Showing papers on "Conductivity published in 1980"

Interaction Effects in Disordered Fermi Systems in Two Dimensions

Abstract: Interaction effects in disordered Fermi systems are considered in the metallic regime. In two dimensions, logarithmic corrections are obtained for conductivity, density of states, specific heat, and Hall constant. These results are compared with a recent theory of localization as well as some experiments.

Optically induced conductivity changes in discharge‐produced hydrogenated amorphous silicon

Abstract: Long exposure to light decreases the photoconductivity and dark conductivity of some samples of hydrogenated amorphous silicon (a‐Si : H). Annealing above ∼150 °C reverses the process. The effect occurs in the bulk of the films, and is associated with changes in density or occupation of deep gap states. High concentrations of P, B, or As quench the effect. Possible models involving hydrogen bond reorientation at a localized defect or electron‐charge transfer between defects are discussed. An example is shown where these conductivity changes do not affect the efficiency of an a‐Si : H solar cell.

RF-field interactions with biological systems: Electrical properties and biophysical mechanisms

Abstract: Electrical properties of tissues, macromolecular solutions, and cell membranes are summarized at frequencies from the extra low frequency (ELF) to microwave range. Previously presented dielectric data are supplemented by new results and a more detailed discussion of the physical mechanisms for the observed temperature coefficients of the dielectric properties. The dielectric data are discussed in terms of the interaction mechanisms which give rise to observed relaxational effects. Possible mechanisms for nonthermal weak interactions between radio-frequency (RF) energy and tissues are discussed and evaluated.

The UHF and microwave dielectric properties of normal and tumour tissues: variation in dielectric properties with tissue water content

Abstract: Dielectric measurements have been made on various soft tumour and normal tissues between 0.01 and 17 GHz at body temperature. At microwave frequencies above 1-5 GHz, the tissue dielectric properties can be fitted to Debye equations with the same relaxation frequency (25 GHz) as found for pure water at 37 degrees C. The tissue dielectric properties correlate well with their water contents. The conductivity of the tissue at 0.1 GHz (which is close to that of the cytoplasm itself) increases with the volume fraction of water in the tissue, in a manner consistent with that previously observed in proteins suspended in electrolyte solution. The contribution of the tissue water to the tissue dielectric permittivity at frequencies below 1 GHz is fitted by a function of water content different to that describing the conductivity data. Empirical equations that may be used to predict the dielectric properties of other soft tissues within this wide frequency range are suggested.

Formation region and characterization of superionic conducting glasses in the systems AgIAg2OMxOy

Abstract: Glass-forming regions were determined for the systems AgIAg 2 OM x O y , where M x O y are B 2 O 3 , GeO 2 , P 2 O 5 , V 2 O 5 , As 2 O 5 , CrO 3 , SeO 3 , and MoO 3 . The regions were found even in the pseudobinary systems of the simple salt (AgI) and silver orthooxysalts (Ag m MO n ) except for M=V and Cr. The IR spectra showed that these pseudobinary glasses were composed of discrete Ag + , I − , and MO 4 m − ions only (referred to as “ionic glasses”) except glasses containing B 2 O 3 or GeO 2 , which included condensed anions of BO 3 and BO 4 groups or GeO 4 and GeO 6 groups (referred to as “condensed glasses”). The transport number of these glasses was found to be unity. The conductivity, ranging from 10 −5 to 10 −2 ω −1 cm −1 at room temperature, varied exponentially with increasing AgI content within the glass-forming region. The extrapolation to 100% AgI gave the conductivity very close to the value for hypothetical α-AgI at 25°C in every system forming the “ionic glasses” and gave lower values in the “condensed glasses”. The higher was the packing density of constituent ions, the larger was the conductivity. From these experimental results it is speculated that the Ag + ion migration takes place in the “diffusion path” composed of iodide ion polyhedra, similar to the case of α-AgI, and that the incorpolation of oxyanions breaks the path to reduce the mobility and also lowers the concentration of “mobile” Ag + ions.

Shallow junctions by high‐dose As implants in Si: experiments and modeling

Abstract: Shallow (<0.2 μm) n+ layers in Si with high conductivity (<40 Ω/⧠) have been formed by high‐dose (2×1016 cm−2) As implants. Experimental observations of As distributions and carrier concentrations are successfully simulated by a computer program which accounts for both the concentration dependent diffusion and As clustering effects. Reduction of electrical carriers in high‐dose As implanted Si during moderate temperature (∼800 ° C) heat treatments is readily explained by the kinetics of As clustering. Physical limitations on the conductivity which can be achieved by thermally annealed As implants in Si are also discussed.

