Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250-400 degrees C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (similar to 10-15 nm) and micron long ITO NWs growth was observed in a temperature window of 300-400 degrees C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300-400 degrees C have shown similar to 2-6% reflection and similar to 70-85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices. (C) 2014 Elsevier Ltd. All rights reserved.

Multivalent Cu-Doped ZnO Nanoparticles with Full Solar Spectrum Absorbance and Enhanced Photoactivity

Full solar spectrum absorbers are widely pursued for applications related to photocatalysis and photovoltaics. Here we report multivalent Cu-doped ZnO nanoparticles which exhibit full solar spectrum absorbance and high photoactivity. Metathesis-based, green-chemical approaches with synthesis yield of similar to 100% are used. Cu incorporation in ZnO results in an increase of average solar spectrum absorbance from a mere 0.4% to 34%. On the other hand, (Zn, Cu)0 composites result in materials with up to 64% average solar spectrum absorbance. Doped systems operate well under both visible and UV illumination. The nanomaterials prepared are characterized by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS). Photocatalysts explored have particle sizes >= 50 nm. This is deliberately done in order to avoid the nanotoxic size regime of ZnO. Despite the large particle size and low specific surface area (<20 m(2).g(-1)), the best catalyst reported here compare favorably with recent reports on ZnO based systems. Using X-photoelectron spectroscopy and synthesis property correlations, we infer that the presence of multivalent Cu (most likely in the form of Cu1+delta) on ZnO surface is responsible for the observed photoactivity enhancement.

Effect of Substrate Temperature on the Microstructure Variation in Sputter-deposited Hydrogenated Amorphous Silicon Thinfilms

Vacancy, void incorporation and Si-H-x configuration in hydrogenated amorphous silicon (a-Si:H) thin films was studied. Films were grown by Direct Current (DC), pulsed DC and Radio Frequency (RF) magnetron sputtering. Fourier Transform Infrared (FTIR) spectroscopic analysis has been carried out on the films and found that, the a-Si: H films grown by DC magnetron sputtering are of good quality compared to pulsed DC and RF deposited films. The effect of Substrate temperature (T-S) on the total hydrogen concentration (C-H), configuration of hydrogen bonding, density (decided by the vacancy and void incorporation) and the microstructure factor (R*) was studied. T-S is found to be an active parameter in affecting the above said properties of the films. The films contain both vacancies and voids. At low hydrogen dilutions the films are vacancy dominated and at high hydrogen dilutions they are void dominated. It is found that T-S favors monohydride (Si-H) bonding at the cost of dihydride (Si-H-2) bonding. This dividing line is at C-H=14 at.% H for DC sputter deposited films. The microstructure structure factor R* is found to be zero for as deposited DC films at T-S=773K. The threshold C-H for void dominated region is found to be C-H=23 at.% H for RF, C-H=18 at.% H for PDC and C-H similar to 14 at.%H for DC sputter deposited films.

Synthesis, characterization and spectroscopic investigation of Cr3+ doped wollastonite nanophosphor

This work explores the preparation of nanocrystalline Cr3+ (1-5 mol%) doped CaSiO3 phosphors by solution combustion process and study of its photoluminescence (PL) behavior. The nanopowders are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red (FTIR) spectroscopy. PXRD results confirm monoclinic phase upon calcination at 950 degrees C for 3 h. SEM micrographs indicates that the powder is highly porous and agglomerated. The TEM images show the powder to consist of spherical shaped particles of size similar to 30-60 nm. Upon 323 nm excitation, the emission profile of CaSiO3:Cr3+ exhibits a narrow red emission peak at 641 nm due to E-2 -> (4)A(2) transition and broad band at 722 nm due to T-4(2g) -> (4)A(2g). It is observed that PL intensity increases with increase in Cr3+ concentration and highest PL intensity is observed for 3 mol% doped sample. The PL intensity decreases with further increase in Cr3+ doping. This decrease in PL intensity beyond 3 mol% is ascribed to concentration quenching. Racah parameters are calculated to describe the effects of electron-electron repulsion within the crystal lattice. The parameters show 21% reduction in the Racah parameter of free ion and the complex, indicating the moderate nephelauxetic effect in the lattice. (C) 2014 Elsevier B.V. All rights reserved.

