Different Types Of Conductivity Research Articles

Mixed proton and electron conduction in graphene oxide films: field effect in a transistor based on graphene oxide

GO films exhibited dual proton and electron conduction. Proton conduction showed the exponential dependence on relative humidity with the activation energy E a = 0.9 ± 0.05 eV. For the electron conductivity (220–273 K) induced by thermolysis and chemical means E a = 1.15 ± 0.05 eV. With increasing humidity, the electron conduction went down, which was associated with recombination phenomena. The GO films can be regarded as a first example of the mixed electron–proton conduction when sample conductivity can be regulated by external influence (humidity). Field effect is detected and studied in the transistor on the basis of the GO in different types of conduction.

Devitrification of Bi- and Ga-containing germanium-based chalcogenide glasses

Novel BixGay(GeSe4)50-(x+y)/2(GeTe4)50-(x+y)/2 glasses are proposed as perspective materials, having potential to combine thermo-electric effect, rare earth solubility, different types of conductivity and topological insulating behavior in one medium. Thermal stability and non-isothermal crystallization kinetics of these materials are studied by differential scanning calorimetry, X-ray diffraction and Raman scattering techniques. Crystallization of at least five different phases is assumed due to the fit of experimental DSC curves. The Dietzel criterion of glass stability is determined and the activation energy for each crystallization process is calculated. The applicability of Johnson–Mehl–Avrami (JMA) equation to describe the crystallization kinetics is verified in these glasses.

Surface morphological instability of silicon (100) crystals under microwave ion physical etching

This paper presents the results of studies of the dynamics of relaxation modification of the morphological characteristics of atomically clean surfaces of silicon (100) crystals with different types of conductivity after microwave ion physical etching in an argon atmosphere. For the first time, the effect of the electronic properties on the morphological characteristics and the surface free energy of silicon crystals is experimentally shown and proven by physicochemical methods.

Dual‐Layered Quasi‐Two‐Dimensional Organic Conductors with Presumable Incoherent Electron Transport

AbstractWe have prepared a series of BEDT‐TTF or BETS‐based radical‐cation salts (D)4MBr4(C6H6–nXn) with tetrahedral anions [MIIBr4]2– (D = BETS, BEDT‐TTF; X = F, Cl, Br; n = 1, 2). The salts (D)4MBr4(C6H6–nXn) are characterized by the different structures of neighboring conducting layers, structural phase transitions, and different types of conductivity, namely, metallic and semiconducting, along and across the conducting layers, respectively. The Fermi surface of the metallic layer of (D)4MBr4(C6H6–nXn) with alternating crystallographically different conducting layers (dual‐layered salts) provides a roadmap for interpreting the transport properties of quasi‐two‐dimensional organic conductors. This review reports on the structures of these compounds, the effect of MBr4 anions and solvent on the occurrence of phase transitions, different Fermi surface topologies in connection with the different structures of neighboring conducting layers, and the possibility of the incoherent transport of charge carriers in such systems.

Mechanochemically prepared ternary hybrid cathode material for lithium batteries

Ternary host–guest nanocomposite based on vanadium oxide and two polymers with different types of conductivity (ionic and electronic) – polypyrrole (PPy) and polyethylene oxide (PEO) – is prepared by solventless mechanochemical synthesis. The nanocomposite can be reversibly cycled with a specific capacity of ∼200mAhg−1 for at least one hundred cycles of full charge–discharge as the active component of the positive electrode of lithium batteries. Electrochemical performance of ternary PPy0.1PEO0.15V2O5 is compared with two-component analog PPy0.1V2O5. The presence of macromolecules of an ion-conducting polymer in the composition of the ternary nanocomposite PPy0.1PEO0.15V2O5 promotes interfacial transfer of lithium ions and also facilitates faster transport inside the particles of the nanocomposite.

Electrical and ionic conductivity effects on magic-angle spinning nuclear magnetic resonance parameters of CuI

