Santosh K. Haram

Determination of Band Structure Parameters and the Quasi‐Particle Gap of CdSe Quantum Dots by Cyclic Voltammetry

Band structure parameters such as the conduction band edge, the valence band edge and the quasi-particle gap of diffusing CdSe quantum dots (Q-dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q-dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi-empirical pseudopotential method (SEPM)-especially in the strong size-confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q-dots, the difference between the quasi-particle gap and the optical band gap gives the electron-hole Coulombic interaction energy (J(e1,h1)). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.

Some aspects of the role of surfactants in the formation of nanoparticles

Abstract The role of surfactants in the formation of nanoparticles is due to the compartmentalization offered by host surfactant assemblies. They affect the growth and particle characteristics significantly. The preparation of Cu2S nanoparticles in reverse micelle and CuS in aqueous micellar hosts has been described. It indicates that different surfactant systems can mediate to give different products even though the basic chemistry is the same.

Chemical bath deposition of cubic copper (I) selenide and its room temperature transformation to the orthorhombic phase

The chemical bath deposition of cubic copper (I) selenide (Cu2-xSe), thin films has been achieved on an inert Pt substrate from a selenosulfite-containing bath at 75 °C. The electrochemical polarisation of this film at −0.78 V vs. SCE leads to the transformation of the compound into the orthorhombic phase. The lattice parameter of the face-centered cubic copper (I) selenide increases from 5.742 A to 5.761 A due to the decrease of the concentration of Cu vacancies upon electrochemical polarisation. The transformation of the cubic to an orthorhombic phase starts to occur when copper vacancies reach a critical value of x < 0.15. This transformation seems to be induced by a Cu3Se2 impurity in the cubic Cu2-xSe phase.

Electroless deposition on copper substrates and characterization of thin films of copper (I) selenide

Abstract Cuprous selenide films are prepared by reacting oxide free copper metal with selenous acid at room temperature (22°C). The formation of Cu(I) oxide is avoided by degassing the bath with argon. From the X-ray diffractograms (XRD) and electron probe microanalysis (EPMA) of such films it can be concluded that copper deficient, orthorhombic Cu(I) selenide is formed.

Electroless deposition of orthorhombic copper(I) selenide and its room temperature phase transformation to cubic structure

Abstract A phase transformation from orthorhombic copper (I) selenide to its cubic (superionic conducting) structure has been carried out at room temperature by controlling the parameters of the electroless deposition. X-ray diffraction analysis of the film suggests that it has Berzelianite structure with a lattice constant 5.719 ± 0.009 A . It is found to be a direct band-gap semiconductor with a band gap of 1.31 eV and having a resistivity of 0.52 × 10−3 Ω cm at 296 K. The transformation of cubic copper (I) selenide to orthorhombic copper (II) selenide and orthorhombic copper (I) selenide were carried out potentiostatically at +0.20 V and −0.78 V vs. saturated calomel electrode respectively. The lattice constants of orthorhombic copper (II) selenide have been evaluated from the X-ray diffraction data: a0 = 3.958 ± 0.11 A, b0 = 6.958 ± 0.017 A and c0 = 17.229 ± 0.025 A.

SWCNT/BiVO4 composites as anode materials for supercapacitor application

In this report, we have systematically investigated the effect of SWCNTs on the electrochemical performance of BiVO4: a material not studied for energy storage. Loading of 20 wt% SWCNTs with BiVO4 exhibited the highest specific capacitance (395 F g−1) and up to 88% coulombic efficiency was obtained over 200 cycles of charge–discharge for this composite.

Electrocatalyst on insulating support?: Hollow silica spheres loaded with Pt nanoparticles for methanol oxidation.

Electrocatalytic oxidation of methanol on silica hollow spheres, loaded with platinum nanoparticles (Pt-SiO2-HS), is reported. The functionalized hollow silica spheres were prepared by the surfactant (lauryl ester of tyrosine) template-assisted synthesis. These spheres were loaded with platinum nanoparticles by γ-radiolysis. Energy-dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS) analyses confirmed presence of Si and Pt in the composite. High-resolution transmission electron microscopy showed the formation of uniformly deposited Pt nanoparticles over the hollow spheres with a predominant Pt(111) lattice plane on the surface. In spite of the poor conducting nature of the silica support, the oxidation potential and current density per unit mass for methanol oxidation were noted to be ca. 0.72 V vs NHE and 270 mA mg(-1), respectively, which are among the best values reported in its class. The composite did not show any sign of a degradation even after repeated use. In fact, the anodic current was found to increase under constant polarization, which is attributed to a facile reaction between adsorbed CO with a surface hydroxyl group present on the silica support. These results are in favor of Pt-SiO2-HS as a promising electrocatalyst material in the direct methanol fuel cell (DMFC) applications.

Synthesis and analysis of ZnO and CdSe nanoparticles

Zinc oxide and cadmium selenide particles in the nanometer size regime have been synthesized using chemical routes. The particles were capped using thioglycerol in case of ZnO and 2-mercaptoethanol in case of CdSe to achieve the stability and avoid the coalescence. Zinc oxide nanoparticles were doped with europium to study their optical properties. A variety of techniques like UV-Vis absorption spectroscopy, X-ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to carry out structural and spectroscopic characterizations of the nanoparticles.

A facile methodology for the design of functionalized hollow silica spheres

A new amino acid derived amphiphile, lauryl ester of tyrosine (LET) is shown to provide a facile methodology for the preparation of hollow silica spheres. In a previous study on the interface adsorption, it was shown that phenolic OH group in LET plays a key role in the formation and stabilization of close packed structures, typically at the oil/water interface. Drawing an analogy between the air/water and the oil/water interface, we detail here a procedure where air droplets are capped with LET aggregated structures, and in turn they are utilized as viable templates in the production of hollow silica spheres. We demonstrate that hollow silica spheres are formed at pH 4.0 specifically under conditions of vortexing within a short period of time (ca. 15 min). The dimensions of the structures are 0.43±0.15 μm in diameter and they have then subsequently been used as templates for directing the synthesis of silica-silver and silica-polyanthranilic composite hollow spheres.

Reduction of graphene oxide by 100 MeV Au ion irradiation and its application as H2O2 sensor

Graphene oxide (GO) synthesized from a modified Hummers method was reduced (referred, rGO) by using 100 MeV Au ion species and its response to the sense H2O2 was investigated. The changes in the atomic composition and structural properties of rGO after irradiation were studied using x-ray diffraction, Fourier transform infrared spectroscopy and x-ray photo-electron spectroscopy. These results suggested that the removal of the oxygen-containing functional groups and the improvement of the electrochemical performance of reduced graphene oxide (rGO) after ion irradiation. Raman spectroscopic results revealed the increase in the disorder parameter (I D/I G) after Au ion irradiation and also the formation of a large number of small sp2 domains due to the electronic energy loss of ion beam. The resultant rGO was investigated for H2O2 sensing using electrochemical techniques and it showed a good response.