Sphalerite-type Structure Research Articles

Structural and optical characterization of CdTe quantum dots thin films

Cadmium telluride quantum dots (CdTe QDs) have been synthesized using hot-injection chemical technique. The CdTe QDs thin films were deposited onto optical flat fused quartz substrates using thermal evaporation technique. The CdTe QDs powder and the as deposited films were characterized using X-ray diffraction and high resolution transmission electron microscope (HRTEM). The X-ray analysis shows that both CdTe QDs powder and the as deposited films crystallize in cubic zinc-blende type structure with lattice parameter 6.46Å and 6.45Å, respectively. The X-ray calculation shows that the average crystallite size of the as deposited CdTe QDs films varied from 1.1nm for the powder to 2.3nm for the thin film. The HRTEM examination of the as deposited films shows that the average particle size vary from 2.5nm for the powder to 2.7nm for the thin film. For the as deposited films, the dependence of (αhν)2 on the incident photon energy indicates that the optical transitions within the film are allowed direct with energies observed at Eg1≅2eV and Eg2≅2.3eV which attributed to quantum confinement effect. The optical band gap increases from 1.5eV for microstructure CdTe to 2eV for nanostructure quantum dots which corresponding to wavelength(620nm) so it is a great benefit to use CdTe quantum dots as solar harvesting devices application in solar spectrum region (400–800nm). Urbach energy is calculated and found to be 360meV which is higher than microstructure CdTe. The refractive index and refractive index dispersion of the as deposited CdTe QDs film has been calculated from transmission and reflection spectra. It has been found that the refractive index is reduced from (2.66) for microstructure CdTe to be (1.7) for CdTe quantum dots. The variation of the refractive index at normal dispersion is well described by Wemple–DiDomenico single oscillator model. The dielectric constant at infinite frequency ε∞ and the ratio of free carriers’ concentration to the effective mass (N/m∗) are calculated and discussed. Finally, the non linear optical parameters are calculated using some empirical relation.

Phase transition and elastic properties of TiN under pressure from first-principles calculations

The structural phase transition and elastic properties of Titanium Nitride (TiN) are investigated using density functional theory (DFT) method within the Perdew–Burke–Ernzerhof (PBE) form of generalized gradient approximation (GGA). Our theoretical equilibrium structural parameters of TiN are in good agreement with the available experimental results and other theoretical values. The predicted phase transition from NaCl-type (B1) to CsCl-type (B2) structure occurs at ca. 341.9GPa. This conclusion is in agreement with that of Ahuja et al., contrary to the calculation of Ojha et al. using a two-body interionic potential theory. In addition, it is found that the zinc-blende type (B3) and WC structures are not stable in the whole pressure range considered. Especially, the elastic properties of B1 and B2 structures for TiN under pressures are studied for the first time. The bulk moduli, shear moduli, compressional and shear wave velocities of B1–TiN and B2–TiN are obtained successfully and these results increase monotonically with increasing pressure. By analyzing of B/G, the brittle-ductile behavior of TiN is assessed. In addition, polycrystalline elastic properties are also obtained successfully for a complete description of elastic properties.

Synthesis, structure and spectro-microscopic studies of polycrystalline HgxPb1−xS thin films grown by a chemical route

The deposition history, growth mechanism, structural, optical and surface morphological features of chemically deposited HgxPb1−xS (0⩽x⩽0.2) thin films prepared under optimized conditions are presented. Effect of growth parameter (x) on the film quality and properties has been studied. The resulting films appeared smooth, uniform and well adherent to the substrate and diffusely reflecting with color changing from grayish-brown to light-brown as x was varied from 0 to 0.2. The EDS analysis showed replacement of Pb2+ atoms from PbS lattice by Hg2+ atoms. The X-ray diffraction revealed crystalline nature with zinc blende type structure with predominant (200) orientation. Both interplanar distance and lattice parameter for (200) and (111) reflections increased with x in the alloyed range (0⩽x⩽0.035). SEM observations showed non-uniform distribution of well defined spherical grains; some of them diffused to form agglomeration/globule like structure. Analysis of the transmission spectra in the 500–3000nm wavelength range showed 20–95% transmittance, absorption coefficient of the order of 104–105cm−1 and energy gap increased from 0.52eV to 1.75eV respectively for the change of x from 0 to 0.2.

