Electrophysical properties of ionic alloys of GaAs obtained by implanting Zn+ (150 keV) with subsequent annealing at 500–1000°C

A study is made of the electrophysical properties (N_s, _eff) of ionic alloys of GaAs obtained by implanting 150-keV Zn ions at 20 and 300°C. The ion dose D=5·10¹³–10¹⁶ ions/cm²; the alloys were subsequently annealed for 10 min in an H₂ atmosphere with temperatures in the range 500–1000°C. The optimal parameters of the ionic alloys are obtained for T_i=300°C and T_a=700°C. Thermal acceptance of the GaAs under a SiO₂ film (d0.2–0.3 m) is observed for T_a>700°C. The limiting concentration of thermal acceptors N_s(TA)3·10¹³ cm^–2) for T=1000°C and t=10 min.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 22–26, March, 1979.     

The temperature dependence of the refractive index of an aqueous suspension of polystyrene microspheres

We report an experimental measurement, based on an interferometric technique, for the determination of the temperature dependence of the refractive index n _L of a liquid suspension of dielectric spheres in the thermal range 20–52° C. In this range we have measured values of n _L /T of order of magnitude 10^–4° C^–1. The observed values are compared with those obtained for water.     

Fast proton conductivity of polycrystalline titanoniobates

The proton conductivity of three layer-type compounds was studied: H₃OTi₂NbO₇. H₂O, HTiNbO₅ and HTiTaO₅. Measurements were made between 20 °C and 90°C on pellets pressed from crystalline powders and soaked with pure water. The hydrated compound had the highest conductivity, (20°C)-6.3–6.9·10^–4 (cm)^–1. Acid ions from the exchange process were quite firmly retained in its layer structure and contributed significantly to the measured conductivity. Consistent results were obtained after prolonged washing with water.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

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.     

Frequency dependences of FMR in films with angular dispersion of the magnetic anisotropy

On the basis of a statistical model of noninteracting blocks, it is clarified that films with high angular dispersion (₀ 15–35°) are characterized by an asymmetric resonance curve whose amplitude _r and width H depend, in contrast to uniaxial films, on the angle of film rotation in its plane in large field domains and whose frequency dependences are related substantially to the angular dispersion; the presence of domains in the angular dependence of the resonance field where H_r is constant; an effective magnetic anisotropy field dependent on the frequency and with the limit valueH _K ^eff =H _K exp(–2a ₀ ² . The theoretical deductions are conformed by experiment.Translated from Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 75–81, July, 1987.     

Time and temperature dependent breakdown characteristics of ZnS:Mn films obtained by rf-magnetron sputtering

Breakdown delay times (t_del) for films of managanese-doped zinc sulfide (ZnS:Mn) were measured in the range 10^–6–10^–1 s. The maximum value was t_del=10^–3–10^–2 s. The electrical strength (E_br) was found to increase as the voltage pulse duration was reduced, the more so the thinner the ZnS:Mn film. The temperature dependence of E_br exhibited a weak reduction in E_br as the temperature was raised to roughly 80°C and a sharp reduction in E_br for T>130°C. A maximum in E_br was observed at T130°C which is presumably explained by a structural modification of the ZnS:Mn film. The experimental results obtained are explained in terms of a combined electronic and thermal breakdown mechanism.State Academy of Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–6, April, 1994.     

Supertransferred hyperfine interaction in magnetic insulators (II)

