Physical properties of very thin SnS films deposited by thermal evaporation

SnS films with thicknesses of 20-65 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible-near infrared spectroscopy at room temperature. The results from XRD, XPS and Raman spectroscopy analyses indicate that the deposited films mainly exhibit SnS phase, but they may contain a tiny amount of Sn₂S₃. The deposited SnS films are pinhole free, smooth and strongly adherent to the surfaces of the substrates. The color of the SnS films changes from pale yellow to brown with the increase of the film thickness from 20 nm to 65 nm. The very smooth surfaces of the thin films result in their high reflectance. The direct bandgap of the films is between 2.15 eV and 2.28 eV which is much larger than 1.3 eV of bulk SnS, this is deserving to be investigated further.     

Thermal conductivity of Zn, Pr and Tb doped YBCO single crystals: Theory and experiment

The thermal conductivity K(T) vs temperature has been measured for (Y,Pr)Ba₂Cu₃O₇, (Y,Tb)Ba₂Cu₃O₇ and YBa₂(Cu,Zn)₃O₇ single crystals from 10T280K. For YBa₂Cu₃O₇(YBCO), a strong enhancement in K(T) is observed for TT_cwith a peak in K(T) at approximately TT_c/2 with a sharp change in slope of K(T) at T_c. These results are similar to those reported previously. For the selectively doped YBCO, the peak in K(T) is shifted to lower temperatures and occurs at T 20K independent of T_c and the impurity concentration. In addition, the sharp change in slope of K(T) at T_c is not apparent for the doped crystals. These results are discussed along with a theoretical model for electronic conduction including both impurity and inelastic scattering from spin fluctuations.     

Electrical strength of thin polyaniline films

The electrical strength of in-situ polymerized polyaniline films converted to non-conducting polyaniline base has been compared with the strength of solution-cast polystyrene and poly(methyl methacrylate) films of sub-micrometre thickness. The electrical lifetime of polyaniline film exponentially decreases with the growing electric-field strength. The electric-field strength at breakdown increases with increasing rate of electric field build-up. The breakdown areas in polyaniline films have been characterized by Raman spectroscopy. The possible physical mechanism of the breakdown in thin polymer films is discussed. The proposed concept is based on the steep increase of current density during the transition from the quadratic law at space-limited charge to the regime of complete saturation of traps. As a result, the Joule heat causes the degradation of polyaniline followed by the evaporation of chain fragments in the breakdown area.     

The carbonization of thin polyaniline films

Polyaniline films on silicon and ceramic supports were prepared in situ during the oxidative polymerization of aniline. The films were heated up to 500 °C in an inert nitrogen atmosphere. The changes in molecular structure during the carbonization have been studied by infrared spectroscopy and Raman scattering using 514, 633 and 785 nm laser excitation lines. The transformation from polyaniline salt to the base form has been detected above 100 °C. The conversion to nitrogen-containing carbon-like material followed above 200 °C. The molecular structure of the films produced during heating to 500 °C contains crosslinked phenazine-like and oxidized quinonoid units. The aniline oligomers deposited on the support in the early stages of aniline oxidation are stable during heating as it has been observed by resonance Raman scattering using 785 nm laser excitation line. The water contact angles changed after carbonization, and the films became more hydrophilic as carbonization progressed.     

Structure and electrical properties of bismuth thin films prepared by flash evaporation method

Polycrystalline Bi thin films with thickness in the range 40-160 nm have been successfully deposited on glass substrates at 453 K by flash evaporation method for the first time. XRD and FE-SEM were performed to characterize their structure and surface morphology respectively. Electrical resistivity measurement was carried out in the temperature range 300-350 K. Hall coefficient, electron concentration and mobility were measured at 300 K. A distinctly oscillatory behavior has been observed for the electrical properties of the Bi thin films.     

Photodecomposition effects of graphene oxide coated on TiO2 thin film prepared by electron-beam evaporation method

Morphological, structural and photocatalytic properties of graphene oxide (GO)/TiO₂ thin-film deposited on quartz substrate were investigated. The TiO₂ film was prepared by electron-beam evaporation and the GO film by spin coating method. The photocatalytic activities of the GO/TiO₂ film were evaluated by photodecomposition of methylene blue. There was synergistic effect between TiO₂ and GO which causes a rapid photo-induced charge separation and the reduction of the recombination of electron-hole pairs under the UV-visible light irradiation. GO on TiO₂ film also promotes the properties of adsorption of the dye, photon scattering probability, and interacting surface area. As a result, it leads to the enhancement of the efficiency of the photodegradation in GO/TiO₂ film.     