Sonochemical synthesis of mackinawite and the role of Cu addition on phase transformations in the Fe–S system

We studied the influence of Cu addition on the first precipitate, near-amorphous mackinawite-type FeS and subsequent phase transformations in the Fe–S system. Despite many studies on the formation and phase transition of Fe sulphides, the structure and physical properties of this first precipitate are still not well explained. To investigate the reaction products, iron and copper chlorides were mixed in different ratios together with sulphur and diethanolamine, and sonicated to achieve efficient mixing; already at this stage, the first FeS precipitate was formed. TEM investigation of Cu-doped mackinawite-like FeS showed enhanced crystallinity accompanied with expansion of the unit cell along the c-axis, proportional to the amount of Cu adsorbed between the (001) layers of the mackinawite structure. The subsequent solvothermal treatment and sulphurization of undoped FeS resulted in formation of pyrite, at low doping Cu-rich mackinawite and cubic (Fe, Cu)S with a sphalerite-type structure were formed, while at higher Cu concentrations the end products were chalcopyrite and bornite, corresponding to the initial amount of Cu in the reagents.

Nanosized CoO Films on the α-Al2O3 (0001) Surface: A Density Functional Study

The structural and magnetic properties of ultrathin CoO films supported on α-Al2O3(0001) surface are investigated on the basis of density functional theory calculations. By examining both stoichiometric and nonstoichiometric submonolayer structures at an atomic level we establish that the preferred surface arrangements are stabilized by the presence of a sublayer of O adatoms, even at the expense of creating O vacancies at the subsurface layer. Further addition of oxygen to this thin CoO layer fills the vacancies resulting in the formation of nondefective, atomically smooth oxygen-terminated surfaces as the preferred structural arrangement. Later, we examine the possible coexistence of rock-salt, wurtzite, or blende-type structures and different arrangements of the Co atoms magnetic moments at higher coverages. The observed structures and magnetic arrangements are rationalized on the basis of the surface dipole moment reduction induced by the O-termination of the overlayers and on the observed intra- and interlayer distances that favor, at these coverages, an intralayer antiferromagnetic arrangement of the Co magnetic moments.

Electron microscopy study of CVT grown Fe-sulphides

Recent studies of {110} twin boundaries in natural pyrite (FeS2) indicated that twinning is triggered by the presence of Cu during crystal growth. Here we investigated the formation sequence of Fe-sulphides produced by the chemical vapor transport (CVT) method at 600°C in an evacuated quartz tube using Fe- and Cu-halides and elementary S as the reaction precursors. Depending on the mobility of elements different Fe-sulphides crystallized through gradually decreasing temperature zones. At the higher temperature zones, where metal ions are present in abundance, the main reaction product is FeS in form of pyrrhotite-3T. The main characteristic of this pyrrhotite is the presence of {111} layers cubic FeS coherently intergrown with the {0001} layers of the hosting hexagonal FeS. While the hosting structure corresponds to distorted troilite (nickeline-type structure) with octahedrally coordinated Fe2+ ions, iron in cubic FeS either remains in octahedral coordination (rocksalt-type structure) or is translated to tetrahedral interstices (sphalerite-type structure). HRTEM analysis suggests that Fe2+ ions in the cubic sequences remain in the octahedral sites, suggesting a new, cubic close-packed, rocksalt-type structure of FeS. Cubic FeS shows a high density of twins and SFs in the {111} planes. Pyrite crystallized in the temperature zone between 500 and 450°C, where the concentration of metal ions is depleted. With a decreasing temperature its morphology changes from {111}→{210}→{100}. Doping with copper did not result in twinning of pyrite, suggesting that different thermodynamic conditions are present in the natural environment. Using the natural seed crystal we showed that the twin boundaries are continued across the interface into the CVT grown epitaxial pyrite, whereas the marcasite-type SFs terminate at the interface.

