Current density-voltage characteristics have been obtained from thin films of lead phthalocyanine particles dispersed in a polymer binder when sandwiched between ohmic gold and blocking aluminium electrodes. At low voltages, the current in the forward direction shows Schottky diode behaviour. The diode parameters are evaluated using the model of Cheung and Cheung. Barrier heights and widths are determined as a function of applied voltage. A number of parameters is evaluated on the basis of the theory of space-charge-limited conduction, and the following values are obtained: p_{0} = 8.5 × 10^{18} m^{-3}, concentration of the traps per unit energy range at the valence band P_{0} ≈ 2.5 × 10^{44} J^{-1}m^{-3}, temperature parameter of trapping distribution T_{c} ≈ 500 K and total trapping concentration, N_{t} ≈ 1.7 × 10^{24} m^{-3}.
Current density-voltage characteristics were obtained from 2,6-diamino anthraquinone samples using ohmic aluminium electrodes. Results showed that at low voltage the conduction process was ohmic, while at high voltage space-charge-limited conduction controlled by a single dominant trap level was presented. Thickness dependence measurements proved that the trapping sites were located at a discrete energy level. The transition voltage, V, between ohmic and space-charge-limited conduction was approximately proportional to the square of the sample thickness and was found to be temperature independent. The temperature dependence of ohmic and space-charge-limited current densities have been investigated. The results were interpreted in terms of extrinsic nature of ohmic conduction. Traps with density ≈ 2 × 10^{24} m^{-3} located at 0.50 ± 0.03 eV below the conduction band edge have been observed.
The energy relaxation in two-dimensional electron gas in In_{0.53}Ga_{0.47}As/InP has been studied in a wide range of electron temperatures (from 0.1 to 10 K). The energy loss rate of electrons is controlled by the interaction of electrons with the piezoelectric potential of acoustic phonons. The value of the piezoelectric constant for InGaAs lattice-matched to InP is deduced from theoretical fits of the experimental data: h_{14}=(1.1±0.1)×10^{7} V/cm. Available data for the piezoelectric constant of In_{x}Ga_{1-x}As are discussed in the light of the results of this work.
The temperature dependence of the DC and AC electrical conductivity were measured for Ge_{1}Se_{1.35}Tl_{0.1} films. The value of DC electrical conduction energy ΔE_{σ} does not depend on film thickness in the investigated range with mean value of 0.72eV. The AC conductivity σ_{AC} is related to frequency by the expression σ_{AC}=Aω^{S}, where S is the frequency exponent which decreases linearly with increasing temperature. This can be explained in terms of the pair (bipolaron) correlated barrier hopping model suggested by Elliott. The frequency and temperature dependence of real and imaginary parts of the dielectric constant were studied for Ge_{1}Se_{1.35}Tl_{0.1} films. The dielectric constant (real part) and the dielectric loss (imaginary part) increase with increasing temperature and decrease with increasing frequency in the investigated range of frequency and temperature. The maximum barrier height W_{M} can be calculated according to the Giuntini equation at different temperatures. The obtained value of W_{M} is in good agreement with the theory of hopping of charge carriers over a potential barrier as suggested by Elliott in case of chalcogenide glasses.
In this paper, an analytical band model is introduced in Monte Carlo simulation of electric transport process in thin film electroluminescent devices. The band structure of ZnS calculated from the empirical pseudopotential method is fitted by using polynomials. The density of states and scattering rates are also calculated from these polynomials. Based on these results, the electric transport process in ZnS-type thin film electroluminescent devices is simulated through the Monte Carlo method. By comparison with others, this model is as fast as the nonparabolic model and as accurate as the full band model. Furthermore, the influence of the band model on the simulation results is also investigated. We show that the dispersion relation and density of states are all important in the simulation.
Based on the calculation about intervalley scattering rates in ZnS, the intervalley transfer process in ZnS-type thin film electroluminescent devices is investigated through the Monte Carlo simulation. The transient time of intervalley transfer is about 0.2-0.3 ps, it coincides with that of electron average energy. Intervalley distribution shifts to high valleys as the electric field increased. The electron kinetic energy distributions in different valleys are also gained. We propose that high valleys could store energies, which could prolong the decay of the electron average energy as the field was removed. These results could be used as the basic data on the study of electroluminescent process and the citation of valley parameters in analytic models should be carefully considered.
