Correlations between the thermodynamic properties of II–VI and III–VI phases

Simple correlation models are considered that can be used to predict unknown and refine questionable thermodynamic properties of II–VI and III–VI semiconductors. An empirical rule is proposed: for a particular combination of Periodic Groups, the enthalpy and Gibbs energy of formation of isostructural A _n B _m compounds are linear functions of the melting point.     

Influence of electron bombardment on recombination and attachment in II–VI—IV–VI film photoconductors

An investigation is made of the action of electron bombardment on wide-gap photosensitive films of II–VI compounds with submicron IV–VI inclusions which form bounded solid solutions with these compounds. It is shown that the radiation resistance of II–VI compounds is enhanced by adding IV–VI compounds. It is observed that the radiation acts differently on shallow and deep levels in the wide-gap semiconductor. An explanation is proposed for the experimental data using a heterophase semiconductor model. Pis’ma Zh. Tekh. Fiz. 25, 66–72 (February 12, 1999)     

Spin Manipulation Using Magnetic II–VI Semiconductors

Recently, efficient spin injection, being the first step towards semiconductor spin electronics, by using BeMnZnSe as a spin filter was accomplished. Such a spin filter made it possible to align the spin orientation of conduction electrons and subsequently inject them into GaAs. However, controlling spin orientation of conduction electrons by an external voltage would be very desirable for semiconductor-based magnetoelectronics. This can be accomplished by using spin switch structures, based on resonant tunneling through magnetic quantum wells, with two separate spin-up and spin-down resonances. Here we summarize both our recent results on spin injection as well as on spin aligner and magnetic resonant tunneling structures. For accomplishing the latter, we have developed magnetic resonant tunneling diodes based on BeTe–ZnMnSe–BeTe structures. Resonant tunneling diode is meant to serve as a spin switch because of the existence of two separate spin-up and spin-down resonances. The tunneling carriers have subsequently been injected into a nonmagnetic GaAs p–i–n light emitting diode. Circular polarization of the emitted light is an indicator of the spin polarization of injected electrons. At constant magnetic field and current, degree of spin polarization could be changed from 81% to 38% by only varying the voltage across the magnetic resonant tunneling device.     

Preparation of II–VI and IV–VI semiconductor films for solar cells by the isovalent substitution technique with a CBD-made substrate

II–VI and IV–VI semiconductor films for solar cell applications, namely, CdTe, CdS, CdSe, PbS, PbSe and PbTe, can be prepared in a two-stage deposition process. In this work we illustrate the two-stage process to obtain PbTe and CdSe films from precursor oxide or hydroxide films deposited by chemical bath deposition (CBD). At the first stage, plumbonacrite Pb₁₀(CO₃)₆O(OH)₆ or cadmium oxide/hydroxide CdO₂/Cd(O₂)_0.88(OH)_0.24 films were deposited onto a glass substrate by CBD, using an ammonia-free low-temperature process in an alkaline aqueous solution with corresponding ion sources. Then, at the second stage, the obtained film was placed in a chemical vapor deposition (CVD) Hot Wall reactor with gas transportation, where it acted as a substrate in the reaction of isovalent substitution of Te or Se for the nonmetallic film component, thus forming PbTe and CdSe films. A nitrogen flux of 0.25 L/min was used as the transporting gas. The source temperature was adjusted between boiling (Tb) and melting point (Tm) to control the flux gas of the source. The substrate temperature was adjusted to improve film quality. Structural and optical investigation of the films proved their high quality, which determines the possibility of using them as solar cell elements, in particular, in multijunction cells.     