We investigate experimentally and theoretically the effects of two different types of conductivity, electrical and ionic, upon magic-angle spinning NMR spectra. The experimental demonstration of these effects involves (63)Cu, (65)Cu, and (127)I variable temperature MAS-NMR experiments on samples of γ-CuI, a Cu(+)-ion conductor at elevated temperatures as well as a wide bandgap semiconductor. We extend previous observations that the chemical shifts depend very strongly upon the square of the spinning-speed as well as the particular sample studied and the magnetic field strength. By using the (207)Pb resonance of lead nitrate mixed with the γ-CuI as an internal chemical shift thermometer we show that frictional heating effects of the rotor do not account for the observations. Instead, we find that spinning bulk CuI, a p-type semiconductor due to Cu(+) vacancies in nonstoichiometric samples, in a magnetic field generates induced AC electric currents from the Lorentz force that can resistively heat the sample by over 200 °C. These induced currents oscillate along the rotor spinning axis at the spinning speed. Their associated heating effects are disrupted in samples containing inert filler material, indicating the existence of macroscopic current pathways between micron-sized crystallites. Accurate measurements of the temperature-dependence of the (63)Cu and (127)I chemical shifts in such diluted samples reveal that they are of similar magnitude (ca. 0.27 ppm/K) but opposite sign (being negative for (63)Cu), and appear to depend slightly upon the particular sample. This relationship is identical to the corresponding slopes of the chemical shifts versus square of the spinning speed, again consistent with sample heating as the source of the observed large shift changes. Higher drive-gas pressures are required to spin samples that have higher effective electrical conductivities, indicating the presence of a braking effect arising from the induced currents produced by rotating a conductor in a homogeneous magnetic field. We present a theoretical analysis and finite-element simulations that account for the magnitude and rapid time-scale of the resistive heating effects and the quadratic spinning speed dependence of the chemical shift observed experimentally. Known thermophysical properties are used as inputs to the model, the sole adjustable parameter being a scaling of the bulk thermal conductivity of CuI in order to account for the effective thermal conductivity of the rotating powdered sample. In addition to the dramatic consequences of electrical conductivity in the sample, ionic conductivity also influences the spectra. All three nuclei exhibit quadrupolar satellite transitions extending over several hundred kilohertz that reflect defects perturbing the cubic symmetry of the zincblende lattice. Broadening of these satellite transitions with increasing temperature arises from the onset of Cu(+) ion jumps to sites with different electric field gradients, a process that interferes with the formation of rotational echoes. This broadening has been quantitatively analyzed for the (63)Cu and (65)Cu nuclei using a simple model in the literature to yield an activation barrier of 0.64 eV (61.7 kJ/mole) for the Cu(+) ion jumping motion responsible for the ionic conductivity that agrees with earlier results based on (63)Cu NMR relaxation times of static samples.

10.1007/s11451-008-2024-x

The dependences of the work function of ytterbium nanofilms on their thickness are studied. The films are evaporated at room temperature on the Si(111)7 × 7 surface of silicon samples doped to different levels and having different types of conduction (n and p). It is shown that these dependences exhibit a pronounced nonmonotonic behavior, which does not depend on the type of silicon used. It is established that the amplitude of the nonmonotonic variations in the work function is governed by the surface microroughness of the deposited layers, so that larger amplitudes correspond to smoother films. The variations in the work function of the films due to the deposition of electrically negative Si atoms on their surface are investigated. It is revealed that the sign of the variation depends on the film thickness. This result strange at first glance is associated with the fact that the electron density distribution at the metal-film-vacuum interface depends nonmonotonically on the amount of deposited ytterbium. This nonmonotonic behavior is a manifestation of electron density standing waves (Friedel oscillations) generated in the films by the ytterbium-silicon interface.

Mechanism of charge transfer in n-CdS/p-CdTe heterostructures with a thick layer of the CdTe1 − x S x solid solution

The current-voltage and capacitance-voltage characteristics of the n-CdS/p-CdTe heterosystem are investigated. An analysis of the results obtained has demonstrated that a high-resistance i layer (the CdTe1 − xSx solid solution), which is inhomogeneous not only in the electrical conductivity but also in the composition, is formed at the n-CdS/p-CdTe heterointerface. The thicknesses of the solid-solution layers are estimated from the capacitance-voltage characteristics, and regions with different types of conduction are found to exist in the intermediate layer. It is shown that the ambipolar diffusion and drift in the high-resistance CdTe1 − xSx solid-solution layers are directed toward each other, thus resulting in the appearance of a sublinear portion in the current-voltage characteristics described by the dependence V = exp(Iaw). The observation of a sublinear portion in the current-voltage characteristics measured in both the forward and reverse electric current directions over a wide temperature range 77–323 K suggests that the diffusion-drift regime can occur in different parts of the i layer, depending on the electric current density and the ambient temperature. The changes observed in the electric current and capacitance, as well as in the current-voltage and capacitance-voltage characteristics, after ultrasonic irradiation indicate that, in the CdTe1 − xSx solid solutions, there exist metastable states, which most probably decay under ultrasonic irradiation and then again form solid solutions with more stable states.

