Electron microscopic investigations of precipitates in doped NaCl crystals

Precipitation morphology of NaCl:CdCl₂ and NaCl:SrCl₂ crystals is investigated by high voltage transmission electron microscopy. The volume fraction of the precipitates and the content of CdCl₂ has been evaluated using the theory developed by Hillard. Selected area diffraction patterns of the precipitates and investigations of the misfit dislocations around the precipitates is presented.     

The Influence of High Temperature Predeformation on Ductility of LiF and BaF2 Single Crystals

The effect of high temperature predeformation on deformation characteristics of ductile LiF and brittle BaF₂ crystals was investigated. The same predeformation, as has been shown previously, leads to the increasing of the limited plastic deformation of MgO crystals by one order of magnitude. It was found that in both investigated crystals, as in the case of MgO crystals, at the test temperature T₂ ≅ 0.1 T_m limited plastic deformation before fracture obviously increases if the specimen was prestrained up to ε_p ≦ 1% at T₁ = 0.5 T_m. This increase is as higher as the plasticity of crystal is lower. In BaF₂ crystals it reaches a factor of 20 and more. The effect is connected with the creation of mobile dislocations during the high temperature predeformation and dislocaton sources for subsequent deformation at lower temperatures and with the homogeneity of the process of plastic deformation. These conditions prevent the appearance of dangerous places in which the fracture can begin.     

Electron Spin Resonance In CuCrS2 and CuCrSe2 Single Crystals

Abstract

Single crystal ESR spectra of CuCrS₂ and CuCrSe₂ have been measured at both X- and Q-band frequencies. Anisotropic signals from the localised Cr³⁺ d-electrons give zero-field splitting parameters of 0.29cm^?1 and 0.31cm^?1 for the sulphide and selenide respectively, suggesting a possible orbital interaction between the Cr and Cu ions. The dependence of the ESR parameters on temperature shows the effect of magnetic ordering.     

Overhauser Shift of the Conduction Electron Spin Resonance in (FA)2PF6 Single Crystals

The shift ΔB _ov of the ESR line due to saturation of the NMR of the hyperfine coupled nuclei (Overhauser shift) was measured for single crystals of the organic conductor (FA)₂PF₆. ΔB_ov , is proportional to [Abar] _tt , being the average hyperfine interaction between the conduction electrons and the protons in resonance, and the dynamic nuclear spin polarization (DNP), respectively. The DNP enhancement factor V was determined for the two orientations of the static magnetic field B _o , perpendicular (V _∥ = 525 ± 40) and parallel (V _∥ = 280 ± 25) to the needle axis a, respectively. The absolute value of the average hyperfine coupling is [Abar]^zz = –(1.16 ± 0.05) Gauss · g_e μ _B . Both, the temperature dependence and the anisotropy of the proton spin relaxation times T ₁ ^p and T ₁ ^p were measured from the time dependence of the Overhauser shift, ΔB_ov (t) after rf-pulses or after switching “on” and “off” the ESR saturation. Within the metallic phase of the crystal the proton relaxation is governed by a Korringa law. The experiments definitely show, that the electron spins, showing up in the ESR are those of the conduction electrons.     

Transport Properties of TlInSe2 Single Crystals

Single crystals of TlInSe₂ were prepared by a special modified Bridgman technique. The influence of temperature on the electrical conductivity, Hall effect, Hall mobility, and the carrier concentration was investigated in the temperature range 190–625 K. The energy gap of conduction was calculated. The scattering mechanism of the charge carrier was discussed in the same temperature range. Beside this, the thermoelectric power was measured in a temperature range extending from 190 up to 485 K.     

Back-Scattered Electron Imaging of Microscopic Segregation in (Si,Ge) Single Crystals

Compositional inhomogeneities of (Si,Ge) single crystals grown by the radio frequency (RF) heated float zone technique have been studied using the back-scattered electron (BSE) mode of a scanning electron microscope. Numerical analysis of the images by Fast Fourier Transformation (FFT) showed that the number of spatial frequencies with substantial amplitudes is increased when investigating longitudinal sections of crystals containing dislocations instead of dislocation-free crystals. This can be attributed to different growth conditions in terms of super-cooling.     

磷锗锌单晶体的腐蚀研究

报道了一种新的ZnGeP2晶体择优腐蚀剂及其腐蚀工艺,即先采用研磨、物理机械抛光和HCl+HNO3热化学抛光获得表面平整无划痕的ZnGeP2晶片,然后将晶片在室温下采用HF(40;):HNO3(65;):CH3COOH(99.5;):H2O:I2=2 mL:2 mL:1 mL:1 mL:4 mg腐蚀剂超声振荡腐蚀8 min;在扫描电镜下观察到ZGP(110)和(204)晶面的腐蚀坑,蚀坑形貌清晰,具有立体感,(110)晶面蚀坑呈四边形,(204)晶面蚀坑呈五边形,取向一致,蚀坑密度(EPD)约为104/cm2.从理论上对蚀坑形貌的形成机理进行了分析.     

