Evolution of hole size and shape in {100}, {110} and {111} monocrystalline thin films of gold

Monocrystalline thin films of gold, containing controlled distributions of small holes, were produced by an epitaxial flash deposition process on heated {100}, {110} and {111} monocrystalline substrates of sodium chloride. These films, ranging from 10 to 20 nm in thickness, were then removed from their substrates, annealed for various periods at temperatures ranging from 180 to 290 °C and subsequently examined by transmission electron microscopy in order to record the evolution of hole size and shape as a function of crystallographic orientation and annealing conditions. During annealing, these holes either grow or shrink, depending on the ratio of hole diameter to film thickness, with growing holes developing clearly defined crystallographic facets aligned normal to the film surface. The evolution of hole size is in satisfactory agreement with a kinetic analysis based on atomic surface mobility, whereas the evolution of hole shape is consistent with anisotropy of the surface energy, as computed from a nearest neighbor bond model.     

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.     

Electrochemical behavior and multilayer films of the sandwich-type polyoxotungstate complex {K10Co4(H2O)2(PW9O34)2}

The electrochemical behavior of the sandwich-type polyoxotungstate complex of K₁₀Co₄(H₂O)₂(PW₉O₃₄)₂ (Co₄(PW₉)₂) was investigated by cyclic voltammetry in aqueous solutions. The polyoxoanion exhibits two successive redox peaks originating from the tungsten-oxo framework. The electrochemical behavior for the Co^II species was not detected. Moreover, the multilayer films consisting of PEI and Co₄(PW₉)₂ were prepared by the layer-by-layer self-assembly method. The films were characterized by UV–vis spectroscopy, cyclic voltammetry and atomic force image. The films exhibit the electrochemical behavior of Co₄(PW₉)₂ polyoxoanion. Moreover, the films can catalyze the electrochemical reduction of NO₂⁻. Electron transfer to Fe(CN)₆^3−/4− redox probe was also investigated.     

Studies on chemically deposited CuInSe2 thin films

Nanocrystalline thin films of CuInSe₂ have been prepared by chemical bath deposition technique at temperatures below 60 °C. X-ray diffraction of the films confirmed the identity of CuInSe₂ and with largely broadened peaks indicated the nanocrystalline nature of the films. Images from scanning electron microscope represented spherical nanoparticles.     

Electrodeposition of CuInSe2 in citrate-containing electrolytes

CuInSe₂ is a frequent constituent of solar cells. Low-cost solar cells can be prepared by electrodeposition from a single bath, provided that the multiple variables affecting the process can be properly tuned. Our design includes an n-layer of TiO₂ (dense and/or nanoporous), on top of which a p-layer of CuInSe₂ is electrodeposited. The TiO₂ layer is supported on conductive glass. When CuInSe₂ is applied onto TiO₂, a p–n junction is formed by which sunlight could be transformed into electricity. CuInSe₂ films have been prepared by electrodeposition from a single bath aqueous solution. Citrate has been used as complexing agent, so as to shift the copper deposition potential in the negative direction, bringing it closer to the In deposition potential. Films are obtained potentiostatically at −0.8 V (vs. standard calomel electrode) for 1 h. The electrolyte consisted of 0.4 mol/L sodium citrate containing 3 mmol/L CuCl₂, 6 mmol/L InCl₃, and 5 mmol/L SeO₂. Different pH values between 4 and 6 are investigated. The samples are annealed in a furnace under flowing Ar at 350 °C for 15 min, which proves to be essential to improve the crystallinity of the CuInSe₂ films. TiO₂ and CuInSe₂ have been characterized using scanning electron microscopy, X-ray diffraction, and optical absorption spectroscopy. The morphology and the physical and optical properties are in good agreement with those reported in the literature. In order to investigate the photoresponse of the cells, current–voltage curves of prototype devices are performed in the dark and under light.     

Photoconductivity effects in CuInS2, CuInSe2 and CuInTe2 thin films

Photoconductivity response spectra for CuInS₂, CuInSe₂ and CuInTe₂ thin films are reported. The temperature dependences of the spectra are utilized to determine the bandgap energies as functions of temperature. Photoconductive response times are measured for these I–III–VI₂ ternary semiconductors and are discussed in terms of deposition parameters and post-deposition treatments. The photoconductive decay times are in the range 10^-3 – 10¹ ms.     

Characterization of stepwise flash-evaporated CuInSe2 films

CuInSe₂ (CIS) films were deposited by stepwise flash evaporation from polycrystalline powder source onto glass substrates held at various temperatures ranging from 100 to 560 K. The phase purity and microstructure were analyzed by transmission electron microscopy. The investigations show that films grown at 300 K and below were amorphous, whereas those grown at 370 K and above were polycrystalline in nature. The grain size in polycrystalline films were found to improve with increase in substrate temperature and during post-deposition annealing. The films had near stoichiometric composition as revealed by Rutherford backscattering spectrometry. Analysis of the optical transmittance spectra of CIS films deposited at 520 K yielded a value of ∼0.97 eV for the fundamental band gap.     

