Synthesis and characterization of manganese sulphide thin films deposited by spray pyrolysis

Manganese sulphide (MnS) thin films have been deposited onto glass substrate by a low cost spray‐pyrolysis technique at 220 °C. The as‐deposited MnS thin films have been characterized using scanning electron microscopy (SEM), energy dispersive X‐ray (EDX) spectroscopy, atomic force microscopy (AFM), X‐ray diffraction, UV visible spectroscopy and photo electrochemical (PEC) measurement. The SEM and AFM images showed that the MnS thin films were well covered onto the substrate surface. The as‐deposited raw thin film was found to be amorphous in nature and perfectly crystalline phase after annealing the sample. Optical band gap of the MnS thin films was found to vary from 3.1 to 3.21 eV and the band gap decreases with the increase in film thickness. Optical constants such as refractive index, extinction coefficient have been evaluated using reflectance and absorbance data. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on the properties of reactively sputtered TiN/NbN multilayers

TiN/NbN multilayer coatings were deposited with various substrate temperatures by DC reactive magnetron sputtering method onto Si (111) and glass substrates. The effect of substrate temperature on the structural and optical properties of TiN/NbN multilayers was investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, Field emission scanning electron microscopy and Photoluminescence measurements. The composition was analyzed by X‐ray photoelectron spectroscopy. X‐ray diffraction results showed that the layers crystallized in cubic structure for TiN and hexagonal structure for NbN. It was found that grain size increased with increase in substrate temperature. The surface morphology of the TiN/NbN thin films showed a dense and smooth surface with substrate temperature upto 200 °C but after 300 °C, the grains became larger and coarse surface was observed. The TiN/NbN multilayer coatings exhibited the characteristic peaks centered at 180, 210 and 560 cm^‐1. Red band emission peaks were observed in the wavelength range of 700‐710 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nucleation of GaN on sapphire substrates at intermediate temperatures by Hydride Vapor Phase Epitaxy

A novel approach to deposit GaN layers directly on a sapphire substrate by Hydride Vapor Phase Epitaxy is presented. The two‐step deposition process includes the growth of GaN nucleation layers at intermediate temperatures in the range of 750 – 900 °C and subsequent high‐temperature overgrowth at about 1040 °C. Closed and non‐closed nucleation layers with a thickness of up to 2 μm were produced and characterized by scanning and transmission electron microscopy, micro‐Raman spectroscopy and X‐ray diffraction. A growth temperature of 780 °C is found to be optimal with respect to density and size distribution of nucleation islands. Raman measurements performed on the nucleation layers reveal nearly zero residual stress indicating effective stress relaxation on cooling down from growth temperature. The results of first overgrowth experiments demonstrate the possibility to grow 10 μm thick, crack‐free GaN layers of high crystalline quality on the nucleation layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of bamboo‐like SiC whiskers from waste silica fume

A process for the utilization of wasted silica fume is proposed in this work. Silicon carbide (SiC) whiskers several tens of micrometers in length and with a bamboo‐like morphology have been successfully synthesized by a carbothermal reduction process using purified silica fume as the silicon source. The morphology and structure of SiC whiskers were investigated by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy, and high‐resolution transmission electron microscopy. Studies found that the as‐synthesized whiskers were grown as single‐crystalline β‐SiC along the (111) growth direction. The whiskers consisted of hexagonal stems randomly decorated with larger‐diameter knots along their whole length. On the basis of the characterization results, a vapor–solid process was discussed as a possible growth mechanism of the β‐SiC whiskers.     

Determination of lateral block size and mosaicity of crystals using X‐ray diffraction from the edge of the sample

In this paper a novel lateral block size characterization method based on X‐ray diffractometry (XRD) is presented. The developed method based on scans of plans perpendicular to the surface visible from the edge of the sample and subconsequent numerical analysis based on Scherrer equation. In presented investigations as a reference sample bulk GaN substrate fabricated by AMMONO Ltd. was used. The GaN layers deposited on sapphire substrate were investigated as a case of study. Moreover, a method of analyzing the magnitude of the tilt and twist mosaicity based on the scans of rocking curves and reciprocal lattice maps (RLM) from the edge of sample is presented. As an example for this methodology highly mosaicited SiC crystal was used. Presented approach allows to directly determine the value of the angular deviation of mosaicity in a direction perpendicular and parallel to the sample surface.     

