Manjunatha Pattabi

Synthesis of cadmium sulphide nanoparticles

Nanoparticles form a link between molecular and bulk state of matter and exhibit size dependent physical and chemical properties. A novel technique of synthesizing nanoparticle films on biological membrane substrates is presented here. Cadmium Sulphide (CdS) nanoparticles were prepared by the chemical reaction of aqueous solutions of Cadmium Acetate and Thiourea. The reacting solutions were allowed to diffuse across the membrane for different periods to control the deposition time. The optical absorption spectra of the membrane after the reaction were recorded with bare membrane as reference. The optical absorption spectra show a clear shift in the absorption edge for films with different deposition times at a fixed concentration. The band gaps calculated from the absorption spectra for films with smaller deposition time were higher than that for the bulk CdS. The particle size, estimated from the band gaps, lie in the nanometer range showing that the particle size and band gap can be tailored by controlling the deposition time and concentration of the precursors.

Structural studies on silver cluster films deposited on softened PVP substrates

Abstract The deposition of metal cluster films on softenable polymer substrates is known to lead to subsurface particulate structure formation for many metal/polymer combinations. The nature of the subsurface film structure is critically dependent on deposition conditions such as polymer substrate temperature, film deposition rate, etc. and the influence of these parameters is now fairly well understood. In this paper, we show that the metal–polymer interaction is a very important parameter which can be used to control the particle size as well as the inter-cluster separation through an investigation of silver cluster films deposited on softened poly(2-vinylpyridine), PVP. The increased wettability of silver in the PVP matrix leads to the formation of relatively small islands separated by small gaps which is in contrast to silver films deposited on polystyrene which yielded highly agglomerated structures with large inter-island separations. The silver/softened PVP film structure has been characterized by scanning electron microscopy (SEM). Further evidence for significant overlap of the electronic properties of the clusters was obtained from electron tunneling measurements as well as by optical absorption spectroscopy. The depth of the silver clusters below the surface was estimated from angle dependent X-ray photoemission spectroscopy (XPS) to be ≈5 nm. The ability to control the particle size as well as to tune the interaction between clusters by varying the metal wettability in the polymer matrix is an aspect of the work which shows promise for further development.

Electrical conductivity and thermoelectric power of amorphous Sb2Te3 thin films and amorphous-crystalline transition

The results of electrical conductivity and thermoelectric studies on antimony telluride, a promising thermoelectric material, in the thin film state are reported. Films were vacuum-deposited on to clean glass substrates with thickness between 50 and 200 nm and studied in the temperature interval 300 to 470 K. On heating the as-grown films, there is a sharp fall both in the Seebeck coefficient and the electrical resistivity at around 340 to 370 K for all the films. This is attributed to an amorphous to crystalline transition, which is confirmed by X-ray diffractogram and electron diffraction patterns.[/p]

Preparation and characterization of silver particulate structure deposited on softened poly(4-vinylpyridine) substrates

Results of the investigations carried out on particulate silver films, deposited at a rate of 0.4 nm s-1 on poly(4-vinylpyridine) coated substrates held at temperatures in the range 440-490 K in a vacuum of 8 × 10-6 Torr are reported in this paper. A morphological study by scanning electron microscopy and x-ray diffraction was further confirmed by optical absorption studies. The shift in the plasmon resonance towards longer wavelength is ascribed to polymer-metal particle interactions. Electrical resistances immediately after deposition and at room temperature show a regular dependence on the thickness for the films in the temperature range studied. The films deposited at lower substrate temperatures show a lower negative temperature coefficient of resistance when compared to films deposited at higher substrate temperatures. X-ray photoelectron spectroscopy studies indicate the formation of a sub-surface particulate structure at higher substrate temperatures.