Phase evolution during CuInSe2 electrodeposition on polycrystalline Mo

Using structural analyses means of ex-situ Raman spectroscopy and X-ray diffraction combined with electrical measurements, we study the phase evolution in the growth by electrodeposition technique of CuInSe₂ on polycrystalline Mo. For this purpose the growth was stopped at different stages, and then the different layers were analysed. First growth steps seem to be controlled by the deposition of secondary phases, like elemental Se and Cu₂Se binary. After the deposition of approximately 300 nm of material, CuInSe₂ ternary and ordered vacancy compounds start to adequately form. At a thickness close to 2000 nm, the formation of binary Cu_xSe is observed, remaining up to the final growth process (4350 nm). All these results are compared with the kinetic model of the system under the consideration of the experimental composition evolution.     

Semiempirical study of metallocenes adsorption on β-MgCl2

This work analyzes the adsorption of four metallocenes with different symmetry on two planes of β-MgCl₂: the (100) and the (110). The selected metallocenes are Cp₂ZrCl₂, Ind₂ZrCl₂, EtInd₂ZrCl₂ and Me₂SiInd₂ZrCl₂. The results of the calculations allow us to speculate that the chiral ansa metallocenes bridged with C₂H₄ could have chemical interaction with certain faces of the MgCl₂ surface during the stage of adsorption and subsequent precursors treatment, while the interaction of the others with the surface generates stable species depending on the surface geometry.     

Effects of hydrolysis on dodecyl alcohol modified β-CaSiO3 particles and PDLLA/modified β-CaSiO3 composite films

In this research, β-CaSiO₃ particles were surface modified with dodecyl alcohol, and Poly-(DL-lactic acid) (PDLLA)/modified β-CaSiO₃ composite films were fabricated with a homogenous dispersion of β-CaSiO₃ particles in the PDLLA matrix. The aim of the study was to investigate the properties of the composite films before and after hydrolytic treatment. SEM images showed retained homogenous dispersion of β-CaSiO₃ particles after hydrolysis and tensile test also showed maintained mechanical property. Simulated body fluid (SBF) incubation experiment suggested that hydrolytic treatment did not affect the formation of hydroxyapatite on the surface of the composite films. The hydrophilicity of the composites was greatly recovered (from 69.82° to 50.28°) after hydrolysis. In addition, cells cultured on composite films after hydrolysis presented the highest cell proliferation rate and differentiation level. All of these results suggested that the surface modification of silicate particles with dodecyl alcohol along with reversible hydrolytic treatment was an effective and feasible approach to fabricate polymer/silicate composite materials with improved properties.     

The electrical properties of CuInSe2 thin films deposited onto CaF2 substrates

CuInSe₂ thin films were deposited onto (111)-oriented CaF₂ substrates by flash evaporation in the substrate temperature range T_s = 650–890 K. Epitaxial growth was found at T_s = 770–800 K; at lower and higher substrate temperatures the films were partly polycrystalline. Films produced at T_s ? 675 K showed n-type conductivity due to a donor with an ionization energy of 78 ± 5 meV ascribed to indium interstitials. At T_s ? 725 K the films exhibited p-type conductivity due to a shallow acceptor with an ionization energy characteristic of indium vacancies. The important role of the substrate material in establishing the electrical parameters of CuInSe₂ thin films is proved by a comparative study of thin films deposited onto GaAs and CaF₂ substrates.     

Optoelectronic properties of β-Fe2O3 hollow nanoparticles

The effect of hollow structure on the optoelectronic properties of β-Fe₂O₃ hollow nanoparticles (HNPs) was determined. Spectrophotometry showed that the optical transmittance of the β-Fe₂O₃ HNPs was less than 40% in the visible-light region. This opaqueness was suggested to be an optical characteristic, commonly found in the authors' previous studies of TiO₂ and δ-Al₂O₃ HNPs. In addition, β-Fe₂O₃ HNPs had a band gap (1.86 eV) between amorphous (1.73 eV) and polycrystalline (1.97 eV) β-Fe₂O₃ thin films, which was a 5–7 nm thick shell that embraced an intermediate volume of the crystal phase, in-between the two thin films.     

Optical transitions in laser-evaporated thin CuInSe2 films

The optical absorption coefficients of highly oriented laser-evaporated thin films were determined from the measured reflectance R(λ) and transmittance T(λ) in the wavelength range 400–1700 nm. The optical absorption spectrum of CuInSe₂ thin films shows three energy gaps, which are associated with the fundamental edge and valence band splitting by the tetragonal crystal-field and spin-orbit effects, and four optical transitions from the copper d levels to the conduction bands.     

