Seminar Series. Fabrication and Characterization of Thin Film Nickel Hydroxide Electrodes for Micro Power Applications ABSTRACT.

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Fabrication and Characterization of Thin Film Nickel Hydroxide Electrodes for Micro Power Applications Hamid Falahati Micro power sources are very attractive for nano and micro scale devices, such as

In the present work, we report on the micro fabrication of patterned α Ni(OH) 2 films on glass substrates which can be used for rechargeable nickel metal hydride (NiMH) and nickel zinc (Ni Zn) micro

1 Fabrication and Characterization of Thin Film Nickel Hydroxide Electrodes for Micro Power Applications Hamid Falahati Micro power sources are very attractive for nano and micro scale devices, such as Point of Care medical diagnostics, where only low power densities are required. In the present work, we report on the micro fabrication of patterned α Ni(OH) 2 films on glass substrates which can be used for rechargeable nickel metal hydride (NiMH) and nickel zinc (Ni Zn) micro batteries aswellasfor micro capacitors. The patterned electrode is fabricated through multi layered films which are deposited by employing e beam evaporation, UV photolithography (using a negative KMPR photoresist), and electro deposition techniques. In detail, thin films of chromium and nickel (40nm) are deposited and used as the adhesion (seed) and current collector layers, respectively. NiOx/Ni(OH) 2 is electrodeposited from NiCl 2 solution followed by electro precipitation of Ni(OH) 2 films in Ni(NO 3 ) 2.6H 2 O aqueous solution to form a grid like patterned layer. The chemical composition and morphology of the micro electrodes are characterized by employing X Ray diffraction/fluorescence (XRD/XRF), Fourier Transform Infrared Attenuated Total Reflectance (FTIR ATR) spectroscopy, X Ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). The feature size of the grid like pattern is determined to be roughly 40 microns in height by using a mechanical profilometry technique. The electrochemical performances are studied via cyclic voltammetry (CV) and galvanostatic charge/discharge methods in a 1M KOH electrolyte. It is found that patterning the electrode results in 2~3 times higher charge content compared to the un patterned electrode. We also observe that electrode patterning improves the adhesion of the α Ni(OH) 2 film to the current collector layer. The electrode fabrication process and the characterization results will be presented.

2 Electrokinetically enhanced sampling of bacteria using quadrupolar microelectrodes Shiva Golchi The detection of biologically infectious agents, such as bacteria, in water is often a cumbersome process that can only be performed by trained personnel in a well equipped laboratory and may require sufficient time (sometimes days) until detectable concentration levels of the pathogen are reached. Recent progress has generated hope that portable microfluidic biosensors, similar to those used for blood glucose monitoring, will one day enable efficient detection of bacteria in portable laboratories. One promising class of such microdevices is the so called surface based biosensors. Their operation relies on the selective capture of the target pathogen from a liquid sample onto the detection surface (a process called sampling ) and their subsequent detection via signal transduction. Sampling currently presents a major bottleneck in the successful operation of these sensors as it relies on the extremely slow diffusive transport of the target particle from the bulk of the sample to the capture surface. When bacteria are present at low concentrations (e.g., <10 3 ml 1 )these sensors suffer from slow detection or even detection failure. The present work investigates how electric field effects produced by planar microelectrode arrays embedded into the sensor s surface can help overcome existing the pathogen transport limitations, thus enabling rapid detection of the target particles. Specifically, numerical and experimental work will be combined toward the analysis of a host of electric field generated phenomena (electrophoresis, electroosmosis, and electrothermal fluid flow) that can potentially guide and enhance the transport of K12 E. coli bacteria to the sensor s surface inside an alternating current (AC) electric field. Proof of principle demonstrations on how antibody functionalized microelectrode arrays can accelerate and selectively capture K12 bacteria (target pathogens) from samples containing debris or mixed bacteria populations will also be demonstrated.

3 Studying the Water Sorption Properties of Ultra thin Nafion Films using a Quartz Crystal Microbalance Key Shim Polymer electrolyte membrane fuel cells (PEMFCs) utilized ion conducting polymers or ionomers for transport of protons within the catalyst layer (CL) and through the PEM from the anode to the cathode. The PEM is a free standing ionomer membrane of thickness greater than 25 microns. On the other hand, the ionomer in the CL is 4 10 nm film covering the platinized carbon aggregates. The most commonly employed ionomer in PEMFCs is Nafion. The proton transport in the Nafion ionomer is water mediated. Whereas much research has been conducted to understand the water transport phenomena in the bulk Nafion membrane (>25 μm), there is limited data and understanding of water behavior in ultra thin Nafion films (<50 nm). Using a Quartz Crystal Microblance, the water sorption properties of self assembled ultra thin Nafion films will be examined.the effect of substrate,thickness, and annealing on the water sorption properties will also be investigated.

