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The lead-free solid-solution (1-x)Ba0.06(Na0.5Bi0.5)0.94TiO3-xNaNbO3; 0 ≤ x ≤ 1.0 have been prepared by the conventional solid-state reaction method and their electrical impedance and conductivity was studied employing the impedance spectroscopy method in the range starting from room temperature to 500°C, with the step of 2°C. The X-ray diffraction analysis of all the compounds confirmed the successful formation of solid-solutions. Ac conductivity registered an increment with the increasing frequency for all the compositions over the entire temperature range. Also, a transfer from low impedance to high impedance was observed with the increasing NaNbO3 content in Ba0.06(Na0.5Bi0.5)0.94TiO3. To ascertain the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed by a theoretical model based on correlated barrier hopping.

In the present study we have made an attempt to make and use a milling map in the mechanochemical synthesis of nanocrystalline lead titanate (PT) ceramics. In order to do this, lead titanate was synthesized by mechanical alloying from a powder mixture of PbO and TiO2. By varying the milling parameters such as milling speed and ball to powder ratio over a wide range, a series of milling energies were obtained.

In this work effect of high energy milling on the structural and electrical properties of Ba(Fe1/2Ta1/2)O3 (BFT) ceramic synthesized using standard solid-state reaction method were investigated. X-ray diffraction studies indicated that the unit cell structure for all the samples to be hexagonal (space group: P3m1). FTIR spectra also confirmed the formation of BFT without any new phase. The milled (10 h) BFT ceramic showed the formation of small grain sizes (

Position sensing is an important part of different timeline based exhibit in science centre and museums. Though currently available technologies suffers from range dependency or low resolution problems. This paper is primarily focused towards developing low cost, high resolution, range independent position sensing methodology using image processing technology.

Markers are primarily used as position indicators, hence estimation of marker position is a very important task in the field of localization. Localization can be done in many ways one of the most popular method of localization is using image processing technique. Sometimes marker localization by image processing needs highly complex processing which becomes extremely difficult in case of real time processing with limited processing capacity like onboard computer of Autonomous robot. Hence here the whole marker localization process is revisited to select propped marker in order to localize it with minimum processing.

β-Ga 2 O 3 3D microstructures were prepared by ethylenediamine (En)-mediated solvothermal technique at low temperature (200 °C). These microstructures were characterized by X-ray diffraction, scanning electron microscopy and field emission scanning electron microscopy. The optical absorbance and photoluminescence spectroscopic studies of these microstructures indicated that the optical property of the microstructures were synthesis parameter dependent. The volume ratio of En to water played a crucial role in the conversion of initial α-GaO(OH) nanowires into β-Ga 2 O 3 nanoflakes and finally to 3D microstructures. Photoluminescence spectra of the samples revealed gallium–oxygen vacancy-related defects in these nano- and microstructures. A plausible growth mechanism for the variation of morphology with synthesis parameter is discussed.

Synthesis and characterization of CuInS2 powder sample prepared by a simple and convenient solvothermal method is reported. The influence of the variation of Cu/In molar ratio from 0.69 to 1.25 on the particle morphology, crystal structure and optical properties of CuInS2 samples was studied. The X-ray diffraction studies indicated that the samples were polycrystalline in nature. SEM images of the samples revealed that the copper-rich products were uniform microspheres with smooth surfaces, whereas microspheres formed by network of interconnected flakes were obtained for indium-rich products. The optical band gaps (Eg) of the products decreased from 1.60 to 1.43 eV with variation of Cu/In molar ratio. The variation of the Urbach tail width with Cu/In molar ratio indicated that the density of the defects is much higher for the indium-rich CuInS2, which was clearly revealed from Raman measurements.

ZnS nanorods doped with 0–15 mol% of Cu have been prepared by simple solvothermal process. With gradual increase in the Cu concentration, phase transformation of the doped ZnS nanorods from wurtzite to cubic was observed. Twins and stacking faults were developed due to atomic rearrangement in the heavily doped ZnS nanorods during phase transformation. UV–vis–NIR absorbance spectroscopy ruled out the presence of any impure Cu–S phase. The doped ZnS nanorods showed luminescence over a wide range from UV to near IR with peaks at 370, 492–498, 565 and 730 nm. The UV region peak is due to the near-band-edge transition, whereas, the green peak can be related to emission from elementary sulfur species on the surfaces of the nanorods. The orange emission at 565 nm may be linked to the recombination of electrons at deep defect levels and the Cu(t2) states present near the valence band of ZnS. The near IR emission possibly originated from transitions due to deep-level defects.