Electrical and Structural Properties of Phosphorous-Doped Glow-Discharge Si:F:H and Si:H Films

Abstract: Doping of Si:F:H and Si:H with P has been performed by a glow-discharge technique using PH3/SiF4+H2, PF5/SiF4+H2, PH3/SiH4+H2 and PF5/SiH4+H2 gaseous mixtures, and high conductive films over 100 ?-1 cm-1 have been obtained. It has also been made clear from X-ray diffraction and Raman-scattering measurements that all the P-doped Si:F:H films (P/Si>5?10-4) as well as high conductive Si:H films deposited under high RF power condition are polycrystalline, while Si:H films prepared under low power remain amorphous and their conductivity is less than 10-2 ?-1 cm-1. It is likely that film conductivity amounting to 100 ?-1 cm-1 should be ascribed to its polycrystalline structure.

Sulfide glasses: Glass forming region, structure and ionic conduction of glasses in Na2SXS2 (XSi; Ge), Na2SP2S5 and Li2SGeS2 systems

Abstract: Na 2 S forms with GeS 2 , SiS 2 and P 2 S 5 stable glasses with a large range of composition as well as a Li 2 SGeS 2 system. A vibrational assignment in terms of terminal (GeS) and bridge (GeSGe) stretching has been made (Na 2 SGeS 2 system). The ionic transport number obtained by e.m.f. measurements (glasses 0.5 Na 2 S0.5 XS 2 (XGe, Si)) was found to be equal to 1. The electrical conductivity of these glasses has been measured over a range of temperature (−20°C, 150°C) and composition by the complex impedance diagram method. The glass 0.5 Li 2 S0.5 GeS 2 exhibits good conductivity 4 × 10 −5 ω −1 cm −1 (20°C) higher than the best conductive glasses currently known. Replacement of the oxygen atom by a sulphur atom (comparison with oxide glasses at the same composition) is found to noticeably improve the ionic conductivity. This may be due to a great polarisability of the sulphur. For the glasses with the same molar ratio in sodium sulfide, the ionic conductivity increases when the electronegativity of the network forming sulfide decreases.

Mean free path and density of conductance electrons in platinum determined by the size effect in extremely thin films

Abstract: A new method was developed to determine the mean free path. ${l}_{\ensuremath{\infty}}$. and the conductivity, ${\ensuremath{\sigma}}_{\ensuremath{\infty}}$, of charge carriers in metals by investigating the thickness dependence of the conductivity of thin films. The method includes also surface effects as given by the specularity parameter $p$ and the surface roughness amplitude $h$. Experimental data taken during film growth could be fitted to theoretical size-effect relations only if nonzero specularity and heterogeneous film cross section caused by the surface roughness is introduced. The method allows determination of the Fermi-surface area and the electron density of the isotropic (amorphous) films. Both are smaller than expected from published bulk material data.

Thermal conductivity of ice

Abstract: The thermal conductivity of ice, the low-pressure $\mathrm{I}h$ phase of ${\mathrm{H}}_{2}$O, is reviewed and good agreement is found with the theoretical calculations of its absolute value and temperature dependence. Measurements under pressure show an anomalous decrease in conductivity with decreasing molar volume. This is explained by the negative Gr\"uneisen parameter for the transverse acoustic modes which dominate the heat transport. The conductivity behaves predominantly like that of a wurtzite lattice of rigid mass points with an atomic mass of 18. Some traces of the interaction of the lattice phonons with the higher-lying librational modes can be seen. The volume dependence of the conductivity of the higher-pressure phases of ice and of N${\mathrm{H}}_{4}$F is related to that of $\mathrm{I}h$ ice.

Electrical conductivity of fluorite and pyrochlore LnxZr1–xO2–x/2 (Ln = Gd, Nd) Solid Solutions

Abstract: The ionic conductivity of ceramic GdxZr1-xO2-x/2 and NdxZr1-xO2-x/2 solid solutions is measured as a function of composition. Both solid solutions are of the defect fluorite type and the fluorite-related ordered pyrochlore phase is present around the stoichiometric compositions Gd2Zr2O7 and Nd2Zr2O7. As a function of composition the conductivity goes through a maximum for stoichiometric Gd2Zr2O7 whereas the conductivity is minimal for Nd2Zr2O7. It appears that at the stoichiometric pyrochlore composition both, activation enthalpy H and pre-exponential factor 0 are minimal and that the absolute magnitude of the pre-exponential factor accounts for the difference in the net conductivity effect of the systems studied. The results obtained from both, single crystalline and ceramic samples can be correlated with the defect structure and ordering in the anion sublattice and with deviations of Vegard's law in the fluorite subcell dimensions. No discontinuity of Q0 or δH is observed at the fluorite-pyrochlore phase boundary. This suggests the existence of a hybrid phase around the fluorite-pyrochlore phase boundary in this type of system.

