Cadmium Vapor Research Articles

Chemical Vapor Deposition of Tantalum Carbide in the TaBr5–CCl4–Cd System

The tantalum carbide coatings were deposited on substrates made of 12Kh18N10T steel, ZhC6 alloy, and molybdenum by reduction of TaBr5 and CCl4 vapors with cadmium vapors at temperatures of 950–1000 K. The average deposition rate of coatings on molybdenum was ~5 μm/h, on ZhC6 alloy was ~6 μm/h, and on 12Kh18N10T steel was ~8 μm/h. The coatings were formed as columnar grains on the substrate surface and as a diffuse layer in the substrate material. The surface layers contained mainly tantalum monocarbide TaCy (y = 0.72–0.86) and a small fraction of tantalum. The coatings on the surface of ZhC6 alloy and 12Kh18N10T steel flaked off with increasing thickness, which was due to different thermal expansion of the coating and substrate, as well as concentration inhomogeneity and phase transitions in the substrate material during coating deposition and during the heating and cooling processes.

Bridgman-Grown (Cd,Mn)Te and (Cd,Mn)(Te,Se): A Comparison of Suitability for X and Gamma Detectors.

This study explores the suitability of (Cd,Mn)Te and (Cd,Mn)(Te,Se) as room-temperature X-ray and gamma-ray detector materials, grown using the Bridgman method. The investigation compares their crystal structure, mechanical and optical properties, and radiation detection capabilities. Both crystals can yield large-area single crystal samples measuring approximately 30 × 30 mm2. In low-temperature photoluminescence analysis, both materials showed defect states, and annealing in cadmium vapors effectively eliminated donor-acceptor pair luminescence in (Cd,Mn)Te but not in (Cd,Mn)(Te,Se). Moreover, harder (Cd,Mn)(Te,Se) exhibited a higher etch pit density compared to softer (Cd,Mn)Te. X-ray diffraction examination revealed uniform lattice constant distribution in both compounds, with variations at a part per million level. (Cd,Mn)Te crystals demonstrated excellent single crystal properties with narrower omega scan widths, while (Cd,Mn)(Te,Se) exhibited a high contribution of block-like structures with significantly larger misorientation angles. Spectroscopic evaluations revealed better performance of a pixelated (Cd,Mn)Te detector, in comparison to (Cd,Mn)(Te,Se), achieving a mean full width at half maximum of 14% for the 122 keV gamma peak of Co-57. The reduced performance of the (Cd,Mn)(Te,Se) detector may be attributed to deep trap-related luminescence or block-like structures with larger misorientation angles. In conclusion, Bridgman-grown (Cd,Mn)Te emerges as a more promising material for X-ray and gamma-ray detectors when compared to (Cd,Mn)(Te,Se).

Adsorption of cadmium vapor by calcium-based adsorbents in simulated flue gas: Experimental and density functional theory studies

Calcium-based adsorbents are considered as effective high-temperature adsorbents for the removal of heavy metal in the furnace. In this work, the adsorption characteristics and reaction mechanism of calcium-based adsorbents for cadmium vapor were investigated by adsorption experiments and density functional theory (DFT) methods. The adsorption experiments showed that the adsorption performance of CaO for cadmium vapor was significantly better than Ca(OH)2, Calcite and CaSO4. The adsorption capacity of CaO adsorbent for cadmium increased firstly and then decreased with the increase of temperature. The enhanced trapping capacity of CaO for cadmium vapor with increasing temperature was associated with enhanced chemisorption, while the decrease in trapping capacity at high temperature could be attributed to adsorbent sintering. In addition, the results of DFT calculations showed that CaO had good adsorption capacity for various Cd species, and the order of the adsorption capacity was: CdO > CdCl2 > CdCl > Cd. The chemisorption mechanism dominated the adsorption of Cd species on the CaO (001) surface, and the central O site was the reactive site and electron transfer channel for the adsorption of Cd. This work provided a reference for the application of heavy metal vapor capture technology based on calcium-based minerals.