Hierarchical nano/micro structures of ZnO have been fabricated by solvothermal approach on sol–gel derived ZnO thin films. Paintbrush like nano/micro rod assembly, double-sided brush and windmill type architectures of ZnO are obtained when the ZnO thin film coated substrates were treated solvothermally in water at pH 10. Aligned nanorods are obtained at pH ∼ 13.5 in water. In ethylenediamine-water solvent divergent micro/nanorod assemblies such as hemispherical dandelion, rice plant type bush of ZnO are obtained. Increase in the percentage of ethyelendiamine resulted in the formation of smaller assemblies of relatively thin nanorods. Initial slow reaction caused by the slow increase of the temperature inside the reaction medium and the different growth kinetics of the ZnO crystals are supposed to be the reason behind the architectural assemblies of the ZnO crystals.

One-dimensional (1D) anatase TiO 2 nanostructures such as nanorods, nanowires and nanotubes with different aspect ratios were synthesized by a simple solvothermal process. The influence of the different organic solvents and the reaction time on the morphology, size and the formation of the nanostructures were investigated. The anatase TiO 2 precursor powder reacted with highly alkaline aqueous solution, yielding layered sodium titanate nanosheets. These nanosheets transformed to different 1D sodium titanates nanostructures like nanorods, nanowires and nanotubes in the different solvents i.e. highly alkaline aqueous solution, highly alkaline water–ethanol and highly alkaline water–ethylene glycol mixed solvent, respectively. Acid treatment of these 1D sodium titanates resulted hydrated titanates and finally dehydration by calcinations at 500 °C in air gave the products retaining the morphology. The synthesized samples were characterized with XRD, SEM and TEM. All the 1D nanostructures showed intense and sharp absorption spectra indicated that the products were almost defect free. Photoluminescence studies of the nanostructures showed photostable UV emission properties that arise from the band-edge free excitation.

Ellipsoidal and prism shaped ZnO nanocrystals with hexagonal cross-sections have been synthesized by a simple solvothermal process. The ellipsoidal ZnO nanocrystals possessed a unique hexagonal cross-section having two sharp pointed ends and a flattened central part. The well faceted prism like particles resembled hexagonal cones in their shape. Dimensions of the nanocrystals increased systematically with the increase in the synthesis temperature. The synthesized nanocrystals exhibited near band edge UV emission centered at ∼400 nm. An additional defect related green emission band at ∼500 nm was observed from the samples synthesized at higher temperatures.

Nanowire arrays of cubic zinc sulfide are synthesized on zinc foil by a simple thermal evaporation route at relatively low temperature (

ZnO is one of the most important semiconductors having a wide variety of applications in photonic, field emission and sensing devices. In addition, it exhibits a wide variety of morphologies in the nano regime that can be grown by tuning the growth habit of the ZnO crystal. Among various nanostructures, oriented 1-D nanoforms are particularly important for applications such as UV laser, sensors, UV LED, field emission displays, piezoelectric nanogenerator etc. We have developed a soft chemical approach to fabricate well-aligned arrays of various 1-D nanoforms like nanonails, nanowires and nanorods. The microstructural and photoluminescence properties of all the structures were investigated and tuned by varying the synthesis parameters. Field emission study from the aligned nanorod arrays exhibited high current density and a low turn-on field. These arrays also exhibited very strong UV emission and week defect emission. These structures can be utilized to fabricate efficient UV LEDs.

ZnS nano and micro structures such as nanoribbons, large sheets and tetrapod shaped crystals were fabricated by direct thermal evaporation of ZnS powder without using any catalyst. Formation of the one dimensional structures such as nanoribbons and micron order sheets was attributed to the vapor-solid growth mechanism. The formation of octahedron nucleus with cubic crystal structures was proposed as the growth unit of the wurtzite crystal structured tetrapods. Appearance of the periodic stacking faults or twining planes in between alternate cubic and hexagonal crystal structured zones along the growth direction of the ribbons provided secondary growth sites for the octahedron nucleus and subsequent crystal growth resulted in to the formation of the tetrapod arrays. These nano/micro structures of ZnS exhibited a green emission band at room temperature.

c-Axis oriented GaN nanocrystalline thin films were fabricated by nitridation of three different thin films of α-GaO(OH), α-Ga2O3 or β-Ga2O3 obtained by sol–gel technique on amorphous quartz glass substrates. All these GaN thin films showed near band edge emission at 390 nm and yellow luminescence at 570 nm. The crystalline nature and c-axis orientation as well as luminescence properties of the GaN thin films increased by several times by using a buffer layer of GaN on the substrate.