Preparation and characterization of electrodeposited indium selenide thin films

Indium Selenide (InSe) thin films were deposited from a mixture of Indium chloride and selenium dioxide in aqueous solution by electrodeposition technique on Indium Tin oxide coated glass substrates. The effects of the parameters during deposition such as current density, deposition potential versus saturated calomel electrode, pH value and concentration of source material were studied. X‐ray diffraction studies were carried out on the films to analyze the microstructure using an x‐ray diffractometer and were examined by RAMAN spectroscopy. The Raman peak position did not change much with chemical concentrations. Raman scattering due to the (LO) phonon was observed at 211 cm^–1. Optical absorption studies were performed with a double beam ultra violet‐visible –NIR spectrophotometer in the wavelength 300–1100 nm. The surface morphology of the layer was examined using a scanning electron micrograph. The composition of the films was studied using an Energy Dispersive Analysis by X‐Rays (EDAX).     

The effect of ZnO buffer layer on structural and optical properties of ZnO nanorods

A low‐temperature synthetic route was used to prepare oriented arrays of ZnO nanorods on ITO conducting glass substrate coated with buffer layer of ZnO seeds in an aqueous solution. The corresponding growth behavior and optical properties of ZnO nanorod arrays were studied. It was found that the nature of the buffer layer had effect on the microstructures and optical properties of the resultant ZnO nanorod arrays. X‐ray diffraction (XRD) results showed the nanorods were preferentially grown along (002) direction, but the diameter of the nanorods prepared with the buffer layer was much smaller than the without one, which can be clearly seen from the scanning electron microscopy (SEM) results. And it also found that the buffer layer was not only enhanced the density of overall coverage but also beneficial to grown the oriented arrays. Photoluminescence spectroscopy (PL) results indicated that the all the samples had the better optical behaviors. By computation, the relative PL intensity ratio of ultraviolet emission (I_UV) to deep level emission (I_DLE) of ZnO nanorods grown with the pure substrate was much higher than that of the sample with the buffer layer. The defects on the surface increased with the size reduction of nanorods caused by the buffer layer may be the main reason for it. And the small shift in the UV emission was caused by the rapid reduction in crystal size and compressive stress from Raman spectra results. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of ZnO nanorods by the thermal reduction process of a mixture of ZnO and Al powder

Single‐crystalline Zinc oxide (ZnO) nanorods were firstly synthesized on gold‐coated Si substrate via a simple thermal reduction method from the mixture of ZnO and Al powder. The growth process was carried out in a quartz tube at different temperature (550‐700 °C) and at different oxygen partial pressure. Their structure properties were investigated by X‐ray diffraction (XRD), scanning electron microscope (SEM), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The length of the as‐prepared ZnO nanorods was up to several micrometers and their diameters were about 130 nm. The X‐ray diffraction patterns, transmission electron microscopic images, and selective area electron diffraction patterns indicate that the one‐dimensional ZnO nanorods are a pure Single‐crystal and preferentially oriented in the [0001] direction. The reaction mechanism of ZnO nanorods was proposed on the basis of experimental data. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and luminescence properties of large‐scale zinc oxide nanotetrapods

Large‐scale zinc oxide (ZnO) nanotetrapods have been grown on p‐type Si (111) substrate by oxidizing zinc pieces in air by thermal evaporation technique without the presence of any catalyst. The size and morphology of the nanostructures was found to depend on experimental parameters. The grown nanostructures were characterized by X‐ray Diffraction (XRD), Photoluminescence (PL), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and analysis of elemental composition was done by Energy Dispersive X‐ray analysis (EDX). The EDX spectrum shows that the grown product contains Zn and O only. The X‐ray diffraction pattern indicates that the microstructure of the obtained products is typical hexagonal wurtzite ZnO. The optical properties were studied using room temperature PL spectroscopy which indicates that the products are of high optical quality and the near band edge UV transition peak intensity increases with decrease in tetrapod size. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth,morphology, spectrographic characterization and thermal properties of 4,5‐bis(benzoylthio)‐1,3‐dithiole‐2‐thione

