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This article presents examples of an application of the finite field method for the computation of the characteristic polynomial of the matching arrangement of a graph. Weight functions on edges of a graph with weights from a finite field are divided into proper and improper functions in connection with proper colorings of vertices of the matching polytope of a graph. An improper weight function problem is introduced, a proof of its NP-completeness is presented, and a knapsack-like public key cryptosystem is constructed based on the improper weight function problem.

We emphasize an improvement of the surface processing procedures for cadmium zinc telluride (CZT) detectors, which is one of the principal problems limiting the technology. A rough surface enhances the leakage current into the medium, creating additional trapping centers and thereby degrading the detector’s performance. Mechanical polishing followed by chemical treatment yields smoother surfaces as required, but chemical treatment, especially with bromine-based solutions, induces unwanted surface features, increases the surface conductivity, and generates chemical species that alter the material’s surface and interfacial properties. It is essential to avoid such adverse consequences of surface etching in the manufacturing of highly efficient radiation detectors. We approached the problem of processing the crystals’ surfaces by using two different solutions (a low-concentration bromine-based etchant mixture in conjunction with a surface-passivation reagent and a non-bromine-based etchant). The chemomechanical treatment yielded smooth nonconductive surfaces with fewer detrimental features, therefore allowing us to fabricate better devices. We determined the surface roughness using atomic force microscopy and optical profilometry (OP). We analyzed the surface structure, orientations of the crystals, and formation of chemical species by x-ray photoelectron spectroscopy techniques and delineated their effects on the devices’ electrical properties and performance. Our experimental data revealed that our new chemical etching process produced nonconductive surfaces with fewer surface defects and so improved the detectors’ charge transport and efficiency. We detail the results of our new etchants and compare them with those for conventional Br-methanol etchants.

CdMnTe offers several potential advantages over CdZnTe as a room-temperature gamma-ray detector, but many drawbacks in its growth process impede the production of large, defect-free single crystals with high electrical resistivity and high electron lifetimes. Here, we report our findings of the defects in several vanadium-doped as-grown as well as annealed Cd^sub 1-x^Mn^sub x^Te crystals, using etch pit techniques. We carefully selected single crystals from the raw wafer to fabricate and test as a gamma-ray detector. We describe the quality of the processed Cd^sub 1-x^Mn^sub x^Te surfaces, and compare them with similarly treated CdZnTe crystals. We discuss the characterization experiments aimed at clarifying the electrical properties of fabricated detectors, and evaluate their performance as gamma-ray spectrometers. [PUBLICATION ABSTRACT]

We studied, by current deep-level transient spectroscopy (I-DLTS), point defects induced in CdZnTe detectors by three dopants: Pb, Bi, and In. Pb-doped CdZnTe detectors have a new acceptor trap at around 0.48 eV. The absence of a V Cd trap suggests that all Cd vacancies are compensated by Pb interstitials after they form a deep-acceptor complex [[Pb Cd ] + -V Cd 2− ] − . Bi-doped CdZnTe detectors had two distinct traps: a shallow trap at around 36 meV and a deep donor trap at around 0.82 eV. In detectors doped with In, we noted three well-known traps: two acceptor levels at around 0.18 eV (A-centers) and 0.31 eV (V Cd ), and a deep trap at around 1.1 eV.

— The effect of the surface state of 316L steel samples, which were obtained by selective laser melting, on the mechanical characteristics, stages and fracture mechanisms, acoustic emission parameters, and the strain-state characteristics, which were estimated by the digital image correlation method, has been studied. A decrease in the static and fatigue strength of as-built samples in the region of low loading amplitudes and an increase in the elongation at fracture have been revealed compared to these characteristics for machined samples. For as-built samples, the appearance of high-amplitude acoustic emission signals indicating the nucleation of surface microcracks at an earlier deformation stage has been detected. It is assumed that knee point on the fatigue curves and amplitude dependences of the characteristic zones size at fracture surfaces are associated with the transition from a plane stress state to a plane strain state of the material with a decrease in the stress amplitude.