Well-crystalline ultrathin GaS nanobelts have been successfully synthesized on silicon substrates by a simple thermal evaporation process. The GaS nanobelts were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), and energy dispersive X-ray analysis (EDAX). The XRD pattern indicates formation of well-crystalline hexagonal phase GaS nanostructures. The SEM image shows uniformly distributed GaS nanostructures covering the entire substrate surface. The TEM results reveal that the GaS nanostructures are “nanobelts” of widths 20 to 50 nm and lengths up to several microns, and some of them are L-shaped. The growth mechanism and formation of GaS straight and L-shaped nanobelts has been explained. The field emission studies revealed that the threshold field required to draw an emission current of ∼1 nA is to be 2.9 V/μm, and a current density of ∼5.7 μA/cm2 can be drawn at an applied field of 6.0 V/μm. The Fowler−Nordheim plot, derive...

In2−xCoxS3 (x = 0 to 0.1) micropompons (diameters ∼3–4 μm) consisting of ∼10–15-nm-thick randomly self-assembled nanoflakes were synthesized hydrothermally. X-ray study indicated a steady variation of lattice parameter ratio up to 5% Co. Detailed investigations of the Co incorporation in In2S3 were carried out by optical absorbance, room temperature photoluminescence (PL), and electron paramagnetic resonance (EPR) studies. Significant blue shift in the absorbance spectra was noticed due to the crystal-field splitting of Co2+ ions in the host lattice structure. Unlike the visible emission found in undoped In2S3, PL spectra of the Co-doped samples were recognized by a strong ultraviolet emission peak at ∼335 nm, introduced by the t2g level of Co2+ ions, with maximum intensity for 5% Co. Room-temperature and low-temperature EPR spectra revealed octet paramagnetic bands up to 5% Co beyond which a single resonance band appeared.

Thin films of indium sulfide (In2S3) micro- and nanorods were successfully prepared by sulfurization of electrodeposited metal indium layers. The films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–vis spectroscopy. From XRD and TEM observations it was concluded that the In2S3 nanorods and microrods have ∼50 nm and ∼0.5 μm diameter, respectively. A plausible top-growth mechanism was proposed for the formation of the nanorods in which the hydroxide layer was found to play an important role. The micro- and nanorods showed optical bandgap of ∼2.2 and ∼2.54 eV, respectively. This facile and cost effective method may be extended to fabricate other metal chalcogenide nanostructures on solid substrates.

Randomly oriented orthorhombic tin oxide nanocrystals formed faceted complex structures like nanocubes, nanopyramids, hexagonal discs, etc. SnCl2·2H2O was used as a precursor in this ethanol−water aided solvothermal synthesis. The growth and self-assembly of primary nanocrystals into complex structures were thought to be aided by thermodynamic energy, viscosity, surface tension, and also by hydrogen bonding, which supported long-range ordering of the nanocrystals. The optical absorbance spectra revealed that the band gap for structured orthorhombic tin oxides is widened from its reported bulk value. The experimentally obtained values of the optical band gap are tallied with the values obtained by using an established theoretical model (Effective Mass Approximation) concerning the interrelation of size and the optical band gap of nanocrystals.

c-axis-oriented gallium nitride (wurtzite GaN) thin films were fabricated by nitridation of acetate derived precursor films deposited on fused silica substrates without any buffer layer on the top of the substrate. The acetate derived precursors were obtained by (i) preparing a gallium-acetate sol by reacting Ga metal with acetic acid, (ii) coating cleared fused silica substrate with the sol and (iii) after drying the coated films at 100 °C, annealing them in air at 300°, 500° and 900 °C. Only films showing crystallization of α-GaO(OH) (300 °C) and (α + β)-Ga2O3 (500 °C) were selected for nitridation. In spite of the amorphous nature of the substrate, the GaN films showed a strong preferred orientation for the basal plane (002) under selected conditions of precursor annealing (300°, 500 °C) and subsequent nitridation (under flowing NH3) temperature and time. In other cases formation of an additional plane, i.e. (101) was indicated as a weaker peak in X-ray diffraction (XRD) patterns. The precursors and nitride films were characterized by Fourier transform infrared spectroscopy, UV–Visible spectroscopy, XRD, high resolution transmission electron microscopy and atomic force microscopy analyses.

