The crystal structure of the intercalates SnTaS2 and SnNbS2

The crystal structure of SnTaS₂ was determined by X-ray and neutron powder diffraction. SnTaS₂ is hexagonal, $\text{a}\text{=3.307}\text{A}\text{?}$, $\text{c}\text{=17.442}\text{A}\text{?}$, space group P6₃/mmc with Ta and Sn at special positions. Ta is in trigonal-prismatic coordination by sulfur forming TaS₂ slabs; Sn is linearly coordinated by sulfur atoms of adjacent TaS₂ slabs. X-ray powder diffraction showed that SnNbS₂ is isostructural with SnTaS₂.     

Improved photodegradation activity of TiO2 via decoration with SnS2 nanoparticles

The particles of TiO₂ modified with various amounts of SnS₂ nanoparticles (TiO₂/SnS₂) were synthesized via the hydrothermal method by reacting SnCl₄·5H₂O with thioacetamide in 5% (vol.) acetic acid aqueous solution in the presence of TiO₂. The obtained products were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis diffuse reflection spectra, scanning and transmission electron microscopy. The photodegradation activities of TiO₂/SnS₂ composites have been investigated by using methyl orange as target in water under the light irradiation of 250–400, 360–600 and 400–600 nm. It was found that the photodegradation activity of TiO₂/SnS₂ composites depended on the mass ratio of SnS₂ and the wavelength of the irradiating light. The composites containing 33% SnS₂ exhibited the maximum activity under the light irradiation of 250–400 and 360–600 nm. However, the more SnS₂ in the composites, the higher activity appeared under the irradiation of 400–600 nm light. All the results reveal that the composites possess much better activity than the pristine TiO_2.     

Optical properties of nanocrystalline SnS2 thin films

Thin films of nanocrystalline SnS₂ on glass substrates were prepared from solution by dip coating and then sulfurized in H₂S (H₂S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 °C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at ∼314 cm⁻¹, which confirmed the presence of nanocrystalline SnS₂ phase.     

Growth and characterization of (SnS2)x-(SnSe2)1−x mixed crystals

(SnS₂)_x-(SnSe₂)_1−x layered crystals were grown using the vertical Bridgman technique for x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.9, 1.0. IR-spectra of these compounds were obtained using a Bruker-spectrometer. The structural properties were studied using transmission electron microscopy (TEM). The variation of the structural and optical properties was studied as a function of the composition x.     

Controlled synthesis and possible formation mechanism of leaf-shaped SnS2 nanocrystals

A sort of novel leaf-shaped SnS₂ nanocrystals have been synthesized by controlled reaction of CH₃CH₂OCS₂K with SnCl₄·5H₂O in aqueous solution in the absence of surfactant. The leaf-shaped nanocrystals consist of very thin sheets with several microns in length and 100–300 nm in width. The structure, composition, and morphology of the as-prepared leaf-shaped SnS₂ nanocrystals were characterized by XRD, Raman spectra, XPS, and FE-SEM, respectively. Elemental analysis, FT-IR spectra, and TEM were further used to study the formation mechanism of the leaf-shaped SnS₂ nanocrystals. A possible mechanism of producing lamellae – breaking into nanosheets – rolling and assembling was suggested for the leaf-shaped SnS₂ nanocrystals formation based on experimental results.     

Synthesis of homogeneous PVP-capped SnS2 submicron particles via microwave irradiation

Homogeneous PVP-capped tin disulfide (SnS₂) submicron particles with narrow size distribution of ca. 300–500 nm have been successfully synthesized via microwave irradiation for 10 min for the first time. The samples were characterized using X-ray diffraction (XRD) and transmission electron microscope (TEM). In contrast, SnS₂ particles without PVP obtained under the same condition have irregular morphology. The experimental result indicated that PVP played an important role in controlling the shape and size distribution of particles, and in reducing the agglomeration degree of SnS₂ particles. The mechanism of PVPs improving the well dispersion of SnS₂ particles was discussed. The influence of solvent on the crystallinity of the as-prepared particles under microwave irradiation was primarily investigated.     