Effect of doping and annealing on resistivity, mobility-lifetime product, and detector response of (Cd,Mn)Te

We present the effect of doping with In, V, and Cl on the values of resistivity (ρ) and mobility-lifetime (μτ) in (Cd,Mn)Te crystals grown by the Bridgman method and with diameters of 2 or 3 in. This material is investigated to use in room-temperature X-ray and gamma-ray detectors. We carried out post-growth annealing processes in cadmium vapors at 500 °C to obtain more homogeneous crystal properties. The EU-ρ-μτ-SCAN machine, which uses the principle of time-dependent charge measurement, allowed us to map the values of resistivity and mobility-lifetime in crystal plates. High values of those two quantities are crucial in nuclear detector applications. Crystals doped with In show inhomogeneous properties, which makes the fabrication of competitive large-area crystals more difficult. Low-temperature post-growth annealing in Cd vapors is insufficient for (Cd,Mn)Te:In crystals, where the decrease of ρ and μτ values is observed. Such annealing works for (Cd,Mn)Te:V crystals, where the mean values of ρ and μτ do not change significantly, but their distributions are more uniform. Both dopants, vanadium and indium, used together with an excess of Te, effectively increased ρ and μτ. Using the 57Co source, the spectroscopic performance of each pixel of the detector co-doped with In and V was shown.

Experimental and theoretical studies on the adsorption characteristics of Si/Al-based adsorbents for lead and cadmium in incineration flue gas

Si/Al-based adsorbents are effective adsorbents for capturing heavy metals in incineration flue gases at high temperatures in the furnace. In this work, the adsorption characteristics and adsorption mechanisms of Si/Al-based adsorbents for lead and cadmium vapors were studied using a combination of experimental and density functional theory (DFT) calculations. The trapping performance of a series of Si/Al-based adsorbents for Pb and Cd vapors was investigated using a self-designed gas-solid two-phase rapid adsorption experimental system. The results showed that kaolinite and montmorillonite exhibited better heavy metal adsorption capacity than SiO2 and Al2O3, and were significantly stronger for Pb than for Cd. Chemisorption dominated the capture of Pb/Cd by Si/Al-based adsorbents at high temperatures. The results of DFT calculations indicated that the chemisorption mechanisms dominated the adsorption of Pb and Cd species on the metakaolinite (001) surface, and the adsorption energy of Pb species on the metakaolinite surface was greater than that of Cd species. The exposed O atoms and unsaturated Al atoms of metakaolinite (001) surface were effective adsorption active sites for heavy metals and their chlorides. In the adsorption reaction, the binding of Pb/Cd atoms and surface exposed O sites, as well as the strong interaction between Cl and unsaturated Al atoms, were responsible for the capture of Pb and Cd chlorides by metakaolinite.

Polarization effects, shape resonances and bound states in low energy positron elastic scattering by Zinc and Cadmium vapours

Low energy elastic positron scattering from Zn and Cd atoms was studied using model correlation potential. Special attention is given to the study of polarization effects through the incorporation of quadrupole polarizabilities and hyperpolarizabilities in the scattering potential. Resonant p-wave shape structures are found for both systems. Results show that these become sharper and move to lower energies as the level of polarization of the potential is increased. Resonance was suppressed in Cd when the second hyperpolarizability γ was taken greater than 46000 a.u. and true p-wave bound states were formed. Comparison to previous calculations and dependence of the results with the scheme adopted to match the correlation and polarization components of the potential is discussed. We find that the elastic cross sections and the resonant effects do not depend on the specific form of the correlation potential but strongly depend on the polarization parameters and the matching point determined by the crossing between the correlation and polarization components of the potential. The value for the dipole–dipole–quadrupole polarizability B for Cd was specifically calculated using the relativistic coupled-cluster approach and is reported for the first time in this work.

