Sphalerite-type Structure Research Articles

On the stability of 𝛃-SiC with respect to chemical disorder induced by irradiation with energetic particles

X-ray diffraction measurements of changes in the long-range structural orderof 𝛃-SiC thin films have been performed during irradiation with energetic ions atlow temperature. The decrease in both the chemical and the topological order wasanalysed in situ using the superstructure (002) and the fundamental (004)reflections of the zincblende-type structure, in a dose range up to completeamorphization. The data indicate that the crystalline-to-amorphous transitionis a continuous process rather than a sudden collapse of a defective crystalstructure and that, in contrast with previous assumptions, 𝛃-SiC remains stablewith respect to amorphization up to a high degree of chemical disorder.

Transition Metal-Substituted Lithium Pnictogenide phases. Synthesis and Crystal Structure Determinations of Novel Phases in the Li–M–X Systems (M=V, Nb, Ta; X=P, As)

Li–M–X systems have been investigated and crystal structures of several phases determined. Li7NbP4 crystallizes in the antifluorite-type structure (cubic, Fm3m, a=5.996(1) Å, Z=1, R(F)=3.02%). LiNbAs2 and Li4.54V1.22As4 display the blende-type structure, cubic F43m space group (LiNbAs2:a= 6.309(1) Å, Z=2, R(F)=2.12%; Li4.54V1.22As4:a=6.167(1) Å, Z=1, R(F)=1.49%). In all compounds, the transition metal statistically occupies some of the tetrahedral sites with lithium. For Li4.54V1.22As4, one of the octahedral sites of the fcc lattice is partially filled with lithium. This feature is also observed for the homologue compounds Lix(Li3.20Nb0.80)As4 and Lix(Li3.64Ta0.36)As4, 0<x≤4 (F43m, Z=1, a=6.190(3) and 6.184(3) Å, R(F)=1.76 and 3.42%, respectively).

Crystal structure and twinning of monoclinic Cu 2SnS 3

Crystals of monoclinic Cu 2SnS 3 have been prepared by a conventional solid-state reaction. The crystal structure has been refined from a twinned specimen using X-ray diffraction data collected with an automatic diffractometer applying a high-dimensional twin refinement technique: space group Cc, a = 6.653(1), b = 11.537(2), c = 6.665(1) Å, β = 109.39(3)°, Z = 4, R F = 0.036, and wR F = 0.038 for 1237 reflections and 52 structural parameters. The structure is a superstructure of the sphalerite type structure, based on cubic close packing of S with order arrangement of Cu and Sn in tetrahedral sites, and it is isomorphic with Cu 2GeS 3 and Cu 2SiS 3.

Investigation of X-ray Satellite Reflections Attributed to Antiphase Boundaries in Epitaxial (Ga,In)P Layers grown on (001) GaAs Substrates

We report on the analysis of additional X-ray reflections that probably arise from antiphase domain boundaries within (Ga,In)P/(001) GaAs heteroepitaxial layers. Due to the preferred cation ordering along the crystallographic directions [1-1 1] and [-1 1 1] which belong to the [110] zone the original sphalerite-type structure of (Ga,In)P changes into a CuPt-like of the cation sublattice. This ordering phenomenon causes a loss of symmetry, i.e. the cubic structure is converted into a rhombohedral one. The antiphase boundaries between ordered domains are assumed to behave similar to at X-ray diffraction. Therefore, additional reflections may occur spatially neighboured to the [001] direction. The presented results of X-ray experiments are discussed in relation to TEM experiments published in the literature in order to explain the origin of the satellite reflections. In the case of the investigated samples (grown on GaAs substrates misoriented 2° towards the azimuthal [010] direction) the APBs run preferentially in directions tilted up to angles of 20° with respect to growth direction. A preferential occurrence of satellite reflections in directions was observed coinciding with {13 2 1} lattice planes whose normals enclose the same angle to the [001] growth direction as the normals of the average characterized by APBs. The appearence of the phenomenon in other directions that are also spatially neighboured to the directions was determined on the basis of the shift of the reflection positions due to tilting the sample around an axis geometrically included in the scattering plane.

Structural transformations in II-VI semiconductor nanocrystals

Colloidal CdS and CdS/ZnS nanostructures were obtained by nucleation and growth in colloidal solution. Their mean sizes range between 3 and 10 nm. The structural properties were studied by the use of high-resolution transmission electron microscopy (HRTEM). Phase transition between the metastable cubic blende-type structure and the stable hexagonal wurtzite-type structure was evidenced to be a function of the size of the CdS clusters. The mechanism of the transition involving stacking faults was determined by the heating of CdS clusters at 200 °C for 30 h. Results concerning structural relations between CdS and ZnS that occur during the epitaxial growth of ZnS on the CdS nanocrystals showed the existence of the hexagonal structure of ZnS, which is the high-temperature phase of ZnS.

