Constructing anisotropic single-Dirac-cones in Bi(1-x)Sb(x) thin films

The electronic band structures of Bi(1-x)Sb(x) thin films can be varied as a function of temperature, pressure, stoichiometry, film thickness, and growth orientation. We here show how different anisotropic single-Dirac-cones can be constructed in a Bi(1-x)Sb(x) thin film for different applications or research purposes. For predicting anisotropic single-Dirac-cones, we have developed an iterative-two-dimensional-two-band model to get a consistent inverse-effective-mass-tensor and band gap, which can be used in a general two-dimensional system that has a nonparabolic dispersion relation as in the Bi(1-x)Sb(x) thin film system.     

Thermal and optical properties of Cd1-x Zn x S thin films by photoacoustics

Ternary compounds Cd_1-x Zn _x S for various Zn concentration in thin films are synthesized by spray pyrolysis and studied by photoacoustics technique for thermal and optical properties. The thermal diffusivity as a function of the alloy composition measured by photoacoustics shows a maximum at x = 0.6. The optical band gap increases with zinc concentration and the continuous change indicates the formation of solid solution.     

Cd_(1-x)Zn_xS(x=0.88)多晶薄膜的制备及性能研究

采用真空共蒸发法制备了Cd1-xZnxS多晶薄膜,研究了Cd1-xZnxS(x=0.88)多晶薄膜的结构与光电特性。XRD的结果表明,0x≤0.9,Cd1-xZnxS薄膜为六方结构,高度择优取向;荧光光谱分析与Ve-gard定理的结果以及石英振荡法监测的Cd1-xZnxS多晶薄膜的组分吻合;制备的Cd1-xZnxS多晶薄膜的光学透射谱的吸收边随Zn含量的增加发生蓝移,其光学能隙调制在CdS与ZnS能隙之间;最后测量了Cd1-xZnxS薄膜室温电阻率及暗电导率随温度的变化情况,计算了Cd1-xZnxS薄膜的电导激活能。     

Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films

Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.     

On the compositional dependence of the optical gap and structural properties of amorphous In x Se1−x thin films

The optical gap of the amorphous In _x Se_1–x thin film has been observed to decrease with increasing content of indium in the film (x). An attempt is made to interpret the compositional dependence of the optical gap in amorphous In _x Se_1–x thin film in an alloy-like approach. It has been found that introduction of higher concentrations of indium imparts greater stability to the structure of the indium selenium alloy. From the study of the radial distribution function (RDF) by X-rays it is observed that there is a correlation between the coordination number and the optical gap of indium selenide thin films.     

Growth and characterization of CuInSe2 thin films

Films of CulnSe₂ have been grown using a technique similar to close-spaced vapour transport. The effect of substrate temperature and the distance of the substrate from the source have been optimised to grow well-oriented chalcopyrite phase of CuInSe₂. D.c. conductivity and Hall coefficient studies have been made in the temperature range 77–300 K. The films grown at a substrate temperature of 350 °C have an electron mobility of 3.4×10³ cm²V^–1 s^–1 at 77 K.     

Crystal Growth and Properties of (CuInSe2) x (2ZnSe)1 – x Solid Solutions

(CuInSe₂) _x (2ZnSe)_{1 – x} crystals are grown by the horizontal Bridgman process and chemical vapor transport, and their composition and structure are determined. The transmission and reflection spectra of the crystals are measured near the intrinsic edge. The results are used to determine the band gap of the (CuInSe₂) _x (2ZnSe)_{1 – x} solid solutions, which is found to vary nonlinearly with composition.     

Fabrication, structural characterization and photoluminescence of single-crystal Zn(x)Cd(1-x)S zigzag nanowires

Large-scale synthesis of ternary Zn(x)Cd(1-x)S zigzag nanowires was achieved in a one-step metal-organic chemical vapour deposition (MOCVD) process with co-fed single precursors of ZnS and CdS. Their morphologies, structures and optical properties were characterized and confirmed by scanning electron microscopy, high-resolution transmission electron microscopy, x-ray spectroscopy, and photoluminescence. The Zn(x)Cd(1-x)S zigzag nanowires are single crystalline, with axis [001], by changing the growth direction from [Formula: see text] to [Formula: see text]. Regarding the formation of zigzag nanowires, we suggest that the shear strain and slight fluctuation of the reaction conditions may be the major factors that make the nanowires change growth direction. In addition, because of the lower temperature and versatility, this new fabrication method might present a new and facile way to form other ternary nanomaterials. Furthermore, the green emission of the nanowires may have potential applications in electronic/optical nanodevices.     