Nonmonotonic dependence of the work function of ytterbium nanofilms deposited on the Si(111)7 × 7 surface at room temperature on the film thickness

The dependences of the work function of ytterbium nanofilms on their thickness are studied. The films are evaporated at room temperature on the Si(111)7 × 7 surface of silicon samples doped to different levels and having different types of conduction (n and p). It is shown that these dependences exhibit a pronounced nonmonotonic behavior, which does not depend on the type of silicon used. It is established that the amplitude of the nonmonotonic variations in the work function is governed by the surface microroughness of the deposited layers, so that larger amplitudes correspond to smoother films. The variations in the work function of the films due to the deposition of electrically negative Si atoms on their surface are investigated. It is revealed that the sign of the variation depends on the film thickness. This result strange at first glance is associated with the fact that the electron density distribution at the metal-film-vacuum interface depends nonmonotonically on the amount of deposited ytterbium. This nonmonotonic behavior is a manifestation of electron density standing waves (Friedel oscillations) generated in the films by the ytterbium-silicon interface.

Effect of Composite Layers Based on Dyes with Different Types of Conductivity on Photovoltaic Properties of CIS Films

The effect of the deposition of layers “polymer-dye” with different types of conductivity on the surface photovoltage (V) of CuInS2 (CIS) has been studied. The influence of composite layers depends on the molecular structure of a polymer, the type of conductivity and photosensitivity of a dye. The photovoltage growth mainly in the region of strong absorption of a dye was observed after the deposition of the composite consisted of the p-type polymethine dye and the carbazole I-contained polymer on the CIS surface. The spectral dependence of this composite in the low-absorption region is only weakly changed. On the contrary, the deposition of the composite consisted of the perylene n-type dye in polymer on CIS leads to a decrease of V, especially in the dye absorption region. A decrease of the short-wavelength slope is caused by the presence of surface recombination centers in CIS films. The above-mentioned results can be explained by the presence of a few concurrent processes, the efficiency of which strongly depends on the used polymer and the type of conductivity of a dye.

Screening physicochemical parameters to tuning the reversible light-triggered control of emulsion type

We have investigated on the properties of an emulsion system consisting of C12Em surfactant(s), a poly(sodium acrylate) grafted with azobenzene chromophore groups (photoresponsive polymer, PRP), n-dodecane, and a sodium nitrate aqueous phase. The system can be reversibly switched under stirring from a direct (dispersion of oil droplets into the water phase) to an inverse (dispersion of water droplets into the oil phase) emulsion by exposure to visible or UV light. Herein, we have reported on the physicochemical conditions required to achieve the reversible light-triggered control of emulsion type (direct or inverse). The effect of changing the photoresponsive polymer concentration and hydrophobicity, surfactant(s) concentration, and salt concentration was studied in details. Because of their great interest for industrial applications, we have also presented the effect of changing the oil to water ratio and described the use of a surfactant mixture (Supplementary materials). Conductimetry was used to determine the emulsion type as a function of temperature, time, irradiation (at 365 or 436nm), and all the parameters given above. Different types of conductivity–temperature behaviours were distinguished, which provide the foundation of a discussion about possible molecular origins of the triggering of emulsion type by light.

Two-dimensional p-n junction under equilibrium conditions

For the first time, the idea of a two-dimensional p-n junction formed as a contact between two regions of a quantum-dimensional film with different types of conductivity is proposed. Under equilibrium conditions, the potential distribution and the potential-barrier height were determined. An expression was derived for the width of the surface-charge layer, which depends linearly on the contact potential (external bias) in contrast to the three-dimensional case. The specific capacitance of a two-dimensional p-n junction is virtually independent of the applied potential and depends only on the ambient permittivity. It was shown that, in spite of the fact that the junction electric field is screened only slightly, the Schottky approximation can be used for a description of the properties of such p-n junctions.

Low-temperature structural variations and interlayer charge transfer in cuprate superconductors

The analysis of the structural variations in cuprates with different types of conductivity has shown that cooling from room temperature prior to the transition into the superconducting state results in transfer of a small part of the charge (approximately several hundredths of an electron charge per unit cell) from the reservoir to the conducting layers. The sign of the charge corresponds to the conductivity type and is positive for a hole conductor and negative for an electron one.

