Electrical properties of photodiodes based on <Emphasis Type="Italic">p</Emphasis>-GaSb/<Emphasis Type="Italic">p</Emphasis>-GaInAsSb/<Emphasis Type="Italic">N</Emphasis>-GaAlAsSb heterojunctions

We have studied the electrical characteristics of photodiodes based on p-GaSb/p-GaInAsSb/N-GaAlAsSb heterojunctions and investigated the mechanisms of current transfer in these heterostructures at various temperatures. A comparison of the theoretical results and experimental data showed that the tunneling charge transfer mechanism dominates at low temperatures (T < 150 K) under both forward and reverse bias conditions. The tunneling current becomes a determining factor at an electric field strength in the p-n junction of no less that 10⁵ V/cm, which is related to a small bandgap width of the materials studied and low effective masses of electrons and holes.     

Photophysical characteristics of microlayer photodiode <Emphasis Type="Italic">p</Emphasis>AlGaInAs(Zn)-<Emphasis Type="Italic">n</Emphasis>GaAs-Au structures

The photoelectric characteristics of photodiode pAlGaInAs(Zn)-nGaAs-Au structures have been investigated. It has been established experimentally that an internal photoelectric amplification arises in these structures when the nGaAs-Au potential barrier is connected in opposition to the (p(Al_0.08Ga_0.82)_0.9In_0.1As-nGaAs) heterojunction. The p(Al_0.08Ga_0.82)_0.9In_0.1As-nGaAs-Au structure operates as an injection photodiode when the p-n junction operates in the forward-bias regime and as a photodiode when this junction operates in the reversebias regime. The influence of the depletion regions of the base zone containing deep impurity centers on the photosensitivity and the spectral range of the indicated structures has been investigated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 1, pp. 166–172, January–February, 2007.     

The thermodynamic properties of liquid binary mixtures of <Emphasis Type="Italic">n</Emphasis>-alkanes: <Emphasis Type="Italic">n</Emphasis>-decane + <Emphasis Type="Italic">n</Emphasis>-hexadecane

Data on sound velocity are used for determining the density, the isobaric expansion coefficient, the isobaric and isochoric heat capacity, and the isothermal compressibility of liquid binary mixture of n-decane + n-hexadecane of three compositions in the temperature range of 298–433 K and pressure range of 0.1–100 MPa. The coefficients of Tait equation are calculated in the above-identified range of parameters. The calculation results are compared with experimental data on density. The divergence does not exceed 0.2% for the most reliable data.     

Sensitivity of dislocation engineered Si <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions to influence of illumination and ultrasound

In this work it is shown that the dislocation engineered Si p-n junctions are sensitive to variations of illumination intensity. It is found that with the aim of ultrasound processing it is possible to purposefully modulate properties of the device structure.     

Asymmetric current transfer in isotype <Emphasis Type="Italic">n</Emphasis>-In<Subscript>2</Subscript>Se<Subscript>3</Subscript>/<Emphasis Type="Italic">n</Emphasis>-InSe heterocontacts

We have studied the mechanisms of current transfer and the capacitance-voltage characteristics of a radiation-resistant isotype n-In₂Se₃/n-InSe heterocontact in which the region depleted of major charge carriers is localized predominantly in a relatively low-ohmic semiconductor—the α-type In₂Se₃ with a large density of defects. The spectrum of the relative quantum efficiency of photoconversion in this structure depends on the thickness of the In₂Se₃ layer and on the geometry of illumination of the heterocontact.     

Electrical impedance of ethylene-carbon monoxide/propylene-carbon monoxide (<Emphasis Type="Italic">EPEC</Emphasis>-<Emphasis Type="Italic">69</Emphasis>) thermoplastic polyketone

Electrical impedance technique was employed to investigate the electrical properties of ethylene-carbon monoxide/propylene-carbon monoxide terpolymer (EPEC-69). The measurements were performed in the frequency range 0.1–10⁵ Hz and in the temperature range 30–110 °C. The results reveal that the dielectric constant, loss factor, modulus, and ac conductivity are dependent of frequency and temperature. A Debye relaxation peak was detected in the plot of Z″ versus frequency where the activation energy was determined and found to be 1.26 eV. When the surface phenomenon effects were separated using the imaginary part of the complex admittance a second dielectric dispersion was observed in the low frequency region. Two models were proposed from the impedance measurements depending on temperature range.     

The speed of sound of <Emphasis Type="Italic">n</Emphasis>-heptane, <Emphasis Type="Italic">n</Emphasis>-octane and their binary mixtures at temperatures <Emphasis Type="Italic">T</Emphasis> = 293.15 to 523.15 K and pressures up to 60 MPa

Speeds of sound in liquid n-heptane, n-octane and their binary mixtures were measured at the temperatures T = 293.15 to 523.15 K and pressures up to 60 MPa. The pulse-echo method with a frequency of 8MHz and uncertainty of ±0.08% was used. The measured values were fitted by polinomials, as functions of temperature and pressure, and the reliability of the present results was proved by comparison with the literature data.     

