Valdek Mikli

Structural and optical properties of sprayed CuInS2 films

Abstract Polycrystalline CuInS 2 thin films have been prepared by spray pyrolysis of aqueous solution of copper chloride, indium chloride and thiourea onto heated glass substrates. It is shown that the parameters critical to structural and optical properties of sprayed CuInS 2 films are growth temperature and ion ratio of Cu/In in spraying solution. Excess of copper in starting solution promotes the recrystallization and growth of crystallites in the film. The X-ray diffraction patterns confirm that the use of copper-rich solutions reduces the temperature required for single-phase composition of CuInS 2 films from 380°C ( Cu/In =1 ) to 290°C ( Cu/In =1.25 ). The formation of CuInS 2 in spray process and chemical nature of additional phases in the films are discussed. Growth temperatures in the range of 320–380°C at Cu/In >1 are determined as optimal for depositing orientated in the (112) direction CuInS 2 thin films with chalcopyrite structure. Sprayed chalcopyrite CuInS 2 films have absorption coefficient ∼10 5 cm −1 in visible and red region of spectra and optical band gap 1.45 eV.

Composition and structure of CuInS2 films prepared by spray pyrolysis

Abstract CuInS2 thin films have been prepared by spray pyrolysis of an aqueous solution of CuCl2, InCl3 and thiourea onto heated glass substrates. The effect of the composition of starting solutions on the phase and chemical composition and the structure of sprayed films is studied. The Cu/In ratio in the films is higher than that in the solution. In-rich and S-rich solutions lead to the multiphase films with poor crystallinity according to X-ray diffraction. It was determined that organic phases as products of the thermal decomposition of thiourea ligand are present in the films at all used solution compositions. The formed organic secondary phases could be responsible for the formation of molten phase which together with copper sulphide act as recrystallisation agent during the growth of copper-rich films. The CuInS2 films, strongly orientated in the (112) direction with crystallites up to 300 nm in the matrix and with large crystals of some microns in agglomerated areas, are formed while the secondary phases segregated on the thin film surface.

Composition of CuInS2 thin films prepared by spray pyrolysis

CuInS 2 films were prepared by spray pyrolysis technique using CuCl 2 , InCl 3 and SC(NH 2 ) 2 as initial chemicals. The content of Cl, O, C and N impurities in sprayed CuInS 2 films were measured by EDS, WDS, RBS and organic elemental analysis. The growth temperatures of 260-280°C result in Cl, C, N content of 8 mass% and the impurity phases contain SCN, CN, NH, SO 4 groups as identified by FTIR. The increase in the growth temperature up to 380°C decreases the concentration of Cl, C, N to 1-2 mass%, concurrently leading to oxidation of inorganic and organic phases resulting in O content of 16.7 at.%. The content of impurities originated from precursors is mainly controlled by the growth temperature and in less extent by the Cu/In ratio in spray solution as Cu-rich solutions result in the films with reduced content of organic residues. Thermal treatments in reducing atmospheres at 450°C improves the crystallinity of the films while annealing in flowing H 2 effectively reduces the content of Cl and O impurities.

Growth and recrystallization of CuInS2 films in spray pyrolytic process

Abstract It is shown that the structure, composition and surface morphology of chemically sprayed CuInS2 films depend on the growth temperature and copper to indium ratio in the spraying solution. In-rich films have flat surface but they are multiphase. The use of Cu-rich initial solutions leads to single-phase films with the rough surface morphology. The important role in the formation of these films plays segregation of molten phase of thermal decomposition products on the surface during the spray process. The possible crystal growth mechanisms in both types of CuInS2 thin films in the spray process are discussed.

Photoluminescence of spray pyrolysis deposited ZnO nanorods

Photoluminescence of highly structured ZnO layers comprising well-shaped hexagonal rods is presented. The ZnO rods (length 500-1,000 nm, diameter 100-300 nm) were grown in air onto a preheated soda-lime glass (SGL) or ITO/SGL substrate by low-cost chemical spray pyrolysis method using zinc chloride precursor solutions and growth temperatures in the range of 450-550°C. We report the effect of the variation in deposition parameters (substrate type, growth temperature, spray rate, solvent type) on the photoluminescence properties of the spray-deposited ZnO nanorods. A dominant near band edge (NBE) emission is observed at 300 K and at 10 K. High-resolution photoluminescence measurements at 10 K reveal fine structure of the NBE band with the dominant peaks related to the bound exciton transitions. It is found that all studied technological parameters affect the excitonic photoluminescence in ZnO nanorods.PACS: 78.55.Et, 81.15.Rs, 61.46.Km

