Wetting transition on grain boundaries in Al contacting with a Sn-rich melt

The contact angle at the intersection of a grain boundary in Al bicrystals with the solid Al/liquid Al–Sn interphase boundary has been measured for two symmetric tilt <011> {001} grain boundaries with tilt angles of 32° and 38.5°. The temperature dependencies (T) present the evidence of the grain boundary wetting phase transition at T_w. The observed hysteresis is consistent with the assumption that the wetting transition is of first order. The determined discontinuity in the temperature derivative of the grain boundary energy is–5.6 J/m²K (T w1=617°C) for the boundary with a low energy (=38.5°) and –17 J/m²K (T w2=604°C) for the grain boundary with a high energy (=32°).     

Photoconductivity of highly excited A IV B VI thin films

We report the results of picosecond photoconductivity measurements in photosensitive electrolytically deposited PbS and vacuum evaporated PbTe polycrystalline films. We determine Auger recombination to be the prevailing carrier recombination mechanism in highly excited PbTe and PbS films and found Auger coefficients _A5×10^–28 cm⁶ s^–1 for PbTe and _A5.3×10^–29 cm⁶ s^–1 for PbS for carrier concentration changes N>10¹⁸ cm^–3. The results indicate that the low mobility values are controlled by intergrain carrier scattering. We have studied the thermal annealing influence on picosecond photoconductivity of the films.     

A μSR study of spin density wave condensation in Cr85Mo15

Zero field SR spectra from Cr₈₅Mo₁₅ are well described by the sum of a lightly damped (0.02s^–1<₁<0.2s^–1) and a heavily damped (2s^–1<₂<15s^–1) exponential. The temperature dependence of these components is discussed in relation to the condensation of the incommensurate spin density wave and the onset of the antiferromagnetic state in this Cr-like alloy below T_N=120K. Evidence is presented for the nucleation of the spin density wave at temperatures greater than 1.5T_N.     

Pulsed 532 nm laser wirestripping: Removal of dye-doped polyurethane insulation

Removal of rhodamine 6G doped polyurethane insulation coated onto 50 m diameter wire is shown to proceed efficiently and cleanly by irradiation with 532 nm Q-switched pulses from a Nd:YAG laser. The stripping action produced by this method is similar in quality to excimer laser wirestripping. Several experimental parameters were explored including fluence, pulse duration, dye concentration, and the number of incident pulses. Acceptable stripping conditions were obtained for a 3–5 s exposure at 10 Hz, using a dye concentration of 10% by weight, and 12 n pulses at 650 mJ/cm². Nearly 0.5 m/pulse is removed at this fluence, which exceeds the threshold fluence of 600 mJ/cm² by only 50 mJ/cm². The measured 532 nm absorption coefficient of the 10% dye-doped polyurethane was 4×10⁴ cm^–1. Lower fluences and/or dye concentrations produced inadequate stripping, while shorter duration pulses caused unacceptable melting of the thin gold layer which covered the copper core of the wire. Pulse-by-pulse photographs of the stripping action clearly show melting of the dye/polymer insulation, and thermal rollback of the insulation near the stripped end. Regardless, excellent edge definition is obtained by this method.     

The form factors of the decays π− → e−¯veγ and K− → e−¯veγ

In the special type of the quark model we obtain the ratio=h _A/h_V of the axial (h_A) and vector (h_V) form factors for the decays ^– e^– ¯v_e and K^– e^–¯v_e different from unity. The low-energy theorem, relating the electric polarizability of the charged pion with the ratio, is analyzed. It is shown that < 1 corresponds to , calculated by accounting the contribution of the scalar meson(700) into the amplitude of the Compton effect on the pion. In the absence of the(700) contribution we have=1.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.     

Gas formation in liquid in initial stages of a pulsed discharge

Gas formation in electrolytes with=10^–2–10^–4–1cm^–1, distilled water = 10^–5-1.5 ·10^{–6 –1}cm^–1, and chemically pure n-hexane in the initial stages of formation of discharge with rectangular voltage pulses of 0.67 and 1.85 sec duration is investigated. The experimental results are compared with the results of approximate calculations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 42–47, November, 1972.The authors thank V. V. Ryumin for taking part in the discussion of the results and V. V. Lopatin for participation in the experiments with electron-optical light amplifier.     