The Interpretation of Ionic Conductivity in Liquids

Abstract: 1. Introduction and Definitions.- 1.1. Introduction.- 1.2. Electrical Conductivity.- 1.3. Diffusion and Viscosity.- 1.3.1. The Diffusion Coefficient.- 1.3.2. Viscosity.- 1.4. The Stokes-Einstein and Nernst-Einstein Relations.- 1.4.1. The Stokes-Einstein Relation.- 1.4.2. The Nernst-Einstein Relation.- 1.4.3. The Walden Product.- 2. Ionic Conductivity in Dilute Electrolyte Solutions.- 2.1. Concentration Dependence of Conductivity of Dilute Electrolyte Solutions-Introduction.- 2.1.1. Derivation of the Conductance Equations.- 2.1.2. The Relaxation Effect.- 2.1.3. The Electrophoretic Effect.- 2.1.4. Conductivity Equations for Nonassociated Electrolytes.- 2.1.5. Conductivity Equations for Associated Electrolytes.- 2.1.6. Test of the Conductivity Equation.- 2.2. The Concentration Dependence of Conductivity at High Pressure and Moderate Temperatures.- 2.3. The Concentration Dependence of Conductivity at High Pressure and Temperature.- 2.4. The Effect of Pressure on Electrical Conductivity at Ambient Temperatures.- 2.4.1. Hydrogen-Bonded Solvents.- 2.4.2. Neutral Solvents.- 2.5. The Effect of Pressure on the Conductivity of Electrolyte Solutions at High Temperatures and Pressures.- 2.6. Excess H+ and OH- Mobility in Aqueous Solutions.- 2.7. The Limiting Ionic Conductivity of Ions in Solution.- 2.7.1. The Molecular Hydrodynamic Approach.- 2.7.2. The Transition State Theory.- 3. Ionic Conductivity in Low-Temperature Molten Salts and Concentrated Solutions.- 3.1. The Transition from Dilute Solutions to Molten Salts.- 3.2. Composition Dependence of Conductance in Concentrated Solutions and Low-Temperature Molten Salts.- 3.2.1. The Dilute Solution Approach.- 3.2.2. The Molten Salt Approach.- 3.3. Temperature and Pressure Dependence of Conductance in Concentrated Solutions and Low-Temperature Molten Salts.- 3.4. Electrical Relaxation in Glass-Forming Molten Salts.- 4. Electrical Conductivity in Ionic Liquids at High Temperatures.- 4.1. The Temperature and Pressure Dependence of Electrical Conductivity in Ionic Liquids.- 4.2. Theories for Electrical Conductivity in Ionic Melts.- 4.2.1. Transition State Theory.- 4.2.2. The Hole Model of Liquids.- 4.2.3. The Theory of Significant Liquid Structures.- 4.2.4. The Kirkwood-Rice-Allnatt Kinetic Theory of Electrical Conductance.- 4.2.5. The "Free Ion" Theory of Conductance of Barton and Speedy.- 4.2.6. Other Theories.- 5. Ionic Conductivity in Molecular Liquids and Partially Ionized Molten Salts.- 5.1. Introduction.- 5.2. The Temperature and Pressure Dependence of Conductivity.- 5.3. Conclusions.- 6. Electrical Conductivity in Liquids of Geological and Industrial Interest.- 6.1. Geological Liquids.- 6.1.1. Seawater.- 6.1.2. Geothermal Waters.- 6.1.3. Silicate Melts and Magmas.- 6.2. Industrial Electrolytes.- 6.2.1. Aqueous Industrial Electrolytes.- 6.2.2. Nonaqueous Electrolyte Solutions.- 6.2.3. Molten Salt Electrolytes.- References.

