Interaction of deep impurities with radiation defects in n-Si at γ-irradiation

This work presents the results of research on peculiarities of radiation defect formation in single crystal n-Si, doped by deep level impurities (Cu, Ni, Ir, Rh, Pt and Au), at irradiation by γ-quanta of ⁶⁰Co. A property of γ-irradiation to create only vacancies and self-interstitial atoms is used to understand the nature of deep levels with participation of these impurities and primary elemental radiation defects. The role of covalence radii and diffusion coefficients in efficiency of radiation defect formation is discussed.     

ESR study on radiation chemical processes in polyvinyl alcohol films at 77°k

Abstract

Trapped electrons (e_t ^?) were detected in irradiated PVA films at 77°K. Yield of e_t ^? was decreased as evaporating water from the films, indicating that water molecules contribute to construct pre-existing traps in the polymer. The radical produced at 77°K was identified as a precursor of the radical produced at room temperature.     

Structural changes in austenitic steel in contact with solid oxide electrolyte at 950°C

Changes in the structure and redistribution of alloying elements in 10Kh23N18 austenitic steel after operating at 950°C for 8800 h in contact with La-Sr-Mn-O electrolyte are investigated to establish the reasons for the degrading of the surface layer of a current collector in a solid-oxide fuel cell over long periods of service. It is established that the degradation of the surface layer of steel is associated with the formation of a network of silicon and aluminum oxides along grain boundaries and the considerable discrepancy between the linear thermal expansion coefficients of steel and the solid electrolyte.     

Rapid nickel diffusion in cold-worked carbon steel at 320–450 °C

The diffusion coefficient of nickel in cold-worked carbon steel was determined with the diffusion couple method in the temperature range between 320 and 450 °C. Diffusion couple was prepared by electro-less nickel plating on the surface of a 20% cold-worked carbon steel. The growth in width of the interdiffusion zone was proportional to the square root of diffusion time to 12,000 h. The diffusion coefficient (D_Ni) of nickel in cold-worked carbon steel was determined by extrapolating the concentration-dependent interdiffusion coefficient to 0% of nickel. The temperature dependence of D_Ni is expressed by D_Ni = (4.5 + 5.7/?2.5) × 10^?11 exp (?146 ± 4 kJ mol^?1/RT) m²s^?1. The value of D_Ni at 320 °C is four orders of magnitude higher than the lattice diffusion coefficient of nickel in iron. The activation energy 146 kJ mol^?1 is 54% of the activation energy 270.4 kJ mol^?1 for lattice diffusion of nickel in the ferromagnetic state iron.     

Righi-Leduc Effect in InSb between 25°C and 300°C

The Righi-Leduc effect has been measured for n-type InSb crystals of various mobilities and was found to increase with temperature in a manner to indicate that the unipolar contribution is prevalent over the bipolar part of the effect. The experimental values measured over the temperature range between 25°C and 300°C agree well withPutley's theory. The Righi-Leduc coefficient was also determined as a function of the magnetic field and the strong decrease observed is explained in terms of the magnetoresistance.     

Effect of plastic deformation on precipitation in Al-30 wt.% Zn alloy aged at 200 °C

The electron microscopic investigation of an Al-30 wt.% Zn alloy reveals that the plastic deformation of quenched samples substantionally modifies the phase transformation processes examined in the alloy aged at 200°C. Whereas the growth kinetics of metastable precipitates and associated solute diffusion are unaffected by cold rolling the alloy specimens from 9% up to 97·5% reduction in thickness, the rate of all observed transformations is enhanced considerably by prior plastic deformation. A corresponding increase of stored strain energy within the lattice provides namely an additional driving force for the establishment of a new precipitate/matrix interface of higher surface energy on the transformation of a metastable precipitate into a more stable one. The sizes of transforming transition precipitates consequently diminish with an increase of cold work and the respective transformations are thus accelerated.High dislocation density in heavily cold worked alloy also reduces the nucleation barrier for a heterogeneous nucleation on dislocations. The formation of platelike coherent_coh precipitates with internal cubic structure on dislocations is observed followed by the transformation of_coh into spheroidical semicoherent precipitates. The non-uniform distribution of stresses and strains in cold rolled specimens leads to the development of deformation bands in the higher strained regions of even lightly deformed alloy. The direct precipitation of equilibrium precipitates in deformation bands is already observed immediately after cold work analogously to the -allotriomorph formation at grain boundaries.     