Annealing effect for SnS thin films prepared by high-vacuum evaporation

Thin films of SnS are deposited onto molybdenum-coated soda lime glass substrates using the high-vacuum evaporation technique at a substrate temperature of 300 °C. The as-deposited SnS layers are then annealed in three different media: (1) H2S, (2) argon, and (3) vacuum, for different periods and temperatures to study the changes in the microstructural properties of the layers and to prepare single-phase SnS photoabsorber films. It is found that annealing the layers in H2S at 400 °C changes the stoichiometry of the as-deposited SnS films and leads to the formation of a dominant SnS2 phase. Annealing in an argon atmosphere for 1 h, however, causes no deviations in the composition of the SnS films, though the surface morphology of the annealed SnS layers changes significantly as a result of a 2 h annealing process. The crystalline structure, surface morphology, and photosensitivity of the as-deposited SnS films improves significantly as the result of annealing in vacuum, and the vacuum-annealed films are fo...

Structural, optical and electrical properties of V doped ZnO thin films deposited by r.f. magnetron sputtering

Structural, optical and electrical properties of V doped ZnO thin films deposited by r.f. magnetron co-sputtering on glass substrates at different temperature, Ts, between 150°C and 500°C are studied. The EDS analyses indicate that the average vanadium content in the films is in the range of 0.86–0.89 at. %. XRD spectra demonstrate preferential (002) crystallographic orientation with c-axis perpendicular to the substrate surface and grains sizes of the films about 21–29 nm. The band gap energy, Eg, values are in the range of 3.44–3.47 eV. The deposited V doped ZnO films have low resistivity − (2–8). 10−3 Ω cm. Raman spectra show vibrational phonons modes typical for ZnO. Comparison with the structural, optical and electrical properties of thin films ZnO and ZnO:Al is given.

Direct CVD Growth of Multi-Layered Graphene Closed Shells around Alumina Nanofibers

In this work, a catalyst-free direct deposition of multi-layered graphene closed shells around highly aligned alumina nanofibers with aspect ratio of 107 is demonstrated for the first time. A single – step chemical vapor deposition process of specified parameters was used for development of hybrid structures of carbon shells around the core alumina nanofibers. Transmission electron microscopy and Raman spectroscopy were used to confirm formation of graphene layers and to understand the morphology of the various structures. The developed routine for growth of peculiar carbon nanostructures opens new opportunities for deposition of the tailored carbon structures on dielectric substrates.

pH impact on the sol-gel preparation of calcium hydroxyapatite, Ca10(PO4)6(OH)2, using a novel complexing agent, DCTA

Aqueous sol-gel chemistry routes — based on ammonium hydrogen phosphate as the phosphorus precursor, calcium acetate monohydrate as the source of calcium ions, and 1,2-diaminocyclohexanetetraacetic acid monohydrate (DCTA) as the complexing agent — have been used to prepare calcium hydroxyapatite (HA). The sol-gel process was performed in aqueous solution at different pH values followed by calcination of the dry precursor gels for 5 h at 1000°C. Phase transformations, composition, and structural changes in the polycrystalline samples were studied by thermoanalytical methods (TG/DTA), infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD), and scanning electron microscopy (SEM). It was shown that pH adjustment has significant impact on the apatite formation process and on the morphology and phase purity of the ceramic samples.

Effect of solution spray rate on the properties of chemically sprayed ZnO: in thin films

ZnO:In thin filmswere grown from 100 mL of spray solution on glass substrates by chemical spray at Ts = 400°Cusing solution spray rates of 0.5-6.7 mL/min. Zinc acetate and indium(III)chloride were used as Zn and In sources, respectively, with [In]/[Zn] = 3 at.%. Independent of solution spray rate, the crystallites in ZnO:In films grow preferentially in the (101) plane parallel to the substrate. The solution spray rate influences the surface morphology, grain size, film thickness, and electrical and optical properties. According to SEM and AFM studies, sharp-edged pyramidal grains and canvas-resembling surfaces are characteristic of films grown at spray rates of 0.5 and 3.3 mL/min, respectively. To obtain films with comparable film thickness and grain size, more spray solution should be used at low spray rates. The electrical resistivity of sprayed ZnO:In films is controlled by the solution spray rate. The carrier concentration increases from 2ċ1019 cm-3 to 1ċ1020 cm-3 when spray rate is increased from0.5 mL/min to 3.3 mL/min independent of the film thickness; the carrier mobilities are always lower in slowly grown films. Sprayed ZnO:In films transmit 75-80% of the visible light while the increase in solution spray rate from0.5 mL/min to 3.3 mL/min decreases the transmittance in the NIR region and increases the band gap in accordance with the increase in carrier concentration. Lower carrier concentration in slowly sprayed films is likely due to the indium oxidation.