Thermodynamic studies of successive phase transitions in BaZnGeO4 and a new solid phase below 186.1 K

The successive phase transitions of BaZnGeO₄ have been studied on meltsolidified samples. A new solid phase (named phase VI) has been found below 186.1 K in samples of large particle size (diameter:D0.1 mm). The higher temperature crystalline phase V can be supercooled easily down to liquid helium temperature. On heating, however, it transforms into phase VI above 95 K in a slow exothermic process. Heat capacities have been measured by adiabatic calorimetry between 14 and 300 K. The enthalpy and entropy of the V–VI phase transition are 187.1 Jmol^–1 and 0.971 J K^–1 mol^–1, respectively. The corresponding data for the IV–V phase transition at 199.8 K are 229.3 J mol^–1 and 1.168 JK^–1 mol^–1. The phase VI does not appear in samples of smaller particle size (D0.1 mm).     

Nonlinear refraction and nonlinear absorption of As2S3 aqueous solution

We report for the first time to our knowledge on the preparation of colloidal solution of chalcogenide semiconductor As₂S₃ by laser ablation and the measurements of its nonlinear-optical characteristics using Z-scan method at the wavelength of Nd:YAG laser radiation ( = 1064 nm, = 25 ns). The nonlinear refractive index was measured to be –7.5 × 10^–18 m² W^–1. Nonlinear absorption coefficient of chalcogenide solution was measured to be 1 cm GW^–1.     

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.     

Far infrared surface electromagnetic waves propagation on A3B5 semiconductors

The real and imaginary parts of surface electromagnetic waves (SEW) refraction index n_ef in n-type InSb, GaAs and InP have been measured in FIR region (=85–142 cm^–1). The n_ef measurements allowed to determine plasma frequency _p and plasmon damping . The obtained nonlinear SEW propagation distance L dependence on Te impurity concentration in GaAs (N=10¹⁷–10¹⁹ cm^–3) was explained taking into account the conduction band nonparabolity as well as the presence of isostructural phase transition at N=2×10¹⁰ cm^–3.     

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.     

Effect of vibrational kinetics of He2 + ions on the afterglow of a discharge in helium

A decaying weakly ionized helium plasma [n_e=(0.2–1.1)·10¹¹ cm^–3, p=(40–70) mm Hg] was studied experimentally. It is shown that the experimental time dependences of the intensities of atomic lines and molecular bands in the afterglow phase can be explained if the vibrational kinetics of He₂ ⁺ ions is included in the analysis. Analysis of the measurements shows that for n_e 10¹¹ cm^–3 and N_a 10¹⁸ cm^–3 deexcitation of He₂ ⁺ ions occurs primarily as a result of inelastic collisions with helium atoms. Based on the experimental data, an approximate value was obtained for the rate constants of the vibrational relaxation of molecular helium ions 10^–16 cm³/sec. These results are used for making a qualitative analysis of the distribution of He₂ ⁺ ions over the vibrational states in the discharge phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 88–96, November, 1986.     

Reflection of brief light pulses by fog and smoke

An experimental study has been made of the characteristics of 8 nsec light pulses reflected from fog and smoke of various optical densities. At low densities, the amplitude, phase, and duration of the pulses reflected from the dispersive medium depend significantly on the attenuation coefficient () and other optical characteristics of the medium. For > 0.4 m^–1, these dependences are not found for the amplitude or phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 3, pp. 80–84, March, 1969.     

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.     

Negative muon precession in nuclei with spin

Polarized negative muons were stopped in various materials containing nuclei with nonzero spin. The TF-SR precession signal of theF ⁺ hyperfine state (frequencyv ₊ > 0) was pronounced for ^–Li and ^–Be, faint for ^–Cl (in NiCl₂), and undetectable for ^–F (in CaF₂ or NiF₂) and ^–P. TheF ^– signal (frequencyv _– < 0) was observed clearly for ^–Be, ^–Al and ^–Na, marginally for ^–K, ^–V and ^–Nb, and not at all for ^–Ga (at 4 kOe) or ^–Co (ferrromagnetic, zero field). In the heavier elements theF ^– signal is fed by transitions from theF ⁺ to theF ^– state at a rateR, as long asR(v ₊ –v _–). [See separate paper on ^–Al in these Proceedings, p. 879.]I am grateful to Alex Schenck and Bruce Patterson for the loan of equipment and samples, to Fred Gygax for helping set up the apparatus, to Jun Imazato for help with the experiment, and to Toshi Yamazaki and Tak Suzuki for valuable comments. I am also indebted to SIN for several weeks of free ^– beam time and to SIN, BOOM, and the University of Tokyo for free time on their VAX computers, which were kept busy for several months in the analysis.     

