Microstructural evolution of ZnS during sintering monitored by optical and positron annihilation techniques

Positron lifetime and optical absorption techniques were employed to track the microstructural evolution of polycrystalline ZnS grown by Chemical Vapor Deposition (CVD). As grown material and material treated with Hot Isostatic Pressure (HIP) was sintered at temperatures ranging from 400 to 1000°C for 2–18 h. A 290 ps defect lifetime could be resolved in all samples, while an additional longer lifetime (=430 ps) was found only in samples annealed at low temperatures. This component gradually disappeared during annealing at 800°C. Associated with the disappearance of the long-lived component, the apparent bulk lifetime of the material changed from 235 to 215 ps. A 215±2 ps bulk parameter was also found for HIP-treated material annealed at temperatures greater than 400°C and hence is taken to represent the delocalized state of the positrons in ZnS. Optical absorption measurements showed that annealing at 800°C also caused the absorption profiles of the CVD and HIP samples to converge. The rate of the bulk lifetime transition correlates with the absorption changes. The observed sharpening of the absorption profile is attributed to a decrease in scattering from grain boundaries and voids, and a decrease in absorption from point defects. The 430 ps lifetime is believed to be due to trapping at voids and grain boundaries, while the 290 ps lifetime likely is due to a monovacancy stabilized as a small complex.Paper presented at the 132nd WE-Heraeus-Seminr on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994     

Structural relaxation in polyethylene in the presence of silver oxide investigated by positron-lifetime spectroscopy

Structural relaxation in high-density virgin polyethylene and silver oxide doped polyethylene has been investigated using positron annihilation lifetime technique at 30 °C and 100 °C ageing temperatures. The ortho-positronium (o-Ps) pick-off lifetime and its intensity show no changes with isothermal ageing time for the virgin sample at 30 °C. In the case of the doped sample at 30 °C, the o-Ps intensity shows exponential relaxation in the short-time range. At 100 °C, the o-Ps lifetime remains almost constant, whereas the o-Ps intensity exhibits an exponential character in the virgin and doped samples, which can be fitted with exponential decay curves. The relaxation times have been evaluated from the structural relaxation function constructed using o-Ps intensity values, and the stretching exponent has been estimated using the Kohlrausch–Williams–Watts (KWW) function. Positron results indicate that the stretching exponent seems to be temperature dependent. PACS 78.70.Bj     

Influence of Hydrothermal Temperature on Structures and Photovoltaic Properties of SnO2 Nanoparticles

Two SnO₂ nanoparticles were synthesized by hydrothermal method at 170°C and 180°C, respectively. Transmission electron microscope observations reveal that the diameters of both the nanoparticles are around 6nm. At the same time, surface photovoltage spectroscopy measurements show that the nanoparticle synthesized at 180°C has more surface electronic states at 0.3eV below the conduction band than the one synthesized at 170°C. This means that the temperatures chosen in hydrothermal synthesis have significant influence on the surface electronic characteristics of resultant SnO² nanoparticles but the effect on their sizes is not obvious. However, after being calcined at 500°C for 2h, the diameter of the nanoparticle synthesized at 180°C increased to 23nm and that of the nanoparticle synthesized at 170°C increased to 32nm as calculated from X-ray diffraction pattern.     

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.     

Effects of annealing temperature on the alloying behavior of the AuGe-GaAs〈100〉 interface

UV(He I) and X-ray photoelectron spectroscopies (UPS and XPS) were used to examine the alloying behavior of AuGe ohmic contacts to silicon-doped 100 oriented n-type GaAs substrates. The reacted interface was then revealed by Ar ion sputter depth profiling at room temperature and after annealing in ultra high vacuum at 300°, 500°, or 700°C. The indiffusion of Au and the outdiffusion of Ga and As are evident. Instead of obtaining a maximum peak of the Ge profile on annealing in forming gas, we observed an increase of Ge indiffusion with temperature. The Au indiffusion results in a decrease in the Au 5d splitting and a shift of both levels to higher binding energy. Au-Ga alloy formation is indicated by the Au 4f levels, and is further supported by the observation of the metallic Ga peak. It has been concluded that the sample annealed at 500°C forms the Au-Ga alloy and the compound of As containing Ge more easily than the samples annealed at 300° or 700°C. This result is consistent with the observations of low contact resistance at the annealing temperature of 500°C for AuNiGe ohmic contacts to n-type GaAs.     

Observed difference between the probabilities of recoilless resonance absorptionf′ and reemissionf″ of gamma-quanta in single crystals of Na2[Fe(CN)5NO]·2 H2O

The recoilless absorption probability factor,f, and recoilless reemission,f, both measured on Na₂[Fe(CN)₅NO]·2 H₂O single crystals using the black filter technique, were found to be different. Unexpectedly, the results found weref>f. In the calculation off, selfabsorption in the scatterer, non-ideality of the black filter and the influence of non-resonant scattering processes have all been taken into account. By varying the scattering geometry for the incoming and outgoing -beam relative to the crystallographic axes only a change in the reemitted valuesf _a, f_b, f_c could be detected because of the long lifetime of the excited nucleus (10^–7 s) relative to the lattice vibration frequencies (10¹² Hz).     