On the mechanism of the induced anisotropy of magnesium ferrites in the range of higher temperatures

A simple mechanism explaining not only the magnitude but also the type of induced anisotropy on the magnesium ferrite Mg_0·78 Fe_2·22 O_4·026 in the temperature range from 400 to 500°K has been designed. The experimentally estimated values of the microscopic bond energyl _p 7×10^–16 erg of the configuration contributing to theF-type anisotropy and the activation energy _exp = 1·1 eV are in good correspondence with the valuesl _d1·6×10^–16erg and _cal = 1·1₅ eV which have been calculated theoretically.Dedicated to Professor Dr. Jaromír Bro on his sixtieth birthday.The author would like to express his thanks to Dr. S. Krupika for valuable discussions and his interest in this paper.     

Electrical properties of GaAs layers irradiated by H4 ions

The quantities(D) and(T) are studied in n- and p-GaAs, irradiated at T = 300°K by H⁺ ions (5 MeV). It is shown that the resistance of lightly doped GaAs specimens increases from original values of ₀ to 10⁹ ·cm upon irradiation by H⁺ ions (5 MeV) to integral fluxes up to D^* – 10¹⁵ H⁺/cm². For D > D^* the layer resistance decreases from 10⁹ ·cm to 1 ·cm at 300°K. It was found that all the GaAs specimens intensely irradiated by H⁺ ions had p-type conductivity near 300°K. Isochronic annealing of radiation defects was studied in the temperature interval 20–700°C.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 39–43, January, 1982.     

The inelastic reactions πp→λ(⌆) K with allowance for the contribution of branch cuts

The method of complex angular moments is used to analyze the experimental data on the inelastic reactions p ()K, taking into account branch cuts in the j-plane in the eikonal approximation. An optical model for the backward scattering is considered. Agreement with experiment is obtained in the region of small angles for the reactions (⁰)K⁰. In the case of ^–P K⁰(^–K⁺) processes, agreement is obtained with the experimental results for large (180) scattering angles.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 26–30, August, 1972.     

Temperature dependence of anisotropy in monocrystalline lithium ferrite films

A study of crystallographic and uniaxial anisotropy in monocrystalline Li-ferrite films in the temperature range 4.2–550°K is presented. The experimental results K₁(T) agree well with calculations based on the one ion model with crystalline field coefficients of a_A=–2.77 ·10^–2 cm^–1, a_B=3.34 · 10^–2 cm^–1. An experimental function K_u(T) is obtained which does not contradict the assumption that anisotropic stresses are responsible for the development of uniaxial anisotropy in Li-ferrite films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 113–116, August, 1973.     

Diffusion of Al in ion-implanted Pd and Pt

The diffusion coefficients of aluminium have been measured in polycrystalline fcc Pd and Pt. The Al-implanted palladium and platinum samples were annealed at 400°–800 °C and 450°–900 °C, respectively. The aluminium profiles were probed using the nuclear resonance broadening (NRB) technique. Values of (1.41±0.09) and (1.38±0.09) eV for the activation energy and (1.5 _–1.0 ⁺⁵ )×10^–6 and (4 _–3 ⁺¹⁰ )×10^–7cm²/s for the frequency factor were obtained for Al in Pd and Pt, respectively. These anomalous results, compared to the normal impurity diffusion, were checked using also Al-evaporated samples.     

