Characteristics of Guajazulene Based Chemosensor Toward CN− and F− Anions

A chemosensor having electron pushing donor and pulling acceptor material based on conjugation bridges, namely D-π-A structural chemosensor, was herein designed and synthesized. This chemosensor 3 contained guajazulene and indole moieties, which was synthesized through a one-step condensation reaction. The synthesized material showed very selective sensing properties towards anions. Upon the addition of CN- and F-, the remarkable changes in absorption spectra were monitored. However, each of others did not show any noticeable optical changes. The original intramolecular charge transfer system of chemosensor 3 was altered by the formation of N- at iindole moiety with anion reaction: caused by the deprotonation of NH at the indole moiety of chemosensor. With intermolecular charge transfer system between chemosensor 3 and anions, the electron density and distribution were determined by frontier calculation method.     

Growth rates of the principal facets of ice between −10°C and −40°C

We describe measurements of the growth rates of the basal and prism facets of ice crystals grown from the vapor phase at temperatures −39°C<T<−10°C. We find that all our data can be well described by a model in which the facet growth is limited primarily by 2D nucleation over this temperature range. The inferred critical supersaturations, and thus the step edge free energies, are essentially identical for the two facets, with values that decrease monotonically with increasing temperature. The growth scaling parameters, on the other hand, exhibit a more complex behavior with temperature that is quite different for the two facets. These data suggest that much of the peculiar behavior seen in ice crystal growth from vapor is due to differences in the surface diffusion of admolecules on the two principal facets.     

Thermal decomposition of energetic materials. 44. Rapid thermal decomposition of the propyl-1,3-diammonium salts of NO 3 − and ClO 4 − , and the crystal structure of the ClO 4 − salt

The temperature dependence of the IR spectra of the condensed phase (dT/dt=5°C min^–1) and the fast thermolysis (dT/dt100°C sec^–1) of propyl-1,3-diammonium dinitrate (PDD) and diperchlorate (PDP) are compared. Rapid-scan FTIR/temperature profiling shows that PDP explodes on heating while PDD decomposes with much less energy. HNO₃(g) is formed by deneutralization in the initial decomposition of PDD, but HClO₄(g) is not detected from PDP. PDP is unique among the compounds studied by this technique in that a solid-solid phase transition can be detected during rapid heating. The initial phase of PDP has been characterized by X-ray crystallography: monoclinic,P2₁/c,a=7.316(2),b=14.428(2),c=9.742(2) Å,=96.81°,V=1021.1(3) ų,Z=4,D=1.789 g cm^–3,R(F)=0.034,R(wF)=0.040.     

Ab initio calculation of vibrational frequencies of GexSe1−x glass

We have used the density functional theory to make the models of Ge_xSe_1?x glass for which the energy is a minimum. The clusters, Ge₂Se₂, Ge₂Se₃, Ge₃Se, Ge₃Se₂, Ge₄Se, GeSe₃, GeSe₄, chain mode zig-zag Ge₄Se₃, corner sharing GeSe₄, and edge sharing Ge₂Se₆, have been made successfully and their vibrational spectra have been calculated from the first principles. We are able to optimize the bond distances as well as the bond angles. The calculated values of the frequencies of vibrations of the various clusters have been compared with those obtained from the experimental Raman spectra of actual glasses, Ge_xSe_1?x(0 < x < 0.3). The local concentration, x within 0.25 nm is nonuniform in the amorphous material. When the same cluster occurs in two stable configurations, low frequency vibrations of frequency, ν < 100 cm^?1, are found. The corner sharing GeSe₄ has low frequency modes at 54 cm^?1 and 93 cm^?1 whereas these modes disappear in the pyramidal configuration. The low frequency modes are therefore associated with the breaking of C₄ symmetry of the pyramidal configuration. The computed vibrational frequencies of clusters Ge₃, Ge₄Se₃, Ge₂Se₃, GeSe₃ and Ge₃Se₂ are actually present in the Raman spectra of the glass, Ge_xSe_1?x(0 < x < 0.3).     