Structural properties of coated nanoparticles: The CdS/ZnS nanostructure

The production of nanosized semiconductor nanostructures composed of a core of CdS nanocrystals coated with a ZnS layer has been attempted by using a method of inverted micelles. The structural aspects of nanocrystals have been investigated by high-resolution transmission electron microscopy. The CdS/ZnS core/shell heterostructure has been evidenced. The epitaxy of ZnS on CdS has been observed, abrupt CdS-ZnS interfaces have been found and the accommodation mode between the two materials has been analysed. It has been shown that the ZnS shell grows with the same structure as the CdS core, which is either in the cubic blende-type structure or in the hexagonal wurtzite-type structure.

Intermetallic Insertion Electrodes with a Zinc Blende-Type Structure for Li Batteries: A Study of Li[sub x]InSb (0≤x≤3)

The intermetallic compound InSb with a zinc blende-type (diamond) structure has been investigated as a host structure for lithium. After one break-in cycle, it appears that lithium can be inserted electrochemically into the structure in a two-step process to the approximate composition Li{sub 2}InSb. X-ray diffraction analysis showed that further lithiation of Li{sub 2}InSb displaces In from the structure to yield a closely related Li{sub 3}Sb-type structure. The electrochemical reaction that occurs between 1.2 and 0.5 V is reversible. The cubic unit cell expands isotropically by only 5.6% upon Li insertion to the end member Li{sub 2+x}In{sub 1-x}Sb at x{approx}0.5. This finding has implications for developing commercially attractive intermetallic insertion electrodes with zinc blende-type structures for lithium-ion batteries.

Epitaxial growth of ZnS on CdS in CdS/ZnS nanostructures

CdS/ZnS core/shell-like nanostructures have been elaborated by using the chemistry of colloids. The structural properties of the CdS core and the CdS/ZnS core-shell have been studied by high resolution transmission electron microscopy (HRTEM). The morphology and the structures of CdS have been determined. In a second step, the epitaxy of ZnS on CdS and the CdS/ZnS interface have been investigated. The accommodation mode between both materials by partial dislocations has been evidenced. Finally, the ZnS layer grows with the same structure as the CdS core, which is either in the cubic blende-type structure or in the hexagonal wurtzite-type structure.

Optical Anisotropy of ZnSe/BeTe Superlattices Probed by Excitonic Spectroscopy

A number of publications devoted to studies of optical anisotropy of heterostructures with no-common atom at interfaces (InAs/GaP, etc.) has been published recently [1-3]. This effect is attributed to a low local syinmetry of a single interface between two different zinc-blende type structures. In heterostructures CA/C'A' (001) with no-common cations (C ≠ C') and anions (A ≠ A'), an interface consists of the two atomic planes with A—C' or A'—C bonds. In this case there exist four different types of quantum-well structures (QWs) and superlattices (SLs). The structures with similar interfaces have the D2d point symmetry and are optically isotropic in the plane of interfaces. If the bonds at the left and right interfaces are different, an ideal structure with no-common atom is characterized by the in-plane anisotropy with the principal axes [110] and [110]. The microscopical reason for this in-plane anisotropy is a mixing of heavy hole and light hole states at the interfaces [3, 4]. In this paper we present an experimental study of the in-plane optical anisotropy in novel ZnSe/BeTe type-II quantum-well structures. Samples were grown by MBE on (100)-oriented GaAs substrates with controlling the type of interfaces. Three types of ZnSe/BeTe (100/50 Α) x 20 samples were grown: with BeSe...BeSe, ZnTe. . .ZnTe and BeSe...ZnTe interfaces. Basic optical properties of excitonic transitions in the ZnSe/BeTe quantum well structures were reported recently in Refs. [5, 6]. The observed two photoluminescence lines with energy positions at ,^s 2.8 eV and 2.0 eV were related to a

X-ray characterisation of Zn 1− xCo xS single crystals grown by chemical vapour transport

Single Zn 1− x Co x S crystals with x up to about 0.285 were grown by the chemical vapour transport method using iodine as the transporting agent. The obtained single crystal grains were typically of up to 3–6 mm in size. The crystal quality was studied with the help of high-resolution diffractometry. The FWHM of rocking curves was of the order of 40″. Lattice constants measured by both, the powder diffractometry and high-resolution diffractometry, are reported and compared with the literature data. The extrapolated lattice constant for hypothetical CoS compound of sphalerite-type structure is 5.343(1) Å. The interatomic distances in Zn 1− x Co x S and in related Fe and Mn containing sulphides are briefly discussed.

