Effect of Te addition on the optical properties of As(2)S(3) thin film

Bilayer thin films of Te/As(2)S(3) were prepared from Te and As(2)S(3) by thermal technique under high vacuum. Optical constants were calculated by analysing the transmission spectrum in the spectral range 400-1100 nm. The optical band gap decreases with the addition of Te to As(2)S(3). The decrease of optical band gap has been explained on the basis of density of states and the increase in disorder in the system. We have irradiated the as-deposited films using a diode pumped solid state laser of 532 nm wavelength to study photo-diffusion of Te into As(2)S(3). The changes were characterised by Fourier Transform Infrared and X-ray Photoelectron Spectroscopy (XPS). The optical band gap is found to be decreased with the light irradiation which is proposed due to homopolar bond formation. The core level peaks in XPS spectra give information about different bond formation. (C) 2011 Elsevier B.V. All rights reserved.

Electrocatalysis and redox behavior of Pt(2+) ion in CeO(2) and Ce(0.85)Ti(0.15)O(2): XPS evidence of participation of lattice oxygen for high activity

Electronic states of CeO(2), Ce(1 -aEuro parts per thousand x) Pt (x) O(2 -aEuro parts per thousand delta) , and Ce(1 -aEuro parts per thousand x -aEuro parts per thousand y) Ti (y) Pt (x) O(2 -aEuro parts per thousand delta) electrodes have been investigated by X-ray photoelectron spectroscopy as a function of applied potential for oxygen evolution and formic acid and methanol oxidation. Ionically dispersed platinum in Ce(1 -aEuro parts per thousand x) Pt (x) O(2 -aEuro parts per thousand delta) and Ce(1 -aEuro parts per thousand x -aEuro parts per thousand y) Ti (y) Pt (x) O(2 -aEuro parts per thousand delta) is active toward these reactions compared with CeO(2) alone. Higher electrocatalytic activity of Pt(2+) ions in CeO(2) and Ce(1 -aEuro parts per thousand x) Ti (x) O(2) compared with the same amount of Pt(0) in Pt/C is attributed to Pt(2+) ion interaction with CeO(2) and Ce(1 -aEuro parts per thousand x) Ti (x) O(2) to activate the lattice oxygen of the support oxide. Utilization of this activated lattice oxygen has been demonstrated in terms of high oxygen evolution in acid medium with these catalysts. Further, ionic platinum in CeO(2) and Ce(1 -aEuro parts per thousand x) Ti (x) O(2) does not suffer from CO poisoning effect unlike Pt(0) in Pt/C due to participation of activated lattice oxygen which oxidizes the intermediate CO to CO(2). Hence, higher activity is observed toward formic acid and methanol oxidation compared with same amount of Pt metal in Pt/C.

V(2)O(5)-Anchored Carbon Nanotubes for Enhanced Electrochemical Energy Storage

Functionalized multiwalled carbon nanotubes (CNTs) are coated with a 4-5 nm thin layer of V(2)O(5) by controlled hydrolysis of vanadium alkoxide. The resulting V(2)O(5)/CNT composite has been investigated for electrochemical activity with lithium ion, and the capacity value shows both faradaic and capacitive (nonfaradaic) contributions. At high rate (1 C), the capacitive behavior dominates the intercalation as 2/3 of the overall capacity value out of 2700 C/g is capacitive, while the remaining is due to Li-ion intercalation. These numbers are in agreement with the Trasatti plots and are corroborated by X-ray photoelectron spectroscopy (XPS) studies on the V(2)O(5)/CNTs electrode, which show 85% of vanadium in the +4 oxidation state after the discharge at 1 C rate. The cumulative high-capacity value is attributed to the unique property of the nano V(2)O(5)/CNTs composite, which provides a short diffusion path for Lit-ions and an easy access to vanadium redox centers besides the high conductivity of CNTs. The composite architecture exhibits both high power density and high energy density, stressing the benefits of using carbon substrates to design high performance supercapacitor electrodes.