Electron donor–acceptor interactions and surface semiconductivity in molecular crystals as a function of ambient gas

Abstract: Quantitative studies of the magnitude, rate and reversibility of changes in surface semiconductivity of single crystals of phthalocyanines, perylene, tetracyanoquinodimethane (TCNQ) and molecular complexes as a function of ambient gas are reported. NO2+ N2O4 increases the surface conductivity of phthalocyanines, by factors of up to 108. At low pressures, the magnitude of the increase follows the Freundlich adsorption isotherm, while the rate obeys the Elovich equation. The saturation conductivity at high pressures is similar for all the phthalocyanines and corresponds to complete surface coverage, each adsorbed molecule producing one ionised state. Reversibility on heating in vacuo depends on the metal : (metal free, Ni, Cu, Zn) > (Co, Mn) > Pb. In all cases, treatment with low pressures of NH3 gives rapid reversal of the effects. BF3 gives smaller, irreversible enhancements. The surface conductivity of perylene is enhanced by a factor up to 108 in BF3 and the effect is reversed on treatment with NH3. NO2+ N2O4 produces smaller effects (104), easily reversible. Perylene—TCNQ shows small conductivity increases (102) with both NO2+ N2O4 and NH3, while TCNQ shows similar effects only with NH3. Semiconduction activation energies in the presence of gases enhancing conductivity are reduced to values comparable with those obtained from temperature dependence of photoconduction (0.1–0.2 eV). Conductivity changes are interpreted in terms of production of ionised states following weak chemisorption involving donor–acceptor interactions. The magnitude and reversibility of the changes depends on the nature of the orbitals involved in these interactions, and provides scope for selective gas detection.

Low‐temperature crystallization of doped a‐Si:H alloys

Abstract: Crystallization of phosphorus‐doped a‐Si:H has been initiated at a substrate temperature below 200 °C, under the deposition conditions of a low flow rate of silane and in the presence of an external magnetic field. Along with the crystallization, the doping efficiency of the resulting Si:H films has been remarkably improved. Room‐temperature conductivity as high as 27 Ω−1 cm−1 has been achieved at a doping ratio of NPH3/NSiH4=5.6×10−3 for a specimen deposited at 30 C. Optical emission spectroscopy during the plasma deposition has revealed that a weak emission intensity of the SiH band with respect to hydrogen lines and the absence of emission from the doubly excited states of hydrogen molecules are necessary conditions for the crystallization of doped Si:H films.

Semiconducting properties of amorphous V2O5 layers deposited from gels

Abstract: Colloidal solutions of amorphous V2O5 are used for preparing semiconducting layers. Reasons for the high measured conductivity (σ≃0.8–1.0 Ω−1 cm−1) are discussed. The temperature dependence of σ is analyzed in terms of a temperature‐dependent activation‐energy model based upon the assumption of a random distribution of the distances between hopping sites.

The Practical Salinity Scale 1978: Fitting the data

Abstract: Three equations have been fitted to new data relating the electrical conductivity of seawater to the Practical Salinity Scale 1978. These equations have been designed for the reduction of in-situ measurements of temperature, pressure, and conductivity from anywhere in the world oceans. The standard deviation of the fit is roughly equivalent to \pm0.0015\permil in salinity depending on the pressure at which the data is taken and, as such is commensurate with the best accuracy attainable with modern instruments.

Structure and ionic transport of superionic conducting glasses in the system AgIAg2OMoO3

Abstract: Infrared spectra, molar volumes, ionic conductivities, and transport numbers of silver ions and electrons were measured for glasses in the system AgIAg 2 OMoO 3 , which contain no ordinary “glass formers”. IR spectra revealed that the coordination number of oxygen to molybdenum is 4 and the glasses with the mole ratio Ag 2 O/MoO 3 = 1, or those in the pseudobinary system AgIAg 2 MoO 4 , contain no condensed macro-anions but only discrete ions of Ag + , I − , and MoO 2− 4 . The strong partial covalency is also proved to be present between Ag + and MoO 2− 4 by IR spectra. The molar volume of pseudobinary glasses showed that their glass structure is primarily determined by the ideal mixing and very dense packing of the constituent anions (I − and MoO 2− 4 ). The conductivity of the glasses, ranging from 10 −2 to 10 −4 ω −1 cm −1 at room temperature, increased exponentially with increasing AgI content, while the total concentration of silver ions remains practically constant; a part of the silver ions are considered to participate in the conduction. The electronic transport number was determined by the Wagner d.c. polarization technique; a glass of total conductivity 1.1×10 −2 ω −1 cm −1 showed the electron conductivity of 8.7×10 −9 ω −1 cm −1 . A structure model is proposed for explaining ionic transport in the glasses.