Влияние условий осаждения из паров металлоорганических соединений на получение эпитаксиальных слоев n-CdTe с использованием изопропилиодида

The dependence of iodine incorporation in CdTe layers on the deposition conditions during metalorganic vapor phase epitaxy is investigated. The growth of the layers was carried out from dimethylcadmium and diethyltellurium in the hydrogen flow in a vertical reactor with a hot wall condition at a total pressure of 20 kPa. The total iodine concentration was determined by secondary ion mass spectrometry, the electrically active concentration was determined from the Hall effect measurement. The iodine incorporation depends on the crystallographic orientation of the substrate (were studied (100), (310), (111)A, (111)B, (211)A and (211)B), the concentration of the doping precursor (flux range 5·10–8–3·10–6 mol/min), the mole ratio of organometallic compounds (DMCd/DETe=0.25–4), growth temperature (335–390°C) and the walls of the reactor above the pedestal (hot wall zone 290–320°C). The total iodine concentration reached 5·1018 cm–3 and the activation efficiency was ~4 %. After thermal annealing in cadmium vapor at 500°C the activation efficiency was ~100 %.

Influence of growth conditions from metalorganic compounds on the preparation of n-CdTe epitaxial layers using isopropyl iodide

The dependence of iodine incorporation in CdTe layers on the deposition conditions during metalorganic vapor phase epitaxy is investigated. The growth of the layers was carried out from dimethylcadmium and diethyltellurium in the hydrogen flow in a vertical reactor with a hot wall condition at a total pressure of 20 kPa. The total iodine concentration was determined by secondary ion mass spectrometry, the electrically active concentration was determined from the Hall effect measurement. The iodine incorporation depends on the crystallographic orientation of the substrate (were studied (100), (310), (111)A, (111)B, (211)A and (211)B), the concentration of the doping precursor (flux range 5·10-8-3·10-6 mol/min), the mole ratio of organometallic compounds (DMCd/DETe = 0.25-4), growth temperature (335-390oC) and the walls of the reactor above the pedestal (hot wall zone 290-320oC). The total iodine concentration reached 5·1018 cm-3 and the activation efficiency was ~4%. After thermal annealing in cadmium vapor at 500oC the activation efficiency was ~100%. Keywords: epitaxial layers, metalorganic vapour phase epitaxy, CdTe, iodine doping, isopropyl iodide, thermal annealing.

Electric and photoelectric properties of vacuum-deposited ZnO:Al/CdS/p-Cd1−xZnxTe heterojunctions

The study of electric and photoelectric properties of anisotypic ZnO:Al/n-CdS/p-Cd1−xZnxTe heterojunctions made on unannealed and annealed substrates at high temperature (T = 1200 K) under conditions of minimum cadmium vapor pressure. Sequential application of CdS and ZnO:Al films to the surface of unannealed substrates of single-crystal p-Cd1−xZnxTe was performed by high-frequency magnetron sputtering. Based on the C-V-characteristics analysis, the main parameters of the barrier region of the obtained structures ZnO:Al/n-CdS/p-Cd1−xZnxTe have been determined and the dynamics of their change when irradiated with light of different wavelengths had been established. A relationship between physical processes that lead to a decrease in the concentration of deep levels in the n-CdS/p-Cd1−xZnxTe interface and the properties of the base material has been established.

Cadmium Vapor Concentration and Lifetime of the Upper Active Level of a He–Cd Nuclear-Pumped Laser at the 5s2 2D5/2–5p2P3/2 Cd II Transition

Cadmium Vapor Concentration and Lifetime of the Upper Active Level of a He–Cd Nuclear-Pumped Laser at the 5s2 2D5/2–5p2P3/2 Cd II Transition

Концентрация паров кадмия и время жизни верхнего рабочего уровня He-Cd-лазера с ядерной накачкой на переходе 5s-=SUP=-2-=/SUP=- -=SUP=-2-=/SUP=-D-=SUB=-5/2-=/SUB=--5p-=SUP=-2-=/SUP=-P-=SUB=-3/2-=/SUB=- Cd II

