Thermoelectric properties of Ag2Se

To obtain information on the temperature and concentration dependence of thermoelectric quality factor Z and to clarify the nature of scattering in Ag₂Se a study was made of electrical conductivity , thermo-emf , and thermal conductivity in silver selenide over the temperature range T=80–450°K at concentration levels of 2–43·10²⁴ m^–3. It is shown that in Ag₂Se the Lorentz number L, determined experimentally from the electronic fraction of the thermal conductivity, is less than the Sommerfeld number L_o. Calculation of L/L_o(n) performed with a theory considering inelastic scattering of carriers, shows that the inelasticity is produced by electron interaction. Comparison of experimental data on the temperature dependence of lattice thermal conductivity with theory permits the conclusion that in Ag₂Se in range 80–300°K the basic role in phonon scattering is played by three-phonon Umklapp processes. It is shown that with increase in T and decrease in n the thermoelectric quality factor of silver selenide increases. The highest value of Z was achieved in a specimen with electron concentration n=2·10²⁴ m^–3 at T=320°K. The rapid decrease in Z upon phase transition is related to discontinuous decrease in and at this point.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–31, October, 1981.     

Distinctive features of creep in silicon whiskers

The phenomenon of creep in silicon whiskers has been studied in the temperature range 300–1100°K at stresses (0.1–5)·10⁸ N·m^–2. On the basis of the tests, analysis of the fine structure of the creep curves, and studies on the crystal structure, the conclusion is drawn that the creep observed in silicon whiskers is due to the heterogeneous nucleation of dislocations at stress concentration sites with the participation of thermal fluctuations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 31–35, October, 1981.     

Formation of palladium silicide by rapid thermal annealing

The formation of palladium silicide Pd₂Si by rapid thermal annealing of Pd layers on silicon has been studied as a function of annealing time (1–60s) in the temperature range 350–500 °C. It is shown that the results found for conventional furnace annealing (long duration, low temperature) can be extrapolated for rapid thermal annealing (shorter time, higher temperature) when taking into account the exact time dependence of the short temperature cycle. The growth rate is essentially diffusion limited and the activation energy is close to 1.1±0.1 eV. Silicide resistivity of about 30–40 cm was obtained for 200–400 nm thick Pd₂Si layers formed at 400 °C for a few seconds.     

Thermally Stimulated Electron–Hole and Ionic Processes in Zinc Oxide Crystals

The principal results of the investigation of thermally stimulated electron–hole and ionic processes in hydrothermal and gas-phase ZnO single crystals preexcited at low temperatures, based on simultaneous study of photo-EPR and thermoluminescence (TL), are presented. The nature of the traps determining the TL peaks at 17, 24, 40, 53, 90–110, 140–150, and 160–200 K is discussed. In particular, it has been established that the lithium paramagnetic centers (Li_Zn ⁺–O^I) play the role of hole traps in ZnO giving green and red TL in the temperature range 160–200 K and, in the case of association with small-sized donors, also TL in the temperature range 90–110 K. The other traps are electronic in character, and in the presence of acceptor lithium in the crystals, they form yellow-orange TL. Optical quenching of TL has been evaluated, and it has been found that there is a difference E 0.75 eV between the thermal and optical energies of ionization of lithium acceptors. Irreversible ionic processes associated with the healing of cationic vacancies at T 360–420 K have been revealed.     

Photokinetic etching of polyethylene terephthalate films by continuous wave ultraviolet laser radiation

Continuous wave laser radiation from an argonion laser in the wavelength range 275–330 nm can be used to etch polyethylene terephthalate (PET) films with as little thermal damage as from a pulsed, ultraviolet laser (248 nm or 308 nm) provided the beam is focussed to a spot of 10–100 kW/cm² of power density and is moved over the surface at speeds at which the transit time over its own diameter (which can be looked upon as a pulse width) is on the order of 10–200 s. In contrast to results which had been obtained previously on the photokinetic etching of polyimide and doped polymethyl methacrylate films under similar conditions, the sensitivity of PET to etching is >5-fold greater than either of these polymers and increases steadily with increasing pulse width. There is lateral thermal damage as the pulse widths increase to >200 s. The material that is removed is vaporized in part. More than 20% is probably ejected in a molten state and resolidifies at the edge of the cut. There is no acoustic report similar to that seen in ablative photodecomposition. The process appears to be largely thermal in nature.     

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.     

Experimental investigation of the lattice parameter and length change near the melting point of gallium in search for premelting effects

The lattice parameter of nearly perfect gallium crystals was measured by x-ray diffraction on (440), (308) and (046) planes between 10°C and 10^–4°C close to the melting point. The thermal expansion coefficients in the three main crystallographic directions are 1.33, 3.19 and 1.62 10^–5 1/°C without anomalies. The length change was measured between 10°C and about 5 mK below the melting point in (100), (010), and (001) direction. The thermal expansion coefficients in these directions are 1.12, 3.38, and 1.85 10^–5 1/°C without anomalies. The change of the vacancy concentration between 283 K and the melting point can be estimated to 4 10^–5, the vacancy formation energy to about 0.23 eV. Premelting effects could not be detected.     