Gallium oxide (beta-Ga2O3) nanoparticles were successfully deposited on quartz glass substrates using sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/n-hexane/ethylene glycol monomethyl ether (EGME) reverse micelle-mediated solvothermal process with different omega values. The mean diameter of Ga2O3 particles was approximately 2-3 nm and found to be approximately independent of omega values of the reverse micelles. However, when the Ga2O3 nanocrystalline films were nitrided at 900 degrees C under flowing NH3 atmosphere for 1 h, the mean diameter of the resulted gallium nitride (wurtzite-GaN) nanoparticles varied from 3-9 nm. Both nanocrystalline films of Ga2O3 and GaN were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy and photoluminescence in order to study their chemical and physical properties explicitly.

Sol–gel synthesized SnO2 nanoparticles with an average size of 2.0 nm obtained at 373 K were gradually annealed to 673 K in air for 25 minutes. Sequentially taken transmission electron microscopy (TEM) images showed that particle agglomeration of these non-matrix SnO2 nanocrystals was a very slow process. The blue shifts of the band gap (∼ 2.3 eV) obtained from the optical absorbance spectra were matched with the theoretical results of the size related excitonic binding energies. These calculations also supported the observed slow grain growth. The depth sensitive hardness measurements of the thin films indicated hardness in the range of 5.03 GPa to 6.79 GPa. These undoped and non-matrix SnO2 nanoparticles were also investigated with the X-ray photoelectrons spectroscopy (XPS), atomic force microscope (AFM), X-ray diffraction spectroscopy (XRD), and ac impedance analyzer.

Uniform as well as flower like patterns of SnS2 nanoflakes were produced by a thermal evaporation process. Interpenetrating phenomenon was observed between the individual nanoflakes during the course of their lateral growth. The interpenetrating growth and controlled vapor concentration as well as the substrate temperature leads to the formation of flower like assemblies of SnS2 nanoflakes. Morphology and growth mechanism of the nanostructures were studied by scanning electron microscopic observations at different stages of the nanoflake growth. The produced nanoflakes were characterized by X-ray diffraction, scanning and transmission electron microscopy, and Raman spectroscopic measurements. SnS2 nanoflakes were perfectly single crystalline and growth direction of the nanoflakes was along the {101}-lattice plane.

The synthesis of CdS/ZnS core/shell nanorods was achieved via a three-step method involving solvothermal preparation of CdS nanorods and then a soft chemical process for functionalization of the CdS surface and subsequent ZnS shell growth. Citric acid was used as the surface functionalizing agent, which ensured the growth of a uniform ZnS shell covering the nanorod surface. The carboxyl groups of citric acid trapped on the surfaces of CdS nanorods with an outward orientation of the -OH functional groups made the surfaces of the nanorods negatively charged, directed the Zn2+ ions to attach to the -OH ions, and helped the formation of a uniform ZnS shell following the addition of a sulfur source. The core/shell nanostructure was confirmed by X-ray study, transmission electron microscopy, and energy dispersive X-ray analysis. The photoluminescence efficiencies and electrical response of the CdS/ZnS core/shell nanorods were significantly enhanced as compared to those of the uncoated CdS nanorods, owing to the...

Mn and Cu doped ZnS nanoparticles in powder form were prepared by a simple solvothermal route. Particle size and crystal structure of the products were investigated through X-ray diffraction study revealing the formation of cubic ZnS nanoparticles of average diameter 2.5 nm. Particle size was also verified by the high resolution transmission electron microscopic images. Blue emission at approximately 445 nm was observed from the undoped sample, which was attributed to the presence of large surface defects. With increasing doping concentration the defect related emission gradually quenches and subsequently the impurity related emissions appeared. Mn doped samples exhibited orange emission at approximately 580 nm which may be attributed to the transition between (4)T1 and (6)A1 energy levels of the Mn2+ 3d states. Whereas, the Cu doped ZnS nanoparticles exhibited a red shifted strong blue emission at approximately 466 nm which is attributed to the transition of the electrons from the surface states to the 't2' levels of Cu impurities.

