Effect of thermal annealing on the cathodoluminescence of evaporated CdS films

Cathodoluminescence (CL) of evaporated undoped CdS films was investigated before and after thermal annealing in air and in vacuum at 300 °C for several hours. Pure CdS single crystals were studied for comparison. CL spectra were obtained at room temperature using the electron microprobe technique. The two well-known (green and red) CL bands of pure CdS were observed for all samples. Annealing of the films in air decreased the green luminescence while vacuum annealing led to its increase. The red luminescence increased under both annealing conditions. The results were explained in terms of radiative transitions attributed mainly to native defects and their complexes. The role of oxygen and residual impurities on the CL of thin films was discussed. A modulation of the CL spectra was obtained in thin films owing to optical interference.     

Effect of annealing on the optical quality of AgGaS2 and AgGaSe2 single crystals

Single crystals of AgGaS₂ and AgGaSe₂ were grown by a modified Bridgman-Stockbarger technique. Pieces of sizes 10 mm × 6 mm × 4 mm and 11 mm × 6 mm × 5 mm of AgGaS₂ and AgGaSe₂ free from lamellar twins, were cut from the crystals for detailed investigations. The results of infrared transmittance and absorbance measurements indicate that the optical quality of the annealed crystals was much better than that of the as-grown crystals. Experiments on thermal etching were also carried out to study the microscopic defects in the crystals.     

Effect of annealing on the spectroscopy performance of YVO4:Ce3+ single crystals

In this study, 1.0 at.% YVO₄:Ce³⁺ single crystals were grown in the protective atmosphere by using the Czochralski method. The crystals were annealed in Ar and H₂ atmospheres at different temperatures. The absorption and fluorescence spectra of the samples before and after annealing were measured. Results showed that the luminescent efficiency of the crystals was significantly enhanced after annealing in H₂ than after annealing in Ar. This phenomenon can be attributed to the existence of some Ce⁴⁺ ions in the crystal lattice. These Ce⁴⁺ ions can be effectively reduced to Ce³⁺ via annealing in H₂. With a fixed annealing time in H₂, the luminescent intensity significantly increased with increasing annealing temperature. The possibility of the crystal as white light material was also discussed according to the luminescence properties.     

Hot deformation and annealing of cube oriented aluminium single crystals

Abstract

Single crystals of the {001}〈100〉 orientation of an Al–0.05Si single phase alloy have been deformed in plane strain compression at temperatures of 300–500°C and strain rates of 0.5–50 s^-1, and annealed in a salt bath at temperatures of 300–450°C. Quantitative texture measurements by electron backscatter diffraction (EBSD)show that, in agreement with previous work, the cube orientation is stable at lower strain rates and higher temperatures (lower Zener–Hollomon parameter Z), whereas this orientation is unstable at higher values of Z. During annealing of the deformed crystals there is a competitive migration of subgrain boundaries of a wide range of orientations, and recrystallisation starts preferably at deformation bands of high orientation gradient. Measurement of subgrain growth has enabled the dependence of the mobility of low angle grain boundaries on misorientation to be determined. The results are in accord with those obtained for lower angle (<6°)boundaries in the same material.     

Effect of annealing on the electrical properties of SnTe crystals

We have studied the effect of annealing on the electrical conductivity σ and thermoelectric power α of SnTe crystals. The results indicate that the temperature dependences of σ and α for both the unannealed and annealed SnTe crystals, as well as the effect of annealing on these parameters, are adequately accounted for in terms of a model that considers two valence bands separated by an energy gap.     

Pulsed cathodoluminescence of calcite crystals of various origins

We have studied the luminescence of calcites from phlogopite-calcite veins, marbles, leucogranites, apatite-calcite ores, and carbonatites in the spectral range 300–800 nm under excitation with nanosecond electron pulses at an electron beam current density of ∼10 A/cm². All of the calcite varieties have a fast emission component, with a broad spectrum in the near-UV and visible spectral regions, whose decay time is comparable to the excitation pulse duration, and a slow emission component, with a peak-emission wavelength of 610–620 nm and decay time of tens of milliseconds. The spectral composition of the emission depends on the nature of the calcite sample. We analyze the evolution of the spectrum after excitation and discuss the luminescence excitation mechanisms and the nature of the emission centers.     

Large triangular single crystals formed by mild annealing of self-organized silver nanocrystals

Nanocrystal organizations represent a new generation of materials with specific properties compared with those of isolated nanocrystals and of the bulk material. Here, we present the first intrinsic crystalline growth properties of highly ordered mono- and multilayers of 5 nm silver nanocrystals. Triangular single crystals with face-centred-cubic structures are obtained by annealing the ordered nanocrystals under atmospheric pressure at 50 degrees C. The triangles are mixed with well-crystallized coalesced particles of various shapes. Their size depends on the initial nanocrystal ordering range on the substrate, which is local on amorphous carbon and highly extended on highly oriented pyrolitic graphite (HOPG). Hence, the single-crystal size is larger on HOPG than on amorphous carbon. These observations show that the crystalline growth properties of silver nanocrystals can be tailored by controlling their organization. Furthermore, on HOPG an epitaxial orientation of the triangles is observed.     

Effect of twins on deformation of graphite single crystals

A detailed investigation has been made of deformation and fracture in graphite single crystals, between 20 and 2400° C, under a tensile stress parallel to the basal plane. Crystals are shown to be inherently weak when twins are present and the low value of modulus recorded in twinned crystals is attributed to dislocation glide within these regions. A mechanism of fracture is proposed which is consistent with the low strength and the fracture characteristics of graphite.It has been shown that graphite single crystals exhibit anomalous behaviour in that the tensile fracture strength increases if tests are made at temperatures greater than 2000° C.This increase in strength is associated with the movement and annihilation of twin boundaries and subsequent reduction in stress concentration. Delamination is also shown to result from twin boundary movement.     