A systematic analysis of defects in ion-implanted silicon

A classification scheme for the different forms of implant-related damage which arise upon annealing consisting of five categories is presented. Category I damage is subthreshold damage or that which results prior to the formation of an amorphous layer. If the dose is increased sufficiently to result in the formation of an amorphous layer then the defects which form beyond the amorphous/crystalline (a/c) interface are classified as category II (end of range) damage. Category III defects are associated with the solid phase epitaxial growth of the amorphous layer. The most common forms of this damage are microtwins, hairpin dislocations and segregation related defects. It is possible to produce a buried amorphous layer upon implantation, If this occurs, then the defects which form when the two a/c interfaces meet are termed category IV (clamshell, zipper) defects. Finally, category V defects arise from exceeding the solid solubility of the implanted species in the substrate at the annealing temperature. These defects are most often precipitates or dislocation loops.In addition to presenting examples of this classification scheme, new results emphasizing category II, IV, and V defects will be presented. For category II defects, the source, dose and mass dependence as well as the influence of pre- and post-amorphization is discussed. The category IV defects which arise from buried amorphous layers in {100} oriented As implanted samples is presented. Half loop dislocations which arise during annealing of high dose As implants, are shown to originate in the category V defects and grow upon dissolution of As clusters and precipitates.     

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.     

Influence of the charge of surface states on the characteristics of mis transistors made of p-type indium antimonide

An experimental investigation was made of metal-insulator-semiconductor transistors with thick insulator and long channel and made of single-crystal p-type InSb (78° K). An empirical relation was obtained for the output drain conductance in the case of carrier degeneracy in the n-type channel. The parameters of the InSb surface after etching were determined.Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 4, pp. 84–88, April, 1980.     

Nucleation process of stacking fault tetrahedra in gold studied by positron lifetime spectroscopy

By component analyses of positron lifetime spectra in quenched gold, it was found that positrons are strongly trapped by stacking fault tetrahedra (SFT) at which the lifetime is about 160 ps remarkably smaller than that for monovacancies (200 ps) or divacancies (220 ps). Positron lifetimes at small vacancy clusters were also estimated in relation to the nucleation process of SFT, with the aid of computer simulation of kinetics of vacancy clustering during quenching and on subsequent isochronal annealing. The results show that large atomic relaxation occurs in small vacancy clusters among which pentavacancies have the largest open-space, thereby having the lifetime of about 230 ps larger than that of trior tetra-vacancies (160ps). It is also suggested that tetra- and penta-vacancies act as prenuclei for stable nuclei of SFT consisting of six or more vacancies.Present situation: Professor Emeritus     

Determination of electrodynamical parameters of dielectric pipe-shaped materials using millimeter wave cavity

Employment ofE _0np modes of cylindrical cavity resonator for measurement of electrodynamical parameters of dielectric pipe-shaped materials in millimeter wavelength band is suggested. Dielectric permittivity and conductivity of a sample can be found by measuring the frequency shift and theQ-factor change of the resonator.Method of mode basis is used for the calculation of sample permittivity and conductivity . Measurements were carried out at 8mm wavelength and related calculations have demonstrated use and possibilities of the method in studying the dielectric properties of samples of cylindrical and other forms.     

The early oxynitridation stages of hydrogen-terminated (100) silicon after exposure to N2:N2O. II. Silicon and oxygen bonding states

The early oxidation stages of hydrogen-terminated single-crystalline (100) silicon have been studied by X-ray photoemission spectroscopy, following the evolution of the Si2p and O1s signals after exposure to N₂:N₂O ambient at 850 °C for different durations. Evidence is given that the usual analysis of the film in terms of the Si2p peak leads to inconsistencies, related to the presence in the film of non-siloxanic bridges, as oxygen-rich defects (like hydroxyl terminations or peroxo bridges) or oxygen-deficient defects (like amino bridges). Information on the film structure is obtained by combining the analysis of the Si2p peak with that of the O1s peak. PACS 82.65.+r; 68.35.Fx; 68.35.Dv; 79.60.Jv     

Temperature dependence of positron annihilation parameters in neutron irradiated molybdenum

Positron lifetime measurements have been performed for molybdenum samples containing different densities of voids and dislocation loops. The samples consisted of single crystal molybdenum exposed to 2.7×10¹⁸ fast neutrons/cm₂ at 60°C, and subsequently annealed at 650°, 725°, 800°, and 875°C in vacuum (p<10^–7 Torr). After each annealing, where the densities of voids and loops were changed, positron lifetime measurements were performed in the temperature interval [–194°, 285°C]. In two-term fits of the measured spectra the longer lifetime, _e2-460 ps corresponds to an intensityI _e2 increasing with sample temperature. The shorter lifetime _e1 decreases with increasing temperature. A three-state trapping model with and without detrapping is discussed, and appears to be incapable of explaining the observed temperature dependences. A four-state positron trapping model including detrapping is necessary and satisfactory. It describes positron trapping to voids and trapping to dislocation loops, which is followed by a competition between detrapping and positron transition to jogs or other dislocation-bound defects. Mathematical expressions of the four-state trapping model including detrapping are worked out and calculations of the intensityI _e2 are compared with the experimental values ofI _e2. By use of special models for the temperature dependence of trapping rates, numerical values can be determined for the positron-dislocation-binding energy and for specific positron trapping rates.     