Monodispersed hollow ZnS microspheres have been successfully synthesized by a facile ethylenediamine tetraacetic acid (EDTA) mediated hydrothermal route. The sizes of the hollow spheres vary from 1.5 to 3.5 microm when the reaction temperature varied from 130 to 230 degrees C. The formation of these hollow spheres is attributed to the oriented aggregation of ZnS nanocrystals around the gas-liquid interface between H(2)S and water. EDTA plays important role as chelating ligand and capping reagent, which regulates the release of Zn(2+) ions for the formation of ZnS hollow spheres. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectroscopy, photoluminescence, and Raman spectroscopy. The obtained ZnS hollow spheres show a sharp and photostable UV emission approximately 370 nm, which is attributed to the recombination process associated with interstitial sulfur vacancy.

Manganese-doped zinc sulfide (MnxZn1-xS) nanorods were synthesized through solvothermal processes and were characterized by x-ray diffraction and scanning and transmission electron microscopy. Positron lifetime and Doppler broadening measure-ments were carried out on powdered samples with different dopant concentrations. A transformation from hexagonal to cubic structure was observed almost concomitantly with the filling of Zn2+ vacancies and/or substitution of Zn2+ ions by Mn2+ ions. The lifetime of positrons annihilating at the surfaces of nanorods decreased with increase in their diameter during increased doping by Mn2+ ions. At concentrations above 20%, pyramid-like coarse crystals of MnS were found coexisting with the ZnS nanostructures. The interior of the nanorods seemed to be free of vacancy-type defects unlike in the case of ZnS nanoparticles. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanorods and nanosheets of tin sulfide (SnS) were synthesized by a novel thioglycolic acid (TGA) assisted hydrothermal process. The as prepared nanostructures were characterized by X-ray diffraction (XRD) study, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD study reveals the formation of well-crystallized orthorhombic structure of SnS. Diameter of the SnS nanorods varied within 30–100 nm. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns identify the single crystalline nature for the SnS nanocrystals. The mechanism for the TGA assisted growth for the nanosheets and nanorods have been discussed.

A solvothermal route has been utilized for the growth of MnS micro and nanocrystals with different morphologies such as pyramid, octahedron, sheet, sphere, hexagonal ring, etc. It was observed that the experimental parameters such as the variation in the precursor salt, molar ratio of the anionic and cationic precursors as well as the solvent play critical role in determining the morphology and crystal structure of the products. X-ray diffraction study reveals the formation of stable and metastable phases of MnS under different experimental conditions. It was observed that irrespective of the nature of the solvent, the presence of sulfur source in higher molar concentration always favored the formation of stable MnS phase. Interpenetrating crystal growth and clustering formation were also observed under certain circumstances. A detailed growth mechanism for the various micro and nanostructures is proposed.

ZnO nanocrystals with various morphologies such as nanorod arrays, flower like assemblies, spherical particles, hexagonal cones, and self assembled microstructures were prepared by a solvothermal approach. It was observed that morphology of the ZnO nanostructures were very much solvent dependent in solvothermal approach. Water, ethylenediamine, and ethylene glycol-water mixture favors the formation of nanorods. Flower like assemblies of ZnO were produced in benzene. Spherical as well as cone like nanoparticles and their assemblies were produced in ethylene glycol. The ZnO nanostructures were characterized by X-ray diffraction, scanning and transmission electron microscopy, and photoluminescence studies.

ZnO–Al 2 O 3 nanocomposite thin films were prepared by sol–gel technique. The room temperature synthesis was mainly based on the successful peptization of boehmite (AlO(OH)) and Al(OH) 3 compounds, so as to use it as matrix to confine ZnO nanoparticles. The relative molar concentrations of x ZnO to (1 − x ) Al 2 O 3 were varied as x = 0.1, 0.2 and 0.5. The optical absorption spectra of the thin films showed intense UV absorption peaks with long tails of variable absorption in the visible region of the spectra. The ZnO–Al 2 O 3 nanocomposites thin films were doped with MgO by varying its molar concentrations as y = 0.05, 0.75, 0.1, 0.125, 0.15 and 0.2 with respect to the ZnO present in the composite. The MgO doped thin films showed suppression of the intense absorption peaks that was previously attained for undoped samples. The disappearance of the absorption peaks was analyzed in terms of the crystalline features and lattice defects in the nanocomposite system. The bulk absorption edge, which is reportedly found at 3.37 eV, was shifted to 5.44 eV (for y = 0.05), 5.63 eV (for y = 0.075) and maximum to 5.77 eV (for y = 0.1). In contrast, beyond the concentration, y = 0.1 the absorption edges were moved to 5.67 eV (for y = 0.125), 5.61 eV (for y = 0.15) and to 5.49 eV (for y = 0.2). This trend was explained in terms of the Burstein–Moss shift of the absorption edges.

