Crystal Cadmium Research Articles

Growth and characterization of thiourea mixed cadmium – lead chloride – a nonlinear optical crystal

AbstractNonlinear optical (NLO) crystal of thiourea mixed cadmium–lead chloride dihydrate Cd[(PbCl3)(NH2CSNH2)].2H2O (TCCPC) have been grown in solution by slow evaporation technique at room temperature. The powder X‐ray diffraction pattern has been recorded and indexed. The UV‐Vis‐NIR transmittance and FT‐IR spectrum have been recorded in the range 200‐1090 nm and 400‐4000 cm‐1, respectively. The lower cut‐off wavelength is 280 nm in the UV region, which is higher than that of pure Cd(PbCl3) (CCPC) crystal. The presence of functional groups has been confirmed by FT‐IR analysis. The TCCPC crystal was characterized by SEM and EDX spectrum. The second harmonic generation (SHG) of the thiourea mixed cadmium–lead chloride (TCCPC) crystal is demonstrated by the Kurtz Perry method using Nd:YAG laser and the results confirm that the grown crystal is roughly three times more efficient than ADP. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of thermal environments on the growth of bulk cadmium zinc telluride (CZT) single crystals

The II–VI compound semiconductor crystal cadmium zinc telluride (CZT) is very important in the field of room-temperature radiation detectors and medical imaging applications. In the present study, bulk CZT single crystal has been grown by (i) oscillatory Bridgman technique, (ii) from vapour phase using pyrolytic boron nitride ampoule in the Bridgman geometry, and (iii) by using a Pt tube used for the ampoule support as a cold finger. Several improvements were found in the thermal environments such as the effects of superheating and reduced growth velocity, as well as improvements in the grain size and zinc composition along the ingot. The compositional homogeneity and its current–voltage characteristic behaviour have been analysed using energy dispersive X-ray analysis and I– V method, respectively.

Mechanisms and species of gold incorporation into crystals of cadmium, lead, and iron sulfides

The mechanisms and species of gold incorporation into crystals of simple sulfides are described. The concept of endocrypty in its modern treatment and the corresponding technique of experimental study were used. The technique is based on the principle of phase composition correlation and variation of parameters specifying the concentrations of active crystal defects. Gold species are determined with the method of statistical samples of analytical data for single crystals (SSADSC). The highest gold incorporation limits have been established for PbS and CdS under high sulfur fugacity (2.4⋅10 −2 and 7⋅10 −3 wt.%, respectively) at 500 °C and 1 kbar. It is shown that in this case, the main crystal defects are metal (Me) vacancies and the gold species is a donor-acceptor pair “Me vacancy– interstitial Au”. Under low sulfur fugacity, Au incorporation might be due to sulfur vacancies, and the gold species is a pair “Au in the Me position–S vacancy”; its concentrations are lower than those at high sulfur fugacity (≤10 −3 wt.%). A specific feature of gold is a tendency to endocrypty. The estimated limiting contents of gold incorporated into sulfide crystals (FeS2, CdS, PbS) at 450–500 °C vary from n⋅10 −4 to n⋅10 −2 wt.%, which is nearly two orders of magnitude higher than the “true” isomorphous capacities of these crystals. For FeS, the incorporation limit of Au does not depend on defects (Fe vacancies). This phenomenon has not been explained yet. In general, the data obtained show that not only the crystallochemical features but also geochemical parameters (first of all, temperature and sulfur fugacity) of the ore formation medium are the main factors for gold concentration in sulfide minerals.

The deformation and fracture behavior of the scintillating crystal cadmium tungstate

Cadmium tungstate single crystals are excellent scintillators and have vast potential as γ- and x-ray detectors. However, they are brittle and as a result, are difficult to manufacture. An understanding of deformation and fracture behavior is necessary in order to improve the ability to fabricate these crystals. Thus, this paper explores the deformation and fracture behavior of CdWO4 single crystals using nano-and microindentation techniques.