Experimental method is described and results of measurement of the cadmium vapor concentration in a nuclear pumped He-Cd laser on the cadmium ion transition with wave length 0.441 μm are presented . It is shown that observed concentration is about ten times less then saturated one for given temperature of laser cuvette. On the base of obtained data the conclusion is made that life time of the upper level for CdII 5s2 2D5/2 -5p2P3/2 transition in a optimum condition of He-Cd laser operation equals about 0.5 μs.

Електричні та фотоелектричні властивості гетеропереходів MoN/p-CdTe та MoN/n-CdTe

Due to the physical properties of MoN and ITO thin films, it was decided to create MoN/p-CdTe and MoN/n-CdTe heterostructures and investigate their electrical and photoelectric properties. The method of reactive magnetron sputtering was used to create thin MoN and ITO films on single crystal CdTe substrates with different conductivity types. To manufacture test heterostructures, the following CdTe crystal substrates were used: 1) p-type conductivity, grown by Bridgman technique at low cadmium vapor pressures; 2) n-type conductivity, grown by Bridgman technique at high cadmium vapor pressures. During the deposition process, the argon pressure in the vacuum chamber was 0.4 Pa. The power of the magnetron was 30 W, the sputtering process continued 5 min at a substrate temperature of 150°C. I-V characteristics of the heterostructures at different temperatures were measured, the height of the potential barrier, the values of the series and shunt resistance were determined. Electrical and photoelectric properties of the heterostructures were studied, and the dominant mechanisms of current transfer at forward displacements was established. The tunnel-recombination mechanism was found to be the dominant mechanism of current transfer in the MoN/p-CdTe and MoN/n-CdTe heterostructures. It was shown that the photoelectric parameters for the MoN/p-CdTe heterostructure are higher than those for MoN/n-CdTe. MoN/p-CdTe heterojunctions have the following photoelectric parameters: open-circuit voltage Voc = 0.4 V, short-circuit current Isc = 24.6 mA/cm2 at an illumination intensity of 80 mW/cm2. This makes them a promising material for the manufacture of detectors of various radiation types.

Room-temperature ferromagnetism in nanostructured submicron Cd/CdO particles

Cd/CdO submicron particle sets (Ps) with average particle sizes of about 1 μm were prepared by using the modified levitation-jet method through condensation of metallic cadmium vapor in helium gas flow with an appropriated in situ oxidation. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and vibrating sample magnetometry were used for the Ps characterization. Room-temperature ferromagnetism with maximum saturation magnetization up to 37 memu/g was discovered in the Ps with nanostructured polymorphic layered (terraced) morphology. This magnetization has achieved its maximum when CdO content was about 1.2 at.%. Ps with maximum magnetization possessed a certain unit cell volume of the Cd component. It is suggested that the observed ferromagnetic ordering may be related to intrinsic Cd defects in the Cd side of Cd/CdO interface areas.

Tantalum chemical vapour deposition on steel and tungsten substrates in the TaBr5-Cd-He system

The composition of coating layers deposited on the surface of 12Kh18N10T stainless steel (similar to 321 AISI) in the TaBr5-Cd-He system at temperatures ranging from 623 К to 1423 К and at a pressure of 1 atm was evaluated using thermodynamic analysis. Tantalum-based coatings were deposited on 12Kh18N10T and tungsten substrates by chemical vapour deposition (CVD) using reduction of tantalum bromide vapour by cadmium vapour at а temperature of 1023 К. The formation of β-Ta, diffuse layers of Ta-Fe as well as Fe2Ta-based Laves phase in the deposited coating layers has been analysed.

