Electrically conducting polyaromatic sulfides

Poly(p-phenylene sulfide), PPS, a melt and solution processible polymer, can be made highly conducting by doping with strong electron acceptors such as ASF5. Virgin PPS is an insulator with a relatively high ionization potential compared to polyacetylene. This, coupled with its high melting and solubilization points, restricts possible dopants to those which are particularly aggressive and capable of reacting with PPS in the solid state. These aggressive dopants induce a variety of chemical changes in the polymer backbone upon doping. While fluorination and crosslinking occur to some extent, infrared spectra and independent chemical synthesis suggest that the predominant chemical change is via intrachain bridging (cyclization) of adjacent phenyl rings. In an attempt to find processible systems with lower ionization potentials and which are less prone to chemical modification, a variety of polyaromatic sulfides were prepared. The influence of polymer structure, morphology, and dopant-induced chemical modifications upon conductivity is discussed.     

Crystallization of amorphous selenium and As0.005Se0.995

The effect of temperature on the crystallization kinetics of bulk amorphous selenium and the alloy As_0.005Se_0.995 has been studied using differential scanning calorimetry. A time-temperature-transformation (TTT) curve has been plotted from isothermal results over the temperature range 320 to 490 K, and shows the presence of two minima for both materials. Using the empirical Avrami expression for solid-state transformations, a number of kinetic parameters has been determined.     

电离对晶体生长的作用

为什么有的晶体材料容易生长,而有的则很难.本文通过分析溶液或熔体的电离状态对晶体生长的影响,认为晶体生长的难易程度主要决定于该晶体材料在液相状态下电离度的大小,电离是所有化学键晶体生长的必要条件.通过比较各类晶体生长难易程度与价键结构及其化学元素组成的关系,认为:以偏离子性键、金属键结合的材料,在熔体状态下的电离度大,容易形成晶相;以偏共价键结合的化合物电离度小,难于生长单晶体,但容易制作非晶或纳米材料.     

Continuous cooling approximation for the formation of a glass

Non-isothermal equations describing the liquid-crystal transformation are derived using the isothermal Avrami equations. A theoretical expression for the critical cooling rate for the formation of a glass is found. Calculations based on this expression are in better agreement with experimental values than those derived from TTT (time-temperature-transformation) curves. A study performed on typical glass forming materials enables the glass forming ability (GFA) to be determined by experimentally measuring crystallization temperatures at different cooling rates which are easily accessible with commonly available technology. The behaviour of the rate constant for crystallization is also obtained from the same data in the experimental range considered. In both cases no previous knowledge of the parameters involved is needed.With some assumptions the values of the viscosity in the crystallization temperature range can be estimated.Although the study was performed for an Avrami index of 4 an extension to other values of n is made under some restricted conditions and a more general treatment is outlined.     

Radiation Defects Research in Single Crystals of Lithium Niobate

An information is given on the kinetics of developing ionization defects by γ-radiation, as well as on the destroying of these defects as a result of thermal treatment in oxidizing atmosphere at different temperatures. The presence of several types of ionization defects developing by γ-radiation is found out. Values of diffusion factor for each type of defects are given.     

Rheology and nano-crystallization of a Zr41.25Ti13.75Ni10Cu12.5Be22.5 bulk metallic glass

Creep of Zr-based bulk metallic glass (BMG) was carried out under hydrostatic pressure of 270 MPa superimposed on uniaxial compressive loads of 30–300 MPa. The temperature of testing was maintained at 633 K, which is close to the glass transition temperature of the BMG. The samples had heat treatment at 676 K for different lengths of time applied prior to testing, which resulted in microstructural changes. Apparent viscosity during flow was derived from the creep measurements. The effect of crystalline volume fraction, temperature, and strain rate are considered. Finally, we have constructed a TTT diagram for this BMG spanning almost three decades of time and 650–690 K temperature range, showing transformation from glassy to crystalline solid as a function of volume fraction.     

Impurity States in CuInSe2

The impurity states occurring in CuInSe₂ crystals after annealing in an atmosphere of Se and in-diffusion of In are determined by electrical measurements. The experimental results suggest the conclusion that the shallow donor with an ionization energy of about 10 meV is due to Se vacancies, the shallow acceptor with about 35 meV due to In vacancies, and the acceptor with about 100 meV due to Se interstitials. The deep acceptor with an ionization energy of about 400 meV is assumed to be due to Fe²⁺ substituted on In sites.     

Activity coefficient and incorporation of Phosphorus into epitaxial CVD Silicon

The present paper is concerned with the dopant incorporation behaviour at high doping concentrations, at which the conditions for diluted solutions are commonly considered no longer fulfilled. The first part contains a brief discussion of the theoretical aspects of ideal, ideally diluted and real solutions, and Raoult's law as well as Henry's law are reduced to the general solution equilibrium, applied to dopant incorporation. The second part considers the dopant ionization equilibrium according to the conception of REISS , additionally taking into account the high deposition temperatures. It had been concluded that at high doping concentrations both the ionization equilibrium and the solution equilibrium of dopants behave analogous to real solutions, and both equilibria need a correction by special activity coefficients.     