Bandgap and effective mass of epitaxial cadmium oxide

The bandgap and band-edge effective mass of single crystal cadmium oxide, epitaxially grown by metal-organic vapor-phase epitaxy, are determined from infrared reflectivity, ultraviolet/visible absorption, and Hall effect measurements. Analysis and simulation of the optical data, including effects of band nonparabolicity, Moss-Burstein band filling and bandgap renormalization, reveal room temperature bandgap and band-edge effective mass values of 2.16±0.02eV and 0.21±0.01m0 respectively.

Laser desorption from the surface of copper phthalocyanine films on silicon and cadmium sulfide

We have studied laser desorption mass spectra of copper phthalocyanine (CuPc) films deposited in vacuum onto single crystal silicon and cadmium sulfide substrates. The desorption was induced by 10-ns pulses of neodymium laser radiation (quantum energy, 2.34 eV) with an energy density E varied from 0.1 to 40 mJ/cm2. It is established that laser radiation produces fragmentation of CuPc molecules and desorption of the fragments. The main fragments observed in the mass spectra are identified. The intensity of the main desorbed species has been studied as a function of the laser pulse energy density. The components of CdS substrates penetrate into the volume of deposited CuPc films in the form of Cd atoms and S2 molecules.

FREE VIBRATION OF TRANSVERSELY ISOTROPIC SOLID AND THICK-WALLED TOROIDAL SHELLS

The frequency of vibration of thick-walled toroidal shells is studied using a finite element formulation wherein the finite element is derived directly in toroidal coordinates. Hexagonal crystals of thallium and cadmium are used as representative transversely isotropic materials. The shell is assumed to be transversely isotropic with respect to the toroidal radial direction, and results based on that assumption are contrasted to a shell that is transversely isotropic with respect to the circumferential toroidal coordinate. It is established that an analysis based on a toroidal coordinate system is superior to an axisymmetric coordinate system and has some advantages over a commercial finite element code. Tables of results are presented that compare frequency of vibration for the above mentioned transversely isotropic materials and isotropic materials.

Design of cdte photoconductor detector and study of some electrical

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The kinetics of electroreduction of peroxodisulfate ions on single crystal cadmium and bismuth electrodes

The electroreduction of the peroxodisulfate anions on the electrochemically polished (EP) Cd(0 0 0 1), Bi(1 1 1) and Bi ( 0 1 1 ¯ ) planes has been studied by cyclic voltammetry, rotating disc electrode and impedance methods. The rate constant values of the heterogeneous electroreduction reaction of the S 2 O 8 2 - anion on the EP Cd(0 0 0 1) and Bi( h k l) planes dependent on electrode polarisation and base electrolyte concentration have been calculated. The values of apparent transfer coefficient α app corrected for the double layer effect ( α app ⩽ 0.15) only very weakly depend on the electrode potential and base electrolyte concentration. The very low values of the apparent charge transfer coefficient for S 2 O 8 2 - electroreduction show that the activationless charge transfer mechanism is valid for EP Cd(0 0 0 1) and EP Bi( h k l) electrodes in various surface inactive base electrolyte solutions. This conclusion is in a good agreement with the theoretical models for the high hydrogen overvoltage metals based on the diabatic charge transfer mechanism from the metal to an ion [R.R. Nazmutdinov, D.V. Gluhov, O.A. Petrii, G.A. Tsirlina, G.N. Botikova, J. Electroanal. Chem. 552 (2003) 261].

Violet luminescence in α-ZnSe heterolayers

Zinc selenide layers of hexagonal modification, characterized by dominating violet emission in the room temperature luminescence spectrum, have been obtained on single crystal cadmium sulfide substrates by method of isovalent substitution.

A kinetic study of CdS photocorrosion by intensity modulated photocurrent and photoelectrochemical impedance spectroscopy

Abstract The steady state and dynamic photoelectrochemical behaviour of single crystal cadmium sulfide in non-stabilising electrolytes has been compared with the response of the same electrode in the hole scavenging electrolyte Na 2 SO 3 . The kinetics of the elementary steps involved in photo-dissolution have been investigated by intensity modulated photocurrent spectroscopy (IMPS) and photoelectrochemical impedance spectroscopy (PEIS). The theoretical PEIS responses for a two hole transfer process have been derived and related to the corresponding theoretical IMPS responses. PEIS and IMPS data as well as the steady state photocurrent characteristics have been analysed within the framework of a model involving hole capture to form a surface bound intermediate species. The effects of the accumulation of this species on the steady state and dynamic response of the electrode are discussed.