Temperature dependent transport studies in InN quantum dots grown by droplet epitaxy on silicon nitride/Si substrate

InN quantum dots (QDs) were fabricated on silicon nitride/Si (111) substrate by droplet epitaxy. Single-crystalline structure of InN QDs was verified by transmission electron microscopy, and the chemical bonding configurations of InN QDs were examined by x-ray photoelectron spectroscopy. Photoluminescence measurement shows a slight blue shift compared to the bulk InN, arising from size dependent quantum confinement effect. The interdigitated electrode pattern was created and current-voltage (I-V) characteristics of InN QDs were studied in a metal-semiconductor-metal configuration in the temperature range of 80-300K. The I-V characteristics of lateral grown InN QDs were explained by using the trap model. (C) 2011 American Institute of Physics. [doi:10.1063/1.3651762]

CO oxidation by CeO(2)-Al(2)O(3)-CeAlO(3) hybrid oxides

A modified solution combustion technique was successfully used to synthesize sub-10 nm crystallites of hybrid CeO(2)-Al(2)O(3)-CeAlO(3). The fuel in the solution combustion was tuned to obtain mixed oxides and solid solutions of the compound. The compounds were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. XRD and TEM analysis showed the substitution of Al(3+) ions in the CeO(2) matrix when a combination of glycine, urea, hexamine and oxalyl dihydrazide was used as fuel for the synthesis. The compounds showed high activity for CO oxidation and the activity of the compounds was dependent upon the composition of the oxide.

Effect of substrate bias voltage on the structure, electric and dielectric properties of TiO(2) thin films by DC magnetron sputtering

Titanium dioxide (TiO(2)) films have been deposited on glass and p-silicon (1 0 0) substrates by DC magnetron sputtering technique to investigate their structural, electrical and optical properties. The surface composition of the TiO(2) films has been analyzed by X-ray photoelectron spectroscopy. The TiO(2) films formed on unbiased substrates were amorphous. Application of negative bias voltage to the substrate transformed the amorphous TiO(2) into polycrystalline as confirmed by Raman spectroscopic studies. Thin film capacitors with configuration of Al/TiO(2)/p-Si have been fabricated. The leakage current density of unbiased films was 1 x10(-6) A/cm(2) at a gate bias voltage of 1.5 V and it was decreased to 1.41 x 10(-7) A/cm(2) with the increase of substrate bias voltage to -150 V owing to the increase in thickness of interfacial layer of SiO(2). Dielectric properties and AC electrical conductivity of the films were studied at various frequencies for unbiased and biased at -150 V. The capacitance at 1 MHz for unbiased films was 2.42 x 10(-10) F and it increased to 5.8 x 10(-10) F in the films formed at substrate bias voltage of -150 V. Dielectric constant of TiO(2) films were calculated from capacitance-voltage measurements at 1 MHz frequency. The dielectric constant of unbiased films was 6.2 while those formed at -150 V it increased to 19. The optical band gap of the films decreased from 3.50 to 3.42 eV with the increase of substrate bias voltage from 0 to -150 V. (C) 2011 Elsevier B. V. All rights reserved.

Kinetics and chemical analysis of photoinduced interdiffusion in nanolayered Se/As2S3 films

We have studied the kinetics of photoinduced effects in nanolayered Se/As2S3 film by in situ optical absorption measurements, which reveal that photodarkening in these films is followed by photoinduced diffusion. An increase in disorder during photodarkening and its subsequent decrease during photoinduced diffusion were also observed. The observation of photodarkening of Se at room temperature when confined between As2S3 layers suggests that the glass transition temperature of Se shifts to higher energy. The analysis shows that the atoms which take part in photodarkening play a vital role in photoinduced diffusion. The x-ray photoelectron spectroscopy measurements show the atomic movements during photoinduced diffusion. It also shows that some of the As–S bonds are converted into As–Se bonds. Since it is energetically difficult to break an As–S bond to form an As–Se bond, we assume that the new bond formations are taking place by the bond rearrangement mechanism.