Morphology and conductivity of polyaniline sub-micron fibers prepared by electrospinning

Sub-micron fibers of pure polyaniline (PANI) doped with sulfuric acid or hydrochloric acid were prepared by electrospinning PANI with suitable molecular weight dissolved in hot sulfuric acid. A modified electrospinning setup was employed with a coagulation bath as a collector, where dilute sulfuric acid was used as coagulation bath. The factors influencing the morphology and conductivity of the synthesized PANI fibers were investigated, including the concentration of dilute H₂SO₄ solution in the coagulation bath, the doped PANI concentration in H₂SO₄ solution, the type of doping acid and the voltage applied to the solution. The morphologies of doped PANI fibers were characterized by scanning electron microscope (SEM). The structure of the resulting fibers was analyzed by Fourier transform infrared spectroscopy and UV–vis spectrometer. The conductivity of PANI fibers were characterized by I–V characteristics. Homogeneous PANI fibers with a diameter of 370 nm and a high conductivity of 52.9 S/cm were prepared. The possible mechanisms of different morphology formation and conductivity of PANI fibers were also discussed.     

Influence of annealing on characteristics of tin disulfide thin films by vacuum thermal evaporation

In this paper, we reported on an approach to prepare tin disulfide (SnS₂) thin films on soda-lime glass substrates by vacuum thermal evaporation using SnS₂ powders as a source. The influence of annealing on the chemical composition, crystal structure, surface morphology, and optical band gap of the SnS₂ thin films was systemically investigated. The as-grown SnS₂ thin film was amorphous, homogeneous, smooth, nearly stoichiometric, with no pinhole and crack free, and with an optical band gap of 2.41 eV. After the SnS₂ thin film was annealed at 300 °C, the crystallization of SnS₂ was demonstrated by X-ray diffraction and scanning electron microscope with a characteristic of a preferred orientation along (001) plane with hexagonal phase and the sheet appearance of the SnS₂ crystals. At the annealing temperature of 350 °C, some SnS₂ crystallites and a few pinholes appeared on the surface of the SnS₂ thin films, though the SnS₂ thin film was not oxidized. When the annealing temperature was increased to 400 °C, SnS₂ was gradually oxidized into an approximate spherical shape of SnO₂ from the top to the bottom of the SnS₂ thin film by trace O₂ in the furnace. Therefore, our experiment suggested that the annealing temperature of the SnS₂ thin film using the vacuum thermal evaporation should not be over 300 °C as a window layer in compound thin film solar cells.     

Synthesis of thermally evaporated ZnSe thin film at room temperature

Zinc selenide (ZnSe) thin film on glass substrates were prepared by thermal evaporation under high vacuum using the quasi-closed volume technique at room temperature (300 ± 2 K). The deposited ZnSe properties were assessed via X-ray diffraction, atomic force microscope (AFM), UV-Vis specrophotometry, Raman spectroscopy, photo-luminescence, Fourier transform infrared spectroscopy (FT-IR) and spectroscopic ellipsometry. The X-ray diffraction patterns of the film exhibited reflection corresponding to the cubic (111) phase (2θ = 27.20°). This analysis indicated that the sample is polycrystalline and have cubic (Zinc blende) structure. The crystallites were preferentially oriented with the (111) planes parallel to the substrates. The AFM images showed that the ZnSe films have smooth morphology with roughness 6.74 nm. The transmittance spectrum revealed a high transmission of 89% in the infrared region (≥ 600 nm) and a low transmission of 40% at 450 nm. The maximum transmission of 89.6% was observed at 640 nm. Optical band-gap was calculated from the transmission data of specrophotometry, photo-luminescence and ellipsometry and was 2.76, 2.74 and 2.82 eV respectively. Raman spectroscopic studies revealed two longitudinal optical phonon modes at 252 cm ^-1 and 500 cm ^-1. In photoluminescence study, the luminescence peaks was observed at 452 nm corresponding to band to band emission. FT-IR study illustrated the existence of Zn-Se bonding in ZnSe thin film. The optical constants were calculated using spectroscopic ellipsometry and were determined from the best fit ellipsometric data in the wavelength regime of interest from 370-1000 nm. These results manifested excellent room temperature ZnSe synthesis and characteristics for opto-electronics technologies.     