Growth and structural properties of Zn1−xCrxTe crystals

Single crystals of Zn_1?xCr_xTe were grown by vapour phase growth method in the composition range of 0?x?0.005. Chemical analysis, surface morphology, structural and microhardness studies were carried out by EDAX, SEM, XRD and Vicker's indentation techniques, respectively. Microscopic variations between the target and actual compositions were noticed. Morphology studies revealed that dislocation aided growth is active in the present crystals. XRD studies showed that samples of all compositions crystallized in zinc blende structure, and the lattice parameters varied linearly with x following Vegard's law. Vicker's hardness (H_v) decreased exponentially with x.     

Extrinsic doping of CdxHg1−xTe— A review

Extrinsic doping by elements which are stable to subsequent processing will become increasingly important in future infra-red device structures based on Cd_xHg_1−xTe. This paper reviews the incorporation and activation of dopants in the most widely used bulk and epitaxial growth methods. Stoichiometry at the growth temperature is shown to be the critical factor affecting dopant activation. Various factors, including stoichiometry, can affect the as-grown electrical properties and the importance of determining the type of conduction in the as-grown state, if successful extrinsic doping is to be accomplished, is stressed. Data on dopant segregation behaviour, in growth from liquids, acceptor ionization energies and carrier lifetimes are also presented and their importance is discussed.     

Selective dissolution of Agx(As0.33S0.67−ySey)100−x chalcogenide thin films

Thin films of As₃₃S₆₇, As₃₃S_33.5Se_33.5 and As₃₃Se₆₇ prepared by vacuum thermal evaporation were selectively etched in alkaline organic solutions of amines i.e. 1,2-diaminopropane, morpholine, aminoethanol, cyclohexylamine, hexylamine, butylamine and propylamine. Dissolution rates v, resolution coefficients γ and surface quality are discussed and compared to recently published results of etching process in inorganic solutions of NaOH, Na₂S and (NH₄)₂S. The resolution coefficients achieved in amine based solutions are by the order of magnitude higher than ones in inorganic etchants. Etching in organic solutions showed increase of the resolution coefficient and decrease of dissolution rate of exposed and unexposed film in the sequence of propylamine, butylamine, hexylamine and cyclohexylamine solution. The role of different type of amine on dissolution rate and resolution coefficient is discussed. The dissolution parameter γ is getting worse in the same type of solvent with increasing content of Se. The dissolution mechanism and relation between photo-structural change and dissolution behavior of films are proposed. New results of negative selective etching of Ag_x(As_0.33Se_0.67)_100?x in NaCN are presented and compared with selective etching curves of recently published Ag_x(As_0.33S_0.67)_100?x and Ag_x(As_0.33S_0.335Se_0.335)_100?x thin films. Potential application is shown in fabrication of ‘microlenses like’ motive into the Ag–As₃₃S₆₇ thin film.     

Bridgman growth of CdxHg1−xTe— A review

Recent developments in the bulk Bridgman growth method for Cd_xHg_1−xTe are reviewed. Both melt mixing and heat flow control techniques have been applied in attempts to produce more uniform material in terms of composition. In the U.K. work has concentrated on application of the Accelerated Crucible Rotation Technique (ACRT) to achieve the required uniformity improvements. Elsewhere, various means to control isotherm shape have been used with the same aim. The ultimate use of the material is in infra-red detectors and Bridgman grown Cd_xHg_1−xTe has produced these successfully for both photoconductive and photovoltaic applications.     

