The effects of exposure to atmosphere (ageing) and light-soaking on coplanar dark- and photo-conductivity of silicon films of varying crystallinity are examined. Dark conductivity generally increases on ageing in films with significant amorphous fraction and decreases in largely crystalline films, and may be reversed by annealing under vacuum at 130 °C consistent with adsorption and desorption of atmospheric components. Thinner films are more strongly affected by ageing. Boron doping appears to compensate charge introduced by ageing, though there are disagreements in detail. In comparison with ageing, moderate light-soaking affects dark conductivity in transitional microcrystalline silicon films only slightly. Both processes change the majority carrier mu–tau product in line with shifts in Fermi level position.
J. Non-Cryst. Solids 352, p. 1075 (2006)

Measurements of dark conductivity, steady-state and transient photoconductivity in undoped and boron-doped microcrystalline silicon films exposed to room air are reported. Two aging processes are identified: (i) an increase in dark conductivity and mobility-lifetime product occurring over several days, that may be reversed by heating to 160 °C under vacuum, and subsequently re-cycled, (ii) an irreversible change in the density of states occurring over a period of several months. It is proposed that the reversible effect is associated with charge transport in a region of electron accumulation induced by weakly-adsorbed water, whereas the irreversible effect, identified from its transient photocurrent signature, is associated with a true change in the density of states within the transport path, possibly as a result of slow chemical reactions at silicon grain boundaries.
J. Non-Cryst. Solids 338, p. 421 (2004)

Due to need of pollution-free and efficient-power-generation devices, in past few years, pace of research has been rapidly driven by fuel cell technology. The thesis contributes in the same regard, in which conventional solid electrolyte of solid oxide fuel cell is replaced by alternate material (Gd-doped-Ceria-GDC) and its performance has been tested. The process parameters of ceramic route and spray-pyrolysis-technique were optimized to obtain dense ‘electrolyte-grade’ GDC-bulk and thin-film samples, respectively. In symmetrical cell configuration, GDC-bulk sample showed open-circuit-voltage of 0.84 volts at 500°C. The grain interior conductivity of 13μm GDC-film deposited onto electrode-grade NiO-GDC substrate is ~0.1S/cm at 500°C.

In the proposed research, it was decided to synthesize the GDC and to demonstrate its use in IT-SOFCs. Initially, it was planned to synthesize the bulk GDC and study its different properties. For this, solid state reaction method was preferred due to its cost effective nature and ease of preparation procedure. The commercially available initial precursor materials were used to synthesize the GDC bulk. The process parameters of solid state reaction method were varied along with doping percentage of gadolinia in ceria to demonstrate its effect on structural, morphological and electrical properties of the prepared samples. This study was expected to provide intimate knowledge of processing parameters of solid state reaction method and its effect on the final product. It was also decided to vary Gd content in ceria to recognize the optimum level of doping for better solid-electrolyte properties. Attempts were made to synthesize samples with best results in electrical performance with an intention to use it in IT-SOFCs. Thin films of GDC for optimum concentration of Gd in ceria were prepared using Spray Pyrolysis Technique (SPT) due to its simplicity, cost effective nature and ease of preparation procedure. In this part of research, it was planned, initially, to prepare GDC films onto glass substrate to understand the film growth mechanism. A systematic variation in different preparative parameters of SPT was considered to prepare the electrolyte-quality films. Further these films were characterized at each step of optimization procedure by XRD, SEM, EDAX, AFM, and were analyzed for better understanding of SPT. Moreover, to demonstrate the solid-electrolyte-grade qualities of GDC films, it was also planned to study its interfacial properties with one of the SOFC electrodes. For this purpose, initially, ceramic anode material (NiO-GDC) as ceramic substrates (flat and thin) was prepared using solid state reaction method. These ceramic substrates were characterized and analyzed for the desired composition, porosity, flatness and thinness. Further, the good-quality GDC films were prepared on to ceramic substrates by the SPT to form electrolyte\electrode structure. The characterization of formed structure (electrode/electrolyte) was carried out during each step of optimization of SPT; using various techniques, such as, XRD, SEM, EDAX, AFM, impedance spectroscopy, etc. These characterizations helped us to narrow down the range of preparative parameters of SPT and post heat treatments. These optimizations were resulted in GDC films with desired properties and a good quality interface with the anode substrate. The formed interface was characterized using impedance spectroscopy. Finally, the samples were characterized for open circuit voltage (OCV) measurements to test its performance in typical fuel cell conditions.

Development of soft chemical processes for the synthesis of interfacial architectures with well-defined structural nano-motifs organized over large areas in two dimensions is an important branch of nanotechnology. The present study deals with the fabrication of gold nanostructures using size-selective chemical etching of continuous gold films on glass support with titanium and chromium adhesive layers. In this process, which is called self-passivated surface etching, a gold film is etched in the presence of citric acid, resulting in gold nanostructures adhering to the metal support. The size-controlled chemical dissolution of gold is driven by a competing reaction between self-organized passivation of surface nano-motifs by citric acid shells and soft etching by a nonoxidative composition containing hydrochloric acid and hydrogen peroxide in water. According to these results, the presence of a chemically stable adhesive layer (titanium), citric acid in solution, and agitation are critical factors to be considered. However, the nature of the adhesive layer is the most influential factor. The following technique presents a simple method for the rapid fabrication of a nanostructured gold substrate that has the ability to support both propagating and localized surface plasmon resonances simultaneously.
Plasmonics 2010, 5, (4), 395-403.