Ageing effect on dielectric properties of SnO2, Sb2O3, and their mixed thin films

Thin films of various thicknesses in the form of MIM structures have been prepared from the powders of high purity of SnO₂, Sb₂O₃, and their mixed powders separately by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. The dielectric properties of these oxide thin films have been studied with ageing time and also with frequency at room temperature. The results obtained have shown that the capacitance and loss tangent of the structures initially fall off rapidly and thereafter they attain a constant value even after ageing the capacitors for about 20 days. The rapid fall of capacitance and loss tangent may be due to the rapid decrease in the density of defects due to ageing time. The results thus obtained on SnO₂, Sb₂O₃, and their mixed thin film capacitors are presented and discussed.     

Study on local structure in amorphous SbS films by Raman scattering

A stoichiometric Sb₄₀S₆₀ film contains SbSb and SS bonds in addition to SbS bonds in an SbS₃ unit. The amount of the SbSb bond rapidly decreases with an increase in the S content beyond the stoichiometric value. On the other hand, as the S content decrease beyond the stoichiometric value, the SbS bond decreases and the SbSb bond increases. Annealing at temperatures near the glass transition decreases the fraction of the SbSb bond in the Sb₄₀S₆₀ film.     

Influence of thermoannealing on crystallinity and optical properties of Sb2S3 thin films

Sb₂S₃ thin films are obtained by evaporating of Sb₂S₃ powder onto glass substrates maintained at room temperature under pressure of 2×10^‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb₂S₃ thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E₀, dispersion energy, E_d) were determined. The static refractive index n(0), static dielectric constant, ε_∞, and optical band gap energy, E_g, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure of bis-(rhodanine)copper(I) iodide,C6H6CuIN2O2S4

The structure of the polymeric rhodanine compound, C₆H₆CuIN₂O₂S₄, was determined by X-rays.M _r =456.8, monoclinic, space groupP2₁/c,a=4.1947(7),b=17.6999(12),c=17.1048(8) Å,=96.15(1)°,V _c =1262.6 ų,Z=4,D _c =2.40Mg m^–3, CuK radiation (graphite crystal monochromator, =1.54056 Å),(CuK)=278.9 cm^s-1,F(000)=872,T=290 K. Final conventionalR-factor=0.029, andR _w =0.044 for 2384 unique reflections and 153 variables. The structure was solved using Patterson methods andDirdif, and refined by full-matrix least-squares methods. The compound forms zigzag chains alonga. The copper atom is in trigonal pyramidal coordination, with two sulfur atoms of the thiocarbonyl group and two bridging iodine atoms. The copper-sulfur distances are 2.278(1) and 2.299(1) Å, and the copper-iodine distances are 2.657(1) and 2.814(1) Å.     

Cs2Ni(SO4)2 · 6H2O (CNSH) crystal: Growth and some properties

Large single crystals of cesium-nickel sulfate hexahydrate Cs₂Ni(SO₄)₂ · 6H₂O of optical quality were grown for the first time. The crystal structure and the optical and thermogravimetric properties of this compound were investigated.     

Synthesis,properties, and molecular structure of bis(thiobenzoato-S)tellurium(II), C14H10O2S2Te(II)

The synthesis, properties, and structural characterization of the title compound, C₁₄H₁₀O₂S₂Te, are reported. The crystals are monoclinic, space groupC2/c (No. 15) witha=24.369(6),b=4.333(2),c=14.569(3) Å, and=109.56(2)°,V=1449.57 ų,M=402, andD _x =1.843 g cm^–3 forZ=4. The structure was solved by the heavy-atom method and refined by full-matrix least squares toR=0.029 andR _w =0.027 for 772 diffractometer data. Crystal structure analysis and IR spectroscopic study indicate that the tellurium is covalently bonded to sulfur. There are weak secondary interactions between tellurium and oxygen which complete an S₂O₂ coordination around tellurium.     

Electrical transport properties of CdTe:Sb films

Hall coefficient and dc conductivity measurements are made on p-type CdTe:Sb films grown by vacuum evaporation technique on glass substrate. The grain boundary potential barrier, which is found mainly to limit the mobility of carriers is calculated as a function of film thickness. The n-type conduction is found to dominate over p-type conduction above about 330 K. The ratio of electron to hole mobility is also calculated.     