MV-Algebra Pasting

Z. Rieanová proved that every D-lattice is a set-theoretical union of MV-algebras. These MV-algebras are blocks in the D-lattice. There is a dual question: How can we construct a D-poset from a given collection of MV-algebras. To solve this problem we use the pasting technique. We define an admissible system of MV-algebras and we prove that the pasting of this system is a D-poset.     

ВЛИЯНИЕ СОДЕРЖАНИЯ К ИСЛОРОДА НА ЭЛЕКТРИЧЕСКИЕ И ТЕ РМОЭЛЕКТРИЧЕСКИЕ СВОЙСТВА ТРОЙНОЙ СИС ТЕМЫ Вi2Те3−x Sе x

, Bi₂Te_3–x Se _x . , , . , , . .

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Influence of oxygen content on electric and thermoelectric properties of ternary system Bi₂Te_3–x Se _x

A study is made of the influence of oxygen, contained in the semi-conducting system Bi₂Te_3–x Sé _x , on the electric and thermoelectric properties. It is shown that the addition of oxygen to the prepared samples Bi₂Te_2.4Se_0.6 causes a decrease in electric conductivity while the thermoelectric force remains unchanged. This influence is connected with a decrease in the mobility of the electrons but their concentration is not influenced by the presence of oxygen. Conclusions are reached as to the influence of oxygen on the efficiency of the conversion of thermal energy into electric energy and vice versa.

     

Die Umwandlung der Fackelentladung in die Hochfrequenz-korona

Zusammenfassung Durch künstliche Senkung der Temperatur der Fackelentladung geht diese Entladung in eine Hochfrequenz-Korona über. Wenn die Temperatur der Entladung sinkt, wächst in ihr die elektrische Feldstärke; dadurch werden die Bedingungen des thermodynamischen Gleichgewichts gestört und es beginnt der Übergang von der thermischen zur elektrischen Ionisation. Die Erläuterung wird durch die Spektralanalyse und das Studium der Fackelentladung mittels einer zeitlich zerlegten Photographie ergänzt.

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Abschließend danke ich Herrn Prof. V. Kunzl für seine anregenden Hinweise.     

Ordering processes and activation energy in Ni3Fe-based ternary alloys

The measurement of electrical resistance () has been used, to study the kinetics of isothermal ordering in the range 200 °–545 ° C in Ni₃(FeMn) alloy quenched from 970 ° C, and the kinetics of ordering at 390 ° C in the alloy quenched from various temperatures in the 600 °–800 ° C range. The sections method and the gradient of the (t) curves were used to find the activation energy for migration and vacancy formation in this alloy on the assumption that the excess vacancies frozen in the alloy by quenching at temperatures above T_c are responsible for ordering. The activation energies for vacancy formation and migration were respectively U₀ = 33 ± 3 kilocal/mole and U_m = 39 ± 4 kilocal/mole, which in total give the activation energy for diffusion Q = 72 ± 7 kilocal/mole in the alloy studied; this approximates to the activation energy for diffusion in pure nickel.     

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.     

Positron lifetimes for neutron-irradiated C60

The neutron-irradiation effects on C₆₀ fullerite powder were studied by positron lifetime spectroscopy. Below 0.5 ns, a single lifetime of 382±1 ps was found for the unirradiated annealed sample and two components were resolved after neutron irradiation with a dose of 2×10¹⁶ n/cm². Possible origins of these components are briefly discussed.Paper presented at the 132nd WE-Heraeus-Seminar on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994     

Threading dislocations in GaAs on Si grown with ∼1 nm thick Si interlayers

Threading dislocation morphologies and characteristics have been investigated in 3 m thick GaAs films with ultrathin (1 nm) Si interlayers grown by molecular beam epitaxy on tilted (2° toward [110]) Si (001) substrates using cross-sectional transmission electron microscopy. Four sample structures are studied in which different numbers of ultrathin Si layers are grown at different positions in the GaAs film, and the results are compared for samples observed before and after ex situ annealing. In all of the sample structures, some mixed-type dislocations are clearly blocked by the Si interlayers, although some of them pass through these layers, resulting in propagation of their threading dislocations to the sample surface. After annealing at 900 °C for 10 s or 800 °C for 30 min, the interactions of the dislocations with the interlayers are enhanced, and there is an increase in the number of dislocations which are bent along the 110 directions at the positions of the Si barrier layers. However, a considerable number of dislocations still escape from the Si barriers by gliding on {111} slip planes during annealing. Moreover, ex situ annealing generates new edge-type dislocations through interactions between moving threading dislocations. The nature of the dislocations that cross the Si barriers is especially discussed.