Photoconductivity Spectra of n-type CuInSe2 Single Crystals

Photoconductivity spectra of n-type CuInSe₂ single crystals are measured in the photon energy range hv = 0.75 – 3.1 eV and as a function of temperature in the range T = 80 – 320 K. It is found that the photoconductivity of as-grown crystals is a nearly pure surface effect, while sensitization of the crystal volume is observed only after sufficiently long annealing in the presence of powdered material. To explain the temperature dependence of the photoconductivity carrier trapping processes must be taken into account.     

Microtopographical Characterization of Vapour-grown SnS2 Single Crystals

Thin flakes of tin disulphide single crystals grown using direct vapour transport have been subjected to characterization to unfold their growth mechanism. Two types of spirals. viz. those having opposite orientation present on the same face and those present on the opposite finished faces are significantly discussed.     

Optical Properties of MnIn2S2Se2 Single Crystals

Optical transmittance and reflectance spectra of MnIn₂S₂Se₂ single crystals are measured in the wavelength range from 0.5 to 30 μm. The interference method is used to determine the refractive index of the compound for wavelengths between 0.8 and 12 μm. From an analysis of the absorption spectrum it follows that the fundamental edge is due to forbidden indirect transitions between parabolic bands for the polarization E ⊥ c with a gap energy of 1.50 eV at room temperature.     

Optical Investigation of Defects in p-type CuInSe2 Single Crystals

Optical absorption spectra in the photon energy range from 0.03 to 1.1 eV and photoreflectance spectra in the range of the fundamental edge are measured on p-type CuInSe₂ single crystals. Besides a dominant contribution to the absorption coefficient due to intervalence band transitions below about 0.75 eV the spectra revealed five additional structures that can be ascribed to defect induced optical transitions with characteristic energies between 0.48 and 0.72 eV. Based on a comparison of the near-edge optical absorption and photoreflectance spectra a shallow defect (donor or acceptor) with an ionisation energy of about 46 meV was identified.     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Growth and Optical Characterization of CdI2 Single Crystals

Single crystals of CdI₂ were grown by employing the horizontal zone refining method. Emission spectra of these crystals were recorded at room temperature and liquid nitrogen temperature. Various emission parameters such as optical gain coefficient, lifetime, gain, stimulated emission cross section were evaluated for the various emission components. The results show high gain at low temperature whereas very low value at rmm temperature. This has been explained by invoking the existence of self trapped excitons in the crystal.     

Electrical and Photoelectrical Properties of n-CuInS2 Single Crystals

The temperature dependences of free electron density and mobility in n-CuInS₂ single crystals have been determined from the Hall effect measurements. The ionization energy of donors and their densities have been estimated. The results of measurements show that the crystals are strongly compensated. The spectral distribution of photoconductivity, the dependence of photoconductivity on excitation intensity, and the photoconductivity decay with time have been measured in the n-CuInS₂ crystals at different temperatures. The results of photo-conductivity measurements suggest linear recombination of photo-electrons at weak excitation and quadratic recombination at high excitation intensity. The compensated deep acceptor probably acts as the recombination centre.     

Some Physical Properties of Ga2Se Single Crystals

Measurements of the electrical conductivity, Hall effect, thermnoelectric power were carried out in a wide temperature range (from about 170 to 475 K) for Ga₂Se compound grown in single crystalline form. The present investigation revealed unusual observations in the Hall effect and the scattering mechanisms of the charge carriers indicating that Ga₂Se is not a simple semiconductor. Also it showed that Ga₂Se has a relatively high value of the thermoelectric power. A lot of physical parameters were deduced in the present study.     

Apparatus for Selfcontrolled Growth of Hg2Cl2 Single Crystals

The device for growth process and quality of the growing calomel (Hg₂Cl₂) single crystals studying is described. The function of the apparatus is based on the analysis of the information modulated on the poychromic light beam passed through the growing crystal. By means of this method the device determinates the temperature and the quality of the growing crystal. In the second part of this paper the special TV equipment is described. By means of that an information about the temperature and quality distribution in the whole growing crystal is obtained.     

Transmission Electron Microscope Study of Secondary Phases in Cr3+:LiCaAlF6 Single Crystals

Cr³⁺-doped LiCaAlF₆ single crystals, considered as promising laser materials, contain secondary phases of different sizes and shapes which can be observed as "needles" or "dust" by light microscopy. TEM investigations presented in this paper give evidence for precipitation as the reason for the so-called microscopic "dust". The elongated shape of the so-called "needles" seems to be a consequence of the microscopic growth of facets which become visible by the decoration of the facet boundaries with microscopic precipitates.     

Electron Microscopy and X-ray Study of the Growth of FeCr2S4 Spinel Single Crystals by Chemical Vapour Transport

The growth features of FeCr₂S₄ spinel single crystals prepared by chemical vapour transport were studied by means of scanning electron microscopy, transmission electron microscopy, high resolution electron microscopy, electron diffraction and X-ray analysis. Our results indicate that the epitaxial growth of the new phases FeCr₇S₁₂ and FeCr₈S₁₂, both based on the NiAs structure, can essentially inhibit the growth of large FeCr₂S₄ spinel single crystals in the octahedral habit. The new phases are fully characterised and the effects of defect ordering in these new phases are also reported.