STM observation of MnAs initial growth surface on GaAs(001)-c(4×4)α and 6×6 reconstructions

MnAs initial growth on two different GaAs(001) reconstructed surfaces, namely As-rich c(4×4)α and Ga-rich 6×6, was investigated by scanning tunneling microscopy, and we surprisingly found that MnAs grows similarly on the both reconstructed surfaces despite large difference in their structures. MnAs layers grew two-dimensionally keeping zincblende-type crystalline structure until the completion of the first monolayer on both the reconstructed surfaces, and Ga atoms consisting of these reconstructed surfaces contributed to the growth, resulting in the anomalous evolution of nominal surface coverage. On the 6×6 substrate, the first monolayer was completed by only 0.1–0.2ML of MnAs growth, while on the c(4×4)α 0.6–0.7ML of MnAs growth is necessary to complete it. However, despite large difference in surface stoichiometry of the two surfaces, the surface structures during the growth closely resembled each other; i.e., both surfaces are essentially characterized by As–As dimers.

THERMOMAGNETIC PROPERTIES OF RARE-EARTH REPLACEMENT CRITICAL MAGNETIC MATERIALS FROM DFT CALCULATION: MnBi AND MnSb

MnBi has gained much attention as a replacement for critical rare earth magnetic material not only due to its strong magnetization and coercive power, but also because of its capability to retain magnetization at elevated temperatures while most other compounds decline. To investigate the origin of this temperature dependence, we have performed a series of first principles electronic structure calculations on the thermomagnetic properties of MnBi and compared it with MnSb , another ferromagnetic material with a strong magnetic energy product, same crystal structure at room temperature and similar Curie temperature. Three structural phases were considered in this study: NiAs -type ( B81 ), MnP -type ( B31 ) and a zincblende-type ( B3 ) structures. Calculated magnetizations demonstrated structural effects on temperature dependent magnetization. For the same NiAs -type structure, MnBi has a monotonic increase in magnetization with increasing temperature while MnSb decreases. In the other two structures, magnetization in MnBi and MnSb are much less sensitive to temperature. Results from this study suggest a structural design rule for the development of new MnBi related materials.

First-principles study of structural, electronic and magnetic properties of AeX (Ae=Be, Mg, Sr, Ba; X=Si, Ge and Sn) compounds

The first-principles study of the electronic structure and ferromagnetism of AeX (Ae=Be, Mg, Sr and Ba; X=Si, Ge and Sn) compounds have been performed in the ground-state CrB-type and hypothetical NaCl- and zinc blende-type structures by spin-polarization and non-spin-polarization calculations. The TBLMTO-ASA program was used for the purpose. In the CrB-type structure, all these compounds exhibit non-magnetic and metallic behavior. The calculations show that in the NaCl- and ZB-type structures BeSi, BeGe, BeSn, MgSi, MgGe and MgSn compounds are non-magnets whereas SrSi, SrGe, SrSn, BaSi, BaGe and BaSn compounds are ferromagnetic and metallic. Apart from this the ZB-type SrSi, SrGe, BaSi and BaGe compounds exhibit half-metallicity at their equilibrium volume with a magnetic moment of 2.0μB per formula unit. However, ZB-type SrSn and BaSn compounds are found to exhibit half-metallic property under expansion of volume. The magnetism arises mainly from the anion p-like states and partial involvement of cation d-like states. The ground state properties like equilibrium lattice parameters, bulk modulus, cohesive energy, magnetic moment, spin-flip-gap and majority spin band gap are calculated and compared with available results. The band structure and density of states are also presented. These materials will be useful for the study of p-electron magnetism and in spintronic devices.