CuInS2 flower vaselike nanostructure arrays were successfully prepared for the first time on Cu-tape substrates by a facile copper indium sulfide on Cu-tape (CISCuT) method without using any templa...

In2O3 nanoribbons were produced directly from In metal foils by using a solvothermal approach. Presence of the excess OH−1 ions was crucial in the formation of the In2O3 nanoribbons, and increase in concentration of the OH−1 ions caused an increase in the density and length of the nanoribbons. The crystal structure and morphology of the products were investigated through X‐ray diffraction and scanning electron microscopic studies. The growth mechanism of the In2O3 nanoribbons was quite similar to that of the high‐temperature‐based vapor‐solid (VS) process.

Nanometric size dependent optical absorption coefficients, dispersive nature of the dielectric constants and ac conductivity are observed for the single layer ZnOx(Al2O3)1-x (x = 0.20 and 0.50) nanocomposites thin films. The sol-gel prepared thin films with thickness approximately 119 nm, contains randomly dispersed ZnO nanocrystallites in the A2O3, matrix. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) revealed homogeneous distributions of the nanoparticles in the matrix. The shifting and broadening of the optical absorption peaks to the lower wavelength region at higher annealing temperatures was analyzed in order to relate the particle-particle interactions and the sizes of the dispersed nanoparticles in the matrix. AC impedance spectroscopy in the frequency range of 500 Hz to 5 MHz was measured at room temperature (300 K), 325 K, 395 K, and 450 K. The dielectric relaxations in each case were found to be of Cole-Cole type. The semicircular pattern of the ac capacitance in the complex plane showed contributions from the grain and grain boundary subject to concentration of ZnO in the matrix. The appearance of the negative capacitance at higher frequency was also analyzed.

Single-layer ZnO–Al2O3 nanocomposite thin films with thickness approximately 119 nm, containing randomly dispersed nanocrystallites of ZnO in the Al2O3 matrix were prepared by sol gel technique. The relative molar concentration of ZnO was 20% in the matrix. The confined nanoparticles ZnO were investigated through ac impedance spectroscopy in the frequency range of 500 Hz to 5 MHz at 315 K, 325 K, 345 K, 355 K, 395 and 450 K. The dielectric relaxations in each case were found to be of Cole–Cole type. The thermally activated relaxation phenomenon was analysed with the help of an equivalent circuit which is proposed on the basis of the experimentally obtained complex capacitance and impedance spectral studies. The temperature dependent electrical conductivity was analysed on the basis of interstitial Zn ions and free electrons in the system. The defect concentration of the nanocomposite thin film was determined from the complex capacitance measurements. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cd(OH) 2 and CdO nano/micro crystals were synthesized in ethanol–water medium using cadmium foil as a source under solvothermal condition. The experimental parameters such as ratio of ethanol to water, concentration of NaOH and synthesis temperature all play important role in determining the size, shape and crystalline phase of the products. The products were characterized by X-ray diffraction and scanning electron microscopy. Nano/micro crystals of CdO were also achieved by thermal treatment of Cd(OH) 2 crystals in air at different temperatures.

ZnS nanoparticles of diameters between 3–4 nm were aggregated to form dense nanospheres of sizes ∼100 nm by a colloidal precipitation method using PVP as the stabilizing agent. XRD studies showed that the ZnS nanoparticles were of zinc blend (cubic) structure. It was observed that the dense nanospheres had a tendency to form supramolecular nanostructures on a solid substrate upon solvent evaporation. The resulting films had highly ordered structures with the aggregated nanospheres interconnected to form dendrite like structures and chains of micrometer length scale. Optical absorption spectra of the samples demonstrated the effect of quantum confinement in the ZnS nanocrystals. Photoluminescence measurements showed a sharp UV emission at ∼370 nm.

ZnS nanoparticles of diameters of 3–4 nm were self-assembled to form dense nanospheres of sizes ∼100 nm by a colloidal precipitation method using PVP as the stabilizing agent. Studies indicated that the ZnS nanoparticles maintained their individual properties inside the nanospheres. Optical absorption spectra of the samples demonstrated the effect of quantum confinement in the ZnS nanocrystals. Room temperature photoluminescence measurements showed a sharp UV emission at ∼370 nm, attributed to sulfur vacancies.

