-row atoms. The valence scattering model demands extensive data sets (probably at low temperatures) or an independent determination of atomic positions and mean square amplitudes of vibration.
255 citations
TL;DR: In this paper, a two-parameter tight-binding theory of the electronic structure of 4:2-coordinated materials is proposed, and the parameters, a covalent and a polar energy, are fitted to the optical absorption spectra.
Abstract: A two-parameter tight-binding theory of the electronic structure of 4:2-coordinated materials is proposed. The parameters, a covalent and a polar energy, are fitted to the optical absorption spectra. The valence energy bands and density of states are calculated. In terms of these a consistent interpretation of all the observed photoemission and x-ray-emission spectra of ${\mathrm{SiO}}_{2}$ is obtained. The x-ray-absorption spectra are also analyzed. A bond-orbital approximation allows a simple calculation of the refractive index (or dielectric constant) of the various allotropic forms of silica and germania. Finally, the variation in total energy and charge distribution with local distortion is analyzed in order to study structural stability, elastic rigidity, and the effective charges (including dynamic contributions) which determine the piezoelectric constants and infrared absorption intensities.
244 citations
TL;DR: The surface potential produced by the adsorption of charged molecules to bilayer membranes is estimated by means of conductance measurements with "probe" molecules on planar black lipid membranes and by Means of electrophoresis measurements on multilaminar unsonicated vesicles.
Abstract: To describe the hydrophobic adsorption of charged molecules to bilayer membranes, one must recognize that the adsorption produces a change in the electrostatic potential at the surface of the membrane. The surface potential produced by the adsorption of the charged molecules can be described most simply by the Gouy equation from the theory of the diffuse double layer. This potential will tend to lower the concentration of the adsorbing ions in the aqueous phase immediately adjacent to the membrane, a phenomenon which can be described by the Boltzmann relation. The number of adsorbed ions is, in turn, a function of the aqueous concentration of these ions at the membrane solution interface and can be described, in the simplest case, by a Langmuir adsorption isotherm. If the ions are regarded as point charges, the combination of the Gouy, Boltzmann, and Langmuir relations may be considered a simplified Stern equation. To test experimentally the applicability of this equation, one should measure both the charge density and surface potential as a function of the concentration of adsorbing molecules in the bulk aqueous phases. Direct, accurate measurements of one of these parameters, the number of moles of 2, 6-toluidinylnaphthalenesulfonate ions bound to vesicles formed from phosphatidylcholine, are available in the literature (Huang, C., and Charlton, J.P. (1972), Biochemistry 11, 735). We estimated the change in the surface potential in two independent ways; by means of conductance measurements with "probe" molecules on planar black lipid membranes and by means of electrophoresis measurements on multilaminar unsonicated vesicles. The two estimates agreed with one another and all of the data could be adequately described by the Stern equation, assuming, at 25 degrees C, a dissociation constant of 2 X 10(-4) M and a maximum number of binding sites of 1/70 A2.
155 citations
TL;DR: In this article, the authors describe the physical properties of the transition metal trichalcogenide NbSe3 including electrical resistivity, magnetic susceptibility, and heat capacity.
136 citations
TL;DR: In this paper, the potential, charge density, energy spectrum, and occupied surface density of states are calculated selfconsistently for two currently popular structural models of the stable 2 \ifmmode\times\else\texttimes\fi{} 1 reconstruction of the Si (100) surface.
Abstract: The potential, charge density, energy spectrum, and occupied surface density of states are calculated selfconsistently for two currently popular structural models of the stable 2 \ifmmode\times\else\texttimes\fi{} 1 reconstruction of the Si (100) surface. The features which emerge are discussed in terms of their relationship to the same features on the unreconstructed surface. We feel that comparison with uv photoemission data favors one model, the pairing model, over the other, the vacancy model.
134 citations
TL;DR: In this paper, a powder sample of VSe2 was made by direct synthesis from the elements and X-ray characterization indicated only the 1T polytype, and the behavior was metallic over the range 1.5 to 300°K.
132 citations
TL;DR: In this article, Spanish montmorillonites from Frente archidona were used to demonstrate the determination of charge density, CEC and, in mixtures, the Montmorillonite content by the aikylammonium method.