The important mechanisms of supertransferred hyperfine (STHF) interactions in N–O–M chains are briefly discussed: (i) spin polarization ofns states in the N-ion due to the s-d exchange interaction,H _STHF ^sd ; (ii) contributions of spin-polarized states of the intervening O-ion,H _STHF ^II ; (iii) transfer of d-electrons of the M-ion to emptyns states in the N-ion,H _STHF ^III . The dependence ofH _STHF upon the N–O–M bond configuration, electronic structure, and orbital state of the M-ion is presented in a convenient form. The STHF interactions in the chains Sn⁴⁺–O^2––Fe³⁺, Cr³⁺ in compounds with slightly distorted Perovskite structure are considered. The STHF field in the chain Sn⁴⁺–O^2––Cr³⁺ is shown to change the sign within the range of angles near 170°. This conclusion is in line with published data on the isoelectronic chain Sn⁴⁺–O²–Mn⁴⁺ in the compounds Ca_1–x Sr _x MnO₃. The results obtained for the N–O–Fe³⁺ chain are rationalized by the predicted angular dependence ofH _STHF=+ cos + cos². Features of the STHF interactions in N–O–M chains with an M-ion in an orbital degenerate state are examplified by a preliminary analysis of N–O^2––V³⁺ chains in orthovanadites.     

39K NMR study of the low temperature phase transitions in KLiSO4

The³⁹K NMR spectra, spin-spin (T ₂) and spin-lattice (T ₁) relaxation times of KLiSO₄ have been measured in the temperature range from 300 K to 90 K. The temperature dependence of the³⁹K (I=3/2) NMR spectra demonstrates the occurrence of a first order phase transition atT _c1=217 K which occurs without a change in the K⁺ site symmetry and another first order transition atT _c2=190 K which is connected with a lowering of the K⁺ site symmetry and the formation of three kinds of ferroelastic domains. From the angular dependence of the second order quadrupole shifts of the³⁹K NMR 1/2–1/2 transitions the electric-field gradient (EFG) tensors at the potassium sites were determined at 290 K, 204 K and 180 K. The symmetry of the ferroelastic phase is monoclinic and not orthorhombic as the K⁺ EFG tensors are tilted away from thec-axis belowT _c2. TheT ₁ data further show the freezing in of the slow reorientational motion 10^–8 s with decreasing temperature from 300 to 90 K.On leave from: J. Stefan Institute, E. Kardelj University of Ljubljana, Ljubljana, Yugoslavia     

R branch tuning characteristics of the13CH3F Raman FIR laser

Summary We described a¹³CH₃F Raman laser pumped by a grating tuned 20 atmospheres CO₂ laser. The emission characteristics of the¹³CH₃F laser extends from 14 cm^–1–35 cm^–1 and from 49 cm^–1–72 cm^–1; about 65% of these frequency ranges can be covered with tunable radiation. The characteristics shows a strong dependence on the rotaional quantum numbers of the states involved in the Raman laser transitions and, within each tuning interval, on the frequency offset with respect to the frequencies of resonant transitions. We obtained, at 51 cm^–1, a maximum FIR laser pulse energy of about 800 J (at a pump energy of 200 mJ), corresponding to a photon conversion of about 8%. In some cases we have observed simultaneous emission at a Raman and a cascade frequency. In addition, FIR emission power dependence on¹³CH₃F gas pressure and pump pulse power were investigated for different J quantum numbers.     

ArF laser CVD of hydrogenated amorphous silicon: The role of buffer gases

ArF laser-induced CVD has been employed to generate hydrogenated amorphous silicon (a-Si:H) from Si₂H₆ gas dilute with He, Ar, or H₂. The formation of amorphous films or powder is found to depend critically on the kind of buffer gas, the stationary total and partial gas pressures, and the substrate temperature. These dependences have been investigated in the 1–5 Torr pressure and 100–400 °C temperature ranges. They are semiquantitatively discussed in terms of ArF laser photolysis of disilane, gas heating by heat flow from the substrate and laser irradiation, diffusion, and gas phase polymerization. Furthermore, photo ionization has been observed but found irrelevant for the a-Si:H layer properties. The photo and dark conductivities ( _ph, _d) of the semiconductor layers are determined by the substrate temperature. The _ph values range between 10^–7 and 10^{–4 –1} cm^–1 and the _d values between 10^–11 and 10^{–8 –1} cm^–1. The maximum ratio _ph/ _d amounts to 4×10⁴. The layers are further characterized by their optical band gap and activation energy. The layer properties are compared to literature values of amorphous films prepared by various photo, HOMO, and plasma CVD methods.     