Anomalous thermal quenching of luminescence in ZnS:Cu phosphor crystals

We studied the thermal quenching of luminescence (TQL) in the case of photoexcitation (PE, _e=313 and 365 nm) and cathodoexcitation (CE) with a high excitation density (10¹⁸ cm^–3· sec^–1) in ZnS:Cu single crystals with various degrees of copper supersaturation, EL-455 and K-83 copper-activated powders, and ZnSCu epitaxial thin films. Our study of TQL in the blue and green bands showed that two types of quenching anomalies are observed in the specimens used. An anomaly of the first type manifests itself in the fact that, with band-to-band excitation (_e = 313 nm and CE). the green band is quenched earlier than the blue band and small steps are observed on the quenching front. This anomaly is explained with the aid of a dislocation model of the blue center. An anomaly of the second type is observed in specimens not supersaturated with copper and consists of the quenching of luminescence beginning earlier at a high excitation (CE) density than at a low excitation (PE) density and proceeds in the same way in the blue and green bands. The thermal depths of the acceptors level are estimated from TQL for the three fundamental luminescence bands 440, 468, and 525 nm which are equal to 0.38 ±0.05, 0.7–0.8, and 0.9–1 eV, respectively.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 38–43, July, 1979.     

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.     

Dimensional evolution of silicon nanowires synthesized by Au–Si island-catalyzed chemical vapor deposition

This study explores the nucleation and morphological evolution of silicon nanowires (Si-NWs) on Si (0 0 1) and (1 1 1) substrates synthesized using nanoscale Au–Si island-catalyzed rapid thermal chemical vapor deposition. The Au–Si islands are formed by Au thin film (1.2–3.0 nm) deposition at room temperature followed by annealing at 700 °C, which are employed as a liquid-droplet catalysis during the growth of the Si-NWs. The Si-NWs are grown by exposing the substrates with Au–Si islands to a mixture of gasses SiH₄ and H₂. The growth temperatures and the pressures are 500–600 °C and 0.1–1.0 Torr, respectively. We found a critical thickness of the Au film for Si-NWs nucleation at a given growth condition. Also, we observed that the dimensional evolution of the NWs significantly depends on the growth pressure and temperature. The resulting NWs are 30–100 nm in diameter and 0.4–12.0 μm in length. For Si (0 0 1) substrates 80% of the NWs are aligned along the 1 1 1 direction which are 30° and 60° with respect to the substrate surface while for Si (1 1 1) most of the NWs are aligned vertically along the 1 1 1 direction. In particular, we observed that there appears to be two types of NWs; one with a straight and another with a tapered shape. The morphological and dimensional evolution of the Si-NWs is significantly related to atomic diffusion kinetics and energetics in the vapor–liquid–solid processes.     

Limiting Modes for the Threshold Characteristics of IR Photodetectors Based on Silicon–Platinum Silicide Barriers with a Highly-Doped Surface Layer

The effect of changes in the potential barrier height due to the formation of a highly-doped surface layer in a semiconductor of PtSi–p-Si-structures on the background radiation photocurrent – dark current density ratio and spectral detectivity of photodetectors for recording thermal radiation in the 3–5 m wavelength range is examined.     

Short-term frequency stabilization of diode-laser-pumped Nd:YAG lasers using double-pendulum suspended cavities

We describe the improvement of short-term frequency stability of diode-laser-pumped Nd:YAG lasers. To improve the vibrational isolation of reference cavities, the reference cavities were suspended by a double pendulum with magnetic damping. The frequency noise was reduced to lower than 1 Hz/Hz at Fourier frequencies higher than 5 Hz and the minimum noise of 7 × 10^–3 Hz/Hz was recorded. The minimum root Allan variance was about 10^–14 for the sampling time of 0.01 s. Heating of the reference cavity by absorbed laser power caused the thermal drift of cavity resonance frequencies. It resulted in the laser linewidth in the range of 30–50 Hz.     

Estimate of the radiative thermal conductivity of conducting media at high temperatures

The radiative diffusion method is used to obtain an equation to calculate the radiative thermal conductivity of a conducting medium from the values of its resistivity, temperature, and refractive index. It is shown that for semiconducting materials with high resistivity ( 10^–3 ·m) the radiative heat transfer compared to the other heat-transfer mechanisms is significant even at room temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 82–85, November, 1978.     

Calculation of the temperature dependence of the thermal emf in amorphous alloys CaxAl1−x and AuxNi1−x

The temperature dependence of the thermal emf of Ca_xAl_1–x and Au_xNi_1–x for four different concentrations of the components of the alloys is calculated on the basis of the concept of dynamic concentrated excitations in amorphous metal systems. It is shown that increasing x from 0.15 to 0.50 in Au_xNi_1–x raises the thermal emf, and a further increase in the Au concentration from 0.50 to 0.80 lowers S(T). For Ca_xAl_1–x the dependence S(T) is calculated in the interval of Ca concentrations from 0.55 to 0.75. In this concentration interval the thermal emf decreases as x is increased. It is shown that for both types of alloys the S(T) curve bends abruptly at a temperature near 10T₀ (where T₀ is the concentration-dependent characteristic temperature of amorphous alloys separating the ranges of strong and weak scattering of electrons by dynamic concentration excitations). The so-called S(T) knee shifts toward lower temperatures when the thermal emf increases with increasing x and toward higher temperatures when S(T) decreases with increasing x. The results agree with experimental data.Institute of Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 43–48, August, 1994.     