Structural behavior of CuxZr100−x metallic glass (x = 35−70)

The structural behavior of rapidly quenched amorphous Cu_xZr_100?x alloys was investigated in a wide composition range between 35 and 70 at.% Cu content. High-energy X-ray diffraction patterns, atomic pair correlation functions, mass density and the thermal stability behavior of the alloys all exhibit monotonic changes with composition. Partial pair correlation functions were determined assuming that they remain unchanged in the different amorphous Cu_xZr_100?x alloys and only the weight fractions become altered with changes in composition. The experimental results can be well described by a solid solution-like replacement of Cu and Zr atoms in the whole composition range. No indications are observed neither for the existence of a special atomic arrangement at a particular chemical composition nor for the presence of phase separation in the glassy state of the binary Cu–Zr system.     

Formation of thesyn-isomer of [Cp*MoO(μ−S)]2

The structure of the title compound,syn-[Cp^*MoO(μ?S)]₂,1, has been determined.1 crystallized in the monoclinic space groupC2/c with dimensionsa=11.758(2),b=12.243(2), c = 15.585(3)Å, β=104.63(3)°. The reaction of Cp^* ₂Mo₂(S₂)(S)(S₂O₃) with Me₂PhP producessyn-[Cp^*MoO(μ?S)]₂ and Me₂PhPO. The compounds [Cp′MoO(μ?S)]₂ [Cp′=Cp, CpMe, Cp^*] can exist as either thesyn- oranti-isomers. The present structure,syn-[Cp^*MoO(μ?S)]₂ is compared with the structure of theanti-isomer and with the previously determined structure ofsyn-[Cp^*MoO(μ?S)]₂ in a different space group.     

Thermodynamic analysis of the W-Al2O3 system near the melting temperature of Al2O3. I. Evolution of the system in the pressure range of 1 × 10−1−1 × 10−4 bar

The changes in the main chemical reactions occurring upon the interaction between tungsten and the evaporation products of Al₂O₃ melt are considered at a fixed temperature (2400 K). The concentrations of the components coexisting in equilibrium in a closed system under isobaric-isothermal conditions are determined by stochastic simulation for low (× 10⁻¹−1 × 10⁻³ bar) and high (1 × 10⁻⁴ bar) vacuum. It is shown that the gas-liquid-solid system is in heterogeneous equilibrium for the basic component ratio W: Al₂O₃ = 1: 1 in the entire pressure range under consideration. A detailed study of the chemistry of this system should facilitate the choice of the optimal conditions for growing leucosapphire crystals from melt.     

Optical properties and structure of amorphous films Agx(As0.33S0.67−ySey)100−x

As₃₃S_67−ySe_y, where y = 0, 16.75, 33.5, 50.25 and 67, amorphous thin films were prepared by a vacuum thermal evaporation technique. The films with known silver concentrations and good optical quality were prepared by thermal vacuum evaporation of a silver film on the top of As₃₃S_100−ySe_y films with sequential step-by-step optically- and thermally-induced diffusion and dissolution (OIDD) of silver. The range of silver content was x = 0–25 at.%. The kinetics of OIDD of silver were measured optically by monitoring the change of thickness of the undoped part of the chalcogenide during broadband illumination. Compositions of the reaction products have been determined by scanning electron microscope with energy-dispersive X-ray microanalyser EDS. Optical properties $(T\text{,}n\text{,}{E}_{\text{g}}^{\text{opt}})$ of thin films were measured and/or calculated by the Swanepoel method [R. Swanepoel, J. Phys. E: Sci. Instrum. 16 (1983) 1214]. The refractive index increase with increasing silver and selenium concentration has been shown. The difference of the refractive index (Δn) between undoped and silver doped films was ∼0.4 and between As₃₃S₆₇ and As₃₃Se₆₇ was films ∼0.42. Non-linear indices of refraction were estimated according to Tichy’s formula [H. Ticha, L. Tichy, J. Optoel, Adv. Mat. 4 (2002) 381]. The values of non-linear refractive index grew with increasing silver and selenium content. The difference of optical bandgap, $\mathrm{\Delta }{E}_{\text{g}}^{\text{opt}}$, between undoped As₃₃S₆₇ and fully doped films with Ag and Se was ∼1 eV. Raman spectroscopy showed a decrease in S–S or Se–Se bonds with increasing silver content.     