Zn2(CuIn)1−S2 photocatalysts synthesis by a hydrothermal process using H4EDTA as complexing agent

Abstract The study of the Zn 2 x (CuIn) 1− x S 2 (0 ≤ x ≤ 1) solid solutions formation by hydrothermal synthesis using ethylenediaminetetraacetic acid (H 4 EDTA) as a complexant and surfactant agent is reported for the first time. Different synthesis parameters were varied: the H 4 EDTA concentration, the initial pH value, the Tu concentration, the duration and temperature of autoclaving process. The as obtained powders were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and UV/vis/NIR diffuse reflection spectroscopy (DRS). The XRD and EDX results show that, with a careful adjustment of the reaction conditions, especially of the H 4 EDTA concentration and initial pH value of the precursor solution, a mixture of solid solutions with sphalerite type structure can be obtained, which transforms into a single phase solid solution after heat treatment. The particles, as revealed by SEM investigations, have nanoporous hexagonal microplates morphology, about 1 μm thick and several microns in diameter. The Cu 0.159 In 0.111 Zn 1.778 S 2 photocatalyst obtained by this method presents photocatalytic activity for hydrogen evolution from aqueous solutions containing S 2− ions as sacrificial agent, even without cocatalyst.

Optoelectronic properties of zinc blende and wurtzite structured binary solids

In this paper, we studied zinc blende (ZB) and wurtzite (Wu) type structured binary solids with conduction electrons and calculated the optoelectronic properties such as high frequency refractive index (n), optical susceptibility (χ), electronic polarizability (αe) and crystal ionicity (fi) using the plasma oscillation theory of solids formalism already employed for ternary chalcopyrite semiconductors. The present method is not limited to tetrahedrally coordinated semiconductors and ternary chalcopyrites, but can be used for all semiconducting compounds. We have applied extended formulae on zinc blende (ZB) and wurtzite (Wu) type structured binary semiconductors and found better agreement with the experimental data as compared to the values evaluated by previous researchers. The high frequency refractive index (n), optical susceptibility (χ), electronic polarizability (αe) and crystal ionicity (fi) of zinc blende (ZB) and wurtzite (Wu) type structure compounds exhibit a linear relationship when plotted on a log–log scale as against the plasmon energy N›ωp (in eV), which lies on a straight line. The results for high frequency refractive index differ from experimental values by the following amounts: ZnS (0%), ZnSe (0%), ZnTe (11%), CdS (11%), CdSe (15%), CdTe (20%), HgSe (5%), BN (20%), AlN (16%), AlP (15%), AlAs (0%), AlSb (13%), GaN (18%), GaP (27%), GaAs (8%), GaSb (7%), InN (8%), InP (5%), InAs (0.3%) and InSb (0.9%); and the results for optical susceptibility differ from experimental values by the following amounts: ZnS (10%), ZnSe (2%), ZnTe (8%), CdS (25%), CdSe (17%), CdTe (7%), AlAs (4.8%), AlSb (16%), GaP (1.6%), GaAs (9.8%), GaSb (22.7%), InP (12.8%), InAs (9%) and InSb (20%) in the present study. Key words: A. semiconductors, D. electronic properties, D. optical properties

Planar-defect characteristics and cross-sections of 〈001〉, 〈111〉, and 〈112〉 InAs nanowires

We report on detailed structural and morphological characterizations of InAs nanowires of 〈001〉, 〈111〉, and 〈112〉 crystallographic directions grown on (001)B InAs wafer substrates using high-resolution transmission electron microscopy. We find that 〈001〉-oriented InAs nanowires are cubic zincblende-type structure and free of planar defects. The 〈111〉- and 〈112〉-oriented InAs nanowires both have densely twinned (111) planar defects that are perpendicular and parallel to the growth direction, respectively. The cross sections of all three types of InAs nanowires are obtained from 3D reconstructions using electron tomography. The characteristics of the planar defects and the 3D wire shape should provide better estimations of microstructure-relevant physical properties, such as conductivity and Young’s modulus of InAs nanowires.

The crystal structure of kesterite type compounds: A neutron and X-ray diffraction study

The atomic structure of the potential photovoltaic materials Cu 2ZnSnS 4 (CZTS) and Cu 2ZnSnSe 4 (CZTSe) is discussed on the basis of a structural analysis of neutron powder diffraction data refined by the Rietveld analysis. Both compounds were found to crystallize in the kesterite type structure, but with a disorder within the Cu–Zn layers at z=1/4 and 3/4. The latter causes Cu Zn and Zn Cu anti-site defects, whose concentration depends on the sample growth conditions. The temperature dependent structural phase transition in CZTS was studied by in-situ high temperature diffraction experiments using high energy synchrotron X-rays. The transition from the tetragonal kesterite to the cubic sphalerite type structure is discussed by means of the interplay of increasing and decreasing cation–anion–cation bond angles in the coordination tetrahedra, reflected by the shift of the anion atomic coordinates to more ideal ( x and y) or non-ideal ( z) values. This striking behavior may be connected with frustrations that occur due to the triangular geometry of the coordination tetrahedra.