A green route approach to the synthesis of Ni(II) and Zn(II) templated metal–organic frameworks

A new synthetic route involving mixing of solid reactants followed by heating has been developed for the preparation of two templated metal–organic frameworks (MOFs). [Ni(NO₃)₂(bipy)₂](pyrene)₂ (1) was obtained by mixing together Ni(NO₃)₂·6H₂O, 4,4-bipyridine and pyrene followed by heating at 85 °C for 4 h, while [Zn₂(fumarate)₂(bipy)] (2) was synthesized by mixing together Zn(O₂CCH₃)₂·2H₂O, fumaric acid and 4,4-bipyridine followed by heating at 160 °C for 16 h. The materials were characterized by elemental analysis, FT-IR spectroscopy and X-ray powder diffraction analysis (XRPD). Comparison of XRPD patterns of the materials with patterns simulated from the single crystal X-ray diffraction data, obtained from Cambridge Structural database, allowed identification of the products. Conversion of solid reactants to MOFs occurs spontaneously even when reactants are not mechanically stressed. Overall, the study suggests that MOFs can be synthesized in solid state simply by mixing together appropriate reactants without co-mill (ball-mill). Compared with traditional synthetic techniques such as solvothermal, ball-milling and solution-based, this method is environmentally friendly and highly efficient in the manufacture of these MOFs on a large scale.     

II–VI semiconductor alloy films: Cd1−xZnxTe

Electrical conductivity and optical properties of undoped and copper-doped Cd_1–xZn_xTe (0.1相似文献   

Low-temperature Grüneisen gamma of II–VI semicoductor ZnS

The theoretical study of low-temperature lattice thermal expansion of the II–VI semiconductor ZnS is attempted. The generalized Grüneisen gammas of the elastic waves propagating in different directions with respect to the [001] crystallographic axis of ZnS are calculated using the second- and third-order elastic constants. The values of mode Grüneisen gammas γ _j are determined and found generally positive except from γ ₂ at θ = 25° to θ = 65°. The low-temperature limit of the Grüneisen gamma is determined and compared with experimental values. Using this we calculated the Brugger gamma γ ^Br and hence the low-temperature volume lattice thermal expansion γ _L. It is expected that the volume expansion is positive down to absolute zero for ZnS.     

Long-term and controlled release of chlorhexidine–copper(II) from organically modified montmorillonite (OMMT) nanocomposites

Drug/metal ion complexes exhibit improved antimicrobial activity and intercalating the above complexes into the interlayer of clay endows a long-term and controlled-release behavior. In this study, chlorhexidine was first complexed with copper (II) ion and then intercalated into the interlayer of MMT to form chlorhexidine–copper (II)/montmorillonite (CHX–Cu/MMT) nanocomposites. The nanocomposites were characterized with Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). A nearly lateral-monolayer arrangement of CHX–Cu was supposed for the intercalation. Release kinetics indicated that the release process satisfied a pseudo-second-order mode. The antibacterial results showed that the CHX–Cu/MMT composites had long-term and controlled-release behavior.     

Size quantization effects in optical and electrical properties of II–VI semiconductor films in nanocrystalline form

The electrical properties of CdTe and optical properties of ZnS in nanocrystalline thin film form are studied with a view to have a clearer understanding of the optical processes and the carrier transport mechanisms in nanocrystalline II–VI semiconductors, in general. Nanocrystalline ZnS and CdTe films were deposited by magnetron sputtering of respective targets in argon plasma. The optical absorption data of nanocrystalline ZnS films (thickness 10–40 nm) could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites. The conductivity of CdTe (grain size within 4–4·7 nm) showed (T ₀/T) ^p dependence withp ∼ 0·5 indicating the presence of a Coulomb gap near the Fermi level. The width of the Coulomb gap varied within 0·02–0·04 eV depending on the deposition condition. The existing theoretical models were used for estimating hopping energy (0·02–0·04 eV) and hopping distance (2·8–5·1 nm) in nano CdTe films.     

Influence of cerium oxide (CeO2) nanoparticles on the microstructure and hardness of tin–silver–copper (Sn–Ag–Cu) solders on silver (Ag) surface-finished copper (Cu) substrates