Crystallization processes of Ag–Ge–Se superionic glasses

The interest in superionic systems has increased in recent years because of the potential application of these materials as solid electrolytes. In this field, amorphous materials present important advantages when compared to the crystalline solids: larger conductivity, isotropy and absence of grain boundaries. In this work, amorphous alloys of compositions (Ge₂₅Se₇₅)_100−yAg_y with y=10, 15, 20 and 25 at.% have been studied. Amorphous samples in bulk were obtained from the liquid by water quenching (melt-quenching technique). The crystallization kinetics of the amorphous alloys have been studied under continuous heating and isothermal conditions by means of differential scanning calorimetry. A glass transition and two exothermic transformations were observed in all the samples. The quenched samples and the crystallization products have been characterized by X-ray diffraction. The primary crystallization of the ternary phase Ag₈GeSe₆ and the secondary phase GeSe₂ was observed. The glass and crystallization temperatures, the activation energy and the crystallization enthalpy are reported. The first step of the crystallization of the Ag₈GeSe₆ phase in all the (Ge₂₅Se₇₅)_100−yAg_y samples is modelled taking into account the Johnson–Mehl–Avrami–Kolmogorov theory and considering that the changes in the composition only modify the viscosity of the undercooled liquid. The transformation diagrams (TTT and THRT) are calculated and the glass forming ability is analyzed. The experimental results are discussed and correlated with the structures proposed for the glass. The present results and conclusions are also compared with those reported by other authors.     

Nonlinear photosensitivity of photo-thermo-refractive glass by high intensity laser irradiation

Photo-thermo-refractive (PTR) glass is a material for high-efficiency phase volume hologram recording which possesses linear photosensitivity in the near UV region from 280 to 350 nm. In this paper nonlinear photosensitivity by 355 nm nanosecond pulses with intensity exceeding 1 MW/cm² and by 783 nm femtosecond pulses with intensity exceeding 1 TW/cm² is demonstrated. No photo-sensitizers are necessary in PTR glass for nonlinear photosensitivity. Photosensitivity by 355 nm nanosecond pulses is determined by glass matrix ionization resulting from two-photon absorption of incident radiation by glass matrix. Photosensitivity by 783 nm femtosecond pulses is determined by glass matrix ionization from nonlinear interaction of fundamental radiation and supercontinuum with modified glass matrix due to strong electric fields of incident radiation.     

Investigation of thermal processes in one-and two-layer materials under irradiation with high-energy heavy ions within the thermal peak model

A system of equations for the electron and lattice temperatures around and along the path of a 700-MeV heavy (uranium) ion in nickel (one-layer material) is solved numerically in the axially symmetric cylindrical coordinate system under the assumption of temperature-dependent specific heat and thermal conductivity. The obtained dependences of the lattice temperature on the radius (distance from the ion path) and depth suggest that the ionization energy loss of a 700-MeV uranium ion in nickel is sufficient to melt the material. A comparative analysis with the linear model is performed and the maximum radius and depth of the region where the target material can melt is estimated. Then, the initial system of equations is solved for the region around and along the path of a 710-MeV heavy (bismuth ²⁰⁹Bi) ion in the two-layer material Ni(2 μm)-W with constant thermophysical parameters. The obtained dependences of the lattice temperature on the radius and depth show that the ionization energy loss of a 710-MeV bismuth ion in this two-layer material is sufficient for melting. The maximum radius and depth of the regions in the target material where phase transitions may occur are estimated.     

Anion Cluster: Assembly of Dihydrogen Phosphates for the Formation of a Cyclic Anion Octamer

Structural characterization of a dihydrogen phosphate complex of triprotonated tris[2-(2-thienylmethylamino)ethyl] amine shows that eight dihydrogen phosphate anions are assembled around the host by strong interactions of H-bond donors and acceptors to form a new type of cyclic anion octamer as (H(2)PO(4) (-))(8), an analogy of cyclic water octamer. The presence of an anion cluster has also been identified by electrospray ionization mass spectrometry and (31)P NMR experiments.     

Phase transformation and crystallization kinetics of melt-spun Ni60Nb20Zr20 amorphous alloy

The glass transition and crystallization kinetics of melt-spun Ni₆₀Nb₂₀Zr₂₀ amorphous alloy ribbons have been studied under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC). The dependence of glass transition and crystallization temperatures on heating rates was analyzed by Lasocka's relationship. The activation energies of crystallization, E_x, were determined to be 499.5 kJ/mol and 488.6 kJ/mol using the Kissinger and Ozawa equations, respectively. The Johnson–Mehl–Avrami equation has also been applied to the isothermal kinetics and the Avrami exponents are in the range of 1.92–2.47 indicating a diffusion-controlled three-dimensional growth mechanism. The activation energy obtained from the Arrhenius equation in the isothermal process was calculated to be E_x = 419.5 kJ/mol. The corresponding three dimensional (3D) time–temperature–transformation (TTT) diagram of crystallization for the alloy has been drawn which provides the information about transformation at a particular temperature. In addition, the intermetallic phases and morphology after thermal treatment have been identified by X-ray diffraction (XRD) and scanning electron microscope (SEM).     