Pulsed laser ablation of a single crystal cadmium tungstate (010) surface studied by time-of-flight mass spectrometry

Pulsed laser ablation of a cadmium tungstate (CdWO4)(010) surface was studied by time-of-flight mass spectrometric analysis at 532 and 266 nm. Single crystal CdWO4(010) surfaces with fewer defects than in previous work [J. Appl. Phys. 77. 6581 (1995)] are used, from which the kinetic energy (KE) of O2+ increased linearly with laser fluence. The KE observed at 266 nm was four times larger than that at 532 nm. This result can be explained by the difference between absorption coefficients of the plasma formed at the two laser wavelengths. This fact suggests an inverse bremsstrahlung process in which the desorbed species are accelerated in the flight path by the remaining part of the laser pulse. The desorption process was studied by changing the temperature of the CdWO4 target from 100 to 900 K at a constant laser fluence. As the temperature of the CdWO4 target increased, intensities of desorbed species increased while their KEs were almost constant. These results can be explained well in terms of a temperature dependence of the thermal desorption process of the photochemically formed desorption precursory state. The activation energy (0.3 eV) implies that the desorption precursory species are physisorbed on the surface. The data were analyzed with shifted Maxwell–Boltzmann velocity distributions, in which Maxwell–Boltzmann temperatures and Mach numbers were elucidated as functions of both laser fluence and CdWO4 target temperature.

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The extracellular secretions are believed to have a significant influence on microorganisms physicochemical properties related to growth, morphological preservation, and environment stress defense. In this study, the response and potential detoxification role of the extracellular secretions in the widely used white-rot fungus, Phanerochaete chrysosporium, was investigated. The results indicated that the EPS production was elevated and the activities of two main ligninolytic enzymes (LiP and MnP) were generally inhibited by cadmium. At the early exposure period (0–8 h), the extracellular protein was induced by 50 μM cadmium. However, an opposite result was observed with further increase in exposure time. The oxalate secretion under cadmium stress increased by 73.2%–218.4% compared to control. The addition of oxalic acid resulted in elevation in P. chrysosporium viability up to 190.6%, which confirms the detoxification of oxalate. The extracellular secretions such as EPS, extracellular protein and oxalate were elevated in some extent by cadmium, which was probably a stress response for P. chrysosporium to bind cadmium ion and cope the toxicity. Moreover, extracellular biosynthesis of cadmium crystal particles was observed, which is a directly evidence of P. chrysosporium extracellular secretions to reduce the mobility and bioavailability of cadmium ion.

Anomalous temperature dependence of the yield stress by [formula omitted] secondary pyramidal slip in cadmium crystals—I. Experiments

Yield stress σ y due to {11 22}〈 1123〉 slip (SPCS) in cadmium crystals is proportional to temperature T (anomalous temperature dependence). An increment of strain rate causes σ y to increase. The deformation proceeds inhomogeneously with the nucleation and growth of bundles of slip steps (BSS) which correspond to etch pit bands (EPB). The strain ϵ B in BSS or EPB is constant independent of applied strain. The density of dislocations in EPB is nearly constant independent of strain, strain rate and T. ϵ B and the mean free path of edge dislocations decrease exponentially with increasing T. The above results suggest that the deformation mode by SPCS is similar to Lüders deformation and the growth rate of BSS or EPB width increases with increasing T and strain rate. The anomalous temperature dependence is interpreted by the immobilization of edge dislocations and the growth rate related with double cross slip.