Abstract: Spanish montmorillonites from Frente Archidona were used to demonstrate the determination of charge density, CEC and, in mixtures, the montmorillonite content by the aikylammonium method. Special attention is directed to heterogeneous montmorillonites and the determination of the charge density distribution. Some problems which arise by application of the method are discussed: relations between layer charge and cation densities, particle size corrections, microstructures and unsymmetric charge distributions in the interlayer spaces.
125 citations
TL;DR: By considering that the electrostatic charge on biological surfaces arises from the presence of multiple ionizable groups, the surface potential of and double-layer force between two plane surfaces were evaluated by numerically solving the non-linear Poisson-Boltzmann equation.
122 citations
TL;DR: In this paper, the authors describe a technique which determines charges, currents, and potentials during the charging process of corona-charged polymer foil electrets, and apply it to Teflon and polyethylene foils.
Abstract: Conventional measurement techniques for the investigation of the behavior of corona‐charged polymer foil electrets allow one to determine the equivalent surface charge and the surface potential decay after termination of the charging process. This paper describes a technique which determines charges, currents, and potentials during the charging process. The application of this technique to Teflon and polyethylene foils show the usefullness of the method. The values of transit times and of the trap‐modulated mobility for polyethylene are obtained.
TL;DR: In this paper, a mechanism was proposed for the transfer of charge from a metal to a polymer which leads to a natural explanation of the linear relationship between the charge density and the metal work-function.
Abstract: A mechanism is proposed for the transfer of charge from a metal to a polymer which leads to a natural explanation of the (previously unexplained) linear relationship between the charge density and the metal work-function. In the simplest case of a single non-sliding contact it is found that the charge density does not depend on the metal. But if the contact is repeated many times, or if the metal slides on the plastic, the final charge density varies linearly with the metal work-function. In a single (non-sliding) contact electrons are believed to tunnel from the metal into trapping levels a short distance from the interface; thermodynamic equilibrium is not achieved because the difference in electrostatic potential across this thin layer of charge is not sufficient to raise the energy of the trapping levels up to the Fermi energy of the metal. But repeated contacts (or sliding contacts) transfer charge to greater depths and make equilibrium possible. This hypothesis predicts an equilibrium charge density linearly dependent on the metal work-function.
TL;DR: Comparison of theory and experiment indicates that the axial phosphate distance b for single‐stranded polynucleotides increases with increasing pH, which is essential for an understanding of ionic effects on charged ligand–polynucleotide interactions.
Abstract: A range of linear charge densities of the ordered and disordered forms of DNA or polynucleotides can be obtained experimentally by acid or alkaline titration, or by the investigation of unusual complexes involving protonated bases or three-stranded helices. The variation of melting temperatures with Na+ concentration for various of these systems is known and in some cases is complemented by structural and thermodynamic information. We have extended the condensation–screening theory of Manning [Biopolymers, 11, 937–955 (1972)] to these systems. The stabilizing and destabilizing effects of Na+ (condensation and screening, respectively) and be independently varied, and the theory is successful in predicting the qualitative (in some cases, quanittative) behaviour that is observed. Comparison of theory and experiment indicates that the axial phosphate distance b for single-stranded polynucleotides increases with increasing pH. Values of the critical parameter ξ are obtained for the various polynucleotide structures. These values are essential for an understanding of ionic effects on charged ligand–polynucleotide interactions.
TL;DR: In this article, the authors studied the pressure dependence of the onset of charge density waves (CDW) in 2H-NbSe 2 and showed that the pressure enhancement is due to the presence of CDW in the crystal and stops when T CDW becomes smaller than T c at P = 36 kbar.
TL;DR: The distribution of a paramagnetic amphiphile between the membranes of charged phospholipid vesicles and the surrounding aqueous medium was studied by electron paramagnetic resonance spectroscopy and the distribution was shown to indicate vesicle surface potential.