Partially crystalline indium sulfide dendrites were obtained via precipitation in presence of CTAB. In absence of CTAB, crude self-assembly of particles was noted. With increasing CTAB concentration and aging time of the solutions, particles were found to self-assemble in a progressive manner to extended hierarchical dendrites. Unlike in commonly known cases where dendrites are unstable but well crystallized, partially crystallized particles can also self-assemble to well-formed dendrites especially when assisted by the surfactant molecules. The X-ay analysis, TEM studies confirmed the partially crystallized nature of the samples. Optical properties when investigated, the dendrites were found to show quantum confinement effects.

In this paper, we report the preparation of vertically aligned ZnO−ZnS core−shell and ZnS nanorod arrays with crystallographic orientation along the c-axis by sulfidation of aligned ZnO nanorod arrays. The ZnO nanorod arrays were prepared by a surfactant assisted soft chemical method on a sol−gel derived ZnO thin film. Partial conversion of the ZnO nanorod surface to ZnS at 400 °C in an H2S and argon gas mixture produces ZnO−ZnS core−shell structures, whereas the complete conversion at 600 °C produces well-aligned ZnS nanorods. The influence of the sulfidation time and annealing temperature on the conversion of ZnO nanorods to ZnO−ZnS core−shell nanorods is investigated. TEM studies revealed that the sulfidation process begins at the surface of the ZnO nanorods, which gradually increase inward, retaining the morphology and following the crystal orientation of the ZnO core. The nanostructures showed enhanced UV emission properties. The described procedures open a way to convert a microstructured material i...

CuInS 2 thin films were prepared by a two-stage ion layer gas reaction (ILGAR) process in which the Cu and In precursors were deposited on glass substrate by using a simple and low-cost dip coating technique and annealed in H 2 S atmosphere at different temperatures. The influence of the annealing temperature (250–450 °C) on the particle size, crystal structure and optical properties of the CuInS 2 thin films was studied. Transmission electron microscopy revealed that the particle radii varied in the range 6–21 nm with annealing. XRD and SAED patterns indicated polycrystalline nature of the nanoparticles. The optical band gap ( E g ) varied from 1.48 to 1.56 eV with variation of particle size. The variation of Urbach tail with temperature indicated higher density of the defects for the films annealed at lower temperature. From the Raman study, it was observed that the FWHM of the A 1 mode at ∼292 cm −1 corresponding to the chalcopyrite phase of CuInS 2 decreased with increasing annealing temperature.

Wurtzite GaN nanowires and nanoribbons were produced directly from Ga metal by an Au catalyst assisted thermal evaporation process in a flowing ammonia atmosphere. We have investigated the effect of different experimental parameters on the morphology of the nanoforms. The diameters of the nanowires were varied between 20 and 40 nm while the widths of the nanoribbons were within 100–250 nm. Microstructural studies by TEM reveals the role of vapor–liquid–solid process in the nucleation of GaN nanoforms. The evolution of the ribbon like morphology was attributed to the vapor–solid process. Photoluminescence study showed UV–blue emission from the GaN nanostructures. Field emission studies indicated the possibility of these materials to be used as the cathode materials in field emission based devices.

Thin films of nanocrystalline SnS{sub 2} on glass substrates were prepared from solution by dip coating and then sulfurized in H{sub 2}S (H{sub 2}S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 deg. C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at {approx}314 cm{sup -1}, which confirmed the presence of nanocrystalline SnS{sub 2} phase.

MnS crystals with different morphologies such as octahedrons, cubes, sheets, spheres and nanotubes have been synthesized by a low-temperature based solvothermal process. The experimental parameters such as solvents, temperature and molar ratio of the Mn to sulfur source play crucial role in determining the morphologies and phases of the MnS crystals. All the faceted MnS crystals are of good crystal qualities as revealed by the X-ray diffraction (XRD) study.

Copper sulphides Cu 9 S 5 and polymorphs of Cu 2 S were synthesized apparently for the first time on copper foil through its solvothermal reaction with sulphur (the former being used both as substrate and reactant), with 75% fill of the autoclave with water, ethanol or ethylenediamine as solvents. Water as solvent produced micron-sized hemispheres of Cu 9 S 5 (composed of much smaller particles of size ∼5–6 nm), truncated by forming interfaces and exhibiting relatively large dihedral angles (80–120°). Ethanol produced fibre-like or thread-like (∼40 nm diameter) morphological form of Cu 9 S 5 , generally woven into network-structures. Ethylenediamine, which produced Cu 2 S (monoclinic), as also β-Cu 2 S (hexagonal), assisted formation of hexagonal micron-sized single crystal rods with a hexagonal end face in conjunction with β-Cu 2 S.