Microplasticity of silicon crystals

The low-frequency (1 Hz) internal friction (Q^–1) method was used to study the microplasticity of silicon whisker crystals grown by the method of chemical gas-transport reactions in a closed ampoule. A study was made of p-type crystals with the growth axis 111, 1–60 in diameter, working length 1–3 mm, both in the original state and after plastic ( 1%) deformtion by torsion. The temperature and amplitude dependences of Q^–1 were studied in 5·10^–5 torr vacuum. The amplitude of alternating vibrations was within the range 10^–5–10^–3 and the axial stresses were 10⁶–10⁷ N/m². The experimental results led to the conclusion that the microplasticity of undeformed silicon whiskers was due to heterogeneous nucleation of dislocations in stress concentration regions near surface defects, assisted by thermal fluctuations. In deformed whiskers the microplasticity was attributed to the nucleation and motion along dislocations of single and double thermal kinks in accordance with the Seeger model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 88–93, May, 1980.     

Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.     

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.     

Superplasticity in single-phase Zn-0·25 wt. % Cd alloy

A single-phase Zn-0·25 wt. % Cd alloy was prepared with the mean grain sized¯ 1m. Superplastic characteristics (A _max=320% andm _max>0·4) were established at room temperature at the strain rates.10^–4s^–1. Because of the absence of any second phase particles the fine-grained structure was not stable and an intense grain coarsening was observed both during the long-term ageing and during straining at room temperature. The increasing temperature accelerated this grain coarsening and suppressed the superplastic behaviour. Nevertheless, the stress relaxation tests suggested that the superplastic behaviour might be expected at higher temperatures in coarser grained specimens, too, but at substantially lower strain rates.     

Photoelectric properties of Pb1−x−y Sn x Ge y Te:In epitaxial films

Pb_1–x–y Sn _x Ge _y Te:In epitaxial films are examined in a wide temperature interval and at various background fluxes. These films have high sensitivity to infrared radiation in the spectral range <20m. The lifetime depends exponentially on temperature and varies from several seconds at T=10 K to 10^–2 s at T=20 K. The two-electron model of Jahn-Teller centers is proposed to explain the results. Multielement photoresistors based on these films are fabricated and D*=1.7×10¹³ cm Hz^1/2 W^–1 at T=25 K is achieved. Noise of the photoresistors is independent of background flux when it varies from 10¹² cm^–2 s^–1 to 10¹⁸ cm^–2 s^–1. As compared with Si:Ga and Ge:Hg photoresistors, the responsitivity is several orders larger at the operating temperature 25–30 K.     

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.     

Frequency Dependence of the Components of Dielectric Permeability and Characteristic Losses of Fluorite

The ₁(E), –Im^–1, and Re^–1 spectra of the fluorite crystal are calculated on the basis of the experimental (10–35 eV) and theoretical spectra ₂(E) (10–27 and 8–20 eV). They were employed to decompose the ₂(E) and –Im^–1 spectra into elementary components. The most intense transverse and longitudinal components of transitions and their parameters have been determined. The correlation between two types of components of transitions and their distinguishing features have been established.     

Electric and tensoelectric study of radiation defects in GaAs

The electric and tensoelectric properties are studied for GaAs crystals which have been irradiated by electrons (2.3 Mev) at 300°K with integrated fluxes of up to 2·10¹⁵ –1·10¹⁹ cm^–2. On the basis of the electrical neutrality equation, including seven energy levels (E1–E5, H0, H1) of the radiation defects, the specific resistivity and the strain sensitivity coefficient are quantitatively analyzed as a function of exposure. The pressure coefficients for the E1–E5 levels with respect to the _c ⁶ point are determined to be (0, 9.6, 11.0, 11.6, 11.6)·10^–6 eV/bar, respectively, at 300°K.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 81–87, October, 1986.     

Energy Spectra of the Local States in the Forbidden Gap of Monoclinic TlInS2xSe2(1?x) Crystals

Near IR properties of the mixed TlInS_2xSe_2(1–x) have been studied previously by the present authors. In this work the temperature and frequency dependence's of the conductivity and the current-voltage characteristics (in relatively weak electric field), have been investigated for monoclinic TlInS_2xSe_2(1–x) crystals, which are perspective materials for IR applications. From the temperature dependence's of conductivity in the direction perpendicular to c- axis the band gap E^g = 2.22 eV was determined for --TlInS₂ crystals. The impurity centres were determined located at 0.43, 0.73 eV and 0.35, 0.48, 1.12 eV for the direction of current i//c and i c, respectively. The concentration of the centres located at 0.48 and 1.12 eV were calculated to be N_A – N_D = 4.8 · 10⁹ cm^–3 and 1.9 · 10¹¹ cm^–3, respectively. It was found that in the solid solutions TlInS_2xSe_2(1–x) for 0.3 x 1, the conductivity follows the dependence (v) = ₀·^s in the temperature range between 100 to 600 K. In the temperature range of 80-400 K charge bounce plays an important role in the conductivity mechanism. Occurrence of the deep and low-levels impurity centres and a tail of the density of energy states in TlInS_2xSe_2(1–x) crystals make them perspective for practical applications: switching and memory effects, N-type current-voltage characteristics, induced conductivity etc.