Solar Radiation Affects Modern Tree-Ring δ13C: Observations at a Cool-Temperate Forest in Japan

Abstract

Tree-ring δ¹³C of shoots in two deciduous tree species (Acer rufinerve and Clerodendrum trichotomum) at the cool-temperate forest in Japan showed similar trends with time for four years. The variation of tree-ring δ¹³C positively correlated with the total solar radiation during the growing season, although it did not always correlate with other climatic parameters. Tree-ring δ¹³C of a tree-core from 1982 to 1993 in A. rufinerve also correlated strongly with the total solar radiation. We conclude that solar radiation most probably affected the tree-ring δ¹³C in this moist cool temperate forest, because increasing solar radiation can cause Ci (intercellular CO₂ partial pressure) to decrease, consequently increasing δ¹³C.     

Decomposition of an Fe-Cr 38 wt.% chromium stainless steel at 475 °C

The physical changes occurring at 475 °C in an Nb and Al stabilized stainless steel containing 38 wt.% Cr have been studied by Mössbauer spectroscopy. The specimen started to decompose when held at 475 °C. Decomposition still continues after 500 hours into a paramagnetic Cr-rich -phase and a nearly pure Fe -phase. The magnetic field distribution of the initial sample indicates that considerable decomposition has already taken place into an -phase with an estimated 15 at.% iron, and an iron-rich -phase with an estimated 18 at.% Cr.     

Generation of far-infrared radiation by hot holes in germanium and silicon inE ⊥H fields

The experimental results obtained by the investigation of stimulated FIR emission from dopedp-type germanium andp-type silicon by hot holes in crossedE andH fields at = 10 and 80 K are reported. The analysis of the emission intensity fromp-type germanium as a function ofE andH fields permits us to draw a conclusion about the important role of quantization of the energy spectrum of light holes and the contribution of light hole transitions with n = 2 to the amplification of FIR radiation. A new region of generation is demonstrated inp-type germanium under uniaxial stress. The first experimental results on stimulated FIR emission fromp-type silicon are reported.     

The room-temperature decomposition of metastable phases precipitated in the Al-Zn alloys at 200 °C

The room-temperature decomposition of metastable phases in the Al-Zn alloys (from 25 to 50 wt. % Zn) was studied by the transmission electron microscopy and X-ray diffraction. Metastable phases, i.e. G.-P. zones, _R-and -phases, were grown at 200 °C and their decomposition into equilibrium -phase at 20 °C was investigated. Ageing times comprised 1 to 999 days.Both the decomposition mechanism and the rate of decomposition of coherent phases were found to be dependent on the particle sizes and their density reached at 200 °C. The local vacancy supersaturation around the -nucleus in a dense system of G.-P. zones leads to an enhanced growth rate of such nucleus and thus to the formation of one large -precipitate at the expense of several neighbouring G.-P. zones. The elastic stress field around this -particle promotes the further nucleation and growth of -precipitates and leads to their gradual spread throughout the matrix. The decomposition of intermediately sized _Rprecipitates results in the development of -precipitates of comparable sizes nucleated on the array of misfit dislocations at the periphery of _R-precipitates. The cooperative effect between neighbouring particles does not influence the decomposition of large _R-precipitated which split then into several smaller -particles. The rate of G.-P. zones or _R to -decomposition increases with the increasing sizes of transition precipitates and with the zinc content of the alloy. The kinetics of to -decomposition was found to be independent both on the annealing time at 200 °C and on the investigated alloy composition. This can be attributed to the constant density of misfit dislocations as nucleation sites for -precipitates along the -matrix interface and to the large mutual separation of -precipitates in all these alloys.In conclusion we would like to express our thanks to Doc. Dr. V.Syneek, CSc. for his valuable discussions and to Ing. V.íma for the preparation of Al-Zn alloys. Our thanks are also due to Mr. Z.iký for his help in the X-ray diffraction measurement and to P.Vyhlídka for the careful chemical analyses of the investigated alloys.     

Comparative study of electrical characteristics for n-type 4H–SiC planar and trench MOS capacitors annealed in ambient NO

The interface properties and electrical characteristics of the n-type 4H-SiC planar and trench metal–oxide–semiconductor(MOS) capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250℃ in NO ambient for above 1 h due to the increasing interface shallow and fast states.These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the(1120) and(1100) faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the(0001) face under the same NO annealing condition. In addition, it is found that Fowler–Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device.However, Poole–Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO_2/Si C interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO_2/Si C interfaces.     