Single crystals of 4,5‐bis(benzoylthio)‐1,3‐dithiole‐2‐thione (BBDT), were grown from methylene chloride and the growth morphology was deduced by the Bravais–Friedel Donnay–Harker (BFDH) model. The grown crystals were characterized by optical absorption, infrared, Raman and X‐ray powder diffraction spectroscopy. The thermal behavior of BBDT has been investigated by means of thermogravimetric analysis and differential thermal analysis measurements in air. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and properties of an organometallic nonlinear optical crystal: bis(isothiocyanato)‐bis(4‐methylpyridine)zinc(II) (Zn(SCN)2(C6H7N)2)

Bis(isothiocyanato)‐bis(4‐methylpyridine)zinc(II)(Zn(SCN)₂(C₆H₇N)₂), (abbreviated as ZBNC) single crystals of optical quality have been grown from acetone solution by the slow temperature‐lowering method. Its solubilities at different temperatures in acetone were measured. The X‐ray powder diffraction (XRPD) spectroscopy of ZBNC crystal was performed at room temperature. The second harmonic generation (SHG) efficiency was determined by powder technique of Kurtz and Perry using Nd:YAG laser, which is equivalent to KDP crystal. The thermal decomposition process was characterized by thermal gravity and differential thermal analysis (TG\DTA). The specific heat of the crystal is 1440.67 J/mol·K at 325 K. The IR spectrum was recorded in the 500∼3500 cm^–1 region, using KBr pellets on a Nicolet 170sx FT‐IR spectrometer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical studies on ZnO films prepared by sol‐gel method

A standard sol‐gel method was used to deposit ZnO thin films of suitable thickness on glass substrate.The optical characteristics of the visible to infrared range on thermal stress were critically observed. Morphological signature of the films was detected by X‐ray diffraction (XRD) and the crystallite size determined by Scherrer method from XRD data were consistent with grain size estimated from spectroscopic data through Meulenkamp equation. The optical band gap value from the transmission spectrum was found to corroborate with the existing works. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optoelectrical properties of Ga‐doped ZnO semiconductor thin films grown by magnetron sputtering

Transparent conductive gallium‐doped zinc oxide (Ga‐doped ZnO) films were prepared on glass substrate by magnetron sputtering. The influence of substrate temperature on structural, optoelectrical and surface properties of the films were investigated by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), spectrophotometer, four‐point probe and goniometry, respectively. Experimental results show that all the films are found to be oriented along the c‐axis. The grain size and optical transmittance of the films increase with increasing substrate temperature. The average transmittance in the visible wavelength range is above 83% for all the samples. It is observed that the optoelectrical property is correlated with the film structure. The Ga‐doped ZnO film grown at the substrate temperature of 400 °C has the highest figure of merit of 1.25 × 10⁻² Ω⁻¹, the lowest resistivity of 1.56 × 10⁻³ Ω·cm and the highest surface energy of 32.3 mJ/m².     

Plasma‐enhanced chemical vapor deposition of 99.95% 28Si in form of nano‐ and polycrystals using silicon tetrafluoride precursor

The process of plasma chemical deposition of silicon was investigated from its tetrafluoride containing 99.99% of ²⁸Si isotope in the form of thin layer of nano‐crystalline silicon on silicon substrate and of thick layer of polycrystalline silicon on the inner surface of quartz reactor. The layers are characterized by the methods of X‐ray diffraction and Raman spectroscopy. Using the SIMS method the mechanism of isotopic dilution was investigated in the PECVD process (the content of ²⁸Si isotope in layers was 99.95‐99.98%). A necessity is indicated in thorough special preparation of the reactor for minimization of isotopic dilution in case of fabrication of silicon containing ≥99.9% of ²⁸Si. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

4H-SiC衬底表面SiC薄膜的同质外延生长

以4H-SiC为衬底,在不同衬底温度下进行SiC薄膜的同质外延生长。利用反射式高能电子衍射(RHEED)、扫描电子显微镜(SEM)、拉曼(Raman)等测试手段,对生长样品的结构和结晶质量进行了表征。根据测试结果发现,在衬底温度为1200℃时能够得到质量较高的薄膜,在另外两个温度(1100℃和1300℃)条件下得到的薄膜质量是较差的。     

Effects of passivation and postannealing on the photoluminescence properties of MgO/SiO2 core‐shell nanorods