High-temperature electrical properties of undoped Cd1-xMnxTe (x = 0.05-0.55) crystals under cadmium vapor pressure

For the first time, the results of a study of the high-temperature electrical characteristics of undoped Cd1-xMnxTe single crystals in a wide composition range x = 0.05-0.55 are described. For this purpose, a study of Hall effect was made at the temperatures of 723–1073 K and isothermal and temperature dependences of electrical parameters were constructed. At 300 K, all the samples studied had a p-type conductivity, and Cd1-xMnxTe crystals with x = 0.02 and 0.15 had a low resistivity (102-103 Ohm×cm) while with x = 0.3 and 0.55 they had a relatively high ρ~ 107 Ohm×cm, which is due to an increase in the band gap with an increase in the MnTe content. The sample with the lowest Mn content (x = 0.02) showed the instability of the impurity-defect system during the first heating-cooling cycles: the conductivity type changed from p- to n- above 750 K and the mobility gradually increased as a result of the introduction of Cd atoms from the gas phase to the interstitial positions of the lattice. In this sample, during the first heating, the influence of donor impurities is noticeable, since the experimental line lg[e-] is significantly (~ 1-1.4 orders of magnitude) higher than that for model (undoped) CdTe, probably due to the donor behavior of Mn atoms. The crystal with the highest MnTe content (Cd0.45Mn0.55Te) also demonstrated the instability of the impurity-defect system, which was reflected in the decrease in the electrical conductivity after heat treatment at 773-873 K by almost one order of magnitude, which can be explained by a superposition of the results of the interaction of donor Cd atoms introduced from the gas phase with its native acceptor point defects (compensation) and the interaction of impurities between the matrix and Te inclusions. It has been established that a peculiarity of Cd1-xMnxTe crystals with a high content MnTe (x = 0.15, 0.55, and partially 0.3) is the inverse dependence of the carrier concentration on the cadmium vapor pressure caused by the onset of mixed conductivity of these crystals at high temperatures (T> 873 K). Accordingly, for these crystals, the value 1/RH at the moment of the onset of mixed conductivity characterizes the conditional rather than real mobility of the charge carriers. On the pressure dependences of the charge carrier concentration, the corresponding dependences are lower than the undoped CdTe (especially at low temperatures) for samples with x≥0.15 indicating that the introduction of a significant amount of MnTe (x≥0.15) leads to a decrease in the charge carrier concentration by 0.5-0.8 orders of magnitude (at ~ 773 K). This is due to the influence of Mn atoms, which form a stronger bond with Te than Cd, and therefore the generation of electrons requires more energy than in pure CdTe.

Accumulators for the Capture of Heavy Metals in Thermal Conversion Systems

A clay ceramic with organic additives (biomass and biochar) was investigated for the development of highly porous accumulators to capture heavy metals in thermal conversion systems. The structure was characterized using X-ray pair distribution function analysis, differential scanning calorimetry, and scanning electron microscopy. It was found that the organic additives transformed into porosity during firing. The morphology of the pores also corresponded to the morphology of the organic additives. Hence, the clay ceramic with a 15-wt% addition of biochar had a porosity of 46 vol% with 20-μm interconnected pores after firing. The resulting accumulator was found to capture cadmium (a model for heavy metals with high volatility) via condensation of the cadmium vapor as 2-μm beads in the pores. The cadmium capture efficiency reached up to 57% using a 15-wt% addition of biochar. Furthermore, cadmium was captured at higher temperatures than the condensation temperature in the atmosphere. This means that heavy metals may be captured before they condense in fly ash to promote the recycling of this material.

Tantalum chemical vapor deposition on substrates from various materials

Tantalum coatings have been produced for the first time by hydrogen-free chemical vapor deposition through reduction of tantalum pentabromide with cadmium vapor, which allowed the deposition temperature to be substantially reduced (by more than 200 K). The coatings consisted of α- and/or β-Ta, depending on the substrate material.