离子辅助蒸发(1-x)TiO2-(x)Ta2O5薄膜及其光学性能研究

采用离子辅助蒸发的方法，以不同配比的Ta2O5和TiO2混合物为初始膜料在K9玻璃上制备了TiO2-Ta2O5混合薄膜，并对其透射性能和光学常数进行研究。实验结果表明，薄膜在可见光范围内的平均透射率在82％以上，并随着Ta2O5含量的增加而增加；薄膜的折射率在1．80～2．07范围内变化（550nm）。对同-Ta2O5含量的薄膜来说，退火后TiO2薄膜和80TiO2—20Ta2O5薄膜的折射率较退火前提高，而90TiO2-10Ta2O5薄膜的折射率较退火前降低。     

Deposition and dielectric properties of (Al2O3) x (TiO2)1−x thin films

The motivation for this study was to obtain an alloy system (Al₂O₃) _x (TiO₂)_1?x , that is thermodynamically stable, in direct contact with Si and possessing a high dielectric constant. In the present study, (Al₂O₃) _x (TiO)_1?x films were investigated. They were prepared by spin coating from a sol solution, with additional thermal annealing. The chemical composition and stoichiometry of the films was studied by X-ray photoelectron spectroscopy. For the electrical characteristics, MIS capacitors were fabricated. The determined relative dielectric constants were larger than the reported values for pure Al₂O₃, due to the presence of TiO₂.     

Chemical synthesis and compositional analysis of mixed [Mo(S1 − x Se x )2] semiconductor thin films

The synthesis of binary MoS₂, MoSe₂ and mixed [Mo(S_{1 – x} Sex)₂] thin films onto a glass substrates using arrested precipitation technique (APT) is presented in this investigation. Growth kinetics and mechanism of film formation were studied for these films and are explained in brief. The stoichiometry of the film is confirmed by analyzing films using Extractive spectrophotometric (ESP), atomic absorption spectroscopic (AAS) and electron difftraction X-ray microanalysis (EDAX) techniques. The semiconductor solution containing Mo(VI) and Se(IV) is extracted with N-n-octylaniline in xylene and determined by ESP, AAS and EDAX techniques. Further these films are characterized for its semiconducting behavior to test the suitability of molybdenum chalcogenides as a photoelectrode to convert radiant energy into electricity. It is found that stoichiometry of the film formed by our recently developed arrested precipitation technique (APT) has strong influence on photoconduction in molybdenum chalcogenide photoelectrodes.     

Nanostructural control in solution-derived epitaxial Ce(1-x)Gd(x)O(2-y) films

A novel mechanism based on aliovalent doping, allowing fine tuning of the nanostructure and surface topography of solution-derived ceria films, is reported. While under reducing atmospheric conditions, non-doped ceria films are inherently polycrystalline due to an interstitial amorphous Ce(2)C(3) phase that inhibits grain growth, a high quality epitaxial film can be achieved simply by doping with Gd(3+) cations. Gd(3+) [Formula: see text] Ce(4+) substitutions within the lattice are accompanied by charge-compensating oxygen vacancies throughout the volume of the crystallites acting as an efficient vehicle to reduce the barrier for grain boundary motion caused by interstitial Ce(2)C(3). In this way, the original nanostructure is self-purified by pushing the amorphous Ce(2)C(3) phase towards the free surface of the film. Once a full epitaxial cube-on-cube oriented ceria film is obtained, its surface morphology is dictated by the interplay between faceting on low energy {110} and/or {111} pyramidal planes and truncation of those pyramids by (001) ones. The development of the latter requires the suppression of their polar character which is thought to be achieved by charge compensation between the dopand and oxygen along [Formula: see text] directions.     

Preparation and characterization of flash-evaporated CuInSe2 thin films

Thin films of CuInSe₂ have been evaporated onto glass substrates by flash evaporation. The as-deposited films are amorphous and annealing in selenium atmosphere produces polycrystalline films. The films were characterized bytem and x-ray diffraction techniques. The optical absorption of the films shows three energy gaps of 1·03, 1·07 and 1·22 eV. The crystal field and spin-orbit splitting are thus found to be 0·04 eV and 0·16 eV respectively. The percentaged-character of the valence band states is ∼35%. The Arrhenius plot of electrical conductivity of films showed impurity ionization ofE _A = 75 meV.     

Birefringence of Zn(x)Cd(1-x)S near the isotropic point

The birefringence of the mixed crystal Zn0.14Cd0.86S has been measured near its isotropic point and found to be highly dispersive. The region of strong dispersion shifts to shorter wavelengths than observed in pure CdS, and its magnitude near the isotropic point is larger. These results are highly significant for the development of narrowband dispersive birefringent filters in the blue-green region of the spectrum.