Effect of annealing on semi-insulating CdZnTe:Cl crystals with variable zinc content

Semi-insulating Cd_1?x Zn _x Te:C1 crystals with variable zinc content (x = 0.0002, 0.005, 0.01, and 0.1) were grown using the method of horizontal directional solidification. The effect of the conditions of post-growth annealing under controlled cadmium vapor pressure and additional low-temperature annealing on the main parameters responsible for the quality of nuclear radiation detectors based on such crystals were studied.     

Effect of orientation on work softening in aluminum single crystals

A single crystal of aluminum, prestrained at low temperature, exhibits a yield drop when it is deformed at a sufficiently higher temperature and this phenomenon has been termed the work softening. In this study, three types of aluminum single crystals with various tensile orientations were stretched at 77 K and 293 K, to clarify the effect of orientation on this work softening phenomenon. The single crystal orientated for single slip shows work softening when deformed at 293 K after prestraining satisfactorily at 77 K. In the deformation of this crystal at 293 K, a coarse slip accompanied by an intimate cross slip, was observed. The single crystal orientated along 1 0 0 also shows work softening at 293 K after giving moderate elongation at 77 K and a clustered slip accompanied by a prominent cross slip was observed in the deformation at 293 K. However, in the deformation of the single crystal orientated along 1 1 1 at 293 K, only a fine triple slip was observed and work softening was not observed even when prestrained to a large strain at 77 K. It is thought that the work softening found at 293 K after prestrain at 77 K is associated with the occurrence and propagation of coarse slip accompanied by cross slip.     

预时效对CuAlNi单晶相变温度的影响

根据有序化理论,提出了预时效概念,并用无析出物形成的预时效处理研究了Cu-13.4Al-4. 0Ni单晶相变温度随预时效工艺的变化,结合DSC和偏光金相分析探讨了预时效与时效的界限.淬冷状态的Cu-Al-Ni单晶其相变温度可以根据需要进行预时效处理,经预时效后,其M s为淬冷态的Ms+0～70 ℃,As为淬冷态的As+0～90 ℃可调. 预时效温度应为淬冷态的Ms+100～200 ℃. 经过预时效的合金在马氏体状态下其相变温度保持稳定. 在高出淬冷态合金Ms点300 ℃以上随着保温温度的升高或保温时间的增长,处理后的 Ms、As等转变温度向高温移动,并且相应的β′1相的数量也会降低,γ′1 相量增加. 尽管此时没有析出物产生,但是单一β′1相转变为β′1+γ′1后,由于γ′1相很差的原位再现性而导致降低形状记忆行为和超弹行为.     

Effect of impurities on the strengthening of CaF2 single crystals

The critical resolved shear stress (CRSS) of pure and aliovalently doped (with Y⁺³ and Na⁺) CaF₂ single crystals have been measured in compression along [1 1 1] axis between room temperature and 873 K. Strain rate cycling and/or stress relaxation experiments were performed to obtain the necessary parameters for the determination of rate-controling mechanism for plastic flow. The measured temperature and concentration dependences of the activation parameters suggest that the elastic interaction of dislocations with impurity cation-lattice anion defect pairs determine the CRSS as in alkali halide crystals. The CRSS for CaF₂ single crystals doped with trivalent Y⁺³ were found an order of magnitude larger than those doped with the monovalent Na⁺. Based on the valence of dopant cations and the magnitude of hardening produced, solution hardening in CaF₂ could be divided into two groups: rapid and gradual hardening.     

Observation via cathodoluminescence of static and sliding damage in sapphire crystals

Surface damage in sapphire crystals was effected by static and sliding contact and then observed using a scanning electron microscope in both the cathodoluminescence and secondary electron modes. It was found that enhanced luminescence appeared at the area of contact damage, and that the lumincescence observed might have been associated with point defects generated during the plastic deformation process. The cathodoluminescence images of sliding damage correlated well with the characteristic frictional properties of sapphire crystals.     

Defect annealing of neutron-irradiated silicon crystals

Doppler broadening positron annihilation spectroscopy has been used to investigate the effects of neutron integrated flux and hydrogen on annealing behaviour of defects in silicon crystals. The concentration of neutron radiation defects was estimated, activation energy of some annealing stages was calculated and some specific annealing phenomena were explained.     

Observations of contact damage in MgO and LiF crystals by cathodoluminescence

Cathodoluminescence (CL) studies in a scanning electron microscope of the static and dynamic contact damage in MgO and LiF crystals are described. The main luminescence for both MgO and LiF was found to be associated with the plastically deformed zone at and around the contact site, although there were differences of details in the CL behaviour of the two materials. It was also found that in MgO the intensity of luminescence from screw dislocations was markedly higher than that from the edge dislocations for all possible orientations of the specimen. It is proposed that this simple and rapid technique can be used for assessing the mechanical state of a surface.     

Effect of electrolytes on brittle failure of single crystals under contact effects

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 1, pp. 70–75, January–February, 1990.     

Effect of rare-earth doping on the electrical properties of InSe single crystals

The effect of rare-earth doping (R = Gd, Dy, Ho) to different levels (0, 10^?5, 10^?4, 10^?3, 10^?2, and 10^?1 at %) on threshold switching and low-frequency current oscillations in single crystals of indium selenide, a layered III–VI semiconductor, has been studied in broad ranges of temperatures (77–400 K), wavelengths (0.30–3.50 μm), and illuminances (up to ～10² lx). The results are interpreted in terms of the anisotropic chemical bonding in n-InSe and its response to rare-earth doping.