Worm-like morphology of semi-rigid substituted poly(<Emphasis Type="Italic">p</Emphasis>-phenylene)

The rheological and dynamic mechanical properties of a semi-rigid substituted poly(p-phenylene) were investigated. At temperatures below the glass transition temperature of 152 °C the amorphous polymer is very stiff compared with flexible chain polymers. Although the material can be processed in the melt, the melt is unusually elastic. Atomic force and transmission electron microscopy revealed a worm-like morphology. Blends with polycarbonate yield transparent materials. Microscopy and X-ray diffraction of these blends indicated that the flexible chain polymer is located in between the worm-like structures of the semi-rigid polymer.     

Detecting quasi-periodic {11<Emphasis Type="Italic">n</Emphasis>} (<Emphasis Type="Italic">n</Emphasis> = 7–11) faces in samples with Ge/Si quantum dots by grazing X-ray reflectometry

High-resolution grazing X-ray reflectometry is used to obtain experimental and theoretical data on the intensity of specular and diffuse reflection from self-organized structures grown by molecular beam epitaxy with single-layer (non-overgrown) and multilayer (overgrown) Ge/Si quantum dots (QDs). Using the positions of diffuse scattering peaks in the direct space, the slopes of quasi-periodic faces have been determined to within ±0.1° by a method employed previously for the investigation of In(Ga)As/GaAs quantum dots. Finding the quasi-periodic {11n} (n = 7−11) faces (typical of the growth of ordered QDs) in the samples with disordered Ge/Si quantum dots is evidence of the generality of mechanisms of QD formation in different systems.     

Impurity Effect on Kramer-Pesch Core Shrinkage in <Emphasis Type="Italic">s</Emphasis>-Wave Vortex and Chiral <Emphasis Type="Italic">p</Emphasis>-Wave Vortex

No Heading The low-temperature shrinking of the vortex core (Kramer-Pesch effect) is studied for an isolated single vortex for chiral p-wave and s-wave superconducting phases. The effect of nonmagnetic impurities on the vortex core radius is numerically investigated in the Born limit by means of a quasiclassical approach. It is shown that in the chiral p-wave phase the Kramer-Pesch effect displays a certain robustness against impurities owing to a specific quantum effect, while the s-wave phase reacts more sensitively to impurity scattering. This suggests chiral p-wave superconductors as promising candidates for the experimental observation of the Kramer-Pesch effect.PACS numbers: 74.25.Op, 74.20.Rp, 74.70.Pq     

Recombination instability and double S-switching in <Emphasis Type="Italic">p</Emphasis>-Ge(Au)

We report on the experimental investigation of p-Ge(Au) samples and compare the results qualitatively to a one-dimensional theoretical model describing the recombination instability of current in gold-compensated germanium in a two-parameter (voltage-emission) space. Experiments showed the existence of three regimes of the system functioning in the parametric space. The second S-switching region was found on the current-voltage characteristic, which is probably related to a noise-induced nonequilibrium phase transition.     

Viscosity and Surface Tension of Saturated <Emphasis Type="Italic">n</Emphasis>-Pentane

Light scattering by thermally excited capillary waves on liquid surfaces or interfaces can be used for the investigation of viscoelastic properties of fluids. In this work, the simultaneous determination of surface tension and liquid kinematic viscosity of n-pentane by surface light scattering (SLS) on a gas–liquid interface was carried out. The experiments are based on a heterodyne detection scheme and signal analysis by photon correlation spectroscopy (PCS). Measurements were performed under saturation conditions over a wide temperature range from about 233 to 363 K. For the whole temperature range the total uncertainty of the liquid kinematic viscosity and surface tension is estimated to be better than 1.0 and 1.2, respectively. The results obtained corroborate the reliability of the SLS technique for the determination of thermophysical properties.     

Microwave switches based on 4H-SiC <Emphasis Type="Italic">p-i-n</Emphasis> diodes

Problems pertaining to the modeling and development of a microwave modulator based on 4H-SiC p-i-n diodes are considered. The results of theoretical and experimental investigations of the microwave characteristics of 4H-SiC p-i-n diodes and the parameters of a microstrip modulator for a 1–10 GHz range based on these diodes are reported for the first time. In the diode switching schemes studied, the transmission losses amount to 0.8–8 dB and the decoupling is within −15 to −18 dB. The experimental characteristics of modulators are determined primarily by the parameters of diodes and agree well with the results of model calculations.     

Electrical properties and positron annihilation study of (Ba<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ho<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)TiO<Subscript>3</Subscript> ceramics

DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba_1−x Ho _x )TiO₃ ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba_1−x Ho _x )TiO₃ is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO₃ by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The local electron density and defect concentration estimated using positron annihilation technique conforms well to the features found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model.     

The Viscosity and Density of <Emphasis Type="Italic">n</Emphasis>-Dodecane and <Emphasis Type="Italic">n</Emphasis>-Octadecane at Pressures up to 200 MPa and Temperatures up to 473 K

A vibrating-wire instrument for simultaneous measurement of the density and viscosity of liquids under conditions of high pressure is described. The instrument is capable of operation at temperatures between 298.15 and 473.15 K at pressures up to 200 MPa. Calibration was performed by means of measurements in vacuum, air, and toluene at 298.15 K. For n-dodecane measurements were made along eight isotherms between 298.15 and 473.15 K at pressures up to 200 MPa while for n-octadecane measurements were measured along seven isotherms between 323.15 and 473.15 K at pressures up to 90 MPa. The estimated uncertainty of the results is 2% in viscosity and 0.2% in density. Comparisons with literature data are presented.     