Epitaxial layers of CuInSe2 on GaAs

CuInSe₂ single-crystal films with (112) orientation and with thicknesses in the range 800–1200 Å were deposited onto semi-insulating (111)A-oriented GaAs substrates by flash evaporation under controlled growth conditions. Epitaxial growth began at a substrate temperature T_sub = 720 K and twins in the 〈221〉 direction were detected in reflection high energy electron diffraction investigations. The twin concentration decreased with increasing growth temperature. At T_sub = 870 K a change of the structure from chalcopyrite to sphalerite was observed. Films produced at T_sub ? 720 K showed n-type conductivity whereas at higher growth temperatures the films were always p type and showed a rapid increase in hole concentration with increasing substrate temperature. Two different acceptor levels with ionization energies of 92 meV and about meV were found.     

Epitaxial growth of CdS on CuInSe2

A single-source, vacuum vapor deposition technique was used to grow epitaxial (0001) CdS films on (112) CuInSe₂ single crystal substrates. Highly uniform single crystal CdS films up to 16 μm thick were produced and their quality assessed by x-ray diffraction, scanning electron microscopy, and electrical characterization.     

Photoconductivity and photomemory in ZnXCd1–XIn2S4 layered crystals

Deep acceptor levels related to the ionization states of a double negatively charged center, A^2?, which cause high sensitivity in Zn_XCd_1–XIn₂S₄ layered crystals grown by chemical vapor deposition, have been investigated. The energy location, the capture cross section ratio and its dependence on the temperature have been determined by photoconductivity and thermal quenching experiments. The origin of a higher sensitivity and a region for the charge storage effect extending toward room temperature has been analyzed in crystals grown at the limit of existence of the quaternary layered phase. A possible origin of such centers due to zinc vacancy whose density increases with the partial substitution of cadmium by zinc atoms has been assumed to prove theoretical predictions and experimental results.     

Epitaxial growth of SnO2 film on Sn-doped TiO2(110)

Using a simple vacuum deposition-and-annealing method, Sn-doped TiO₂ (110) single crystals were prepared. Compared with the case of a pure TiO₂ substrate, the lattice mismatch between SnO₂ and the Sn-doped TiO₂ was reduced to −2.85% for the a-axis from −3.25 to −2.85% and for the c-axis from −7.35 to −6.62%. Surface morphologies of deposited SnO₂ films were compared on the Sn-doped TiO₂ (110) and on the pure TiO₂ (110). Results showed that the use of Sn-doped TiO₂ (110) single crystal as a substrate was favorable for growing epitaxial SnO₂ (110) films.     

Characterization of CuInTe2 crystals

A single crystal of CuInTe₂ (CIT) was prepared from melt by using a vertical Bridgman technique. The crystal was characterized by X-ray diffraction. Electrical conductivity, Hall effect and thermoelectric power (TEP) measurements were performed over a wide range of temperature. From these measurements, various physical parameters such as carrier mobilities, effective masses of charge carriers, diffusion coefficient, relaxation time, and diffusion length for both majority and minority carriers were estimated. In addition, the energy gap was determined as 1.057 eV and the type of conduction was observed to be p-type as indicated from the positive sign of both the Hall coefficient and thermoelectric power.     

Epitaxial integrated dE1 − dE2 silicon detectors

Epitaxial integrated dE₁ ? dE₂ silicon detectors have been developed by using the multilayer epitaxial crystal growth technique combined with the chemical preferential etching technique. These detectors are useful for eliminating events affected by channeling and blocking effects in the identification of heavy ions using multiple detector telescope systems. Characteristics of dE detectors of the integrated dE₁ ? dE₂ type are confirmed to as good as those of integrated E ? dE detectors.     

Single crystals of In2Te5

Single crystals of semiconducting compound In₂Te₅ were grown by chemical transport employing iodine as a transport agent. The crystals had a plate-like habit with the [100] direction perpendicular to the flat surface of the platelets. Nominal dimensions are 10 × 1 × 0.05 mm. In₂Te₅ has a monoclinic structure with dimensions of the base centered cell: $\text{a}\text{= 13.47}\text{A}\text{?}$, $\text{b}\text{= 16.51}\text{A}\text{?}$, $\text{c}\text{= 4.365}\text{A}\text{?}$, β = 92°5′. The space group is $\text{C}{}_{\mathrm{<mtext>2</mtext><mtext>c</mtext>}}$. Pycnometric density is 5.96 g/cm³. The single crystals were all p-type. The conductivity, thermoelectric power and hardness were about 10^?5Ω^?1cm^?1, 650 mkV/°C, and 30 kg/mm², respectively. The minimum energy gap is 1.26 eV.     