Composite n–p semiconducting titanium oxides as gas sensors

Anatase and rutile thick films generated from the same source of titania were found to exhibit different types of conductivity upon exposure to CO and CH 4 at 600°C in a background of 5% O 2/95% N 2. Anatase behaved as a n-type semiconductor, with a decrease in resistance with reducing gas, whereas rutile exhibited p-type conductivity. The morphology of the particles were different, with anatase consisting of spherical particles of 100–200 nm dimensions, whereas rutile appeared as elongated rods of ∼1 μm lengths. The n-type behavior of anatase can be explained based on the oxygen vacancies. For explanation of the p-type behavior of rutile, impurities in the sample have to be taken into account. The impurity contents in both samples were similar, and doping of the lower valent impurities into the TiO 2 lattice should lead to creation of interstitial titanium defects. During anatase to rutile conversion at temperatures of 1000°C, the titanium interstitials can help incorporate excess oxygen, leading to formation of holes and p-type conductivity in the rutile phase. Resistance changes upon interaction of reducing gas with composites of anatase–rutile was also studied. It was found that samples with <50% rutile upon CO exposure exhibited resistance changes similar to that of anatase. The sample with 75% rutile also showed n-type behavior, though the change in resistance was diminished as compared to anatase. Rutile samples showed p-type behavior indicating a crossover from n- to p-type response at a composition between 75% rutile and pure rutile. The resistance changes with CH 4 followed a similar pattern. However, since the overall response of CH 4 was smaller than that of CO, the 75% rutile sample showed no change upon exposure to CH 4, while exhibiting an n-type response to CO, indicative of a selective CO sensor at temperatures of 600°C. A polychromatic percolation model was developed to explain the electrical data. Two independent, parallel pathways involving the n-type anatase and p-type rutile were considered to be important in the conductivity. Using experimental data related to the extent of sintering, and appropriate particle sizes, the model predicted that n–n percolation would occur from 0 up to 94.5% rutile and p–p percolation would begin at 75.1% rutile. In between 75.1 and 94.5% rutile, both n- and p-pathways would percolate, resulting in the observed diminished changes in resistance.

Effect of random defect density fluctuations on the Fermi level in highly compensated semiconductors

A statistical model of random defect density fluctuations is proposed to determine the Fermi level distribution in compensated semiconductors. The model is based on the assumption for Gaussian defect distribution. It is shown that highly compensated materials convert into multi-component systems, containing regions with different types of conductivity. Thus an effective potential barrier in the sample appears, which is related to the degree of compensation. It is shown that this model is appropriate for materials which contain inhomogeneously distributed shallow as well as deep levels. The model is illustrated for the case of semi-insulating GaAs:Cr at 300 K.

Effect of chemical surface treatment on p-layer formation in the interface region of directly bonded Si wafers

We have identified a p-type layer on both sides of the interface formed by two directly bonded silicon wafers. The thickness and the hole concentration of the p-layer vary with the pretreatment of the wafer surface, temperature and bonding time. It is shown that the p-layer is formed by the diffusion of uncontrollable Al impurities adsorbed on the hydrophilic silicon surface. The layer is responsible for the barrier properties of the interface in n+-n and n-n structures and for a large p-n junction depth in bonded wafers with different types of conductivity.

Electrification of a dielectric in a field of braking radiation

Numerical investigations have shown that the charging of dielectrics occurs most effectively at low intensities of {gamma}-radiation, since then the effective charge mobility is small. The type of conductivity of the dielectric plays an important role here. Dielectrics with electron conductivity charge more efficiently. An increase in the radiation intensity reduce the difference in the accumulated charge in dielectrics with different types of conductivity. The radiation geometry is an important factor which influences the charge accumulation: when a dielectric with an open surface is irradiated the electric field produced is greater than in the case of a shorted dielectric.

Observation of various types of electrical transport in oxygen-deficient garnets

When heated in a hydrogen atmosphere, insulating garnets of formula A 3B 5O 12 acquire a finite conductivity. According to their degree of oxidation, we find different types of conductivity including simple thermal activation or Mott variable hopping over wide ranges of temperature.

Laser-induced grating spectroscopy of cadmium telluride

Laser-induced transient gratings produced by two-photon absorption of picosecond pulses at 1.064 μm were used to examine the room-temperature nonlinear optical responses of CdTe crystals with different types of conductivity. Pulse-probe degenerate four-wave mixing measurements of grating dynamics on subnanosecond time scales were used to measure the ambipolar diffusion coefficient (Da) of charge carriers in the crystals. The value of Da =3.0 cm2 s−1 which was obtained is in very good agreement with theoretical estimates. A long-lived contribution to the signal consistent with a trapped charge photorefractive effect was observed at large grating spacings for n-type conductivity, and is tentatively attributed to a larger trap density in this sample. Measurements of the relative scattering efficiencies of successive diffracted orders in the Raman–Nath regime allowed for calculation of the laser-induced change in the index of refraction, due to the creation of free carriers. The value of Δn=4×10−4 which was obtained is in good agreement with theoretical estimates.

Electrical conduction in solution-grown polycarbonate films

The electrical conduction in solution-grown polycarbonate films was studied at different voltages between 1 and 104V as a function of thickness from 25 to 65 μm at a constant temperature of about 385 K and as a function of temperature in the range 328–430 K at a constant thickness of about 50 μm. The results show two distinct regions corresponding to different types of conduction: region I at low or moderate fields where the slope of the current-voltage characteristics is about 2 and region II at high fields where the slope is about 4. The Richardson-Schottky effect was suggested as the dominant mode of conduction at moderate fields whereas at high fields the currents were found to be space charge limited.