Nano-sized, non-reacting, non-coarsening CeO₂ particles with a density close to that of solder alloy were incorporated into Sn–3.0 wt%Ag–0.5 wt%Cu solder paste. The interfacial microstructure and hardness of Ag surface-finished Cu substrates were investigated, as a function of reaction time, at various temperatures. After the initial reaction, an island-shaped Cu₆Sn₅ intermetallic compound (IMC) layer was clearly observed at the interfaces of the Sn–Ag–Cu based solders/immersion Ag plated Cu substrates. However, after a prolonged reaction, a very thin, firmly adhering Cu₃Sn IMC layer was observed between the Cu₆Sn₅ IMC layer and the substrates. Rod-like Ag₃Sn IMC particles were also clearly observed at the interfaces. At the interfaces of the Sn–Ag–Cu based solder-Ag/Ni metallized Cu substrates, a (Cu, Ni)–Sn IMC layer was found. Rod-like Ag₃Sn and needle-shaped Cu₆Sn₅ IMC particles were also observed on the top surface of the (Cu, Ni)–Sn IMC layer. As the temperature and reaction time increased, so did the thickness of the IMC layers. In the solder ball region of both systems, a fine microstructure of Ag₃Sn, Cu₆Sn₅ IMC particles appeared in the β-Sn matrix. However, the growth behavior of the IMC layers of composite solder doped with CeO₂ nanoparticles was inhibited, due to an accumulation of surface-active CeO₂ nanoparticles at the grain boundary or in the IMC layers. In addition, the composite solder joint doped with CeO₂ nanoparticles had a higher hardness value than the plain Sn–Ag–Cu solder joints, due to a well-controlled fine microstructure and uniformly distributed CeO₂ nanoparticles. After 5 min of reaction on immersion Ag-plated Cu substrates at 250 °C, the micro-hardness values of the plain Sn–Ag–Cu solder joint and the composite solder joints containing 1 wt% of CeO₂ nanoparticles were approximately 16.6 and 18.6 Hv, respectively. However after 30 min of reaction, the hardness values were approximately 14.4 and 16.6 Hv, while the micro-hardness values of the plain Sn–Ag–Cu solder joints and the composite solder joints on Ag/Ni metallized Cu substrates after 5 min of reaction at 250 °C were approximately 15.9 and 17.4 Hv, respectively. After 30 min of reaction, values of approximately 14.4 and 15.5 Hv were recorded.     

Unusual photoluminescence of Cu–ZnO and its correlation with photocatalytic reduction of Cr(VI)

Cu–ZnO was synthesized by sol–gel route with a varied copper concentration of 1, 2 and 3 mol%. The synthesized materials were structurally characterized with powder X-ray diffraction and Raman spectroscopy, morphologically using a field emission scanning electron microscope, and electronic properties were studied with UV–visible spectroscopy and photoluminescence spectroscopy. Variation in Cu doping showed enhancement/quenching in photoluminescence of ZnO. This special characteristic is reflected in photocatalytic reduction of Cr(VI).     

Deformation characteristics and real structure around indents on {111}A-surfaces of II–VI solid solutions

The microhardness of II–VI compounds and their solid solutions has been measured at temperatures from 0.2 to 0.44T _m. Deformation effects around indents on {111}_A-surfaces have been studied by means of selective etching. Changes in the real structure, reflected in the hardness-temperature slope, are discussed in terms of different rate-controlling mechanisms, e.g. dislocation slipping and climbing, and of solid solution hardening effects. Deformation by indentation is characterized, for the investigated temperature range, by an activation energy ofQ0.1 eV in the case of (Cd, Zn) (Te, Se) and ofQ=0.12 ... 0.23 eV for Hg-containing compounds. A slightly different hardness between {111}_A- and {111}_B-faces occurs in Hg_0.32Cd_0.68Te at temperatures between 360 K and 500 K. Critical stresses for -dislocation motion, derived from dislocation configurations around the indents, yield values ranging from 12.5 MPa at 295 K to 1.2 MPa at 500 K. Micro-twinning is one of the deformation modes of (Cd, Zn) (Te, Se) below 400 K.     