In_{2}Te_{3} thin films were prepared by thermal evaporation technique. The composition of the films is checked by energy dispersive X-ray analysis. X-ray analysis showed that the as-deposited In_{2}Te_{3} films as well as films annealed at temperatures ≤473K have crystalline structure. The ac conductivity σ_{ac}(ω), the dielectric constant ε_{1} and the dielectric loss ε_{2} of In_{2}Te_{3} films were studied in the temperature range 303-373K and in the frequency range 100Hz-100kHz. The ac conduction activation energy ΔE_{σ}(ω) was found to be 0.065eV for the as-deposited films. The ac conductivity was found to obey the relation σ_{ac}(ω)=Aω^{s}, where s is the frequency exponent. The obtained temperature dependence of s is reasonably interpreted by quantum mechanical tunneling model. Both the dielectric constant ε_{1} and the dielectric loss ε_{2} increased with temperature and decreased with frequency in the investigated range. The frequency and temperature dependencies of σ_{ac}(ω), ε_{1}, and ε_{2} for the annealed samples have the same behavior as that for the as-deposited samples. However, values of σ_{ac}(ω), ε_{1}, and ε_{2} measured at any frequency and temperature increased with annealing temperature up to 473K. It was found also that ΔE_{σ}(ω) decreased with annealing temperature.
The p-d hybridised single-hole states of the transition-metal-oxygen tetrahedron (TMO_{4}) are collectivised due to the direct p-p hopping between oxygens of different clusters. The lowest-lying energy band is always narrow and fully occupied. The first excited band gets occupied as an effect of valence-uncompensated doping, so it can be almost localised. The possible hole excitations to the two higher energy bands, which are wider, may imply the Mott-like hopping form of charge transport in these systems.
Knowing that conductivity is a temperature function σ = f(T) allows us to estimate the thermal stability of collagen preparations from fish skin. Measurements can provide information, which is crucial for technologies applying this type of collagen. Conductivity σ measurements were performed in a constant electric field E = 1 kV/m, in the temperature range of 290-480 K. White collagen lyophilisate was used as control material. It contained neither elastin nor melanin dopants nor non-organic dopants such as gold, copper, silver or zinc. Gold, copper, silver and zinc belong to the group of transitional metals and they have intermediate properties of both alkaline metals and metals in the p block of the periodic table. The common feature of most of these elements is their ability to form coordination complexes of intense color. In the measured materials peaks were found in the temperature range of 303-323 K. Peak temperature and its shape depend on the type of material. In the case of nano-gold doping a drop in peak temperature and a decrease in conductivity were observed. The measured materials are characterized by lower thermal resistance than bovine collagen. Nevertheless, thermal stability of fish skin collagen is high enough for fish skin collagen to replace bovine collagen. The measurement results obtained for white collagen and white collagen with Zn^{2+} may indicate better bonding of free water. The presence of nano-silver and nano-copper as doping agents in graphite collagen may lead to a decrease in hygroscopy of the material and, as a result, may increase its resistance to bacteria.
We have found a novel organic semiconductor, BTQBT, with a high electrical conductivity of about 10^{-3} S cm^{-1} and a high Hall mobility of about 3 cm^{2} V^{-1}s^{-1} at room temperature. We have also succeeded in measuring the temperature dependence of the Hall mobility. It varies with temperature as Τ^{-1.6}, which agrees with the theoretical Τ^{-1.5} dependence for the mobility determined by lattice scattering. The characteristic transport property of BTQBT results from strong intermolecular interactions in the crystal, which is convinced by the energy dispersion with a bandwidth of about 0.5 eV from the theoretical and experimental band structures.
Collagen is the major biopolymer of a living organism, which physical properties depend on water content. The observed transmission of spongiform encephalophaties (BSE) to humans resulted in the development of new sources of collagen. Fish skin seems to be one of such safe sources of collagen. Measurements of electrical conductivity as a function of temperature provides information, among other things, on the water release process. Experiment was carried out for fish skin (FSC) collagen (type I) and bovine Achilles tendon collagen (type I). Each sample was heated two times. Current-voltage characteristic was determined for FSC collagen to determine the range, within which the relation is linear. The primary differences appeared to be in electric conductivity, which was higher for FSC collagen than for BAT collagen. Electric conductivity varied from 10^{-6} S/m to 10^{-10} S/m depending on material and temperature. The process of free and bound water release was manifested as a peak on electrical conductivity-temperature curve between 320-350 K. The activation energy of the charge conduction process, determined on the basis of the Arrhenius plot, was material dependent and considerably higher for FSC collagen.
Indications for the observation of the diamagnetic shrinkage of the boron acceptor wave function (WF) in Si are reported. Uniaxial stress (X) was used to split the ground state (GS) of the boron acceptor into two energy levels with spatially complementary WF. The magnetic field selectively induces a shrinking of one of the two WF, depending on whether it is applied parallel or perpendicular to the X axis. As a result, the hopping transitions between lower and higher energy levels are redistributed, leading to significant changes in the activation energy ε_{3}. This effect was borne out by experiment.
The object of this work was to investigate structure, electrochemical behavior and semiconducting properties of the TiO₂ oxide layer on the Ti-15Mo implant alloy surface in normal and inflammatory conditions of physiological saline solution. X-ray photoelectron spectroscopy measurements confirm the presence of the oxide layer on the Ti-15Mo alloy surface. Electrochemical studies indicate excellent corrosion resistance of Ti-15Mo alloy in physiological saline solution. It was found that the investigated material under normal and inflammatory conditions behave like an insulator and n-type semiconductor, respectively.