Growth and characterization of InxBi2−xTe3 single crystals

The V–VI group narrow band gap compounds are known to have important photoconductivity and thermoelectric properties. Among these, Bi₂Te₃ is the most potential material for thermoelectric devices having a direct band gap of 0.16 eV. There has been ample study reported on crystal growth and polycrystalline thin films of both pure and indium doped Bi₂Te₃ pertaining to its basic semiconducting, optoelectronic and thermoelectric properties. It has been shown that on exceeding certain limiting concentration of indium in Bi₂Te₃, the conductivity changes from p-type to n-type. However, there is hardly any work reported in literature on crystal growth, dislocation etching and optical band gap of In_xBi_2?xTe₃ (x=0.1, 0.2, 0.5) single crystals. The authors have grown their single crystals using the zone melting method. The freezing interface temperature gradient of 70 °C/ cm^?1 has been found to yield the best quality crystals obtainable at the growth rate of 0.4 cm/h. The as-grown crystals have been observed to exhibit certain typical features on their top free surfaces. The crystals have been characterized using XRD technique. A chemical dislocation etchant has been used for estimating perfection in terms of dislocation density in the crystals. The optical absorption was measured in the wave number range 500 to 4000 cm^?1. The transitions in all the cases were observed to be allowed direct type. The detailed results are reported in the paper.     

Stoichiometry–structure correlation of epitaxial Ce1−xPrxO2−δ (x=0−1) thin films on Si(111)

Epitaxial oxide thin film layers are of interest for model catalytic studies. We report the growth of Ce_1?xPr_xO_2?δ mixed oxide layers of different stoichiometries (x=0–1) and oxygen deficiency (δ>0) on Si(111) by co-evaporating molecular beam epitaxy. The main objective is to identify the crystal phases and to investigate the correlation between compositions and crystal structures. X-ray photoemission spectroscopy was performed to quantify the stoichiometries. An extensive laboratory and synchrotron based X-ray diffraction analysis was carried out to determine the vertical and lateral lattice orientations and the strain status of the layers. The study revealed that single crystalline Ce_1?xPr_xO_2?δ/Si(111) heterostructures can be epitaxially grown on Si(111) for model catalytic studies. In addition to the structure–stoichiometry relationship typical to mixed oxide bulk powders, we identified a hexagonal mixed Ce–Pr oxide thin film phase not yet reported in bulk studies.     

Thermodynamic description of CdXHg1−XTe growth process by LPE

The paper presents a thermodynamic analysis of the Cd_XHg_1?XTe growth process through liquid phase epitaxy. The diffusion-limited model has been applied to describe the process. The analysis includes the isothermal LPE kinetics of the solid solution’s layers and the influence of their elastic strains. Good correspondence with experimental data has been achieved in various regimes of time and temperature.     

The composition dependence of electrical switching behavior of Ge7Se93−xSbx glasses

Bulk Ge₇Se_93?xSb_x (21 ? x ? 32) glasses are prepared by melt quenching method and electrical switching studies have been undertaken on these samples to elucidate the type of switching and the composition and thickness dependence of switching voltages. On the basis of the compressibility and atomic radii, it has been previously observed that Se-based glasses exhibit memory switching behavior. However, the present results indicate that Ge₇Se_93?xSb_x glasses exhibit threshold type electrical switching with high switching voltages. Further, these samples are found to show fluctuations in the current–voltage (I–V) characteristics. The observed threshold behavior of Ge₇Se_93?xSb_x glasses has been understood on the basis of larger atomic radii and lesser compressibilities of Sb and Ge. Further, the high switching voltages and fluctuations in the I–V characteristics of Ge–Se–Sb samples can be attributed to the high resistance of the samples and the difference in thermal conductivities of different structural units constituting the local structure of these glasses. The switching voltages of Ge₇Se_93?xSb_x glasses have been found to decrease with the increase in the Sb concentration. The observed composition dependence of switching voltages has been understood on the basis of higher metallicity of the Sb additive and also in the light of the Chemically Ordered Network (CON) model. Further, the thickness dependence of switching voltages has been studied to reassert the mechanism of switching.     