Ferroelectric and pyroelectric properties of rare earth based tungsten–bronze compounds

Complex polycrystalline materials [Li₂Pb₂R₂W₂Ti₄Nb₄O₃₀ (R = Dy, Sm)] of the tungsten bronze structural family have been synthesized using a high-temperature solid-state reaction (mixed-oxide) technique. The formation of the single phase compounds was checked using preliminary X-ray structural data/pattern. The nature and distribution of grains in the samples in the scanning electron micrographs confirm the good quality of the samples used for electrical characterization. Detailed studies of dielectric constant, tangent loss and electrical polarization as a function of temperature at different frequency confirmed the existence of ferroelectric properties in the materials at room temperature. Study of electrical properties (impedance, modulus, conductivity, etc.,) of the materials exhibits a strong correlation between their micro-structures (i.e., bulk, grain boundary, etc.) and electrical parameters. The frequency dependence of ac conductivity suggests that the materials obey Jonscher’s universal power law. Pyroelectric study shows that the materials have good pyroelectric coefficient and figure of merit.     

Structural and optical properties of inorganic–organic hybrid material of acetanilide tetrachloromercurate(II)

The crystal growth of acetanilide tetrachloromercurate(II), an inorganic–organic hybrid derivative has been achieved by solution growth through slow cooling method. The X-ray diffraction structural analysis of the hybrid material results that the compound exist in orthorhombic space group P2₁2₁2₁ with lattice parameters; a?=?13.111(2) ?, b?=?11.311(2) ?, c?=?8.355(6) ?, α?=?β?=?γ?=?90° and unit cell volume?=?1436.24 ?³. The fourier transform infrared spectroscopy profile shows that the C–C and C–N stretching modes of acetanilide ring and the observed spectra falls in mid-infrared range υ(526–2850) cm^?1. The field emission scanning electron microscope image confirms that the hybrid material has a prismatic shape with an average granular size of ~25 nm. The energy dispersive X-ray spectroscopy analyzes the elemental proportions of the hybrid materials. Transmission electron microscopy image shows the narrow distribution of nano-spatial agglomeration of secondary interactions in inorganic–organic particles. The optical band gap (Eg?=?3.75 eV) as calculated by linear fit profile of Tauc plot for allowed transition predicts that the hybrid material has potential applications in solar cells, electronic and opto-electronic devices.     

Comparative photocatalytic performance and therapeutic applications of zinc oxide (ZnO) and neodymium-doped zinc oxide (Nd–ZnO) nanocatalysts against Acid Yellow-3 dye: kinetic and thermodynamic study of the reaction and effect of various parameters

Zinc oxide (ZnO) nanoparticles (NPs) were synthesized hydrothermally and doped with 4% Neodymium (Nd). The produced NPs were characterized using UV–Vis spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray analysis, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Photoluminescence (PL) spectroscopy. With the addition of 4% Nd, the bandgap reduced from 3.20 to 3.00 eV which confirmed successful doping with Nd which also evident from FTIR study. The XRD study showed hexagonal structure of the synthesized material, while SEM study confirmed that Nd-doped ZnO (Nd–ZnO) NPs are well dispersed as compare to ZnO. TGA study revealed that synthesized NPs were much stable to temperature and only 11.3% and 7.2% the total loss occurred during heating range (40–600 °C) in case of ZnO and Nd–ZnO NPs, respectively. The PL intensity of the visible peaks of ZnO reduced after doping with Nd. The degradation of Acid yellow-3 over both the catalysts followed first-order kinetics. The activation energy calculated for the photodegradation reaction was 43.8 and 33.7 kJ/mol using pure ZnO and Nd–ZnO NPs, respectively. About 91% and 80% dye was degraded at the time interval of 160 min using Nd–ZnO and ZnO NPs, respectively. High percent degradation of dye was found at low concentration (10 ppm) and at optimal dosage (0.035 g) of the catalyst. The rate of Acid yellow-3 dye degradation was found to increase with increase in temperature (up to 50 °C) and pH(8) of the medium. The recyclability study showed that both pure ZnO and Nd–ZnO NPs could be reused for the degradation of the given dye. With the addition of H₂O₂ up to 5 µL, the rate of reaction increased clearly indicating the effect of OH^· generation during photocatalysis. When compared with Nd–ZnO NPs at low concentrations, ZnO NPs at higher concentrations were found to be less hazardous. Both the NPs showed best antibacterial activities against Staphylococcus aureus. The hemolytic study indicated that at low concentration, pure ZnO was non-hemolytic as compared to Nd–ZnO.