Aktashite Cu6Hg3As4S12 from the Aktash deposit, Altai, Russia: Refinement and crystal chemical analysis of the structure

The composition and structure of aktashite from the Aktash deposit, Gorny Altai, Russia, have been studied by electron microprobe and X-ray structural analysis. On the basis of close compositions and crystal structures, the identity of aktashite from the Gal-Khaya and Aktash deposits has been demonstrated. Crystals of aktashite are of trigonal symmetry; the unit-cell dimensions are: a = 13.7500(4), c = 9.3600(3) A, V = 532.54(8) A3, space group R3, Z = 3 for the composition of Cu6Hg3As4S12, R = 0.043. The structure of aktashite as a framework of vertex-shared HgS4− and CuS4− tetrahedrons of the same orientation is intimately related to the sphalerite-type structure. The earlier identified uncommon cluster group [As4] has been verified and its parameters have been refined. It is shown that the structure may be represented as construction blocks (As4S12)12− packed according to the law of the distorted cubic I-cell.

Full potential calculation of structural, elastic properties and high-pressure phase of binary noble metal carbide: ruthenium carbide

We present in this paper the results of an ab initio theoretical study within the local density approximation (LDA) to determine in rock-salt (B1), cesium chloride (B2), zinc-blende (B3), and tungsten carbide (WC) type structures, the structural, elastic constants, hardness properties and high-pressure phase of the noble metal carbide of ruthenium carbide (RuC). The ground state properties such as the equilibrium lattice constant, elastic constant, the bulk modulus, its pressure derivative, and the hardness in the four phases are determined and compared with available theoretical data. Only for the three phases B1, B3, and WC, is the RuC mechanically stable, while in the B2 phase it is unstable, but in B3 RuC is the most energetically favourable phase with the bulk modulus 263 GPa, and at sufficiently high pressure ( P t =19.2 GPa) the tungsten carbide (WC) structure would be favoured, where ReC–WC is meta-stable. The highest bulk modulus values in the B3, B2, and WC structures and the hardnesses of H(B3)=36.94 GPa, H(B1)=25.21 GPa, and H(WC)=25.30 GPa indicate that the RuC compound is a superhard material in B3, and is not superhard in B1 and WC structures compared with the H(diamond)=96 GPa.

Jewelry Box of Morphologies with Mesoscopic Length Scales – ABC Star‐shaped Terpolymers

Among several star molecules studied so far, the results for two similar but slightly different systems composed of all hydrophobic components, i.e. one low T(g) arm and two high T(g) arms were compared and discussed mainly. They are polyisoprene-arm-polystyrene-arm-poly(2-vinylpyridine) stars and polystyrene-arm-polybutadiene-arm-poly(2-vinylpyridine) ones, and are abbreviated as ISP and SBV, respectively, in the original literatures. Several periodic Archimedean tiling patterns can be naturally formed when the relative lengths of three chains are similar one another in both series. Core-shell type morphologies and actually three-phase four layer lamellar structures were also commonly observed for two series. A quasicrystalline tiling with dodecagonal symmetry can also be conformed at the targeted composition of ISP/homopolymer blend and a zinc-blende type structure was created at just a little outside of tiling region for the same blend. Furthermore, the several interesting structures from amphiphilic molecules, composed of a hydrophilic component, poly(ethylene oxide), a hydrophobic component, polymethylmethacrylate and a highly water-repellent polymer poly(perfluoropropyleneoxide) are described and introduced.

ChemInform Abstract: Anisotropic Hexagonal Boron Nitride Nanomaterials: Synthesis and Applications

AbstractReview: 176 refs.