Reactive pulsed laser deposition and characterization of niobium nitride thin films

We present a systematic study to explore the effect of important process variables on the composition and structure of niobium nitride thin films synthesized by Reactive Pulsed Laser Deposition (RPLD) technique through ablation of high purity niobium target in the presence of low pressure nitrogen gas. Secondary Ion Mass Spectrometry has been used in a unique way to study and fix gas pressure, substrate temperature and laser fluence, in order to obtain optimized conditions for one variable in single experimental run. The x-ray diffraction and electron microscopic characterization have been complemented by proton elastic backscattering spectroscopy and x-ray photoelectron spectroscopy to understand the incorporation of oxygen and associated non-stoichiometry in the metal to nitrogen ratio. The present study demonstrates that RPLD can be used for obtaining thin film architectures using non-equilibrium processing. Finally the optimized NbN thin films were characterized for their hardness using nano-indentation technique and found to be similar to 30 GPa at the deposition pressure of 8 Pa. (C) 2011 Elsevier B.V. All rights reserved.

Photocatalytic Activity of Combustion Synthesized ZrO(2) and ZrO(2)-TiO(2) Mixed Oxides

Tetragonal ZrO(2), synthesized by solution combustion technique, was found to be photocatalytically active for the degradation of anionic dyes. The compound was characterized by FT-Raman spectroscopy, X-ray photoelectron spectroscopy, FT-infrared spectroscopy, UV-vis spectroscopy, BET surface area analysis, and zero point charge pH measurement. A high concentration of surface hydroxyl groups was observed over the catalyst, as confirmed by XPS and FUR. The photocatalytic degradation of orange G, amido black, remazol brilliant blue R, and alizarin cyanine green (ACG) was carried out with this material. The effect of pH, inorganic. salts, and H(2)O(2) on the activity of the catalyst was also studied, and it was found that the catalyst maintained its activity at a wide range of pH and in the presence of inorganic salts. Having established that ZrO(2) was photocatalytically active, mixed oxide catalysts of TiO(2)-ZrO(2) were also tested for the photocatalytic degradation of ACG, and the 50% ZrO(2)-TiO(2) mixed oxides showed activity that was comparable to the activity of TiO(2).

Simulation and experimental study on compositional evolution of Li-Co in LiCoO2 thin films during sputter deposition

The compositional evolution in sputter deposited LiCoO2 thin films is influenced by process parameters involved during deposition. The electrochemical performance of these films strongly depends on their microstructure, preferential orientation and stoichiometry. The transport process of sputtered Li and Co atoms from the LiCoO2 target to the substrate, through Ar plasma in a planar magnetron configuration, was investigated based on the Monte Carlo technique. The effect of sputtering gas pressure and the substrate-target distance (dst) on Li/Co ratio, as well as, energy and angular distribution of sputtered atoms on the substrate were examined. Stable Li/Co ratios have been obtained at 5 Pa pressure and dst in the range 5−11 cm. The kinetic energy and incident angular distribution of Li and Co atoms reaching the substrate have been found to be dependent on sputtering pressure. Simulations were extended to predict compositional variations in films prepared at various process conditions. These results were compared with the composition of films determined experimentally using x-ray photoelectron spectroscopy (XPS). Li/Co ratio calculated using XPS was in moderate agreement with that of the simulated value. The measured film thickness followed the same trend as predicted by simulation. These studies are shown to be useful in understanding the complexities in multicomponent sputtering.

Supercapacitor studies on globular polypyrrole microstructures developed by a facile electrochemical route

Micrometre-scale polypyrrole (PPy) structures are synthesised for electrochemical supercapacitor applications by a facile electrochemical route. Globular polypyrrole microstructures of size < 5 μm are grown on stainless steel (SS-304) substrate by electro-polymerisation of pyrrole on oxygen microbubble templates electrochemically generated and stabilised in the presence of surfactant/supporting electrolyte/ dopant b-naphthalene sulfonic acid (b-NSA). Microstructures obtained with scan range of 0??1.6 V (against Ag/AgCl) are uniformly distributed over the surface with high coverage density of 5 x 105 to 8 x 10 cm-2. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the formed microstructures are of Β-NSA doped PPy. Scanning electron microscopy showed the uniform spread and good coverage of microstructures over the substrate. Supercapacitor properties of PPy films are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge methods with 1.0 M KCl as electrolyte in a three-electrode electrochemical cell. Specific capacitance of 583 Fg-1 is obtained, which is greater than the values (350-400 Fg-1 highest) usually reported for this material. Electrochemical impedance spectroscopy proves the superc

Supercapacitor studies on globular polypyrrole microstructures developed by a facile electrochemical route