Deep bandtail states picosecond intensity-dependent carrier dynamics of GaN epilayer under high excitation

Picosecond carrier dynamics of deep bandtail states (3.1 eV) in an unintentionally n-doped GaN epilayer at room temperature under high excitation densities (i.e., N ₀ = 1.0× 10¹⁹– 1.1× 10²⁰ cm^–3) have been investigated with nondegenerate femtosecond pump–probe (267/400 nm) reflectance ( R/R ₀). All R/R ₀ traces possess a 2 ps buildup time that represents an overall time for the initial non-thermal carrier population to relax towards the continuum extremes and then into the probed tail states. We observe a saturation of R/R ₀ initial (first 10 ps) recovery rate _i at a density of 5– 6×10¹⁹ cm^–3 close to the Mott transition threshold obtained from time-integrated PL measurements. Such a saturation phenomenon has been identified as the trap-bottleneck due to the bandtail states and deep traps. As N ₀ is further increased, _i accelerates due to the onset of Auger recombination as the trap-bottleneck becomes effective. The best fit by the Auger model for N ₀ in the range of the mid-10¹⁹–10²⁰ cm^–3 yields an Auger coefficient of C _a 5.0× 10^–30 cm⁶ s^–1.     

Temperature dependence of the effective work function for the BaO - W system

The temperature dependence of the work function has been examined for the BaO-W system for degrees of coating less than 1 and about 1 in the range 700–1400 °K; it is found that a monomolecular film gives a negative sign of this coefficient in this temperature range ( /T 10^–4 –10^–3 eV/deg). At 1000–1200 °K, the temperature coefficient is almost zero, while at 1200–1400 °K there is a positive value. If the covering is less than monomolecular, the sign is positive throughout the entire temperature range (/T 10^–4 eV/deg).Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 9, pp. 65–70, September, 1971.We are indebted to N. I. Éngovatova for direct assistance with the measurements, and to V. Rumyantsev for advice.     

IR Reflection of Thin Bi4Ge3O12 Films

The spectra of IR reflection of the systems thin Bi₄Ge₃O₁₂ film–substrate made of molten -SiO₂ quartz in the region 10–1600 cm^–1 at 295 K are investigatedterpretation of fundamental vibrations in the region 10–800 cm^–1 and two phonon processes in the region 800–1600 cm^–1 are considered.     

Defects in pulsed laser and thermal processed ion implanted silicon

The evolution of the nature and concentration of the defects produced by 100 or 300 keV As ions at fluences 1 to 4×10^–12 cm^–2 inn-type, Fz Silicon doped with 10¹⁵ to 10¹⁶ cm^–3 has been studied as function of thermal treatments (in the range 500°–900 °C) and of the energy density (in the range 0.3–0.6 J cm^–2) of a light pulse from a ruby laser (15 ns, 0.69 m). Deep-level transient spectroscopy (DLTS) combined with capacitance — voltage (C-V) measurements were used to get the characteristics (energy level, crosssection for the capture of majority carriers) of the defects and theirs profiles. The difficulties encountered in the analysis of the results, due to the large compensation of free carriers in the implanted region and to the abrupt defect and free carrier profiles, are discussed in detail and the corrections to apply on the C-V characteristics and the DLTS spectra are described. The defects resulting from the two types of treatments are found to be essentially the same. Only, for laser energies higher than 0.5 J cm^–2, the laser treatment appears to introduced new defects (atE0.32 eV) which should result from a quenching process. The fact that a laser energy smaller than the threshold energy for melting and recrystallization is able to anneal, at least partially, the defects produced by the implantation, demonstrates that the annealing process induced by the laser pulse is not a purely thermal process but is enhanced by a mechanism involving ionization.     

Behaviour of implanted arsenic in silicon single crystals subjected to transient heating with incoherent light

The behaviour of ion-implanted arsenic in 100-oriented silicon single crystals exposed to continuous incoherent light from a xenon arc lamp has been analyzed with sheet resistivity measurements, Rutherford backscattering spectrometry, and ion channeling including angular scans. Redistribution, substitutionality, and electrical activity of arsenic were followed as functions of exposure time (6–20s) and induced temperature (1000°–1100°C). Redistribution was observed for implanted concentrations exceeding 4×10²⁰ at.%/cm³. High substitutional fractions, between 95% and 99%, and low sheet resistivities were found for all annealed samples. Formation mechanism of arsenic substitutional solid solutions during transient heating of implanted layers is discussed.     