Synthesis and luminescence properties of Sm3+ doped CaTiO3 nanophosphor for application in white LED under NUV excitation

CaTiO3:Sm3+ (1-11 mol%) nanophosphors were successfully synthesized by a low temperature solution combustion method LCS]. The structural and morphological properties of the phosphors were studied by using Powder X-ray diffractometer (PXRD), Fourier transform infrared (FTIR), X-ray photo electron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). TEM studies indicate that the size of the phosphor is similar to 20-35 nm. Photoluminescence (PL) properties of Sm3+ (1-11 mol%) doped CaTiO3 for NUV excitation (407 nm) was studied in order to investigate the possibility of its use in White light emitting diode (WLED) applications. The emission spectra consists of intra 4f transitions of Sm3+, such as (4)G(5/2) -> H-6(5/2) (561 nm), (4)G(5/2) -> H-6(7/2) (601-611 nm), (4)G(5/2) -> H-6(9/2) (648 nm) and (4)G(5/2) -> H-6(11/2) (703 nm) respectively. Further, the emission at 601-611 nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for the application for near ultra violet (NUV) excitation. Thermoluminescence (TL) of the samples irradiated with gamma source in the dose range 100-500 Gy was recorded at a heating rate of 5 degrees C s(-1). Two well resolved glow peaks at 164 degrees C and 214 degrees C along with shouldered peak at 186 degrees C were recorded. TL intensity increases up to 300 Gy and thereafter, it decreases with further increase of dose. The kinetic parameters namely activation energy (E), frequency factor (s) and order of kinetics were estimated and results were discussed in detail. (C) 2014 Elsevier B.V. All rights reserved.

Diffusion pattern in MSi2 and M5Si3 silicides in group VB (M = V, Nb, Ta) and VIB (M = Mo, W) refractory metal-silicon systems

Group VB and VIB M-Si systems are considered to show an interesting pattern in the diffusion of components with the change in atomic number in a particular group (M = V, Nb, Ta or M = Mo, W, respectively). Mainly two phases, MSi2 and M5Si3 are considered for this discussion. Except for Ta-silicides, the activation energy for the integrated diffusion of MSi2 is always lower than M5Si3. In both phases, the relative mobilities measured by the ratio of the tracer diffusion coefficients, , decrease with an increasing atomic number in the given group. If determined at the same homologous temperature, the interdiffusion coefficients increase with the atomic number of the refractory metal in the MSi2 phases and decrease in the M5Si3 ones. This behaviour features the basic changes in the defect concentrations on different sublattices with a change in the atomic number of the refractory components.

Electronic band Structure and Photoemission Spectra of Graphene on Silicon Substrate

Synergizing graphene on silicon based nanostructures is pivotal in advancing nano-electronic device technology. A combination of molecular dynamics and density functional theory has been used to predict the electronic energy band structure and photo-emission spectrum for graphene-Si system with silicon as a substrate for graphene. The equilibrium geometry of the system after energy minimization is obtained from molecular dynamics simulations. For the stable geometry obtained, density functional theory calculations are employed to determine the energy band structure and dielectric constant of the system. Further the work function of the system which is a direct consequence of photoemission spectrum is calculated from the energy band structure using random phase approximations.

Suppression of grain boundary relaxation in Zr-doped BiFeO3 thin films

Here, we present the results of temperature dependent dielectric studies on chemical solution processed Zr-doped BiFeO3 (BFO) thin films deposited on Pt/Si substrates. We find that in contrast to the undoped BFO films, Zr doping at Fe-site suppresses the low frequency dielectric relaxation originating from the grain boundaries, attributed to the increased dipolar rigidity due to stronger Zr-O bonds. Temperature dependent dc conductivity obtained from impedance and modulus analyses shows two distinct conduction processes occurring inside the grains. At temperature below similar to 423K, conductivity is nearly temperature independent, while in the high temperature regime (above similar to 423K), conduction is governed by the long range movement of oxygen vacancies with an activation energy of similar to 1eV. (C) 2014 AIP Publishing LLC.