Nanocrystalline thin films consisting of pure phases of α-GaO(OH), α-Ga2O3 and β-Ga2O3 have been prepared. These were synthesized by sol–gel technique through varying annealing temperature from 300 °C to 1100 °C in air ambient. Single phase α-GaO(OH) was obtained at annealing temperature of 300 °C. With increase in annealing temperature a mixed phase of α-GaO(OH) and α-Ga2O3 was found. Pure α-Ga2O3 could be prepared at 500 °C. As the annealing temperature was further increased, α-Ga2O3 started to convert into β-Ga2O3. Only β-phase was observed at annealing temperature 700 °C and above. The average crystallite size of α-GaO(OH) and α-Ga2O3 phases was found to be ∼3 nm and ∼16 nm respectively, while that of β-Ga2O3 increased from ∼14 nm to ∼24 nm with increase in annealing temperature (700–1100 °C). The optical band gaps of α-GaO(OH) and α-Ga2O3, determined from transmittance measurements were 5.27 and 4.98 eV respectively and higher than that of β-phase. A nominal variation of band gap of β-phase (4.8–4.7 eV) was observed with the variation of annealing temperature (700–1100 °C). The structural defects of this phase, estimated from transmittance spectra using Urbach tail widths, were found to decrease with increase in crystallite size.

This review article presents the synthesis and important properties of bulk, thin film and different nanoforms of GaN. The nanoforms include nanocrystalline powder, nanowires and nanorods. The preparation and critical aspects of p-type and n-type GaN has been discussed in detail as the semiconducting proterties of this material have already been utilized in the industries for the fabrication of optoelectronic devices. Discussion in relation to improvement of light emitting diode application and some other probable applications based on typical properties of pure and doped GaN have been made.

ZnO doughnutlike cluster particles were prepared by a simple solvothermal route using an ethylene glycol (EG)−water solvent system. It was observed that ZnO doughnuts were obtained when an equal or higher volume fraction of EG was used in the solvent. Microstructural studies revealed that these doughnut-shaped particles were clusters of small hexagonal plates arranged in a regular fashion. Because of the capping property of EG, these constituent hexagonal plates arranged in an angular oriented attachment scheme with a view to minimize their surface energies. The resulting assemblies were concave from one side and convex from the reverse side. With the increasing percentage of EG, the concentration of the capping element increased, resulting in the reduction of the size of the constituent plates, which in turn helps the formation of more and more densely packed ZnO doughnuts. Increases in temperature and pressure also favor the formation of densely packed ZnO doughnuts. These ZnO samples exhibited a strong...

Gallium oxide nanoparticles embedded in silica matrix with different molar ratios were synthesized by the sol–gel method. Powdered nanocomposite samples were annealed at 400, 500 and 900 °C. The gallium oxide nanoparticles (2–5 nm) crystallized in the β-phase at a very low temperature (~400 °C) as against the expected temperature (>700 °C), indicating a depression of crystallization temperature under the present condition. This may be a signature of the behaviour of confined nanosized particles. The indications of only Ga–O bonds and Si–O–Si bonds in FTIR spectra and peaks of gallium, oxygen and silicon in energy dispersive x-ray analysis (EDAX) confirmed the non-existence of any impurity. Room temperature photoluminescence study of the samples shows a strong blue emission at ~460 nm.

Crystalline SnS wires of micro- and nanometer scale have been synthesized over tin metal foils at room temperature using a simple surfactant-assisted approach. Scanning electron microscopy, transmission electron microscopy, UV−Vis−near infrared (NIR) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the SnS nanowires. X-ray diffraction (XRD) analysis confirmed the formation of the pure orthorhombic phase of SnS. The optical band gap of the samples was found to be ∼1.4 eV. From the investigation, the formation of nanowires could be explained in two steps: initial cracking/splitting of the nanoflakes was followed by a top-growth mechanism to form ultralong nanowires. Effects of various experimental parameters on the growth mechanism were investigated. Present studies have shown that this facile process also can be extended for the synthesis of other low dimensional structures.