     

Evaluation of the potential of the Np(VII)/(VI) couple in acid solutions using the reaction Ag(I) + Np(VII) ⇄ Ag(II) + Np(VI)

The reaction of Np(VII) with Ag(I) was studied by spectrophotometry with the aim to evaluate the potential of the Np(VII)/(VI) couple in acid solutions. In perchloric acid solutions with pH 1.5 and 3.05, the potential E is 1.93 and 1.85 V, respectively. Extrapolation to a solution with pH 0 gives 2.20 ± 0.01 V. A close value (E = 2.22 V) is obtained by extrapolating the potential from a 1 M NaOH solution (pH 13.83, E = 0.582 or 0.587 V) to acid solutions (pH 0).     

Sol–gel synthesis and characterization of mesoporous manganese oxide

Mesoporous manganese oxide (MPMO) from reduction of KMnO₄ with maleic acid, was obtained and characterized in detail. The characterization of the material was confirmed by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffractometry (XRD) and N₂ sorptometry. The results showed that MPMO is a pseudo-crystalline material with complex network pore structure, of which BET specific surface area is 297 m²/g and pore size distribution is approximately in the range of 0.7–6.0 nm. The MPMO material turns to cryptomelane when the calcinating temperature rises to 400 °C. The optimum sol–gel reaction conditions are KMnO₄/C₄H₄O₄ molar ratio=3, pH=7 and gelation time>6 h.     

Development of biomimetic coatings on Sm oxide doped ELB (Eu–Li–borate) glasses

The in-vitro biomineralization of Eu/Li–borate glasses containing Sm₂O₃ was investigated by immersion in simulated body fluid (SBF) up to 72 h. Back scattering scanning electron microscope supplemented with EDX was used to follow the development of the phosphatic layer post 72 h SBF immersion. Biochemical analyses of calcium and inorganic phosphorus (Ca²⁺ and iP) ions were conducted using relevant biochemical kits and spectrophotometer. Spectra of TF-X-ray analyses and Fourier transform infrared were obtained for the samples post 72 h immersion and compared to the host one.The role of Sm₂O₃ in the biomineralization and crystallinity of the (ELB) borate glasses is proved by the developed rounded nano particles and the presence of elemental Eu and Sm in the formed layer beside Ca and P as presented by EDX. The continuous reduced values of ionic iP accompanying the adsorption and release of Ca ions in SBF with time assured the biolayer formation. The formed phosphatic layer presented shifted XRD peaks due to ionic incorporations especially of Sm³⁺. FT-IR proved the selectivity of BO₃ group for phosphatic deposition. Deconvolution of ν₄ and ν₃ regions, for carbonates and phosphates, respectively, proved the enhanced peak areas with increased Sm³⁺ content.     

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO₂ (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO₂ = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO₂ = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO₂ = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.     

Electrical properties of Ni–Mn–Co–(Fe) oxide thick-film NTC thermistors prepared by screen printing

Ni–Mn–Co–(Fe) oxide thick films were coated on an alumina substrate by a screen-printing technique. The electrical properties of the thick films, as a function of composition and sintering temperature, were investigated. All the thick-film negative temperature coefficient (NTC) thermistors prepared showed a linear relationship between log resistivity and the reciprocal of the absolute temperature, indicative of NTC characteristics. As the amount of Mn₃O₄ in (Ni_2–x Mn _x Co_1.0)O₄ (0.6x1.8) thermistors increased, the resistivity and the coefficient of temperature sensitivity decreased to a minimum value and then increased again. Also, at a given Ni–Mn oxide content, the resistivity and the coefficient of temperature sensitivity for (Ni_1.0Mn_1.0Co_1–x Fe _x )O₄ (0.25x1.0) and (Ni_0.75Mn_1.25Co_1–x Fe _x )O₄ (0.25x0.75) thermistors increased with increasing Fe₂O₃ content. The influence of composition and sintering temperature on the electrical properties of the thermistors is discussed.