Electrochemical characterization of tungsten carbonyl compound for oxygen reduction reaction

Abstract The results of electrochemical studies carried out on Wx(CO)n electrocatalyst are presented in this article. Wx(CO)n was synthesized from W(CO)6 in xylene at 140°C. The kinetic studies were carried out in 0.5 M H2SO4 solution under a three-electrode configuration. Linear voltametry studies on Wx(CO)n reveal significant catalytic activity of the material for oxygen reduction. Koutecky–Levich analysis of the voltametry data shows that the reaction follows first-order kinetics and the value of the Koutecky–Levich slope indicates a multi-electron charge transfer in the oxygen reduction reaction. The value of Tafel slope is found to be −120 mV / decade from the mass-transfer-corrected Tafel plots. The charge transfer coefficient and exchange current density were found to be 0.66 and 8.4×10 −5 A/cm 2 , respectively.

Preparation and characterization of copper indium diselenide films by electroless deposition

The preparation of copper indium diselenide (CIS) films by electroless deposition technique is reported. The films have been deposited on molybdenum substrates. The deposition bath consisted of aqueous solutions of copper chloride, indium chloride, selenous acid and lithium chloride. The pH of the bath was adjusted to 2.2 by adding dilute HCl. The Mo substrate was short-circuited with the aluminum counter electrode for the electroless deposition. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), inductively coupled plasma spectroscopy (ICP), Auger electron spectroscopy (AES) and optical spectroscopy. The results indicate that reasonable quality CIS films can be grown by simple electroless deposition process followed by recrystallization in selenium atmosphere.

Aging studies on discontinuous silver films in ultrahigh vacuum

Abstract The results of aging studies carried out on discontinuous silver films deposited on glass substrates held at room temperature in a vacuum of 2×10 −8 Torr are presented in this article. The films were prepared by electron beam deposition at a rate of 0.2 A/s. Discontinuous silver films show considerable aging for extended period even in a clean ultrahigh vacuum (UHV) obtained using a turbomolecular pump when the oxygen partial pressure is as low as 10 −11 Torr, thus ruling out the possibility of oxidation being responsible for the aging in these films. The coalescence rate values in UHV and in a vacuum of 2×10 −6 Torr obtained using an oil diffusion pump are nearly the same. This indicates that the aging of island films is not due to oxidation. A film with an initial resistance of 2 MΩ/□ showed a drastic fall in resistance after about 30 min of aging. This interesting discontinuous–semicontinuous transition observed in a conservative system is a clear evidence for the mobility of islands.

Preparation and characterisation of silver particulate films on softened polystyrene substrates

The preparation of silver particulate films on softened polystyrene (PS) substrates and their characterisation using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and optical absorption spectroscopy is reported in this paper. Silver films of 150 nm thickness were vacuum deposited onto PS coated glass substrates held at temperatures in the range 415-475 K at different deposition rates of 4 to 12 A/s. SEM studies indicate that films deposited at 415 K are close to a semicontinuous structure and the structure is discontinuous at higher temperatures. The film morphology is strongly dependent on the deposition rate at any given substrate temperature. The film agglomeration increases with increasing rate of deposition. In the XPS studies, considerable attenuation of the signal corresponding to silver is observed at lower electron take of angles (ETOAs). This indicates that Ag is formed beneath the PS surface. Optical absorption studies showed an interesting red shift of the plasmon resonance wavelength for lower deposition rates again indicating that a sub-surface particulate structure is formed at lower deposition rates. These results are consistent with reported observations.

Synthesis and characterization of thiosalicylic acid stabilized gold nanoparticles

We report the synthesis of photoluminescent Au nanoparticles of varying sizes stabilized with a carboxylate group terminated aromatic thiol, thiosalicylic acid. The formation of Au nanoparticles and its stabilization with the thiol has been characterized by different spectroscopic and thermal methods. The water solubility, along with the low degree of aggregation and photoluminescence, enhances their suitability for biological applications. The photoluminescence may be due to charge transfer of the Au core with the stabilizing ligand.

Photoelectrochemical characterization of SiC

The current-voltage (I-V) studies for p-SiC in KOH and n-SiC in Na 2 SO 3 in a two-electrode configuration indicated that SiC-based photoelectrochemical systems can be a possibility for water splitting. With illumination there is appreciable photocurrent generation at the semiconductor-electrolyte interface, which correspond to water splitting to form hydrogen and oxygen at the respective electrodes. The C-V analysis gave an idea about the flat-band potential and carrier concentration.