Anomalous temperature dependence of the yield stress by [formula omitted] secondary pyramidal slip in cadmium crystals—II. Mechanism

The yield stress due to {11 22}〈 1123〉 second order pyramidal slip in cadmium crystal increases with increasing temperature. The mechanism of this anomalous temperature dependence is proposed on the basis of experimental results shown in our previous paprer. A ( c + a) edge dislocation is dissociated into a c sessile dislocation and an a basal one by thermally activated process, and the ( c + a) edge dislocation is immobilzed as a result. The immobilization causes the mean free path of the edge dislocations and the strain in slip bands to decrease with increasing temperature. Consequently, double cross slip of ( c + a) screw dislocations must be activated thermally by a increment of applied stress to increase propagation velocity of slip band width. Since each of the mean free paths and the strain slip bands is nearly constant independent of strain and strain rate, the increasing of propagating velocity with increasing strain rate is achieved also by an increment of applied stress.

AXIALLY ASYMMETRIC STRESSES IN A TRANSVERSELY ISOTROPIC, SHORT CYLINDER SUBJECTED TO SECTORIAL PRESSURES ON THE END FACES

An analysis of axially asymmetric stresses in a transversely isotropic, short cylinder subjected to sectorial pressures on the end faces is presented. The generalized Elliott solution is used for the analysis. The solution yields two different elasticity solutions to be necessary for satisfying boundary conditions at the end faces and the side surface. Magnesium and cadmium crystals and an isotropic material are treated. Numerical results for displacements and stresses in these materials are illustrated. The effect of anisotropy on the displacements and stresses is examined through a comparison with the isotropic material.

Angular dependence of the PAC spectrum in a quenched single crystal of cadmium

To examine the orientation and magnitude of the electric field gradient (EFG) created by a vacancy at the111In probe site, PAC spectra were measured in a Cd single crystal as a function of the crystal orientation after a quenching and aging treatment at 120 K. The results are compared with calculated spectra based on a point charge model of the EFG created by a vacancy at the site of the probe atom.

Picosecond Optical Second Harmonic Studies of Adsorbate Reduction Kinetics on Cadmium Sulfide

AbstractTime resolved surface second harmonic generation has been used to probe the photoreduction kinetics of malachite green adsorbed onto single crystal cadmium sulfide. A detailed analysis is presented of how the adsorbates and the noncentrosymmetric substrate contribute separately to the total second harmonic signal. Conditions under which the adsorbates can be cleanly detected are described. To complement kinetic measurements of adsorbate reduction, the time evolution of conduction band carriers was determined using sum frequency up conversion of the recombination luminescence. In addition, the formation and decay of surface trapped carriers was monitored using near infrared transient absorption. Comparing the time scale for photoreduction with the relaxation kinetics of mobile and trapped charge carriers indicates that short lived mobile carriers rather than longer lived surface trapped carriers dominate interfacial charge transfer in this system.

Photoelectrochemical behaviour of polypyrrole coated cadmium telluride

Abstract The electrochemical polymerization of pyrrole to polyprolle on the surface of single crystal cadmium telluride is faster and takes place at lower potential under illumination than in the dark due to photoproduced holes. Photoelectrochemical characteristics of bare and coated electrodes are examined in polysulphide and polyiodide electrolytes. While the performance of both bare and coated electrodes is poor in polysulphide, in polyiodide photocorrosion of cadmium telluride is partially suppressed.

TEM Studies of Er+ – implanted CdTe

AbstractThe structure and the depth distribution of radiation damage caused by erbium implantation (Ei = 100 keV, D = 5 × 1015 cm−2, Ti = LNT) in 〈111〉 cadmium telluride have been investigated by means of planar‐view and cross‐sectional TEM techniques. It is found that the implantation disturbes the CdTe target up to the depth well‐beyond the calculated projected range (that is ≳ × 5Rp). The resulting damage structure consists of well‐defined defects: precipitates, stacking faults, dislocation loops, and dislocation networks, which appear to be segregated with depth forming a sequence of homogeneously faulted zones. This characteristical and deep damage is suggested to be formed on dynamic annealing in response to internal stresses (caused by lattice parameter mismatch) which are high enough to produce plastic relaxation with dislocation generation and slip.This study is aimed at describing the ion‐implantation‐induced damage in single crystal cadmium telluride caused by Er+ ions by means of transmission electron microscopy.