Let's Make Crystal Models!! BB-dan Model.

BB-dan is Japanese brand name of ball bullets for toy guns. The bullets are plastic spheres with a diameter of 6mm, and are very cheap, for example 4, 000 bullets costs you about 1, 000 yen (equivalent to approximately 8 US dollars). Ball crystal models called some times “marble ball models” are constructed by using these tiny ball bullets. Here I give the name BB-dan model, because the bullet is called BB-dan. The constructing methods are detailed. The pictures of models for a hexagonal compact structure, a body centered cubic structure, a zinc-blende type structure and a Si(111) 7×7 reconstructed structure are given.

Angular dispersion of optical phonon frequencies in strained cubic crystals

The use of Raman spectroscopy for strain characterization of materials often requires scattering configurations in which the optical phonon wavevector does not coincide with any of the strain-modified phonon eigenvectors. It is shown that the optical phonon frequencies in strained zincblende crystals exhibit angular dispersion similar to that of optical phonons in unstrained biaxial and uniaxial crystals. The entire formalism is developed on the basis of the relative magnitude of the longitudinal-transverse frequency splittings and the strain-induced frequency splittings. The shifts produced at grazing incidence are above the usual spectroscopic limits of accuracy and can influence the interpretation of data in terms of strain relaxation or defects. The model is applied to diamond- as well as zincblende-type structures. Specific examples are worked out in detail for scattering geometries under grazing incidence in [001] and [111] strained heterojunctions.

Influence of growth conditions on the structural properties of CdSxSe1−x (x = 0.4 and x = 1) nanocrystals

The structural properties of CdSxSe1−x nanocrystals elaborated by two different methods have been studied by means of high resolution transmission electron microscopy and optical absorption. In the first method, CdS0.4Se0.6 nanocrystals are grown in glass matrix and show a size distribution characterized by a standard deviation σ nearly proportional to the nanocrystals mean diameter d, the value σd being about 0.25. They are crystallized in the stable structure of wurtzite-type from the beginning of growth. Their morphology depends on the size: it changes from sphere to hexagonal prism as the size increases. In the second method CdS nanocrystals are grown in solution and show narrower size distribution; the ratio σd is about 0.15. The structure depends on the nanocrystal size: the blende-type structure is dominant at small diameter (d = 3 nm) and the wurtzite-type structure is more important at larger diameter (d > 5 nm). Their morphology also changes from quasi-sphere at small size (< 4 nm) to polyhedron-like at larger size.

A basic factor of dual epitaxy: the symmetry of similarity of zinc blende structure

The symmetry of the similarity of the surface step structure in zinc blende (sphalerite) type structures is investigated by studying the crystal planes that are parallel to the [01 \bar 1] axis. The symmetry transformations of the similar plane pairs are derived. Plane sets (111) and (311) are the planes of symmetry. The similarity of the surface step structure exists among three sets of planes. The surface geometric characteristics of similar planes are discussed. The result can be applied to explain dual epitaxy and optimize the interface quality by designing dual epitaxy in the heteroepitaxy.

Characterization of ordered and disordered Ga 0.51In 0.49P domains by micro Raman spectroscopy

Ga 0.51In 0.49P layers have been grown by metalorganic vapor phase epitaxy on GaAs(001) substrates misoriented 9° off towards [ 1 10] patterned on a 40 μm scale with grooves along [110]. Large (several (μm) domains of highly ordered material of the CuPt-type and of disordered zincblende-type structure coexist in the Ga 0.51In 0.49P layers as demostrated by transmission electron microscopy (TEM). Micro Raman and cathodoluminescence spectroscopy on (110) cleavage planes is applied to evaluate the impact of variation of composition and ordering effects on lattice dynamical and electronic properties with a spatial resolution of less than 1 μm. The ordered (C 3v) and disordered (T d) domains can be clearly identified from their different polarization selection rules observed in the Raman spectra. The combination of both Raman and luminescence measurements allows the determination of structure, composition (from the frequency positions of the optical phonon modes with an accuracy of 1%), and of the band gap at one location on the sample. A band gap shift of 145 meV at 5 K is measured between highly ordered and disordered domains of same composition. Furthermore, in partially ordered regions in other regions of the pattern the degree of ordering can be monitored from the transverse optical/longitudinal optical (TO/LO) intensity ratio obtained by Raman spectroscopy.