Evaluation of cadmium concentration in vapour phase by a novel approach

An indirect way of assessing cadmium concentration in confined volume was attempted. This aim was met by measuring the oxygen concentration before and after reaction with cadmium vapour. The deduced cadmium concentration value corroborated with the data obtained from cadmium vapour pressure at different temperature.

Controlling the BET Surface Area of Porous Carbon by Using the Cd/C Ratio of a Cd-MOF Precursor and Enhancing the Capacitance by Activation with KOH.

Herein, four new cadmium metal-organic frameworks (Cd-MOFs), [Cd(bib)(bdc)]∞ (1), [Cd(bbib)(bdc)(H2 O)]∞ (2), [Cd(bibp)(bdc)]∞ (3), and [Cd2 (bbibp)2 (bdc)2 (H2 O)]∞ (4), have been constructed from the reaction of Cd(NO3 )2 ⋅4 H2 O with 1,4-benzenedicarboxylate (H2 bdc) and structure-related bis(imidazole) ligands (1,4-bis(imidazol-1-yl)benzene (bib), 1,4-bis(benzoimidazol-1-yl)benzene (bbib), 4,4'-bis(imidazol-1-yl)biphenyl (bibp), and 4,4'-bis(benzoimidazol-1-yl)biphenyl (bbibp)) under solvothermal conditions. Cd-MOF 1 shows a 2D (4,4) lattice with parallel interpenetration, whereas 2 displays an interesting 3D interpenetrating dia network, 3 exhibits an unusual 3D interpenetrating dmp network, and 4 presents a 3D self-catenated pillar-layered framework with a Schäfli symbol of [43 ⋅63 ]2 ⋅[46 ⋅616 ⋅86 ]. The structural diversity indicates that the backbone of the bis(imidazole) ligand (including the terminal group and spacer) plays a crucial role in the assembly of mixed-ligand frameworks. By using the pore-forming effect of cadmium vapor, for the first time we have utilized these Cd-MOFs as precursors to further prepare porous carbon materials (PCs) in a calcination-thermolysis procedure. These PCs show different porous features that correspond to the topological structures of Cd-MOFs. Significantly, it was found that the specific surface area and capacitance of PCs are tuned by the Cd/C ratio of the MOF. Furthermore, the as-synthesized PCs were processed with KOH to obtain activated porous carbon materials (APCs) with higher specific surface area and porosity, which greatly promoted the energy-storage capacity. After full characterization, we found that APC-bib displays the largest specific surface area (1290 m2 g-1 ) and total pore volume (1.37 cm3 g-1 ) of this series of carbon materials. Consequently, APC-bib demonstrates the highest specific capacitance of 164 F g-1 at a current density of 0.5 A g-1 , and also excellent retention of capacitance (≈89.4 % after 5000 cycles at 1 A g-1 ). Therefore, APC-bib has great potential as the electrode material in a supercapacitor.

Magnetocapacitance in CdCr1.8In0.2S4Single Crystal Annealed in Cadmium Vapor

CdCr2S4 single crystal was reported by Hemberger et al. to be multiferroic with the evidences of relaxor ferroelectricity and colossal magnetocapacitance (CMC), but whether these effects are intrinsic is under debate. Recently, we reported a one-to-one correlation between CMC and colossal magnetoresistance (CMR) in CdCr2S4 polycrystalline samples, and argued that CMC could be explained by the superposition of the CMR and the Maxwell–Wagner effects. In this paper, we further examined the magnetic, dielectric, and electric transport properties of CdCr2S4 and CdCr1.8In0.2S4 single crystals before and after annealing in cadmium vapor. The CdCr2S4 single crystal sample has no relaxor ferroelectricity and CMC, and in contrast to the CdCr2S4 single crystal reported by Hemberger et al. , only the annealed CdCr1.8In0.2S4 displays CMC, but still does not exhibit the relaxor behavior. At the same time, it also shows CMR. All these results are in accordance with the results of our polycrystalline samples, and further confirm the resistive origin of the CMC in the CdCr2S4 system.