Epitaxial growth of MgAl2O4 spinel crystals by solid-state reaction of MgO crystal with molten Al metal

Single crystals of MgAl₂O₄ spinel have been prepared epitaxially by a solid-state reaction of MgO crystal with molten Al metal under vacuum of 10^?5≈10^?6 torr at 1000≈1100°C. The growth rate was estimated to be about 0.1≈0.2 mm/hour in this temperature range. The as-grown crystals were black and opaque with low crystallinity, which was improved by heating above 1350°C. Chemical analysis showed that the crystals were slightly contaminated with Mg metal which was easily oxidized above 900°C in air.     

Dielectric and photoconducting properties of Ga2Te3 and In2Te3 crystals

Single crystals of defect III–VI semiconductors Ga₂Te₃ and In₂Te₃ have been grown by the Bridgman method. Capacitance vs frequency measurements have been carried out from which the low frequency dielectric constants ?₅ have been determined to be 10.95 ± 0.26 and 12.3 ± 0.13 respectively. These values are compared with the high-frequency dielectric constants ?₆₀ calculated from the Phillips' model. Dark conductivity and photoconductivity have been studied as a function of annealing upto 210°C, maxinum photosensitivity being obtained for both crystals for T_anneal = 80°C. This behaviour has been related to lattice ordering through x-ray diffraction studies. Measurements of photo conductive gain indicate carrier life-times of 2 × 10^?4s and 5 × 10^?4s respectively at room-temperature.     

氟化钙晶体的生长与缺陷研究

采用真空坩埚下降法在石墨坩埚中生长了大尺寸CaF2晶体.通过高温氟化获得无水高纯原料,自发成核发育籽晶,以＜2mm/h的生长速率,成功生长了直径170mm的CaF2晶体.研究了晶体的顶部析晶形貌、包裹体、解理等生长缺陷.     

Epitaxial growth and relaxation of γ-Al2O3 on silicon

0.5-10 nm-thick single crystal γ-Al₂O₃ films was epitaxially grown, at high temperature, on Si(001) and Si(111) substrates using electron-beam evaporation techniques. Reflection High Energy Electron Diffraction studies showed that the Al₂O₃ films grow pseudomorphically on Si (100) up to thickness of 2 nm. For higher thicknesses, a cubic to hexagonal surface phase transition occurs. Epitaxial growth and relaxation were also observed for Si(111). The film surfaces are smooth and the oxide-Si interfaces are atomically abrupt without interfacial layers.     

Epitaxial growth of ferromagnetic CrO2 films in air

Epitaxial growth of CrO₂ films under atmospheric pressure has been investigated. Single crystal films of CrO₂ were obtained by the thermal decomposition of gaseous CrO₃ onto the substrates of rutile single crystals in air. The optimum temperature of the substrate for the pure CrO₂ epitaxial films was found to be 390°C. At the substrate temperature of 380°C, the obtained film included Cr₂O₅ as impurities, and Cr₂O₃ appeared at 400°C. Magnetic domain patterns of these films were observed by longitudinal Kerr effect. The growth patterns of domain were obtained with applied field.     

Luminescence properties of Sn2P2Se6 crystals

A large family of Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) semiconductor-ferroelectric crystals were obtained by the Bridgman technique. The photoluminescence properties of the Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) family crystals strongly depend on their chemical composition, excitation energy and temperature. The influence of the Pb → Sn and S → Se isovalent substitutions on the luminescence properties of a crystal with the Sn₂P₂Se₆ basic composition was investigated. A broad emission band observed in the Sn₂P₂Se₆ crystal with a maximum roughly at 600 nm (at T = 8.6 K) was assigned to a band-to-band electron-hole recombination, whereas broad emission bands, peaked near 785 nm (at T = 8.6 K) and 1025 nm (at T = 44 K) were assigned to an electron-hole recombination from defect levels localised within the bandgap. Possible types of recombination defect centres and specific mechanisms of luminescence in the Sn₂P₂Se₆ semiconductor-ferroelectric crystals were considered and discussed on the basis of the obtained results and the referenced data.