Micro and Nanosystems - Volume 4, Issue 3, 2012

Electrochemical behavior of electro-generated poly-pyronin B (PyB) film was reported at a screen-printed carbon electrode (SPCE). The poly(PyB) modified SPCE showed excellent redox activity in neutral and alkaline media. Surface topography of poly(PyB) film modified electrode was analyzed by using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Poly(PyB) film coated electrode was characterized by electrochemical impedance spectroscopy (EIS), UV–visible absorption spectroscopy (UV–vis) and cyclic voltammetry (CV). The poly(PyB) modified electrode showed electrocatalytic response to the reduced form of nicotinamide adenine dinucleotide (NADH) in physiological condition, and was used for the detection of NADH with high selectivity. The anodic peak current was linearly related to concentrations of NADH over the range from 1x10-5 M to 5.2x10-4 M, and the detection limit was 5x10-7 M (S/N = 3).

An alternate energy storage device for high power applications are supercapacitors. They store energy either by pure electrostatic charge accumulation in the electrochemical double layer or as pseudo capacitance from fast reversible oxidation reduction process. However, they have low energy density. The electrodes in the Electrochemical Double Layer Capacitors (EDLC) are made of high surface area carbon. The carbon that can be used range from activated carbon to Graphene, with varying particle size, surface area, pore size and pore distribution. The main emphasis in the development of EDLCs is fabrication of electrodes having high surface area which would enhance the storage density of the EDLC. The EDLCs are assembled with different electrolytes which determine the operational voltage. Solid electrolytes can also be used as electrolyte and have an advantage in that we can avoid electrolyte leaks and are easy to handle. This would improve the reliability. They can also be shaped and sized to suit the application. The perflurosulfonic acid polymer as electrolyte has been used by various groups for EDLC application. The perflurosulfonic acid polymer possesses high ionic conductivity, good thermal stability, adequate mechanical strength and excellent chemical stability. The EDLCs, which are based on high-surface area carbon materials, utilize the capacitance arising from a purely non-Faradaic charge separation at an electrode/electrolyte interface. Carbon is widely used for many practical applications, especially for the adsorption of ions and molecules, as catalyst supports and electrode materials. The chemical characteristics of carbon determine the performance in all these applications. It is now possible to synthesize one-, two-, or three-dimensional (1-, 2-, or 3-D) carbons. Thus, carbon materials are very suitable candidates for super capacitor electrodes. We can overcome some of the problems in activated carbon like varying micro or meso pores, poor ion mobility due to varying pore distribution, low electrical conductivity, by using Graphene. Many forms of Graphene have been used by various groups. Graphene nanoplates (GNP), with narrow mesopore distribution have been effectively used to enhance charge storage performance. It has been found that graphene shows smaller decrease in storage capacity with increasing scan rate.

IrO2 as an anodic electrocatalyst for the oxygen evolution reaction (OER) in solid polymer electrolyte (SPE) electrolysers was synthesised by adapting the Adams fusion method. Optimisation of the IrO2 electrocatalyst was achieved by varying the synthesis duration (0.5 – 4 hours) and temperature (250 - 500°C). The physical properties of the electrocatalysts were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD). Electrochemical characterisation of the electrocatalysts toward the OER was evaluated by chronoamperometry (CA). CA analysis revealed the best electrocatalytic activity towards the OER for IrO2 synthesised for 2 hours at 350°C which displayed a better electrocatalytic activity than the commercial IrO2 electrocatalyst used in this study. XRD and TEM analyses revealed an increase in crystallinity and average particle size with increasing synthesis duration and temperature which accounted for the decreasing electrocatalytic activity. At 250°C the formation of an active IrO2 electrocatalyst was not favoured.

Development of reliable method for the green synthesis of gold nanoparticles (AuNPs) using medicinally valued Adhatoda vasica Nees has been studied here. The color change and the Surface Plasmon Resonance (SPR) confirmed the formation of AuNPs. The biosynthesized AuNPs were characterized using UV-visible Spectroscopy (UV-vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDAX) and Transmission Electron Microscopy (TEM) analysis. The nanoparticles synthesized were predominantly monodisperse, stable spherical in nature with well-defined dimensions of size ranging from 22 to 47 nm. The crystalline nature of the synthesized particles was also evident by the X-ray diffraction analysis.

Titanium nitride (TiN)/nickel (Ni) composite coatings were synthesized by plasma assisted metal-organic chemical vapour deposition (PAMOCVD) using organo-metallic and metal-organic complexes namely dichlorobis(η5- cyclopentadienyl)titanium (IV) for titanium and N,N'-ethylene-bis(2,4-pentanedion-iminoato)nickel(II) for nickel. The growth of such films was investigated in nitrogen (N2) plasma environment in the substrate temperature range of 450- 550ºC at a deposition pressure of 0.5-1 mbar. Prior to the deposition of films, the Ti precursor was subjected to the equilibrium vapour pressure measurements by employing TG/DTA in transpiration mode, which led to the value of 109.2 ± 5.6 kJ mol-1 for the standard enthalpy of sublimation (ΔHo sub). The phase identification using glancing incidence x-ray diffraction showed Ni/TiN is a nanocomposite coating containing nanocrystals of Ni and TiN with face centered cubic structure. Scanning electron microscopy revealed a uniform surface morphology of the films, while chemical analysis by energy dispersive analysis confirmed the presence of titanium, nickel and nitrogen in the composite films.