Calcium-aluminum-silicate-hydrate “cement” phases and rare Ca-zeolite association at Colle Fabbri, Central Italy

Abstract Very high temperature, Ca-rich alkaline magma intruded an argillite formation at Colle Fabbri, Central Italy, producing cordierite-tridymite metamorphism in the country rocks. An intense Ba-rich sulphate-carbonate-alkaline hydrothermal plume produced a zone of mineralization several meters thick around the igneous body. Reaction of hydrothermal fluids with country rocks formed calcium-silicate-hydrate (CSH), i.e., tobermorite-afwillite-jennite; calcium-aluminum-silicate-hydrate (CASH) — “cement” phases - i.e., thaumasite, strätlingite and an ettringite-like phase and several different species of zeolites: chabazite-Ca, willhendersonite, gismon-dine, three phases bearing Ca with the same or perhaps lower symmetry of phillipsite-Ca, levyne-Ca and the Ca-rich analogue of merlinoite. In addition, apophyllite-(KF) and/or apophyllite-(KOH), Ca−Ba-carbonates, portlandite and sulphates were present. A new polymorph from the pyrrhotite group, containing three layers of sphalerite-type structure in the unit cell, is reported for the first time. Such a complex association is unique. Most of these minerals are specifically related to hydration processes of: (1) pyrometamorphic metacarbonate/metapelitic rocks (natural analogues of cement clinkers); (2) mineralization between intrusive stocks and slates; and (3) high-calcium, alkaline igneous rocks such as melilitites and foidites as well as carbonatites. The Colle Fabbri outcrop offers an opportunity to study in situ complex crystalline overgrowth and specific crystal chemistry in mineral phases formed in igneous to hydrothermal conditions.

Multibandk⋅pmodels for strained zincblende crystals: Application to the fine structure of ZnO

The elementary-matrix blocks of multiband $\text{k}\ensuremath{\cdot}\text{p}$ models are derived for strained zincblende crystals using methods of group theory. The general viewpoint we adopted is exploited in two opposite directions: the global description of the first Brillouin zone and the fine structure of the valence-band maximum. First, full-zone models are completed: strain contributions originating from the orbital and spin-orbit parts of the Hamiltonian are included in the 30-band model while the next 54-band model is introduced. Second, a 16-band spin-orbit Hamiltonian is constructed for ZnO with zincblende-type structure. The reversed level order at the valence-band maximum is attributed to the ${T}_{2}\text{\ensuremath{-}}{T}_{2}$ $pd$ -like coupling actually taken into account. We perform ab initio calculations in the local-density approximation including relativistic effects to estimate the coupling parameter ${\ensuremath{\zeta}}_{12}=250\text{ }\text{meV}$ that gives an amount of $pd$-like interband mixing of about 10%.

Synthesis, Structure, and Bonding in K12Au21Sn4. A Polar Intermetallic Compound with Dense Au20and Open AuSn4Layers

The new phase K(12)Au(21)Sn(4) has been synthesized by direct reaction of the elements at elevated temperatures. Single crystal X-ray diffraction established its orthorhombic structure, space group Pmmn (No. 59), a = 12.162(2); b = 18.058(4); c = 8.657(2) A, V = 1901.3(7) A(3), and Z = 2. The structure consists of infinite puckered sheets of vertex-sharing gold tetrahedra (Au(20)) that are tied together by thin layers of alternating four-bonded-Sn and -Au atoms (AuSn(4)). Remarkably, the dense but electron-poorer blocks of Au tetrahedra coexist with more open and saturated Au-Sn layers, which are fragments of a zinc blende type structure that maximize tetrahedral heteroatomic bonding outside of the network of gold tetrahedra. LMTO band structure calculations reveal metallic properties and a pseudogap at 256 valence electrons per formula unit, only three electrons fewer than in the title compound and at a point at which strong Au-Sn bonding is optimized. Additionally, the tight coordination of the Au framework atoms by K plays an important bonding role: each Au tetrahedra has 10 K neighbors and each K atom has 8-12 Au contacts. The appreciably different role of the p element Sn in this structure from that in the triel members in K(3)Au(5)In and Rb(2)Au(3)Tl appears to arise from its higher electron count which leads to better p-bonding (valence electron concentrations = 1.32 versus 1.22).