A possible effect caused by spin fluctuations in CuO2 planes in HTSC

In the present letter, we study the magnetic contribution to the thermal expansion of Cu–O layer in YBa₂Cu₃O_7– with the nearly antiferromagnetic Fermi liquid model. Our analysis suggest that this additional thermal expansion due to antiferromagnetic spin fluctuation is the origin of the Cu–O plane buckling.     

Tooth ablation using a CPA-free thin disk femtosecond laser system

Caries – the most frequent cause for dental surgery – still is mainly treated with conventional mechanical drills, although lasers have meanwhile been successfully applied to various clinical disciplines. Since ultrashort laser pulses with sufficient pulse energies have only been available at low repetition rates (< 1 kHz) in recent decades, solely continuous wave radiation or pulse durations longer than thermal diffusion processes were applied with the result of severe thermal damage and pain. In this report we present results on dental tissue ablation obtained with a novel thin disk Yb:KYW regenerative amplifier system that does not require chirped pulse amplification (CPA). We show that femtosecond laser pulses provide us with todays optimal tool to treat dental decay in an acceptable time, in an excellent quality, and with unsurpassed caries selectivity. The superior quality is a result of the non-thermal laser-tooth interaction. All our results are based on environmental scanning electron microscopy. PACS 42.62.–b; 06.60.Jn; 82.80.–d     

A possible structure of the Moon's surface layer

An analytical expression for the equivalent thermal conductivity of bodies of various structures is established. The solution of the converse problem—to determine the structure of a body from its equivalent thermal conductivity—is considered. Considerations concerning the possible structure of the Moon's surface layer are put forward, based on an analysis of radio-astronomical data of the parameter =(c)^–1/2 and some additional assumptions.Izvestiya VUZ. Radiofizika, Vol. 9, No. 5, pp. 849–857, 1966     

Peculiarities of the low-temperature conductivity of radiation-treated p-Ge

It is shown that nonconservation of the transverse component of momentum when the electron-phonon interaction takes place around a dislocation leads to the dependence of the relaxation time of the momentum given by (p) p^–7/2 in the case of the hole energy being much less than thermal energy and by (p) p^–7 in the case of hole energy being much greater than thermal energy. Results are compared with experimental data on dislocation conductivity of radiationtreated p-Ge.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 61–64, May, 1984.Authors are grateful to V. P. Dobrego for bringing this subject to their attention and for fruitful discussions.     

Grain size refinement and magnetostriction of ferromagnetic shape memory Fe–Pd–Rh alloys

This paper reports the forging of bulk ferromagnetic shape memory (FSM) Fe–30Pd–2Rh (at%) alloys to a 40% reduction in thickness, followed by thermal annealing at 950–1100 °C for various times and quenching in ice brine to induce recrystallization (i.e. grain size refinement). Investigation with the Vickers microhardness test reveals that the process of recrystallization results in increased ductility of the fine grains. TEM and magnetostriction investigations reveal two kinds of twins contained in the strain-forged sample annealed at 950 °C for 3 h, i.e. deformation and transformation twins, and these twins also improved a higher magnetostriction as well as ductility in the alloys that may be useful in magneto-mechanical applications (such as microactuator or spring).     

Estimation of the Optimum Concentration Interval of the Contents of Praseodymium, Neodymium, Europium, Holmium, and Erbium in a Solution

Based on the electronic absorption spectra of Pr³⁺, Nd³⁺, Eu³⁺, Ho³⁺, and Er³⁺ ions in 1 M aqueous solutions of chloric acid, calibration graphs have been constructed in a concentration of metals–optical density of a solution format for different frequencies. The band for praseodymium was used at 22,520 cm^–1, for neodymium at 17,380, 13,480, and 12,560 cm^–1, for europium at 25,380 cm^–1, for holmium at 18,580 and 15,580 cm^–1, and for erbium at 39,160, 26,480, and 19,160 cm^–1. The errors in determining the concentration of the indicated elements as a function of their content have been calculated. It is shown that for perchloric solutions of praseodymium it is possible to correctly determine its contents within the concentration range 0.1–1.5% at a frequency of 22,520 cm^–1; for neodymium the ranges are 0.4–1.0, 0.3–1.0, and 0.5–1.0% at 17,380, 13,480, and 12,560 cm^–1, respectively; for europium 0.4–1.5% at 25,380 cm^–1; for holmium — 0.2–1.5 and 0.4–1.5% at 15,580 and 18,580 cm^–1, and for erbium the range is 0.4–1.0% at frequencies of 39,160, 26,480, and 19,160 cm^–1.