Understanding of self- and dopant-diffusion in semiconductor devices is essential to our being able to assure the formation of well-defined doped regions. In this paper, we compare obtained in the literature up to date the Arrhenius’ parameters ( D = D 0 exp(−Δ E a / kT )) of point-defect diffusion coefficients and the I-VII groups impurities in CdTe crystals and films. We found that in the diffusion process there was a linear dependence between the pre-exponential factor, D 0 , and the activation energy, Δ E a , of different species: This was evident in the self-diffusivity and isovalent impurity Hg diffusivity as well as for the dominant IIIA and IVA groups impurities and Chlorine, except for the fast diffusing elements (e.g., Cu and Ag), chalcogens O, S, and Se, halogens I and Br as well as the transit impurities Mn, Co, Fe. Reasons of the lack of correspondence of the data to compensative dependence are discussed.

The influence of preliminary cyclic loading on the strength characteristics of additive 316L steel manufactured by selective laser melting, its damage, acoustic emission parameters, and characteristics of deformed state estimated by the digital image correlation is studied. The stages of fracture are analyzed during material tension before and after preliminary cycling taking into account the kinetics of changing acoustic emission parameters and deformation characteristics (maximum principal strains and the plastic zone areas). The fatigue characteristics of the additive 316L steel are found to be substantially lower than those of the 316L steel manufactured by traditional technology. Preliminary cyclic loading causes opening of technological defects in a structure and the formation of small cracks. Tensile tests of such specimens are found to lead to the growth of the residual strength and the fracture energy, and these characteristics decrease sharply at a relative life of 0.7 of the number of cycles to failure. The main fracture mechanism of the additive 316L steel is the opening and growth of small cracks initiated on technological defects. The growth of small cracks during cyclic loading influences the kinetics of acoustic emission parameters estimated during tension of previously cycled specimens, which confirms high informativeness of this method for analyzing the fracture stages of materials.

Surface passivation reportedly is an effective technique for controlling surface leakage current and its related electronic noise. Several chemical agents have been effectively used for passivating cadmium zinc telluride (CdZnTe or CZT) surfaces; however, the long-term stability and the adverse effect on the metal contacts remain questionable. In this study, we reviewed two popular passivating agents, viz. hydrogen peroxide (H 2 O 2 ) and a mixture of ammonium fluoride and hydrogen peroxide (NH 4 F + H 2 O 2 ). Our aim was to identify an ideal one that can effectively and permanently lower surface leakage currents without adversely affecting the metal contacts. We characterized their topographic features and their long-term effectiveness in terms of detector performance, and compared the results to understand their nature. We determined which chemical species were formed, and recorded the peaks of elemental Cd and Te via x-ray photoelectron spectroscopy (XPS) and micron-scale spatial resolution x-ray fluorescence ( μ -XRF). We describe in detail the formation of new chemical species and the material nonuniformity of differently treated surfaces. Their effectiveness was assessed from experimental findings of their electrical properties and the spectral response. Our results imply that both passivating agents lowered the surface leakage current, and improved the detection efficiency of the CZT detectors, but their effectiveness was unstable over time.

The kinetics of microcracks accumulation and fracture at various stages of tension of grade 20 steel samples with coarse-grained and ultrafine-grained (UFG) structure obtained by equal-channel angular pressing (ECAP) has been studied. To research the effect of mechanical degradation, a part of the samples were subjected to preliminary cycling to a relative lifetime of 50%, followed by tensile tests, during which the parameters of acoustic emission and deformation fields obtained by digital image correlation were evaluated, and the intensity of the residual magnetic field was measured. The length and density of surface microcracks were measured by optical microscopy using computer image analysis. It is established that pre-cycling causes hardening of the material and a decrease in its plasticity. The fracture stages were revealed, and the origins of fatigue cracks were found on the internal delaminations of samples with a UFG structure after preliminary cyclic loading. It is shown that the formation of the UFG structure after the ECAP of samples made of grade 20 steel leads to hardening and reduction of the fracture work, the area of the plastic zone, maximum major deformations and damage, as well as to an increase in the number of AE signals and the intensity of the residual magnetic field.

We investigated the effects of post-growth annealing on cadmium zinc telluride crystals intended for use as room-temperature radiation detectors. Annealing under Cd vapor effectively eliminated Te inclusions. The material’s resistivity was lowered, and loss of Zn component was observed. Annealing under Cd + Zn vapors similarly removed Te inclusions. Furthermore, after exposure to the two vapors, we noted a change in the crystal surface morphology, i.e., formation of patterns of parallel lines. In contrast to annealing under Cd vapor alone, high resistivity was maintained after suitably controlling the Cd and Zn pressures.