MgO nanorods were grown by the thermal evaporation of Mg₃N₂ powders on the Si (100) substrate coated with a gold thin film. The MgO nanorods grown on the Si (100) substrate were a few tens of nanometers in diameter and up to a few hundreds of micrometers in length. MgO/SiO₂ core‐shell nanorods were also fabricated by the sputter‐deposition of SiO₂onto the MgO nanorods. Transmission electron microscopy (TEM) and X–ray diffraction (XRD) analysis results indicated that the cores and shells of the annealed core‐shell nanorods were a face‐centered cubic‐type single crystal MgO and amorphous SiO₂, respectively. The photoluminescence (PL) spectroscopy analysis results showed that SiO₂ coating slightly decreased the PL emission intensity of the MgO nanorods. The PL emission of the MgO/SiO₂ core‐shell nanorods was, however, found to be considerably enhanced by thermal annealing and strongly depends on the annealing atmosphere. The PL emission of the MgO/SiO₂ core‐shell nanorods was substantially enhanced in intensity by annealing in a reducing atmosphere, whereas it was slightly enhanced by annealing in an oxidative atmosphere. The origin of the PL enhancement by annealing in a reducing atmosphere is discussed with the aid of energy‐dispersive X‐ray spectroscopy analyses. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoacoustic study of the thermal properties of calcium carbonate – the major constituent of pancreatic calculi

The study of the thermal properties of condensed matter is very essential both for crystallizing and thermal energy induced fracturing of solid materials. Photoacoustic spectroscopy (PAS) is a recently developed, nondestructive testing (NDT) tool, used for analyzing the surface properties of materials. This method is used here to determine the thermal diffusivity and thermal conductivity of the gel grown single crystals of calcium carbonate (CC), which is the major constituent of pancreatic calculi. Characterization of CC was made using single crystal X‐ray diffraction and density determination. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Substrate temperature effect on the optical properties of amorphous Sb2S3 thin films

Sb₂S₃ amorphous thin films were prepared by thermal evaporation of corresponding powder on thoroughly cleaned glass substrates held at temperature in the range 300‐473 K. X‐ray diffraction and atomic force microscopy have been used to order to identify the structure and morphology of surface thin films. The optical constants of the deposition films were obtained from the analysis of the experimental recorded transmission data over the wavelength range 400‐1400 nm. An analysis of the absorption coefficient values revealed an optical indirect transition with the estimation of the corresponding band gap values. It was found that the optical band gap energy decrease with substrate temperature from 1.67 eV at 300 K to 1.48 eV at 473K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of nanoflakes‐based self‐assembling crossed structure of stannous oxide and photocatalysis property

Self‐assembling nanoflakes‐based crossed architectures of stannous oxide (SnO) were successfully synthesized via template‐free hydrothermal growth method by using SnCl₂·2H₂O and KOH as precursors. Crystal structures, morphology, chemical composition and optical properties were examined by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FESEM), energy dispersive X‐ray analysis, and Raman spectroscopy, respectively. The results indicate that the as‐synthesized product belongs to tetragonal phase SnO with crossed morphology self‐assembled by nanoflakes. Furthermore, UV‐vis spectrophotometry was used to determine optical band gap of the SnO nanostructures and the direct band gap of 2.90 eV was obtained. The photocatalysis of the product has been evaluated with methyl orange and the high degradation ratio of 87% is obtained in 240 minutes under the measuring condition which is attributed to the wide band gap and large specific surface area of the nanoflakes‐based crossed SnO architectures. A possible growth mechanism is proposed in the end.     

Fabrication of ferric oxide/reduced graphene oxide/cadmium sulfide heterostructure photoelectrode for enhanced photoelectrochemical performance

A novel high‐efficiency photoelectrode (Fe₂O₃/reduced graphene oxide/CdS) built from heterostructure and conductive scaffold has been successfully designed and synthesized. Reduced graphene oxide works as a “bridge” which benefits for electron and hole transport. The obtained heterostructure photoelectrodes were systematically characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The photoconversion efficiency (η) and photocurrent densities vs. time (I‐t) curves responding to monochromatic lights have been further investigated in‐depth, which reveals that introduction of CdS and reduced graphene oxide played an important role in the enhancement of photoelectrochemical performance.