Z. Swiatek

Electrodeposition of Zn-Ni protective coatings from sulfate-acetate baths

Abstract The electrodeposition conditions for Zn–Ni alloys from sulfate–acetate electrolytes have been studied with the view of preparing protective coatings. The influence of electrolyte composition (different [Ni(II)]/[Zn(II)] ratios, pH, buffer), cathode current density, cathode potential and hydrodynamic conditions on the composition of coatings, cathode current efficiency and corrosion resistance were determined. For all of the conditions examined, strong inhibition of nickel reduction with simultaneous increase in the rate of zinc discharge characteristic of an anomalous system, have been observed. The Zn(II) discharge becomes diffusion-controlled at more negative cathode potentials, whereas the partial nickel current densities are independent of electrode rotation speed. Consequently, nickel content and current efficiency are reduced with decreasing thickness of the diffusive layer. An increase in pH above 3.3 causes a significant catalysis of Zn–Ni deposition with a simultaneous decrease of the nickel in coatings. This effect may be related to the formation and increasing concentration of Zn(II) and Ni(II) acetate complexes in this condition. The Zn–Ni coatings obtained (5–18% Ni) characterise improved corrosion resistance in comparison to Zn layers deposited under the same conditions.

Influence of structural factor on corrosion rate of functional Zn–Ni coatings

Abstract The electrocrystallization processes of Zn–Ni coatings from weakly acid sulfate solutions with the addition of citrate and acetate complexing compounds have been compared. The deposition kinetics and the influence of electrolyte composition on the Zn–Ni alloy composition and on some physicochemical properties (corrosion resistance, texture, phase composition, morphology) were determined. It was found that the properties of coatings obtained under the same operating conditions in electrolytes with the same [Ni(II)]/[Zn(II)] concentration ratio and pH but containing different complexing agents were different. The composition of the deposits and their texture as well as phase structure were found to depend on the complexing species present. Coatings deposited from acetate solutions are richer in Ni than those from citrate solutions. The corrosion resistance of a Zn–Ni alloy depends in practice on the percentage of Ni, but in sulfate–citrate electrolytes, layers containing less Ni were obtained with the same corrosion resistance as Ni-rich coatings deposited from acetate solution. The corrosion current decreases more rapidly with increasing Ni content. This effect is connected mainly with phase composition. In citrate solutions practically single-phase (hexagonal η) deposits were obtained which provide better protection with a lower corrosion rate in comparison with alloys consisting of three phases (hexagonal η, monoclinic δ, regular γ) deposited from acetate baths.

Thermostability of physical properties of cadmium telluride crystals

Time-dependent changes of electrical properties are investigated in the range of relative low heating temperatures (Ta 320 to 450 K) for undoped p-CdTe grown by various methods. It is established that the character and direction of the observed changes depend on the level of uncontrolled impurities (Cu preferably), their charge state and the association degree of impurities with intrinsic (VCd) defects. CdTe:Ge (Sn,Pb) crystals are characterized with a high thermostability of electrical properties. q 2000 Elsevier Science S.A. All rights reserved.

Photo and X-ray sensitive heterostructures based on cadmium telluride

In the given paper spectral and dose sensitivity characteristics of heterojunctions with cadmium telluride as one of the components were investigated. Possibilities of investigated structures use for solar cells and X-ray irradiation detectors are being discussed.

Theoretical study of the photovoltaic effect in thin variable-gap semiconductor layers

The report presents the results of a theoretical investigation of the photovoltaic effect in thin variable-gap semiconductor layers whose thickness is comparable with the ambipolar diffusion length. The cases of layers of extrinsic and intrinsic types of conductivity with a linear coordinate dependence of band-gap are analyzed in detail. The layers are assumed to be subjected to illumination by highly absorbed light from the wide-gap surface. It is shown that, due to the presence in the photovoltage of both the field and Dember components, sign inversion points may occur on the spectral dependence of the photovoltaic effect. The possibilities of practical use of the specific features of the photovoltaic effect in thin variable-gap layers on the basis of CdHgTe solid solution are discussed.

New X-ray diffraction method for materials science

Abstract A new and very promising X-ray diffraction method for the texture and internal stress investigation is described. This method, based on the conventional pole figure measurements in the back-reflection technique, affords possibilities for investigations of the diffraction effects due to layers on a given depth in a material. The condition of constant information depth is attained by abandoning the Bragg–Brentano localization geometry, using an appropriate offset angle for each sample tilt angle. During such measurement, after selection of the adequate offset angle, its corresponding change proceeds automatically. In order to obtain satisfactory integrated intensities, a pseudo-position sensitive detection technique is applied. The proposed method in this non-symmetrical mode is both a recommendable and useful tool for studying textured and epitaxial thin films as well as multi-layer systems.

Structural changes in graded band-gap epitaxial layers HgCdTe after ion implantation

The results of X-ray AFM, SEM, and SIMS studies of near-surface regions of HgCdTe graded-gap epitaxial layers obtained by high-temperature annealing in vapour of the main components have been presented. We used ISOVPE layers of HgCdTe grown on CdTe substrates the surface of which was implanted by As ions. The AFM investigation has shown that the morphology of surfaces of HgCdTe structures obtained at the same conditions is significantly influenced by the crystal orientation of the initial substrates of CdTe. By means of SIMS and SEM analysis a substantial increase of the molar content of HgCdTe solid solution on the surface of ion-implanted epitaxial layers after high-temperature annealing has been observed. It is shown that large gradients of composite HgCdTe solid solution are formed in the near-surface regions of the epitaxial layers due to small changes in the thermodynamically equilibrium conditions of the process of high-temperature annealing.

Controlled arsenic diffusion in epitaxial CdxHg1−xTe layers in the evaporation–condensation–diffusion process

Abstract The results of controlled doping of Cd x Hg 1− x Te epitaxial layers are presented. The investigated layers were obtained by the evaporation–condensation–diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly doped in the process of synthesis and unalloyed with ion implanted surface layer, have been used as sources of As diffusant. Comparative analysis of galvanomagnetic measurements and SIMS spectra was carried out. The results of investigations indicate the very high, almost 100%, electrical activity of As dopants in the Cd x Hg 1− x Te epitaxial grown layer.

Photoelements based on CdTe diodes with a surface barrier

Abstract The possibility of using ITO–pCdTe and Au–nCdTe compounds for photovoltaic purposes was investigated. For n-CdTe samples under AM2 illumination at 300 K, an efficiency of 13% was achieved.

Photoelectric properties of cadmium-zinc telluride heterojunctions

Abstract Integral and spectral characteristics of photodiodes with cadmium–zinc telluride heterojunction were investigated. The samples were obtained by solid phase substitution method using n-CdTe and p-ZnTe substrates with low resistivity. The application possibilities of heterojunctions studied are discussed.