Hot pressed silver doped hydroxyapatite biomaterials with bactericidal properties against magnetotactic bacteria

Hydroxyapatite (HA) is widely being researched for hard tissue replacement for its good osseointegration and biocompatibility property. However, the inferior antibacterial property of HA often results in infection at host site, and this leads to rejection of the implant. The antibacterial property of silver (Ag) is well known and in the past decade or so, the application of Ag is reinvented in medicinal applications like catheters, vascular grafts and orthopaedic implants. In this respect, the present work reports the synthesis of Ag doped HA using hot pressing in argon atmosphere. This work also reports the effect of HA-Ag composition on bacterial colonisation during in vitro study. The bactericidal property of Ag doped HA has been investigated against magnetotactic bacteria, a `magnetite' containing bacteria. Magnetotactic bacteria were seeded onto pellets, and the adhesion of bacteria was evaluated using scanning electron microscopy. It was confirmed that incorporation of Ag in HA leads to improved bactericidal property.

Metal-metal charge transfer and interfacial charge transfer mechanism for the visible light photocatalytic activity of cerium and nitrogen co-doped TiO2

Nanosized cerium and nitrogen co-doped TiO2 (Ce-TiO2-xNx) was synthesized by sol gel method and characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), FESEM, Fourier transform infrared, N-2 adsorption and desorption methods, photoluminescence and ultraviolet-visible (UV-vis) DRS techniques. PXRD analysis shows the dopant decreases the crystallite sizes and slows the crystallization of the titania matrix. XPS confirm the existence of cerium ion in +3 or +4 state, and nitrogen in -3 state in Ce-TiO2-xNx. The modified surface of TiO2 provides highly active sites for the dyes at the periphery of the Ce-O-Ti interface and also inhibits Ce particles from sintering. UV-visible DRS studies show that the metal-metal charge transfer (MMCT) of Ti/Ce assembly (Ti4+/Ce3+ -> Ti3+/Ce4+) is responsible for the visible light photocatalytic activity. Photoluminescence was used to determine the effect of cerium ion on the electron-hole pair separation between the two interfaces Ce-TiO2-xNx and Ce2O3. This separation increases with the increase of cerium and nitrogen ion concentrations of doped samples. The degradation kinetics of methylene blue and methyl violet dyes in the presence of sol gel TiO2, Ce-TiO2-xNx and commercial Degussa P25 was determined. The higher visible light activity of Ce-TiO2-xNx was due to the participation of MMCT and interfacial charge transfer mechanism.

Impact of spray flux density and vacuum annealing on the transparent conducting properties of doubly doped (Sn plus F) zinc oxide films deposited using a simplified spray technique

In this investigation transparent conducting properties of as-deposited and annealed ZnO:Sn:F films deposited using different spray flux density by changing the solvent volume (10 mL, 20 mL ... 50 mL) of the starting solutions have been studied and reported. The structural analyses of the films indicate that all the films have hexagonal wurtzite structure of ZnO with preferential orientation along (002) plane irrespective of the solvent volume and annealing treatment whereas, the overall crystalline quality of the films is found to be enhanced with the increase in solvent volume as well as with annealing. This observed enhancement is strongly supported by the optical and surface morphological results. From the measurements of electrical parameters, it is seen that, the annealed films exhibit better electrical properties compared to the as-deposited ones. Annealing has caused agglomeration of grains as confirmed by the surface morphological studies. Also, the annealing process has led to an improvement in the optical transparency as well as band gap. It is found from the analyses of the characteristics of the as- deposited and annealed films that the annealed film deposited from starting solution having solvent volume of 50 mL is optimal in all respects, as it possesses all the desirable characteristics including the quality factor (1.60 x 10(-4) (Omega/sq.)(-1)). (C) 2014 Elsevier Ltd. All rights reserved.