X-ray diffraction study of the crystallographic characteristics of TlInS x Se2 − x solid solutions

Crystallographic parameters of TlInS _x Se_{2 ? x} solid solutions have been measured by X-ray diffraction. Dependences of the unit-cell parameters on the composition are determined. It is established that the values of parameters a, b, and c and the angle β decrease with an increase in x. It is shown that the TlInS _x Se_{2 ? x} system includes a continuous series of solid solutions based on the TlInSe₂ compound with tetragonal symmetry at x values ≤ 0.4, while at x ≥ 0.6 solid solutions based on the TlInS₂ compound with a monoclinic structure are formed.     

A composition dependent thermal behavior of GexSe35−xTe65 glasses

Alternating differential scanning calorimetric (ADSC) studies have been performed to understand the thermal behavior of bulk Ge_xSe_35?xTe₆₅ glasses (17 ? x ? 25); it is found that the glasses with x ? 20 exhibit two crystallization exotherms (T_c1 & T_c2). On the other hand, those with x ? 20.5, show a single crystallization reaction upon heating. The exothermic reaction at T_c1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at T_c2 is associated with the additional crystallization of rhombohedral GeTe phase. The glass transition temperature of Ge_xSe_35?xTe₆₅ glasses is found to show a linear but not-steep increase, indicating a progressive, but a gradual increase in network connectivity with Ge addition. It is also found that T_c1 of Ge_xSe_35?xTe₆₅ glasses with x ? 20, increases progressively with Ge content and eventually merges with T_c2 at x ≈ 20.5 (〈r〉 = 2.41); this behavior has been understood on the basis of the reduction in TeTe bonds of lower energy and increase in GeTe bonds of higher energy, with increasing Ge content. Apart from the interesting composition dependent crystallization, an anomalous melting behavior is also exhibited by the Ge_xSe_35?xTe₆₅ glasses.     

Structural and magnetic properties of ZnO and Zn1−xMnxO nanocrystals

Chemical precipitation of metal-ions from aqueous solution has been successfully used to produce Zn_1?xMn_xO nanocrystals, in the form of nano-powder. X-ray diffraction (XRD) measurements reveal that the as-prepared samples are single-phase materials and their lattice constant changes with the variation of Mn-concentration, which indicates the incorporation of Mn²⁺ into the hosting ZnO. These findings are corroborated by the observation of the well defined six hyperfine lines of Mn²⁺ ion in the electron paramagnetic resonance (EPR) spectra of the samples with a low Mn-concentration, and of a broad EPR line, which manifests the onset of Mn–Mn exchange interaction, in the samples with an elevated value of x.     

Growth and characterization of lead-free Ba(1−x)CaxTi(1−y)ZryO3 single crystal

A lead-free Ba_(1?x)Ca_xTi_(1?y)Zr_yO₃ (BCZT) single crystal (x=0.08, y=0.26) was grown by the Czochralski (CZ) method in a mixed flux of TiO₂ and ZrO₂. The composition of as-grown BCZT was analyzed by electron probe micro-analysis. The structure, dielectric properties and phase transition were investigated at different temperatures. The X-ray diffraction results confirmed that the structure of the as-grown BCZT crystal was cubic both at 25 °C and 500 °C. The temperature dependence of the dielectric constant and Raman spectra characterization revealed that there was a phase transition from cubic to tetragonal, which happened between 200 K and 250 K. With increasing frequency, the Curie temperature shifted towards high temperature.