Scattering of conduction electrons by vacancies in aluminium

The low-field Hall coefficientR _H ⁰ and transverse magnetoresistance /₀ were measured in high-purity polycrystalline aluminium samples which were quenched from temperatures between 350 and 500°C. The measurements were made at 4.2 K in magnetic fields up to 40 kG. It was found that the low-field Hall coefficientR _H ⁰ of aluminium containing vacancies lies between –1.0 and –2.5×10^–5 cm³ A^–1s^–1, which is in good agreement with the calculation of Pfändner, Böning and Brening.     

Stress-relaxation determination of the parameters m and D in alkali halide crystals

Stress relaxation of the alkali halide crystals LiF, NaCl, and KCl has been studied from –196 °C to +150 °C. These relaxation curves are analyzed in terms of their relationship with the dislocation velocity v under the influence of an applied stress. Dislocation blocking is shown to play a decisive role in stress relaxation between –20 and +150 °C, and there is a satisfactory correspondence between the theoretical relaxation curves based on the v = v₀(/₀)^m dependence at the lower temperatures.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 5, pp. 76–84, May, 1969.The authors thank E. I. Raikhel's, L. M. Soifer, and I. V. Smushkov for graciously furnishing the crystals and for discussion of these results.     

Infrared absorption of silane,ammonia, acetylene and diborane in the range of the CO2 laser emission lines: Measurements and modelling

Absorption spectra of the gases SiH₄, NH₃, C₂H₂ and of SiH₄/Ar and SiH₄/B₂H₆ mixtures have been measured in the spectral range of the CO₂ laser from 9.2 to 10.8 µm. In agreement with literature, silane shows the highest absorption (absorption coefficient = 3.3 × 10^–2 Pa^–1 m^–1). The deviation of the measured absorption behaviour of silane from literature, as far as the pressure dependence is concerned, can be explained by the enhanced spectral energy density in our experiment. This is confirmed by a rate-equation model involving the basic mechanisms of V-V and V-T energy transfer between vibrationally excited silane molecules. In contrast to silane, the absorption coefficient of NH₃ at the 10P(20) laser line is 4.5 × 10^–4 Pa^–1 m^–1 atp = 20 kPa and has its maximum of 4.5 × 10^–3 Pa^–1 m^–1 at the 10R(6) laser line. For C₂H₂ and B₂H₆, is even less ( 2.1 Ò 10^–5 Pa^–1 m^–1 for C₂H₂).     

Phase Transformations in the Fe-Co System

X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and magnetic studies of Fe₅₀Co₅₀, Fe₆₅Co₃₅ and Fe₃₅Co₆₅ alloys have been performed after different isothermal heat treatments of the alloys at 500–1200°C. It is shown that in the A2 region of the diagram the separation into fcc Co and bcc Fe occurs in a thin surface layer, and partially in the bulk (5–10%). The conclusion is made that B2 ordering of the alloy quenched starts with the precipitation of globular particles consisting of the species, which are in excess relative to the stoichiometric composition of the B2 phase. Prior to the B2 ordering onset, the separation-ordering phase transition occurs; this is accompanied by changes in the electronic structure of the valence band of the Fe₅₀Co₅₀ alloy. The so-called 550°C anomaly is the result of the phase transformation, which proceeds according to a martensitic mechanism and leads to a small increase of the lattice parameter. The conclusion is made that the dependence of the magnetic properties of Fe-Co alloys on B2 ordering is not clearly expressed.     

Temperature and pressure dependence of magnetic and electric hyperfine interactions in metallic Samarium

The magnetic and electric hyperfine interaction at¹¹¹Cd impurities in Samarium has been investigated by TDPAC measurements. The quadrupole frequency is _Q=20.0(2) MHz at 290 K and has a linear temperature dependence with the same slope (dln_Q/dT)_290K=–7.3(2) 10^–4 K^–1 in the rhombohedral and the hcp phase. The pressure dependence up to 7 kbar is (dln _Q/dT)=+8.7(1.4) 10^–3 kbar^–1. The magnetic hyperfine field of¹¹¹Cd in Sm is H_hf=242(6) kG at 4.2 K. Its temperature dependence confirms the existence of 2 different magnetic phases in Sm. The crystal field parameters B ₂ ⁰ and B ₄ ⁰ have been estimated from a comparison of H_hf(T) with molecular field models. The TDPAC spectra in the magnetic phases suggest that the impurities preferentially occupy the hexagonal Sm sites.     