Experimental and theoretical analysis of selective hydrogenation of <Emphasis Type="Italic">p</Emphasis>-nitroanisole to <Emphasis Type="Italic">p</Emphasis>-anisidine over Pd/C: kinetics and catalyst deactivation

The selective reduction of nitro compounds to the corresponding amines in multi-functional moieties is attempted in a variety of industries using polluting processes including iron–acid and sulfide/polysulfide reduction processes. In the current work, selective hydrogenation of p-nitroanisole (PNA) to p-anisidine (PA) has been carried out using supported metal catalysts. 5% Pd/C was found to be highly effective in comparison with other metal catalysts used. Kinetic interpretation has been made by studying the important process parameters using 5% Pd/C as the catalyst. The experimental results show that conversion of PNA reaches 100% under the appropriate reaction conditions. The reaction was found to be 100% selective towards PA. It was possible to determine both the rate constant and adsorption equilibrium constant for the reaction. The activation energy of reaction and free energy of adsorption were found to be 10.25 and –2.4 kcal mol^–1, respectively, indicating that the reaction is Langmuir-Hinshelwood kinetically controlled. The catalyst was found to be deactivated due to the blocking of channels by product precipitation, which was considered as independent deactivation. A deactivation model was developed and it was found to fit the data very well. A complete theoretical and experimental analysis is presented. Electronic Publication     

Magneto-Peltier cooling of single-crystal Bi<Subscript>1-<Emphasis Type="Italic">X</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">X</Emphasis></Subscript> (<Emphasis Type="Italic">X </Emphasis>= 0.12 and 0.15) alloys

The cooling temperatures of rectangular parallelepiped Bi_1-X Sb _X (X = 0.12 and 0.15) single-crystals with the same thickness of t = 2 mm but different width W were measured at 113 K and 290 K as a function of electric current in the magnetic field B up to 2.17 T. The magnetic field was aligned along the thickness t of a sample and the current flows along its length L through the copper leads soldered to both end surfaces of cross section (W × t), where W, t and L are parallel to the binary, bisector and trigonal axes of the single-crystal, respectively. The thermoelement was not in contact with a heat sink. The cooling temperature of Bi_0.85Sb_0.15 at 290 K was increased with an increase of B and was almost symmetric for the reverse of the field direction, while at 113 K it exhibited a maximum at B = ±0.25 T and a strong asymmetry for the field direction. The largest maximum cooling temperature ΔT _max of Bi_0.85Sb_0.15 was achieved when a thermoelement has optimum dimensions so that heat energy is hardly generated at the cold side. When the single-crystal Bi_0.85Sb_0.15 alloy has optimum dimensions of L = 15 mm, W = 4 mm and t = 2 mm, the ΔT _max at 290 K increased from 4.2 K in B = 0 T to 9.6 K in B = +2.17 T, so that it exceeded ΔT _max values of 5.7 K obtained for a typical Bi₂Te₃ and 8.5 K measured previously for Bi single-crystal in B = +2.17 T.     

<Emphasis Type="Italic">hg</Emphasis>-index: a new index to characterize the scientific output of researchers based on the <Emphasis Type="Italic">h</Emphasis>- and <Emphasis Type="Italic">g</Emphasis>-indices

To be able to measure the scientific output of researchers is an increasingly important task to support research assessment decisions. To do so, we can find several different measures and indices in the literature. Recently, the h-index, introduced by Hirsch in 2005, has got a lot of attention from the scientific community for its good properties to measure the scientific production of researchers. Additionally, several different indicators, for example, the g-index, have been developed to try to improve the possible drawbacks of the h-index. In this paper we present a new index, called hg-index, to characterize the scientific output of researchers which is based on both h-index and g-index to try to keep the advantages of both measures as well as to minimize their disadvantages.     

Citrate–nitrate combustion route to the synthesis of (1−<Emphasis Type="Italic">x</Emphasis>)LaCrO<Subscript>3</Subscript>–<Emphasis Type="Italic">x</Emphasis>BiCrO<Subscript>3</Subscript> solid solution

Solid solution of (1−x)LaCrO₃–xBiCrO₃ (x = 0, 0.10, 0.15, 0.20 and 0.25) was prepared via the citrate–nitrate combustion synthesis. Pure perovskite phase was obtained at 800 °C, a much lower synthesis temperature than that needed in the solid-state reactions. The thermodynamics of phase formation and the ceramic sintering mechanism were investigated. The substitution of Bi³⁺ for La³⁺ was found to give a separate exothermic decomposition event in the gels and the precursor did not produce a transient liquid phase while heating to 1200 °C, as was found in ceramics prepared by solid state reaction. This finding shows that the role of Bi₂O₃ in the sintering of the La_1−x Bi _x CrO₃ ceramics depends on the processing method.