4 Computational Analysis of the Reacting Flow in a Micro Structured Reformer Using a Multi Scale Approach Ali Naseri A multi scale methodology is presented to analyze the transport and reaction processes in the catalyst coating of a microstructured reformer and to elucidate the effect of catalyst morphology on transport limitations and the reformer performance. This analysis includes three dimensional simulations of methane steam reforming at both reactor level and catalyst microstructure level. Hypothetical catalyst microstructures are generated using an in house particle packing code. Based on the generated structures, the effective transport properties of the porous catalyst and the average reaction rates in the microstructure are determined to be applied in the pseudo homogeneous model used in the macro scale simulation. Parametric study is done to demonstrate the significant effect of the catalyst intra particle, inter particle porosity and the particle size on the effectiveness factor and methane conversion. This study shows that an optimal catalyst coating has a decreasing porosity along the reformer length based on the difference in the degree of diffusion limitation.

5 Electroosmotic flow in porous borosilicate material Rakesh Saini Electrical charges originate at many solid surfaces in contact with liquids. The surface charges attract mobile countercharges in the liquid, usually ions. The accumulation of counter ions in vicinity to the solid surface results in violation of the liquid s electro neutrality. This liquid domain, where we can find an excess of counter ions over co ions, is called the Electrical Double Layer (EDL). When we apply an external electric field tangential to the EDL, an electroosmotic flow is induced. This phenomenon can be employed in microfluidic systems where often highly porous materials are used as they are quite capable of generating significant flow rates and pressures. Most of the models used to analyze electroosmotic flow through porous media are based on the so called parallel capillary flow model. In terms of porous packed beds, these models have the disadvantages of simplifying the geometry to tortuous capillaries, while neglecting intra porous connections, varying pore geometries and the influence of the packed bed walls. In the current research, we employ dimensional reasoning (Buckingham PI theorem) to derive semi empirical correlations which relate the electroosmotic flow to the characteristics of packed bed material, structure and liquid parameters. Experiments are carried out using a relatively simple and cost effective set up including different sets of packed beds having a wider range of porosities. These packed beds are prepared by sintering of borosilicate glass micro spheres. Various experiments are performed with varying applied electric field, porosity of the packed bed and zeta potential. The zeta potential is the representative parameter of the EDL and can be varied by using Sodium Chloride electrolyte solutions having different ionic strengths and ph values. To determine the zeta potential independently, the so called streaming current method is used for borosilicate wafers having similar chemical composition as the micro spheres in the packed beds. Here an in house designed parallel plate cell based set up is used to measure streaming current values at increasing pressure.

6 FRAP measurements of solute diffusion through hydrogels Nick Hadjiev Diffusion is fundamental to the migration of agents such as nutrients, signaling molecules, and drugs in the body. In recent years, extensive efforts have been devoted to the development of site specific drug delivery systems to prolong, localize, and treat diseased tissue.among numerous systems, which have been employed as vehicles or rate controlling barriers, the hydrogel has gained considerable interest for its unique properties and potential biocompatibility. In drug delivery, the distribution of therapeutic agents prior to release from a carrier like the hydrogel directly influences their rate of absorption at the desired site of action. It is, therefore, useful to be able to predict the diffusion coefficient of these molecular compounds in hydrogels. The obstruction model demonstrates excellent predictive capabilities for solute diffusion in polymer solutions using an assortment of molecular agents as shown through the work of Zhang and Amsden. Its application assumes that the mobility of an individual chain in a polymer network is substantially limited relative to the velocity of a mobile probe. To extend its application to hydrogels, the model relies on the assumption that the physical properties of a polymer in the gel state are analogous to those in the solution state. This research strives, on one hand, to confirm the validity of this assumption by comparing the predictions of the obstruction model to fluorescence recovery after photobleaching (FRAP) measurements of FITC dextran (MW: 4, 10, 20, 40 KDa) in alginate hydrogels; and the other, to assess the utility of the obstruction model as a working tool for diffusion estimates that may describe a wide variety of hydrogels. The model was tested against a custom FRAP protocol and found to provide a good fit for FITC dextran4,10,and20kdainhydrogelsofvaryingcross link density. The data reveals an inconsistency between the observed and the predicted in cases when the solute radius of the probe would exceed the correlation length of the polymer network, i.e. FITC dextran 40 KDa. This inconsistency was attributed to reptation effects of the dextran agents.

Chapter - 8. Summary and Conclusion

Chapter - 8. Summary and Conclusion Chapter - 8 Summary and Conclusion The present research explains the synthesis process of two transition metal oxide semiconductors SnO 2 and V 2 O 5 thin films with different morphologies and studies