The investigation of electrical conductivity, coefficient of thermal electromotive force, Hall coefficient, microhardness and mobility in Pb_{1-x}Ge_{x}Te (x = 0 ÷ 0.1) alloys in the temperature range of 77-300 K was carried out. Anomalies were detected in isotherms of properties in the vicinity of x = 0.008. The anomalies were treated as a manifestation of concentration phase transitions occurring in solid solutions of any kind and associated with existence of critical concentration (percolation threshold) at which the uninterrupted chain of interactions between impurity atoms is formed.
In this study, electromagnetic shielding effectiveness of ceramic bodies produced with natural zeolite illuminated by an electromagnetic pulse is investigated. A matrix model is used to calculate the propagation of electromagnetic pulse through sample. Shielding effectiveness of sample is determined for both transmitted electric and magnetic fields. Mathematical theory of the interaction and the shielding effectiveness of the sample is determined as a function of frequency, thickness of the material and the incidence angle of electromagnetic pulse. Zeolites used in this study were supplied from ETI Holding Company located in Turkey. Water was added as a binder and disc samples were shaped by uniaxial dry pressing at pressing pressure of 1.5 tone. Samples were fired in an electric furnace with a heating rate of 10°C/min at 1150C with a period of 60 min. Electrical measurements are performed to determine the dielectric constant and dielectric loss tangent at 25C constant temperature between frequency range from 1 kHz up to 2 MHz.
This paper discusses molecular beam epitaxy with particular emphasis on the production of state of the art electronic and optoelectronic low dimensional structures and devices. The molecular beam epitaxy process is outlined briefly and the practical problems associated with producing "state of the art" (Al,Ga)As/GaAs structures are considered. Examples include high mobility electron and hole gases, low threshold current lasers and the multi-quantum well solar cells.
Ceramic composites (100 - n)Bi_{4}V_{2}O_{11-z}-nCe_{0.9}Gd_{0.1}O_{1.9} with n=0÷25 wt% were prepared and studied by the X-ray diffraction, dielectric spectroscopy, and impedance methods. Slight increase in the unit cell volume accompanied by monotonous decrease in temperatures and broadening of the α-β and β-γ phase transitions with increasing fluorite content was observed in the composites studied. Increase in melting temperatures of composites with n ≥ 10 with the retention of their high ionic conductivity was also proved.
Ceramic solid solutions (Bi_{1-y}La_{y})_{4}(V_{1-x}Zr_{x})_{2}O_{11-z} with x = 0-0.05, y = 0-0.16 have been prepared by the solid state reaction method. The samples were studied by differential thermal analysis, X-ray diffraction, dielectric spectroscopy, and impedance methods. The concentration and temperature stabilization regions of the polymorphous α-, β-, γ'-, γ-modifications have been determined. The effects observed in dielectric properties, conductivity, and impedance data confirmed the influence both of intrinsic oxygen vacancies and those "pinned" at ferroelectric domain boundaries on the temperature hysteresis of α-β phase transition and their contribution to mechanism of oxygen ion transport.
Simple electric transport versus T = 20-400 K in metallic n-GaAs annealed single crystals with Te impurity concentration ∿(0.4-1.7) × 10^{19} cm^{-3}, which is above the equilibrium doping limit, is reported and compared with modern theory of electron mobility in degenerated n-GaAs by Szmyd, Hanna, Majerfeld. An overcome of the equilibrium doping limit in annealed n-GaAs is manifested by a lowered electrical activation of Te donors and by an onset of ≈ 0.1-1 μm regions of local strain in the crystal lattice known from high resolution X-ray studies. These preliminary results of transport show that the electron mobility μ(T) measured for n-GaAs with local strains is not consistent with predictions of Szmyd et al. model for any degree of compensation assumed. This surprising result indicates that electric transport in materials above the equilibrium doping limit is not well understood assuming the scattering by ionized impurities. The nature of defects responsible for an observed strong reduction of free carrier concentration (here ≈ 80%) in annealed heavily doped n-GaAs seems not to be related with electrical compensation. We point here at the possible role of effects of free carrier scattering due to static lattice distortions (local strains) related to a chemical aggregation of impurity atoms. We also notice that transport in metallic n-GaAs with local strains shows features similar to a weak localization σ_{xx} ∝ log T.
Magnetic susceptibility, electrical resistivity, and thermopower of the series of the R_3Cu_3Sb_4 compounds (R=La-Sm) were measured over the temperature ranges 1.9-300 K (susceptibility and resistivity) and 80-370 K (thermopower). Below 25 K, resistivity of these compounds grows exponentially with decreasing temperature. For some compounds, R = Ce, Sm, a maximum on temperature dependence of resistivity is observed. Ce_3Cu_3Sb_4 compound undergoes a magnetic transition at 12 K.
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