Habib M. Pathan

Deposition of metal chalcogenide thin films by successive ionic layer adsorption and reaction (SILAR) method

During last three decades, successive ionic layer adsorption and reaction (SILAR) method, has emerged as one of the solution methods to deposit a variety of compound materials in thin film form. The SILAR method is inexpensive, simple and convenient for large area deposition. A variety of substrates such as insulators, semiconductors, metals and temperature sensitive substrates (like polyester) can be used since the deposition is carried out at or near to room temperature. As a low temperature process, it also avoids oxidation and corrosion of the substrate. The prime requisite for obtaining good quality thin film is the optimization of preparative provisos viz. concentration of the precursors, nature of complexing agent, pH of the precursor solutions and adsorption, reaction and rinsing time durations etc.In the present review article, we have described in detail, successive ionic layer adsorption and reaction (SILAR) method of metal chalcogenide thin films. An extensive survey of thin film materials prepared during past years is made to demonstrate the versatility of SILAR method. Their preparative parameters and structural, optical, electrical properties etc are described. Theoretical background necessary for the SILAR method is also discussed.

Preparation and characterization of nanocrystalline CdSe thin films deposited by SILAR method

The successive ionic layer adsorption and reaction (SILAR) method has been used for the first time to deposit nanocrystalline CdSe thin film onto glass substrates. The SILAR method is a modified version of chemical bath deposition (CBD) method in a way that substrates are immersed in cations and anions alternatively and film growth takes place on the substrates. The preparative conditions such as concentration, pH, temperature, immersion time, immersion cycles, etc. are optimized to get nanocrystalline CdSe films. The films are characterized by high resolution transmission electron micrograph (HRTEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, optical absorption and electrical resistivity measurements.

Some structural studies on successive ionic layer adsorption and reaction (SILAR)-deposited CdS thin films

Cadmium sulfide thin films have been deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method from aqueous as well as non-aqueous media. The CdS films have been characterized by X-ray diffraction (XRD), scanning electron microcopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analyses (EDAX) and Rutherford back scattering (RBS). X-ray studies showed the hexagonal crystal structure of CdS films. The surface morphology is found to be smooth and dense from SEM images for both the films. High resolution TEM (HRTEM) showed that the films consist of nanoparticles. The EDAX and RBS studies showed stoichiometric formation of CdS from both the media. Inclusion of oxygen is observed from RBS studies.

XRD, SEM, AFM, HRTEM, EDAX and RBS studies of chemically deposited Sb2S3 and Sb2Se3 thin films

Abstract Nanocrystalline thin films of Sb 2 S 3 and Sb 2 Se 3 are obtained at low temperature by simple chemical deposition method. The preparative parameters are optimized to get nanocrystalline films. The films are characterized for structural, surface morphological and compositional analyses by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), high-resolution transmission electron micrograph (HRTEM), energy-dispersive X-ray analyses (EDAX) and Rutherford back-scattering (RBS). XRD study confirms orthorhombic structure of Sb 2 S 3 and Sb 2 Se 3 . Nanocrystallinity is evidenced from SEM, AFM and HRTEM studies with some random distribution of nanocrystallites. Stoichiometry of films are studied from EDAX and RBS analyses which showed some inclusion of oxygen in the films which is unavoidable for chemically deposited chalcogenides films.

Growth of silver dendritic nanostructuresvia electrochemical route

Silver dendritic nanostructures were prepared on indium tin oxide coated glass substrate by electrochemical deposition from an aqueous solution of AgNO3 in the presence of citric acid. The silver dendritic nanostructures were characterized by using scanning electron microscopy, X-ray diffraction and UV-Visible absorption spectroscopy. Results showed that the morphology and growth of dendritic structures can be controlled with deposition time. A diffusion-limited aggregation model is used to explain the growth mechanism of silver nanostructures. The UV-Visible absorption spectra showed a wide range of absorption in the visible region by silver dendritic nanostructures.

Preparation and characterization of copper telluride thin films by modified chemical bath deposition (M-CBD) method

Abstract Copper telluride thin films were deposited using modified chemical method using copper(II) sulphate; pentahydrate [CuSO4·5H2O] and sodium tellurite [Na2TeO3] as cationic and anionic sources, respectively. Modified chemical method is based on the immersion of the substrate into separately placed cationic and anionic precursors. The preparative conditions such as concentration, pH, immersion time, immersion cycles, etc. were optimized to get good quality copper telluride thin films at room temperature. The films have been characterized for structural, compositional, optical and electrical transport properties by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Rutherford back scattering (RBS), optical absorption/transmission, electrical resistivity and thermoemf measurement techniques.