Scaling properties of fluctuations in stationary turbulence

Turbulent fluctuations are treated using a stationary distribution functionw _st for an order parameter field representing a fluid. Naive scale invariance ofw _st yields thek ^–5/3 spectral law in three dimensions andk ^–3 in two dimensions. The noise parameter of the stationary distribution is connected with energy flow or enstrophy conservation, respectively. In order to include fluctuations of the local energy dissipation a grand distribution function is introduced.     

C Chemical Shift and C–N Dipolar Coupling Tensors Determined by C Rotary Resonance Solid-State NMR

This work explores the utility of simple rotary resonance experiments for the determination of the magnitude and orientation of ¹³C chemical shift tensors relative to one or more ¹³C–¹⁴N internuclear axes from ¹³C magic-angle-spinning NMR experiments. The experiment relies on simultaneous recoupling of the anisotropic ¹³C chemical shift and ¹³C–¹⁴N dipole–dipole coupling interactions using 2D rotary resonance NMR with RF irradiation on the ¹³C spins only. The method is demonstrated by experiments and numerical simulations for the ¹³C^α spins in powder samples of -alanine and glycine with ¹³C in natural abundance. To investigate the potential of the experiment for determination of relative/absolute tensor orientations and backbone dihedral angles in peptides, the influence from long-range dipolar coupling to sequential ¹⁴N spins in a peptide chain (¹⁴N_i–¹³C^α_i–¹⁴N_i+1 and ¹⁴N_i+1–¹³C′_i–¹⁴N_i three-spin systems) as well as residual quadrupolar–dipolar coupling cross-terms is analyzed numerically.     

Spin-dependent photoabsorption at theL-edges of ferromagnetic Gd and Tb metal

The spin-dependent absorption of circularly polarized x-rays is studied at theL-edges of ferromagnetic Gd and Tb metal. At theL ₁-edge a spin-dependent part of the absorption coefficient of 10^–3–10^–2 is observed. Strong resonance absorption known as white line occurs at theL ₂- andL ₃-absorption onset. Correlated with it one finds large spin-dependent absorption effects with amplitudes of a few percent. The spin-dependent absorption spectra reflect the profiles of the spin densities of the states populated in the absorption process. Thep-states show spin densities correlated with the first two flat bands above the Fermi level. The spin density of thed-like states is concentrated in the energy range of the white line. In Gd a splitting of (0.5–0.6) eV of the unoccupied 5d spin up and spin down bands is indicated for both spin-orbit partners. In Tb a large dependence of the 5d spin density on the spin-orbit configuration is observed. The experimental results on the spin densities in Gd are compared with band structure calculations for the ferromagnetic ground-state. The theoretical and experimental spin density profiles agree well for thep-states but not for thed-states. The discrepancy concerning thed-states may be attributed to core-hole polarization effects in the absorption process.     

Growth kinetics of antiphase domains in the alloy Ni4Mo

Using the methods of transmission and diffraction electron microscopy, we analyze the laws governing the growth kinetics of antiphase domains in the alloy Ni₄Mo during its isothermal ordering at 840, 800, and 700°C. The size distributions of the antiphase domains as well as the mean size and central moments of the distributions are determined. It is shown that the growth of the antiphase domains obeys the equation Dⁿ-D ₀ ⁿ =Ae^–Q/kT. The value of the parameter n is 2.5 for 840 and 800°C, and 5 for 700°C. By considering the isochronous cross section of the kinetic curves, we calculate the activation energy for the growth of antiphase domains; it equals 65 kcal/mole.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 84–89, January, 1977.     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.