A study of the breakdown of Friedel's law in electron backscatter Kikuchi diffraction patterns: application to zincblende-type structures

The breakdown of Friedel's law has been observed in backscatter Kikuchi diffraction patterns (BKDP) obtained in the scanning electron microscope (SEM) from a series of zincblende structures including GaAs, InP, GaSb, CdHgTe and the minerals sphalerite (ZnS), chalcopyrite (CuFeS2) and tetrahedrite (Cu12Sb4S13). Differences in intensities were observed between the reflections 51{\bar 1} and 5{\bar 1}{\bar 1} in InP, GaSb, CdHgTe and sphalerite, thus allowing the non-centrosymmetric point group {\bar 4}3m to be determined. In GaAs, differences in intensities were noted between {\bar 5}11 and {\bar 4}{\bar 1}. In chalcopyrite and tetrahedrite, non-equivalent intensities were observed between {\bar 2}15 and 2{\bar 1}{\bar 5} and between 3{\bar 1}{\bar 2} and 31{\bar 2}, respectively. In addition, BKDPs obtained from chalcopyrite revealed a small displacement at the point where the pair of equivalent reflections {\bar 4}06 and 460 intersect within the Kikuchi band 02{\bar 2}. The presence of this displacement together with observation of the breakdown of Friedel's law confirmed the tetragonal point group {\bar 4}2m for chalcopyrite. Although the point groups of GaAs, chalcopyrite and tetrahedrite were derived successfully using BKDPs, determination of their space groups proved unsuccessful. The superstructure reflections were invisible because the structure factors are very small. The behaviour of the invisible 200 reflection in GaAs is investigated using many-beam dynamical intensity profiles calculated across the h00 systematic row of reflections. Dynamical intensity profiles calculated across the h00 systematic rows of reflections for Ge, InP and sphalerite are also discussed.

Structure of the ZnSe/GaAs heteroepitaxial interface

Interfaces of pseudomorphic (100) ZnSe/GaAs heterostructures grown by molecular beam epitaxy have been studied by transmission electron microscopy. The observation of three different heterostructures suggests the existence of a transition structure at the ZnSe/GaAs interfaces which have formed on As-deficient GaAs surfaces. The transition structure appears as a bright line in dark field images of the 200 reflection, while it becomes a dark line in dark field images of the 400 reflection. These observations are explained by assuming the existence of an interface layer which has a zinc blende type structure having vacancies in one of the face centered cubic sublattices.

Homogene, abschreckbare Hochdruckphasen mit NaCl-Struktur in den systemen CdTe-SnTe und CdTe-PbTe

The formation of solid solutions in the systems CdTe-SnTe and CdTe-PbTe has been investigated at high pressures and temperatures. At suitable reaction conditions homogeneous, quenchable high-pressure phases Cd x M 1 − x IV Te with NaCl-type structure can be recovered in the region 0 ⩽ x ⩽ 0.75 which are metastable at ambient pressure. For higher values of x the high-pressure phases are not quenchable; CdTe with zincblende-type structure is formed after release of pressure. There is a linear relationship between the lattice constant a of the NaCl-type phases and the composition x. Extrapolation of a for x → 1 gives for each system a lattice constant for the NaCl-type modification of CdTe at normal pressure. The mean value is a = 6.045 A ̊ . Data for the electrical conductivity of the NaCl-type solid solutions are presented.

Raman Scattering on SiC Polytypes –Probe for Evaluation of the Lattice Vibrational Amplitudes–

Long period SiC polytypes exhibit a number of Raman bands which reflect their stacking sequence of atomic planes. The Raman spectra of these polytypes can provide information on the phonon frequencies and vibrational amplitudes in the basic polytype (cubic, zincblende structure). Assuming a zincblende type structure as an approximate structure of SiC polytypes, the relative Raman intensity of folded modes in two SiC polytypes is calculated with several models of lattice dynamics and compared with the observed spectra. In the framework of a simple bond-polarizability model we show how the analysis of intensities can be used to rate different phenomenological models.

Debye-Waller parameters of diatomic crystals

The Debye-Waller parameters, the effective valuesBeff, the dynamic component,Bd, and the static component,Bs, of each constituent atom and also of the bulk were measured for some diatomic crystals with NaCl- and zinc blende-type structures. The dominant effect of heavy constituent atoms on the dynamic component of bulk crystals was found, and the mean square displacement in bulk crystals was approximated well by the atomic mass averaged mean square displacements of the constituent atoms. A remarkable effect of structural defects onBeff, particularly onBs, was observed in NiO samples with different degrees of non-stoichiometry. The different extents of the SiC-forming reaction between solid carbon and fused silicon resulted in quite differentBeff values; the larger theBeff value the smaller the extent of the reaction.