Effects of surface modification of β-CaSiO3 on electrospun poly(butylene succinate)/β-CaSiO3 composite fibers

In this experiment, pure PBSU fibers, PBSU/12.5% β-CaSiO₃, and PBSU/25% β-CaSiO₃ composite fibers were fabricated by electrospinning. In order to investigate the effects of surface modification of β-CaSiO₃ on composite fibers, β-CaSiO₃ nanowires were surface esterified using dodecyl alcohol. SEM micrographs showed that composite materials with modified β-CaSiO₃ have homogeneous fibrous structures similar as that of pure PBSU fibers, while the fibers containing unmodified β-CaSiO₃ were inhomogeneous and much larger in diameter, and also junctions where β-CaSiO₃ agglomerated could be found. Mechanical testing showed that with the addition of unmodified β-CaSiO₃ into PBSU matrix, the tensile strength of fibrous materials decreased obviously, and the decrease degree increased with increased β-CaSiO₃ content. However, the tensile stresses of composite materials after surface modification of β-CaSiO₃ turned back and increased about 40% compared to those containing unmodified β-CaSiO₃. All of these results suggested surface modification of β-CaSiO₃ was an effective approach to obtain composite fibrous materials with better morphologies and enhanced mechanical properties, and this method is supposed to be feasible in other fibrous material systems.     

Kinetic Monte Carlo simulation of {1 1 1}-oriented SiC film with chemical vapor deposition

A three-dimensional atomic-scale kinetic Monte Carlo (KMC) model of {1 1 1}-oriented SiC film deposited by chemical vapor deposition is established in this paper. The growth process of {1 1 1}-oriented atomic-scale SiC film is simulated. The model includes two parts: the first is kinetic process of chemical reaction and the second is deposition and diffusion of substrate surface. In this model, the relationship between temperature and growth rate, surface roughness and relative density and the relationship between growth rate and surface roughness and relative density are studied. The result indicates that the growth of film has three stages including formation of little islets, mergence and expanding of islets and dynamic balance between islets. With increase of substrate temperature, deposition rate, surface roughness and height of film all increase. With increase of deposition rate, surface roughness increases while relative density decreases.     

Composition and Morphology of Electrodeposited CuInSe2 Precursor Films

CuInSe₂ (CIS) precursor films have been prepared by electrodeposition in aqueous solution. The electrodeposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) for structural, morphological and componential properties. The influence of deposition potential and Na-citrate concentration on composition and morphology of electrodeposited films was studied in detail. It is found that the film morphology is strongly influenced by deposition potential and Na-citrate concentration. Films with large and homogenous grain size and ratio of Cu/In approaching 1 were obtained at deposition potentials of -0.7 and -0.75 V vs the saturated calomel electrode (SCE) and Na-citrate concentration of 500 mmol/L. Chalcopyrite phase CuInSe₂ is contained in precursor films that have poor crystallinity.     

H ESD observed from β-state NH3 adsorbed on Pt(111)

H⁻ ions were detected from ammonia covered Pt(111) surfaces. We found that H⁻ electron-stimulated desorption (ESD) ions can only be detected when adsorbed β-state ammonia is present on the Pt(111) surface. The H⁻ kinetic energy distributions (KEDs) obtained from Pt(111) surfaces covered with adsorbed β-state ammonia exhibit a very narrow peak appearing at 3 eV with a FWHM of less than 1 eV. The total removal cross-section measured from H⁻ ESD ion-yield curves is in good agreement with the total removal cross-section obtained from H⁺ ESD ion-yield measurements and other measurements, which are described elsewhere (C. Bater, J.H. Campbell, J.H. Craig Jr., Surf. Interface Anal. 26 (1998) 97). A total removal cross-section of 5.6×10⁻¹⁷ cm² was obtained from the H⁻ ESD ion-yield curves obtained in this work.     

Flexible CuInSe2 photovoltaic cells fabricated by non-vacuum techniques

In this work, CuInSe₂ based flexible photovoltaic cells have been fabricated completely using non-vacuum low-cost techniques. Thin films were deposited on molybdenum thin foil substrates by electrodeposition using a buffered aqueous electrolyte with the deposition of subsequent layers performed by spray pyrolysis. In addition, the buffer layer CdS was replaced with a wider bandgap ZnS (3.7 eV) and analysis undertaken of the fabrication pathway, morphological and compositional changes resulting from the different precursor route. The deposited films were annealed in a Se atmosphere at 450 °C. The influence of annealing temperature and time on the properties of the films are briefly discussed. Characterisation of thin films was performed using aqueous electrolyte contacts. Capacitance measurements were made as a function of applied bias on thin films deposited on metal substrates with blocking electrolyte contacts where analysis of the impedance gave values of the space charge capacitance from which the doping density and flat band potential were derived. The structural characterisation was carried out using X-ray diffraction and Raman spectroscopy. The structure and device properties of Mo (SS)/CuInSe₂/ZnS/n⁺-ZnO/Ni were characterized using current-voltage technique and photocurrent spectroscopy.     

硒化方式对CuInSe2薄膜结构、成分和形貌的影响

采用直流磁控溅射技术,首先在玻璃衬底上制备Mo薄膜,然后制备CuIn预制层。以固态硒粉为硒源,采用硒薄膜法和硒蒸气法两种硒化工艺,经过三步升温硒化方式对CuIn预制膜进行硒化制备CuInSe2薄膜。通过X射线衍射、能量散射谱和扫描电镜测试分析手段,分析CuIn预制膜和每一步硒化热处理后薄膜结构和形貌的变化。结果表明:两种方法硒化后均形成具有单一黄铜矿相结构的CuInSe2薄膜,薄膜具有(112)面择优取向,硒蒸气法形成的晶粒较大,但均匀性差。