Structural studies on some doped CdS thin films deposited by thermal evaporation

The influence of the Mn, Se and Sb impurities on the structure and morphology of CdS thin films grown on p⁺ Si wafers was studied. The starting powders were mixed in the same molar ratios (0.3%) and deposited in the same conditions by vacuum thermal evaporation. X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and reflectance studies made on thermal treated thin films (573 K, 2 h in air) evidenced that thin films have a hexagonal oriented structure, and that dopants enter into the CdS lattice merely by substitution. The dopant nature influences the thin film thickness and chemical composition. The doped CdS thin films have roughness in nanometer region and a reflectivity lower than 40%. Silicon substrate acts as a template and favors the retention of Mn and scatters the Sb dopants. The CdS:Se thin film is thicker than CdS:Mn and CdS:Sb ones and is a mixture of doped and undoped nanocrystals.     

Electrical and optical properties of copper-complexes thin films grown by the vacuum thermal evaporation technique

In this work, the synthesis and characterization of molecular materials formed from K₂[Cu(C₂O₄)₂], 1,8-dihydroxyanthraquinone and its potassium salt are reported. These complexes have been used to prepare thin films by vacuum thermal evaporation. The synthesized materials were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), fast atomic bombardment (FAB+) mass and ultraviolet–visible (UV–vis) spectroscopy. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.36–0.65 eV, were calculated from their Arrhenius plots. Optical absorption studies in the 100–1100 nm wavelength range at room temperature showed thin films' optical band gaps in the 2.3–3.9 eV range for direct transitions. On the other hand, strong visible photoluminescence (PL) at room temperature was noticed from the thermally-evaporated thin solid films. The PL of all investigated samples were observed with the naked eye in a bright background. The PL and absorption spectra of the investigated compounds are strongly influenced by the molecular structure and nature of the organic ligand.     

Effects of thermal annealing on Zr-N doped magnetron sputtered copper

A barrierless metallization scheme was proposed using Cu-based materials with enhanced thermal stability. Cu(Zr-N) films were deposited on Si substrates by magnetron sputtering and annealed at temperature up to 500 °C in vacuum. The beneficial effects of a minor insoluble Zr-N on the grain refinement and thermal stability improvement were confirmed. By doping insoluble Zr-N into pure copper, some of the additive atoms precipitate at the grain boundaries, which can block the path of diffusion between copper and silicon, and inhibit the interaction between copper and silicon. In addition, ZrO₂ or Zr(N,O) development near the Cu(Zr-N)/Si interface during annealing also contributes to the thermal stability of Cu(Zr-N)/Si samples. The results of X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and sheet resistance measurement show that Cu(Zr-N) seed layers has better thermal stability after 500 °C annealing and is suitable for advanced barrierless metallization.     

(Photo)conductivity of conjugated oligomer films: mobile charge carrier formation by oxygen

Electrical dark and photo conductivities, (σ_d and σ_p, of vapor deposited films of -sexithiophene, 4,4′-distyrylstilbene, and titaniumoxophthalocyanine were investigated as function of temperature, exposure time to oxygen of variable pressure, irradiation time and intensity. Molecular oxygen increases σ_d and σ_p by orders of magnitude. Careful removal of oxygen at elevated temperatures under high vacuum and assistance of irradiation will reduce both σ_d and σ_p to almost negligible values. From the rise and decay kinetics of conductivity and from luminescence quenching it is concluded that oxygen must be complexed with the film constituting molecules in order to act as separation center for electrical charge. The complex is formed already in the dark, but more efficiently upon irradiation. The interaction with oxygen is essentially reversible but leads in a side reaction also to irreversibly oxidized photoproducts.     

CuInS2薄膜的单源热蒸发制备及其性能研究

本文以烧结合成的CuInS2粉末为原料,采用单源热蒸发技术在玻璃基底上沉积CuInS2薄膜。随着退火温度的升高,薄膜的结晶性能增强,表现出高度的(112)晶面择优取向,SEM观察显示:350℃退火后,薄膜致密,晶粒细小,大小为数十纳米。同时,热探针测试发现:薄膜的导电类型为弱N型。光学性能方面,当退火温度高于250℃时,CuInS2薄膜的禁带宽度为1.50 eV,接近吸收太阳光谱所需的理想禁带宽度值。     

Structural, electrical, and optical properties of copper indium diselenide thin film prepared by thermal evaporation method