Abstract: The distribution of a paramagnetic amphiphile, N,N-dimethyl-N-nonyl-N-tempoylammonium ion, between the membranes of charged phospholipid vesicles and the surrounding aqueous medium was studied by electron paramagnetic resonance spectroscopy. By systematically varying the surface charge of the vesicles and the aqueous electrolyte concentration, the distribution was shown to indicate vesicle surface potential. At each fixed phospholipid composition, the surface potential exhibited a dependence on aqueous NaCl concentration very similar to that predicted by the Gouy equation. The ability to sense and quantitate surface potentials makes this facile and sensitive technique of value in the study of cell and organelle surfaces.
TL;DR: The charges are shown to exert an electrostatic surface pressure on the lipid chain packing which leads to a shift in the phase transition of membranes and the results confirm the interpretation of experimental data.
TL;DR: In this article, a two-dimensional mathematical model is developed to predict the internal behavior of power transistors operating under steady-state conditions, which includes the internal self-heating effects in the transistors and is applicable to predict transistor behavior under high current and high-voltage operating conditions.
Abstract: A two-dimensional mathematical model is developed to predict the internal behavior of power transistors operating under steady-state conditions. This model includes the internal self-heating effects in power transistors and is applicable to predict the transistor behavior under high-current and high-voltage operating conditions. The complete set of partial differential equations governing the bipolar semiconductor device behavior under nonisothermal conditions is solved by numerical techniques without assuming internal junctions and other conventional approximations. Input parameters for this model are the dimension of the device, doping profile, mobility expressions, generation-recombination model, and the boundary conditions for external contacts. Computer results of the analysis of a typical power transistor design are presented for specified operating conditions. The current density, electrostatic potential, carrier charge density, and temperature distribution plots within the transistor structure illustrate the combined effect of the electrothermal interaction, base conductivity modulation, current crowding, base pushout, space charge layer widening, and current spreading phenomena in power transistors.
TL;DR: In this article, the authors used X-ray diffraction data to obtain the charge distribution in the superconducting alloy V3Si and found strong covalent bonding between adjacent vanadium atoms within the infinite chains.
TL;DR: In this paper, temperature dependent X-ray photoemission spectroscopy (ESCA or XPS) studies on the Ta 4f lines in 1T-TaS2, 1T -TaSe2 and 2H-TaSe 2 are reported.
Abstract: Temperature dependent X-ray photoemission spectroscopy (ESCA or XPS) studies on the Ta 4f lines in 1T-TaS2, 1T-TaSe2, 1T-Ta0.97Hf0.03S2 and 2H-TaSe2 are reported. Striking effects arising from charge density waves (CDWs) are observed at low temperature. While electron diffraction evaluates the periodicity and direction of the CDWs, these XPS observations allow the different configurations of the CDWs with respect to the crystal lattice to be deduced. The results indicate the existence of CDW fluctuations in commensurate phases, and that in some incommensurate and ‘quasi-commensurate’ phases the CDWs cannot maintain long-range coherence. In 1T-Ta0.97Hf0.03S2 the Hf impurities pin the incommensurate CDWs into domains.
TL;DR: In this article, an electrically thin dielectric insulating shell on an antenna composed of cylindrical wires is examined, and the insulation is accounted for entirely through a modification of the symmetric impedance matrix.
Abstract: An electrically thin dielectric insulating shell on an antenna composed of electrically thin circular cylindrical wires is examined. A moment method solution is obtained, and the insulating shell is modeled by equivalent volume polarization currents. These polarization currents are related in a simple manner to the surface charge density on the wire antenna. In this way the insulating shell causes no new unknowns to be introduced, and the size of the impedance matrix is the same as for the uninsulated wires. The insulation is accounted for entirely through a modification of the symmetric impedance matrix. This modification influences the current distribution, impedance, efficiency, field patterns, and scattering properties. The theory is compared with measurement for dielectric coated antennas in air.
TL;DR: In this paper, the elastic electron scattering from 4 He at medium momentum transfers is presented and the charge density and rms-radius (1.674 ± 0.012 fm) are obtained from a model independent analysis of all available electron scattering data.
TL;DR: In this article, the basic quantities characterizing the superconducting behavior of pure 2H-NbSe 2 single crystals have been determined from specific heat measurements, performed between 0.3 and 10 K in magnetic fields up to 55 KG.
TL;DR: A priori estimates of the suitability of a particular crystal for charge density analysis are discussed in terms of a simple criterion based on core electron concentration and a more detailed evaluation of the anticipated errors in the final deformation density maps as discussed by the authors.