Substrate temperature effect on the optical properties of amorphous Sb2S3 thin films

Sb₂S₃ amorphous thin films were prepared by thermal evaporation of corresponding powder on thoroughly cleaned glass substrates held at temperature in the range 300‐473 K. X‐ray diffraction and atomic force microscopy have been used to order to identify the structure and morphology of surface thin films. The optical constants of the deposition films were obtained from the analysis of the experimental recorded transmission data over the wavelength range 400‐1400 nm. An analysis of the absorption coefficient values revealed an optical indirect transition with the estimation of the corresponding band gap values. It was found that the optical band gap energy decrease with substrate temperature from 1.67 eV at 300 K to 1.48 eV at 473K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optically induced crystallization in amorphous Agx(Sb0.33S0.67)100−x films

Amorphous films of Ag_x(Sb_0.33S_0.67)_100−x composition, where x was between 0 and 25 at.% Ag, were prepared by pulsed laser deposition and optically induced silver dissolution into the binary Sb-S chalcogenides deposited by vacuum evaporation techniques. We have studied the effect of silver content in the host materials and Ar⁺ ion laser exposure on the optical properties and structure of the films. Optically induced crystallization was demonstrated in films and the kinetics of the crystallization were studied. This work is anticipated to be applicable to optical memories.     

Influence of temperature on the microcrystalline structure of thermally evaporated Sb2S3 thin films

Thin films of antimony trisulfide (Sb₂S₃) were prepared by thermal evaporation under vacuum (p=5×10^–5 torr) on glass substrates maintained at various temperatures between 293 K and 523 K. Their microstructural properties have obtained by transmission electron microscopy (TEM). The electron diffraction analysis showed the occurrence of amorphous to polycrystalline transition in the films deposited at higher temperature of substrates (523 K). The polycrystalline thin films were found to have an orthorhombic structure. The interplanar distances and unit‐cell parameters were determined by high‐resolution transmission electron microscopy (HRTEM) and compared with the standard values for Sb₂S₃. The surface morphology of Sb₂S₃ thin films was investigated by scanning electron microscopy (SEM). The optical transmission spectra at normal incidence of Sb₂S₃ thin films have been measured in the spectral range of 400–1400 nm. The analysis of the absorption spectra revealed indirect energy gaps, characterizing of amorphous films, while the polycrystalline films exhibited direct energy gap. From the photon energy dependence of absorption coefficient, the optical band gap energy, E_g, were calculated for each thin films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photo and thermal induced effects on (As2S3)0.85Sb0.15 amorphous thin films

Exposure with above band gap light and thermal annealing at a temperature near to glass transition temperature, of thermally evaporated amorphous (As₂S₃)_0.85Sb_0.15 thin films were found to be accompanied by structural effects, which in turn, lead to changes in the optical properties. The optical properties of thin films induced by illumination and annealing were studied by Fourier Transform Infrared spectrometry, X-ray Photoelectron Spectroscopy and Raman Spectroscopy. Photodarkening or photobleaching was observed in the film depending upon the conditions of the light exposure or annealing. These changes of the optical properties are assigned to the change of homopolar bond densities. The photodarkening in the as-prepared film was seen at low temperature (4.2 K).     

Structure and electrical conduction of Sb2O3 thin films

Antimony trioxide (Sb₂O₃) thin films have been deposited onto glass substrates using thermal evaporation technique at room temperature. The structural feature and surface morphology were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Sandwich‐type structures were deposited with films thickness d = 0.55 μm using evaporated electrodes of silver. Current‐voltage (J‐U) characteristics have been measured at various fixed temperatures in the range 293‐473 K. In all cases, at low electric field (E <10⁴ V/cm), ohmic behavior is observed. However, at high electric field (E >10⁴ V/cm), non‐ohmic behavior is observed. An analysis of the experimental data indicates that in the range of high‐applied electric field, the dominant conduction mechanism is space charge limited currents (SCLC). Using the relevant SCLC theory, the carrier concentration, total trap concentration and the ratio of free charge to trapped charge have been calculated and correlated with changes in the structures of antimony trioxide thin films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth,structure, and some transport properties of topological insulators based on bismuth chalcogenide single crystals

Single crystals of topological insulators—bismuth chalcogenides Bi₂Te₃, Bi_{2 ? x} Sn _x Te₃, Bi₂Se₃, and Bi_{2 ? x} Cu _x Se₃ with different charge-carrier densities—are grown by the modified Bridgman method. Their composition and structure are investigated and temperature dependences of the electric resistance and magnetic field dependences of the Hall voltage are obtained.     