Orbiting test masses for an equivalence principle space experiment

Deviations from the equivalence principle can be found by observations of the orbital periods of masses in a two body system, in a drag free satellite in geosynchronous orbit. At this altitude the Earth gravitational field tides allow close stable circular motion, within a 30 cm lobe, of a small test mass around the centre of the primary mass, of 75 kg. The repulsive fifth force ought to slow the orbital Newtonian period. A precise clock and laser interferometry provide the determination of in the range between 1 and 10²cm and of if larger than 10^–4.2 or 10^–5, for an uncertainty of the value of the constant of gravitation equal to 10^–5 or 10^–6, respectively ( and are the coupling coefficient to gravity and range of action of the fifth force). In the latter case, for around 10 cm, the fifth force may be detected for larger than 10^–5.5. This experiment may verify the principle of equivalence at short range improving the actual limits from one to two and a half orders of magnitude. The range of action,, up to several meters can be observed with this local experimental concept, but only for large values of, which have been excluded recently by ground experiments.     

Rates of change in high temperature electrical resistivity and oxygen diffusion coefficient in Ba2YCu3Ox

The change in electrical resistance with time for bulk, thick-film, and thin-film Ba₂YCu₃O_x at atmospheric pressure is described as a function of the oxygen partial pressure (100 to 0.001%) and temperature (320°–750°C). The potential usefulness of these materials as oxygen sensors is demonstrated. The rate of equilibration is faster during oxygen uptake than during its loss. Time constants to reach equilibration (1/e remaining), qualitatively scale with sample dimensions. For a 1m film at 600° C, <1 s for the range of P_O2 (O2 being a shorthand for O₂) from 100% to 0.001%. The rate increases markedly with increasing P_O2. The actual resistance decreases with P_O2 at a rate of log/log P_O2 = 0.4 at 700° C showing adequate sensitivity for sensor purposes. Times for the transient resistance change in the sample where used to estimate the oxygen diffusion coefficient in the ceramic. The diffusivities obtained are 4·10^–11–1·10^–12 cm²/s in the 435°–320° C range, with an activation energy of 27 kcal/mole.     

Electron states of manganese luminescence centres in A1N

The energy spectrum of manganese luminescence centres in AlN was studied by means of excitation and emission spectra. Two regions of excitation were found: in the first region (from 40 000 to 31 000 cm^–1) excitation occurs as a result of transfer of energy from other impurity centres to the manganese centres; in the second region (from 26 000 to 17 000 cm^–1) the manganese centres are excited directly. In the excitation band with a peak at about 19 200 cm^–1 a phonon structure was observed having a temperature dependence analogous to that of the phonon structure of the emission band. The phonon energy at excitation differs from that at emission (_exc260 cm^–1, _em160 cm^–1). A scheme of electron-phonon levels of manganese centres in AlN is presented, and problems relating to the structure of these centres are discussed.Na Slovance 2, Praha 8, Czechoslovakia.The authors would like to thank Dr. L. Kratina and Dr. F. Kubec (Institute of Radio Engineering and Electronics, Czechoslovak Academy of Sciences), who kindly performed the EPR measurements, and to Professor M. Trlifaj and Dr. J. Pastrák for valuable discussions.     

Micro-Raman spectroscopy in polycrystalline CuInSe2 formation

The crystalline formation of CuInSe₂ thin films has been investigated using micro-Raman spectroscopy and AES composition analysis. It is confirmed that the Raman peaks are stongly dependent on the surface morphology and the Cu:In:Se ratio. In the films annealed at 315°C, crystalline grains larger than 2 m show Raman peaks at 174 cm^–1 and 258 cm^–1. The In content is very low and the Cu:Se ratio is about 1:1 in these grains. The low In concentration is thought to be due to the formation of In₂O₃ on the surface. On the other hand, random structures of 1–2 m grains found in films annealed at temperatures below 305°C show peaks at 174 cm^–1 and 186 cm^–1 instead of 258 cm^–1 and have a Cu:In:Se ratio of 1:1:3–4. Thus the 186 cm^–1 peak is thought to be related to a Cu, In-deficient phase when compared to stoichiometric CuInSe₂. The optimum annealing condition was found by analyzing the Raman spectra and composition of different crystalline CuInSe₂ grains. Films annealed under this condition exhibited a clear Raman peak at 174 cm^–1 and consisted of clusters of crystals less than 1 m in size.