Micrometre-scale polypyrrole (PPy) structures are synthesised for electrochemical supercapacitor applications by a facile electrochemical route. Globular polypyrrole microstructures of size <5 mu m are grown on stainless steel (SS-304) substrate by electro-polymerisation of pyrrole on oxygen microbubble templates electrochemically generated and stabilised in the presence of surfactant/supporting electrolyte/dopant beta-naphthalene sulfonic acid (beta-NSA). Microstructures obtained with scan range of 0-1.6 V (against Ag/AgCl) are uniformly distributed over the surface with high coverage density of 5 x 10(5) to 8 x 10 cm(-2). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the formed microstructures are of beta-NSA doped PPy. Scanning electron microscopy showed the uniform spread and good coverage of microstructures over the substrate. Supercapacitor properties of PPy films are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge methods with 1.0 M KCl as electrolyte in a three-electrode electrochemical cell. Specific capacitance of 583 Fg(-1) is obtained, which is greater than the values (350-400 Fg(-1) highest) usually reported for this material. Electrochemical impedance spectroscopy proves the supercapacitance behaviour and explains the special inductive component of impedance observed in the high-frequency regime because of the globular structures of PPy deposited

In-situ formation of graphene-lead oxide composite and its use in trace arsenic detection

Reduced graphene oxide-lead dioxide composite is formed when EGO coated surface is electrochemically reduced along with lead ions in the solution. This composite has been shown to be an excellent material for low level detection of arsenic. Various functional groups present on EGO, in a wide pH range of 2-11, are responsible for the favorable interaction between metal ion and the modified electrode surface and subsequent trace level detection. X-ray photoelectron spectroscopy and Raman spectroscopic techniques confirm the formation of composite and its composition. Thin layer of lead dioxide along with reduced exfoliated graphene oxide has been shown to be responsible for the enhanced activity of the surface. The detection limit of arsenic is found to be 10 nM. This study opens up the possibility of using the composites for sensing applications and possibly simultaneous detection of arsenic and lead. (C) 2011 Elsevier B.V. All rights reserved.

Mercury Segregation and Diselenide Self-Assembly on Gold

We have investigated the self-assembly of didecyldiselenide on gold containing mercury using X-ray photoelectron spectroscopy, cyclic voltammetry and infrared spectroscopy. The analysis of intensity and chemical shift of selected Se, Hg, and Au photoelectron lines on samples with increasing Hg content, show that didecyldiselenide adsorption strongly contributed to segregation of bulk Hg to the surface. The voltammetry results support this conclusion and suggest the formation of Hg-Au surface amalgam. The Hg surface segregation effect must be related to the restructuring of the surface following initial adsorption, and to the strong selenophilicity of Hg. The reflectance absorbance infrared spectroscopy studies show that the molecular layer on Hg-Au substrates lacks good order.

Antimicrobial Properties of Nanostructured TiO2 Plus Fe Additive Thin Films Synthesized by a Cost-Effective Sol-Gel Process

We prepared thin films composed of pure TiO2 or TiO2 with an Fe additive (at concentrations of 0.2-0.8 wt%) via a simple and cost effective sol gel process, and tested their antifungal properties (against Candida albicans (MTCC-1637), Candida tropicalis (MTCC-184), Candida parapsilosis (MTCC-2509), and Candida glabrata (MTCC-3019) and antibacterial properties (against Staphylococcus faecalis (NCIM-2604) Staphylococcus epidermidis (NCIM-2493), Staphylococcus aureus (NCIL-2122), and Bacillus subtilis (NCIM-2549)). The films were deposited on glass and Si substrates and subjected to annealing at 400 degrees C for 3 h in ambient air. The film structural and morphological properties were investigated by X-ray photoelectron spectroscopy profilometry and scanning electron microscopy, respectively. Antifungal and antibacterial tests were conducted using the drop test method. Among the species examined, Candida albicans (MTCC-1637), and Staphylococcus aureus (NCIL-2122) showed complete colony formation inhibition after exposure for 4 h for the TiO2 loaded with 0.8 wt% Fe thin films. These results indicate that increasing the Fe concentration increased the antimicrobial activity, with complete inhibition of colony formation after 4 h exposure.