Beam steering characteristics in high-power quantum-cascade lasers emitting at∼4.6µm

A beam steering effect of high-power quantum cascade(QC) lasers emitting at 4.6 μm was investigated. The continuous wave(CW) output power of an uncoated, 6-mm-long, 7.5-μm-wide buried-heterostructure QC laser at 25℃ was as high as 854.2 m W. The maximum beam steering angle was offset by ±14.2° from the facet normal(0°) in pulsed mode. The phenomenon was judged explicitly by combining the diffraction limit theory and Fourier transform of the spectra. It was also verified by finite element method software simulation and the calculation of two-dimensional(2 D)effective-index model. The observed steering is consistent with a theory for coherence between the two lowest order lateral modes. Therefore, we have established an intrinsic linkage between the spectral instabilities and the beam steering by using the Fourier transform of the spectra, and further presented an extremely valid method to judge the beam steering. The content of this method includes both three equidistant peak positions in the Fourier transform of the spectra and the beam quality located between once the diffraction limit(DL) and twice the DL.     

Single-spin asymmetry for charged hadrons produced in proton-nucleus collisions at 40 GeV for c.m. production angles in the range 40°–79°

The transverse single-spin asymmetry for charged hadrons (π ^±, K ^±, p, $\bar p$ ) produced in proton-nucleus collisions was measured for c.m. production angles in the range 40°–79°. The measurements were performed with the FODS-2 setup by using a 40-GeV polarized proton beam originating from the accelerator of the Institute for High Energy Physics (Protvino) and hitting carbon and copper nuclear targets. The data in question were obtained in the polarized-proton-fragmentation region (0.0 < x _F < 0.7, 0.6 < p T < 2.5 GeV/c). In agreement with data obtained at other energies, the single-spin asymmetry for π ^± mesons is significant at high x _F. For the first time, a sizable analyzing power, which changes sign at x _F = 0.43, is observed for protons. The dependence of the analyzing power on the target-nucleus mass is insignificant.     

Phase relationships in the Gd–Co–Al ternary system at 500°C

The phase relationships in the Gd–Co–Al ternary system at 500°C have been investigated mainly by X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The existence of two ternary compounds GdCo_0.74Al_1.26 and Gd₂Co₂Al has been confirmed. Twenty-two single-phase regions (including solid solution regions of the binary compounds), 43 two-phase regions, and 22 three-phase regions were found to exist at this isothermal section. In this work, no new binary or ternary phase was found.     

Structure and superconducting properties of nonstoichiometric YBa2Cu3Oy annealed at 300°C in a dry argon atmosphere

Using the full-profile X-ray analysis of diffraction lines, the behavior of YBa₂Cu₃O _y nonstoichiometric ceramics upon annealing at 300°C in a dry inert atmosphere has been investigated. It has been established that, in the YBa₂Cu₃O_6.3 sample with the initial tetragonal structure, this treatment leads to nucleation of an orthophase with a low degree of rhombicity, which becomes prevailing after annealing for 56 h. In this case, superconductivity with an initial temperature of the transition of ∼50 K occurs in the sample. In the YBa₂Cu₃O_6.7 sample with the initial orthorhombic structure, the orthophase with a somewhat enhanced rhombicity arises during annealing and becomes prevailing after annealing for 56 h; in this case, T _c of the system grows from 57 to 63 K. Data of the magnetic measurements for both cases can be interpreted as the presence of two orthorhombic phases with different temperatures of transition to the superconducting state in the samples after annealing.     

Point defects related to 260 K thermostimulated luminescence in α-Al2O3

Abstract

Thermo- and photostimulated processes are studied in reduced hydrogen containing α-Al₂O₃ excited by UV light. It is found that UV excitation in F absorption band at 90 K results in a ionization of the F-centers and capture of released electrons at defects thus producing an anisotropy absorption band at 4.2 eV and the dominant thermoluminescence (TL) peak at 260 K. The 260 K TSL peak is accompanied by complete bleaching of the 4.2 eV absorption band and vice versa—by light stimulation in the region of the 4.2 eV band the 260 K TSL peak disappear and released electrons recombine with F⁺-centers. Both the effect of the preliminary high-temperature thermal treatment of samples on formation of 4.2 eV-centers and the observed dichroism characteristics allows to conclude that corresponding complex defect contains hydrogen and can involve vacancy pair.     

Relaxation and hysteresis internal friction in ultra-fine-grained copper at temperatures of up to 400°C

The temperature- and amplitude-dependent internal friction and elastic moduli of copper samples (99.95% Cu) subjected to deformation by equal channel angular pressing with a pass number of 1, 4, and 8 along the Bc route in the hertz range of loading frequencies at room temperature and temperatures of up to 400°C are investigated. The effect of deformation and subsequent recrystallization on the parameters of thermally activated internal friction peaks due to grain-boundary relaxation and the recrystallization of intensively deformed copper, and on amplitude-dependent internal friction due to dislocation hysteresis, is determined.