Rainbow Emission from an Atomic Transition in Doped Quantum Dots

Although semiconductor quantum dots are promising materials for displays and lighting due to their tunable emissions, these materials also suffer from the serious disadvantage of self-absorption of emitted light. The reabsorption of emitted light is a serious loss mechanism in practical situations because most phosphors exhibit subunity quantum yields. Manganese-based phosphors that also exhibit high stability and quantum efficiency do not suffer from this problem but in turn lack emission tunability, seriously affecting their practical utility. Here, we present a class of manganese-doped quantum dot materials, where strain is used to tune the wavelength of the dopant emission, extending the otherwise limited emission tunability over the yellow-orange range for manganese ions to almost the entire visible spectrum covering all colors from blue to red. These new materials thus combine the advantages of both quantum dots and conventional doped phosphors, thereby opening new possibilities for a wide range of applications in the future.

Fabrication and characterization of gold coated hollow silicon microneedle array for drug delivery

In this paper, we present the fabrication and characterization of Ti and Au coated hollow silicon microneedles for transdermal drug delivery applications. The hollow silicon microneedles are fabricated using isotropic etching followed by anisotropic etching to obtain a tapered tip. Silicon microneedle of 300 mu m in height, with 130 mu m outer diameter and 110 mu m inner diameter at the tip followed by 80 mu m inner diameter and 160 mu m outer diameter at the base have been fabricated. In order to improve the biocompatibility of microneedles, the fabricated microneedles were coated with Ti (500 nm) by sputtering technique followed by gold coating using electroplating. A breaking force of 225 N was obtained for the fabricated microneedles, which is 10 times higher than the skin resistive force. Hence, fabricated microneedles can easily be inserted inside the skin without breakage. The fluid flow through the microneedles was studied for different inlet pressures. A minimum inlet pressure of 0.66 kPa was required to achieve a flow rate of 50 mu l in 2 s with de-ionized water as a fluid medium. (C) 2014 Elsevier B.V. All rights reserved.

Magnetism and superconductivity in Sb-doped binary and ternary iron chalcogenide single crystals

We report the single crystal growth of antimony doped Fe1+yTe and Fe1+yTe0.5Se0.5 (Fe1+ySbxTe1-x (x=0, 2%, 5%) and Fe1+yTe0.49Se0.49Sb0.02) by a modified horizontal Bridgman method. Growth parameters are optimized to obtain high quality single crystals. The antiferromagnetic (AFM) transition at T-N = 62.2 K which is a first order transition, shifts to lower temperature on doping in Fe1+yTe. Alternately when the chalcogen site of the ternary compound Fe1+yTe0.5Se0.5 is doped with Sb, superconductivity is preserved albeit the superconducting transition temperature (T-C) falls slightly and a concomitant reduction occurs in superconducting volume fraction. (C) 2013 Elsevier B.V. All rights reserved,

Boron doped defective graphene as a potential anode material for Li-ion batteries

Graphene with large surface area and robust structure has been proposed as a high storage capacity anode material for Li ion batteries. While the inertness of pristine graphene leads to better Li kinetics, poor adsorption leads to Li clustering, significantly affecting the performance of the battery. Here, we show the role of defects and doping in achieving enhanced adsorption without compromising on the high diffusivity of Li. Using first principles density functional theory (DFT) calculations, we carry out a comprehensive study of diffusion kinetics of Li over the plane of the defective structures and calculate the change in the number of Li atoms in the vicinity of defects, with respect to pristine graphene. Our results show that the Li-C interaction, storage capacity and the energy barriers depend sensitively on the type of defects. The un-doped and boron doped mono-vacancy, doped di-vacancy up to two boron, one nitrogen doped di-vacancy, and Stone-Wales defects show low energy barriers that are comparable to pristine graphene. Furthermore, boron doping at mono-vacancy enhances the adsorption of Li. In particular, the two boron doped mono-vacancy graphene shows both a low energy barrier of 0.31 eV and better adsorption, and hence can be considered as a potential candidate for anode material.