Analysis of a flexible capacitive microsensor is described to measure both normal and shear forces simultaneously and instantaneously for the potential application of gait analysis. The microsensor consists of two pairs of sensing electrodes and an in-between dielectric layer. When normal force is applied to the microsensor, the capacitances of two sensing electrodes increase because of the uniform compression of the dielectric layer. When shear force is applied, deformation of the dielectric layer induces the capacitance difference between two sensing electrodes. Therefore, by measuring the capacitance values and capacitance difference, the normal and shear force can be determined directly and simultaneously. Since the microsensor is designed for measuring large forces, polydimethylsiloxane (PDMS) is selected as the material of the dielectric layer because it has the advantages of high dielectric constant and tunable elasticity. But PDMS is an elastic material that has highly non-linearity of stress-strain relationship. In this work, PDMS characterization was conducted to investigate the stiffness under different mixing ratios of PDMS pre-polymer and the curing agent. PDMS in 16:1 mixing ratio was selected since it has the most linear stress-strain relationship with the highest elasticity based on our results. Hence, analysis of mechanical and electrical properties of the microsensor was performed and the capacitance changes under normal and shear stresses were calculated. The microsensor was design to support the maximum normal stress of 1.39MPa and shear stress of 85KPa based on the requirement of foot pressure measurement. The microsensor is designed using flexible materials and it is easy to access to the curved surface to measure its interfacial force with minimum disturbance. It has the potential to develop portable real time microsensor for many biomechanical applications.

Calcium sulfate crystals with microrod morphology have been synthesized by a simple hydrothermal process using calcium oxide and sodium sulfate as the raw materials. X-ray diffraction, scanning electron microscopy and infra-red spectrum have been used to characterize the calcium sulfate crystals with microrod morphology. The calcium sulfate crystals with microrod morphology possess orthorhombic CaSO4 phase and the diameter and length are 500 nm-10 μm and 10-100 μm, respectively. The hydrothermal temperature and reaction time play essential roles on the formation and size of the calcium sulfate crystals with microrod morphology. The nucleation and crystalline growth process are proposed to explain the formation and growth of the calcium sulfate crystals with microrod morphology.

Zinc Oxide(ZnO) thin films with appropriate thickness (300nm) were produced with repeated coating of Zinc(Zn) film followed by thermal oxidation ,(multi-layer,100+100+100, 200+100, 300 nm). The effect of this way of deposition on the optical and the structural properties of ZnO thin films are investigated. The sample, which was obtained with three steps of coating, showed higher transmittance and lower structural defects due to a lower Urbach energy and photoluminescence intensity and also it showed good optical stability with temperature and period of annealing. To study the structural characterization X-Ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) of the produced ZnO samples were carried out and the obtained results from these analysis on the grain size studies showed good agreements.

ZnSe quantum dots of three narrow size distributions are prepared through an environmentally friendly chemical route. Then the samples are systematically characterized by UV-Vis absorption spectroscopy and transmission electron microscopy. UV-Vis absorption spectra reveal blue shift of 0.56 eV, 0.19 eV and 0.02 eV respectively indicating strong quantum confinement while transmission electron micrograph displays images of ZnSe quantum dots in the samples in the ranges 2-5 nm, 3-7 nm and 4-8 nm respectively. Then optical emission is studied by fluorescence and electroluminescence spectroscopy. Both the luminescence studies are in good agreement with one another with output peak in and around violet-blue region. Hence, ZnSe quantum dots can be used as efficient LED with better compatibility and faster response.

The characteristics of perovskite-structure oxides and its role in the reforming of hydrocarbons are presented in this review. The main difficulties in these processes have been pointed as the coke formation, sulphur poisoning and thermal stability of metallic particles. In this context, the perovskite structure ABO3 represents attractive systems for those catalytic processes due to their easy-to-control physical and chemical properties derived from the wide range of ions and valences which can be accommodated in their structure. The B-site metal in perovskite oxide forms the primary active site, while the A-site metal has a strong effect on the stability. An overview is provided about perovskites studies (selection of formulation and control of the synthesis of perovskites for customising the crystallinity, electronic structure and morphology of catalysts at nanometric scale) adopted in the search for reforming catalysts that respond to the above challenges). Catalysts for reforming from perovskites have made remarkable progress in recent years, but there are various technical challenges, mainly activity and durability, that need to be addressed for future improvement.