Abstract: A priori estimates of the suitability of a particular crystal for charge density analysis are discussed in terms of a simple criterion based on core electron concentration and a more detailed evaluation of the anticipated errors in the final deformation density maps. Predictions are compared with the results obtained in a series of studies and the implications for the design of a charge density analysis are discussed. It is found that counting statistics has often been a major contributor to the standard deviation of the charge density.
TL;DR: In this paper, the dependence of the Madelung constant upon the relative phase and distance between the charge density waves, occurring on the parallel chains of the chain system, was calculated and the position of the most unstable mode for the Peierls instability was discussed.
TL;DR: Calculation of the electrostatic repulsive force using measured charge densities indicates the existence of an attractive force which may be acting over several hundred angstroms.
TL;DR: In this article, the relativistic correction to the nuclear charge distribution coming from the electromagnetic structure of the nucleon has been accomplished by assuming a linear superposition of Gaussian shapes for the proton and the neutron charge form factor.
Abstract: In the present work we have calculated the differential cross sections for the elastic electron scattering from $sup 208$Pb using the charge distributions resulting from various corrections. The point proton and neutron mass distributions have been calculated from the spherical wave functions for $sup 208$Pb obtained by Kolb et al. The relativistic correction to the nuclear charge distribution coming from the electromagnetic structure of the nucleon has been accomplished by assuming a linear superposition of Gaussian shapes for the proton and the neutron charge form factor. Results of this calculation are quite similar to an earlier calculation by Bertozzi et al., who have used a different wave function for $sup 208$Pb and have assumed exponential smearing for the proton corresponding to the dipole fit for the form factor. Also in the present work, reason for the small spin orbit contribution to the effective charge distribution is discussed in some detail. It is also shown that the use of a single Gaussian shape for the proton smearing usually underestimates the actual theoretical cross section. (AIP)
TL;DR: In this article, the authors studied the effect of static and dynamic charging on the particle motion in the presence of gravity and standard atmosphereic air, and showed that the charge distribution received tends to remove any particle from the wall.
Abstract: Dielectric and metallic paricles (both spherical and irregular in shape) in the range 29−4760 μm in diameter are electrically charged while in dynamic or stationary contact with either wall of a charged parallel‐plate capacitor. The charge distribution received tends to remove any particle from the wall. Particles larger than 127 μm are studied individually with dc electric field strengths of 2−15 kV/cm. Smaller particles are studied mainly in the form of clouds. In the presence of gravity and standard atmosphereic air, the particle motion, once initiated, is continuous between the parallel plates both dynamic and stationary charging and the resulting particle motion are experimentally and theoretically studied considering the particles as capacitors in themselves. For copper particles a single formula of the form Q= (πe) a2EK applies 2EK applies with K=1.64 whether or not charging is dynamically or statically acquired. The presence of an oxide film does not alter K. Dielectric particles followed a simila...
TL;DR: In this article, the Madelung energy of Tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) has been calculated as a function of assumed charge transfer, charge distribution, and temperature, using a modified Evjen summing criterion.
Abstract: The Madelung energy of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) has been calculated as a function of assumed charge transfer, charge distribution, and temperature, using a modified Evjen summing criterion. A large, temperature-independent, Madelung energy, ${E}_{M}\ensuremath{\approx}\ensuremath{-}2.3$ eV/molecule (\ensuremath{\cong} -53 kcal/mole), was calculated for the case of delocalized unit charges on the molecules. ${E}_{M}$ alone is shown to be insufficient to stabilize charge transfer in TTF-TCNQ, and the polarization energy is shown to be the most plausible source of additional energy gain upon charge transfer. The near-neighbor Coulomb interactions are evaluated and shown to be the major source of energy gain upon charge delocalization on the molecule.
TL;DR: In this article, the electronic properties of submonolayers on a metal substrate were investigated on the example of the Cs-W system using Lang's jellium model for the substrate adsorbate system.
TL;DR: Raman scattering measurements performed between 5 K and 300 K on 2H-TaSe2 reveal new modes which are assigned to the modes of the charge density wave, observed in light scattering due to the Fermi surface induced distortion as mentioned in this paper.