Positron annihilation spectroscopy of vacancy-related defects in semiconductors

We use positron lifetime studies of GaAs materials to discuss the defect properties which can be investigated by implanting positive positrons in semiconductors. The studies concern native and electron irradiation induced defects. The results show that vacancy charge state and vacancy ionization levels can be determined from positron annihilation. They show also that positrons are trapped by negative ions and give information on their concentration.     

Growth and electrical properties of liquid phase epitaxial layers of GaxIn1-xP lattice-matched to GaAs substrates

From the measurement of the evaporation rate of phosphorus the favourable conditions for the layer growth were determined. Further, we have studied the influence of zinc and silicon on the growth and the morphology. The mobilities, the electron and hole concentrations in the temperature range from 77 to 300 K are presented. In the Si-doped samples we could not find a correlation between the silicon concentration in the melt and the donor concentrations in the layer. An estimation of the acceptor ionization energy in Zn-doped samples yields E_A = (15 ± 4) meV.     

Influence of substrate orientation on the electrical properties of CuInSe2 epitaxial layers on GaAs substrates

The electrical properties of CuInSe₂ epitaxial layers on (111)A-, (110)-, and (100)-oriented GaAs substrates are investigated. At substrate temperatures T_sub ≧ 820 K the p-type conductivity observed is governed by an acceptor state with an ionization energy of about 110 meV independent of the substrate orientation. At T_sub ≦ 770 K three different acceptor states are found in dependence on the substrate orientation: 390 meV for (111)A-, 110 meV for (110)-, and a very shallow acceptor for (100)-oriented substrates. A possible correlation between these acceptor states and intrinsic defects is proposed.     

Identification of the dynamics of plasma‐induced damage in a CuInSe2 thin film by fractal processing

A planar ionization system for rapid visualization and recording the resistance inhomogeneity and photoconductivity distribution in a chalcopyrite‐type semiconductor (CuInSe₂) copper‐indium‐diselenide film is studied. A part of the discharge energy is transferred to the electrodes of the system by the bombardment of the electrode surface due to an electron‐ion flow. This process leads to the sputtering mechanism of the electrode surface material. It is shown that the plasma‐induced damage (PID) in a CuInSe₂ thin film was primarily due to the effectiveness of sputtering and physico‐chemical interactions in the discharge gap during the transition from Townsend to the glow type. At the same time a nondestructive method is suggested for the analysis of the dynamics of PID in the CuInSe₂ thin film by fractal processing in the planar ionization system. Some properties of the device have been evaluated, such as a relative change of the resistance inhomogeneity is determined by a relative change of discharge light emission (DLE) intensity when a current is passed through an ionization cell. For the quantitative analysis of the change in the dynamic feature of PID of CuInSe₂ thin films, fractal dimension analysis was used following the records of the DLE intensity. The quality of the film was analyzed using both the profile and spatial distributed DLE intensities data showing the surface inhomogeneity and damage in the thin film as function of time. Thus, by using fractal concept, the order of the surface damage and the quality of the CuInSe₂ as function of time can be assessed exactly and the size and location of the surface inhomogeneities in thin film to be ascertained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic mechanism of thermal destruction of radiation-induced E'-centers in crystalline and glassy SiO2

The thermal decay regularities for radiation-induced E'-centers in crystalline and glassy SiO₂ were investigated. The results obtained point out that the destruction of E'-centers can be described as ionization process of deep centers in electric field. In terms of used model, the electric field and electron–vibration coupling parameters are sensitive to structural disorder. The most weak electron–phonon coupling in E'-centers is observed for amorphous systems.     

On the Origin of Trapping Centres in Organic Molecular Crystals

Traps for current carriers in molecular crystals may be due either to imperfections of the crystal structure (structural traps) or to chemical impurities introduced into the lattice (chemical traps). In the present paper simple hypotheses are presented explaining the formation of traps of the two groups. Perturbations of the crystal structure are not localized in one unit cell, but may extend over several farther cell. The local values of the polarization energy of the crystal lattice will change near to the centre of the defect, thus the “perturbed” molecules can act as traps for currentcarriers.Energetic distributions of traps as calculated under such conditions are foundto be in a good agreement with those determined experimentally. Trapping states may be also formed by impurity molecules having either greater electron affinity or smaller ionization energy than the host ones. The depth of the chemical traps estimated from the relationships given in the paper has been compared with the experimental data.     

Theoretical study on the electronic structures and spectral properties of two series of osmium(II) complexes with different substituent groups

Two series of osmium(II) complexes with different substituent groups (-CF₃, -N(CH₃)₂) have been studied by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, to investigate their electronic structures, absorption, and emission properties. The influence of different substituted groups on their photophysical properties has also been explored. The lowest energy absorption and emission wavelengths calculated are in good agreement with the available experimental values. Besides, ionization potential (IP), electron affinities (EA), and reorganization energy (λ) were calculated to evaluate the charge transfer and balance properties between hole and electron. It is expected that the theoretical studies could provide valuable information for the phosphorescent osmium(II) material for use in the organic light-emitting diodes.