Influence of oxidization temperature on Zn(O,S) films deposited by electron beam evaporation

Zn(O,S) films were fabricated by oxidizing ZnS thin films deposited by electron beam evaporation method onto glass substrates at temperatures of 350–500℃ for 2 h in an atmosphere of oxygen. The XRD and EDX confirmed that the Zn(O,S) films were obtained successfully. The influence of the oxidization temperature on the optical and electrical properties of the Zn(O,S) thin films was investigated. The experimental results show that the Zn(O,S) thin film oxidized at the temperature of 400℃ exhibits better properties than others, with the transmittance of 86% in the visible region, the band gap energy of 3.36 eV and the resistivity of 3.22 × 10³ Ω·cm, which makes it a potential buffer layer of solar cell.     

Effect of temperature on dielectric properties of SnO2/Sb2O3 mixed thin films

Thin films of various thicknesses in the MIM structure have been prepared from the powder of SnO₂/Sb₂O₃ mixed sample by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. Dielectric properties of SnO₂/Sb₂O₃ mixed thin films have been studied with temperature starting from LNT to RT and above RT and frequency ranging from 100 Hz to 16 kHz. The activation energy for the migration of charge carriers in SnO₂/Sb₂O₃ mixed thin films has been calculated and it is found to be 0.23 eV. The results thus obtained on dielectric properties of SnO₂/Sb₂O₃ mixed thin films are presented and discussed.     

Structural and optical properties of Zn(Mg,Cd)O alloy films grown by remote-plasma-enhanced MOCVD

We report the structural and optical properties of wurtzite-structure Zn(Mg,Cd)O ternary alloys. Wurtzite (0 0 0 1) Zn_1−xCd_xO and Mg_yZn_1−yO films were grown on (11–20) sapphire substrates using remote-plasma-enhanced metalorganic chemical vapor deposition. The large bowing parameters of Zn_1−xCd_xO and Mg_yZn_1−yO ternary alloys are 3.0 and 3.5, respectively, which reflects the large difference of each binary’s electronegativity. We have analyzed the broadening of photoluminescence (PL) in Zn(Mg,Cd)O alloys on alloy content by taking into account the statistical alloy fluctuation and the localization of the exciton, and have clarified that the localization of the exciton strongly affects to PL full-width at half-maximum (FWHM) in Zn(Mg,Cd)O alloys. The alloy broadenings in steady-state PL of Zn(Mg,Cd)O alloys are in good agreement with the calculated tendency by the theoretical model based on the statistical alloy fluctuation, while PL FWHM of Zn_1−xCd_xO is three times larger than the calculated results. Moreover, as another way to confirm alloy broadening, we also have done time-resolved PL measurements and derived the localized depth of the exciton in ZnO-based system, indicating a good agreement with the tendency of PL FWHM broadening.     

Growth,structure and properties of thin monocrystalline InSb films grown by recrystallization in a narrow gap

The results of investigation of recrystallization kinetics of (≦ 500 Å) InSb films are described with the aid of a laser refractometer. The thermodynamic process characteristic considered to the gap thickness and substrate material are investigated. It was revealed that the method of producing a protective SiO_x coating greatly affects the electric properties of InSb films.     

Bimolecular relaxation kinetics observed in radiation-optical properties of Ge–As(Sb)–S glasses

Numerical parameters of decaying bimolecular relaxation kinetics are analysed for radiation-optical properties of chalcogenide glasses within ternary stoichiometric As₂S₃–GeS₂ and Sb₂S₃–GeS₂ as well as non-stoichiometric As₂S₃–Ge₂S₃ systems in dependence on their composition. It is shown, that the observed compositional dependences of bimolecular relaxation parameters have a monotonic character in the glasses of both stoichiometric systems, while the anomalous extremum-like behavior is observed in the vicinity of average coordination number close to 2.7 in non-stoichiometric glasses.     

Optically-induced darkening and crystallization in amorphous Ag–Sb–S films

The amorphous films of Sb₃₃S₆₇ and Ag_x(Sb_0.33S_0.67)_100−x composition, where x was between 0 and 25 at.% Ag, were prepared by different techniques, i.e. by vacuum evaporation, optically-induced silver dissolution into the binary Sb–S chalcogenides deposited by vacuum evaporation or by spin-coating techniques. Ternary Ag–Sb–S amorphous films were also prepared directly by pulsed laser deposition. We have studied effect of silver content in the host materials and Ar⁺ ion laser exposure on optical properties and structure of the films. The optically-induced darkening and crystallization was proved in studied films and their potential application in optical memories could be expected.