Stoichiometric compound of copper indium diselenide (CuInSe₂) was synthesized by direct reaction of high-purity elemental copper, indium and selenium in an evacuated quartz ampoule. The phase structure and composition of the synthesized pulverized material analyzed by X-ray diffraction (XRD) and energy dispersive analysis of X-rays (EDAX) revealed the chalcopyrite structure and stoichiometry of elements. Thin films of CuInSe₂ were deposited onto organically cleaned soda lime glass substrates held at different temperatures (i.e. 300 K to 573 K) using thermal evaporation technique. CuInSe₂ thin films were then thermally annealed in a vacuum chamber at 573 K at a base pressure of 10^− 2 mbar for 1 h. The effect of substrate temperature (T_s) and thermal annealing (T_a) on structural, compositional, morphological, optical and electrical properties of films were investigated using XRD, transmission electron microscopy, EDAX, atomic force microscopy (AFM), optical transmission measurements and Hall effect techniques. XRD and EDAX studies of CuInSe₂ thin films revealed that the films deposited in the substrate temperature range of 423-573 K have preferred orientation of grains along the (112) plane and near stoichiometric composition. AFM analysis indicates that the grain size increases with increase of T_s and T_a. Optical and electrical characterizations of films suggest that CuInSe₂ thin films have high absorption coefficient (10⁴ cm^− 1) and resistivity value in the interval 10^− 2-10¹ Ω cm influenced by T_s and T_a.     

Enhanced electrochromism in cerium doped molybdenum oxide thin films

Cerium (5-15% by weight) doped molybdenum oxide thin films have been prepared on FTO coated glass substrate at 250 °C using sol-gel dip coating method. The structural and morphological changes were observed with the help of XRD, SEM and EDS analysis. The amorphous structure of the Ce doped samples, favours easy intercalation and deintercalation processes. Mo oxide films with 10 wt.% of Ce exhibit maximum anodic diffusion coefficient of 24.99 × 10⁻¹¹ cm²/s and the change in optical transmittance of (ΔT at 550 nm) of 79.28% between coloured and bleached state with the optical density of (ΔOD) 1.15.     

真空热蒸发镀CIAS薄膜

采用真空热蒸发方法在普通玻璃基底上制备Cu In0.7Al0.3Se2(CIAS)薄膜,并对之进行450℃真空硒化退火处理。结果表明,制备的CIAS薄膜具有黄铜矿结构并且以(112)晶面优先生长。真空硒化退火后,薄膜晶体结构更完整,晶粒长大,成分分布均匀,更接近CIAS晶体的化学计量比。薄膜为P型半导体,退火后的薄膜禁带宽度减小至1.38 e V,带电粒子数下降至2.41E+17 cm-3,带电粒子迁移率增加至5.29 cm2/(N·s),电阻率升高至4.9Ω·cm。     

Absorption and photoreflectance spectroscopy of zinc phthalocyanine (ZnPc) thin films grown by thermal evaporation

Optical properties of the as-deposited and annealed ZnPc layers have been investigated using absorption, reflectance and modulated photoreflectance methods. The absorption coefficient of ZnPc layers was directly determined from the transmission and reflection spectra. The absorption spectra were analyzed in terms of the mixed Lorentz–Lorenz model. We found that annealing thin layers at 580 K caused a structural transformation, which results in the decrease of the absorption coefficient and the shifting of all peak position to lower energies except for the peak of the N-band. Photoreflectance spectroscopy confirmed that there exist three transitions in the Q-band region of the studied material. Complex refractive index and dielectric constants of the ZnPc layer were directly found from the spectral data.     

Current transport mechanism in CdS thin films prepared by vacuum evaporation method at substrate temperatures below room temperature

CdS thin films were deposited by vacuum deposition method at low substrate temperatures instead of the commonly used vacuum deposition at high substrate temperatures (T_S > 300 K). The effect of low substrate temperature on the current transport mechanisms in polycrystalline CdS thin films has been studied as a function of temperature over the temperature range 100-300 K. Both thermally assisted tunneling of carriers through and thermionic emission over the grain boundary potential have contributions to the conduction in the range 250-300 K for the sample prepared at 300 K substrate temperature. The dominant conduction mechanism of the samples prepared at 200 K and 100 K is determined as thermionic emission over 200 K and Mott's hopping process below 200 K. The Mott's hopping process is not applicable for the sample prepared at 300 K.     

Influence of substrate temperature on CeF3 thin films prepared by thermal evaporation

We have investigated the effect of substrate temperature on the structural, compositional and electrical properties of cerium fluoride thin films prepared by thermal evaporation method. The structure of cerium fluoride is hexagonal and the growth orientation changes with increase in substrate temperature. The substrate temperature favors the growth of vertical nanorods on the surface of the thin films. The compositional analysis confirms the formation of cerium oxyfluoride, leading to free fluoride ions. Electrical conductivity increases with increasing substrate temperature.