Structural characterization of chemically deposited Bi2S3 and Bi2Se3 thin films

Abstract Simple and inexpensive chemical deposition methods were used to deposit bismuth trisulfide (Bi 2 S 3 ) and bismuth triselenide (Bi 2 Se 3 ) thin films onto amorphous glass substrate at relatively low temperatures. Deposition parameters are optimized to get nanocrystalline films. These films are used for structural, surface morphological and compositional analyses. Stoichiometry and film formation are confirmed by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX) and Rutherford back scattering (RBS) analyses. Surface coverage and roughness of the films are studied from scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. High resolution transmission electron microscopy (HRTEM) study has confirmed the nanostructure of Bi 2 S 3 and Bi 2 Se 3 films.

Oxidative degradation of industrial wastewater using spray deposited TiO2/Au:Fe2O3 bilayered thin films

The Fe2O3, Au:Fe2O3, TiO2/Fe2O3 and TiO2/Au:Fe2O3 thin films are successfully prepared by the spray pyrolysis technique at an optimised substrate temperature of 400 °C and 470 °C, respectively onto amorphous and F:SnO2 coated glass substrates. The effect of TiO2 layer onto photoelectrochemical (PEC), structural, optical and morphological properties of Fe2O3, Au:Fe2O3, TiO2/Fe2O3 and TiO2/Au:Fe2O3 thin films is studied. The PEC characterization shows that, maximum values of short circuit current (Isc) and open circuit voltage (Voc) are (Isc = 185 μA and Voc = 450 mV) are at 38 nm thickness of TiO2. Deposited films are polycrystalline with a rhombohedral and anatase crystal structure having (104) preferred orientation. SEM and AFM images show deposited thin films are compact and uniform with seed like grains. The photocatalytic activities of the large surface area (64 cm(2)) TiO2/Au:Fe2O3 thin film photocatalysts were evaluated by photoelectrocatalytic degradation of industrial wastewater under sunlight light irradiation. The results show that the TiO2/Au:Fe2O3 thin film photocatalyst exhibited about 87% and 94% degradation of pollutant in sugarcane and textile industrial wastewater, respectively. The significant reduction in COD and BOD values from 95 mg/L to 13 mg/L and 75 mg/L to 11 mg/L, respectively was also observed.

Effect of photoanode surface coverage by a sensitizer on the photovoltaic performance of titania based CdS quantum dot sensitized solar cells.

In spite of the promising design and architecture, quantum dot sensitized solar cells (QDSSCs) have a long way to go before they attain the actual projected photoconversion efficiencies. Such an inferior performance displayed by QDSSCs is primarily because of many unwanted recombination losses of charge carriers at various interfaces of the cell. Electron recombination due to back electron transfer at the photoanode/electrolyte interface is an important one that needs to be addressed, to improve the efficiency of these third generation nanostructured solar cells. The present work highlights the importance of conformal coverage of CdS quantum dots (QDs) on the surface of the nanocrystalline titania photoanode in arresting such recombinations, leading to improvement in the performance of the cells. Using the successive ionic layer adsorption and reaction (SILAR) process, photoanodes are subjected to different amounts of CdS QD sensitization by varying the number of cycles of deposition. The sensitized electrodes are characterized using UV-visible spectroscopy, cyclic voltammetry and transmission electron microscopy to evaluate the extent of surface coverage of titania electrodes by QDs. Sandwich solar cells are then fabricated using these electrodes and characterized employing electrochemical impedance spectroscopy and J-V characteristics. It is observed that maximum solar cell efficiency is obtained for photoanodes with conformal coating of QDs and any further deposition of sensitizer leads to QD aggregation and so reduces the performance of the solar cells.

Dye sensitized solar cell with lawsone dye using a ZnO photoanode: experimental and TD-DFT study

The spectral features of lawsone (2-hydroxy-1,4-naphthoquinone), an active component of the natural dye henna, are analyzed in ethanol using experimental and computational methods. The calculated UV-Vis absorption spectrum from the time-dependent density functional theory (TD-DFT) approach is compared with the experimental results, allowing a detailed assignment of the UV-Vis spectral features based on molecular orbitals. Further, we have analyzed the light intensity dependent J–V characteristics and electrochemical impedance spectrum of a dye sensitized solar cell fabricated with lawsone and a ZnO photoanode. The photovoltaic data of the sensitizer adsorbed on ZnO films exhibited a reasonable power conversion efficiency, i.e. 0.68% at 26 mW cm−2 light intensity.