High-Contrast, High-Sensitivity Aqueous Base-Developable Polynorbornene Dielectric

ABSTRACT: The impact of multifunctional epoxy-based additives on the crosslinking, photolithographic properties, and adhesion properties of a tetramethyl ammonium hydroxide developable, polynorbornene (PNB)-based dielectric was investigated. Three different multifunctional epoxy additives were investigated: di-functional, tri-functional, and tetra-functional epoxy compounds. The tetrafunctional epoxy crosslinker enhanced the UV absorbing properties of the polymer at 365 nm wavelength. It was found that the epoxy photo-catalyst could be efficiently activated without a photosensitizer when the tetra-functional epoxy was used. The polymer mixture with additional (3 wt %) tetra-functional epoxy crosslinker and without a UV sensitizer showed improved sensitivity by a factor of 4.7 as compared to a polymer mixture containing the same number of equivalents of non-UV sensitive epoxy with a UV sensitizer. The contrast improved from 7.4 for the polymer mixture with non-UV absorbing epoxy and a UV sensitizer to 33.4 for the new formulation with 3 wt % tetra-functional epoxy and no UV sensitizer. The addition of the tetra-functional epoxy crosslinker also improved the polymer-to-substrate adhesion, which permitted longer development times, and allowed the fabrication of high-aspectratio structures. Hollow-core pillars were fabricated in 96-mm thick polymer films with a depth-to-width aspect-ratio of 14 : 1. The degree of crosslinking in the cured films was studied by nanoindentation and swelling measurements. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000-000, 201

Electrical conductivity, ionic conductivity, optical absorption, and gas separation properties of ionically conductive polymer membranes embedded with Si microwire arrays

The optical absorption, ionic conductivity, electronic conductivity, and gas separation properties have been evaluated for flexible composite films of ionically conductive polymers that contain partially embedded arrays of ordered, crystalline, p-type Si microwires. The cation exchange ionomer Nafion, and a recently developed anion exchange ionomer, poly(arylene ether sulfone) that contains quaternary ammonium groups (QAPSF), produced composite microwire array/ionomer membrane films that were suitable for operation in acidic or alkaline media, respectively. The ionic conductivity of the Si wire array/Nafion composite films in 2.0 M H_(2)SO_4(aq) was 71 mS cm^(−1), and the conductivity of the Si wire array/QAPSF composite films in 2.0 M KOH(aq) was 6.4 mS cm^(−1). Both values were comparable to the conductivities observed for films of these ionomers that did not contain embedded Si wire arrays. Two Si wire array/Nafion membranes were electrically connected in series, using a conducting polymer, to produce a trilayer, multifunctional membrane that exhibited an ionic conductivity in 2.0 M H_(2)SO)4(aq) of 57 mS cm^(−1) and an ohmic electrical contact, with an areal resistance of ~0.30 Ω cm^2, between the two physically separate embedded Si wire arrays. All of the wire array/ionomer composite membranes showed low rates of hydrogen crossover. Optical measurements indicated very low absorption (<3%) in the ion-exchange polymers but high light absorption (up to 80%) by the wire arrays even at normal incidence, attesting to the suitability of such multifunctional membranes for application in solar fuels production

Electrochemical Study of the Gold Thiosulfate Reduction

ABSTRACT The electrochemical reduction of gold thiosulfate has been studied and compared to the reduction of gold cyanide. Gold thiosulfate is a potential replacement for gold cyanide in electro and electroless plating baths. Gold thiosulfate has a more positive reduction potential than gold cyanide and eliminates the use of cyanide. The standard heterogeneous rate constant, transfer coefficient, and diffusion coefficient for gold thiosulfate reduction were found to be 1.58 &gt;&lt; 1O cm/s, 0.23 and 7 x 10 cm2/s, respectively. The effect of sulfite as an additive to gold thiosulfate solutions was examined

Experiences in deploying metadata analysis tools for institutional repositories

Current institutional repository software provides few tools to help metadata librarians understand and analyze their collections. In this article, we compare and contrast metadata analysis tools that were developed simultaneously, but independently, at two New Zealand institutions during a period of national investment in research repositories: the Metadata Analysis Tool (MAT) at The University of Waikato, and the Kiwi Research Information Service (KRIS) at the National Library of New Zealand. The tools have many similarities: they are convenient, online, on-demand services that harvest metadata using OAI-PMH; they were developed in response to feedback from repository administrators; and they both help pinpoint specific metadata errors as well as generating summary statistics. They also have significant differences: one is a dedicated tool wheres the other is part of a wider access tool; one gives a holistic view of the metadata whereas the other looks for specific problems; one seeks patterns in the data values whereas the other checks that those values conform to metadata standards. Both tools work in a complementary manner to existing Web-based administration tools. We have observed that discovery and correction of metadata errors can be quickly achieved by switching Web browser views from the analysis tool to the repository interface, and back. We summarize the findings from both tools' deployment into a checklist of requirements for metadata analysis tools

Nucleation of Electrodeposited Lithium Metal: Dendritic Growth and the Effect of Co-Deposited Sodium

Higher energy density batteries are desired, especially for mobile electronic devices. Lithium metal anodes are a possible route to achieving high energy and power density due to their light weight compared to current graphite anodes. However, whisker growth during lithium electrodeposition (i.e. charging) represents a serious safety and efficiency concern for both lithium metal batteries and overcharging of graphite anodes in lithium-ion batteries. The initial morphology of deposited lithium nuclei can have a significant impact on the bulk material deposited. The nucleation of lithium metal from an organic ethylene carbonate: dimethyl carbonate (EC:DMC) and an ionic liquid (trimethylbutylammonium bis(triflouromethanesulfonyl)imide) electrolyte has been studied. Whisker extrusion and tip-based dendrite growth was observed ex-situ, and confirmed by in-situ optical microscopy experiments. The nucleation of a non-dendritic sodium co-deposit is also discussed. A model based on nuclei geometry is provided which gives insight into the deposition rate at constant overpotential. The lithium metal anode was first used in a primary battery because of the metal&apos;s light weight and negative potential. When the anode was tested in a secondary battery, whiskers, also called dendrites, appeared upon recharging were identified as a hazard, leading to the safer graphite intercalation anodes commercialized in secondary batteries today. 1 Lithium whisker growth has been studied, but not fully understood. The mechanism of lithium dendrite growth and mitigation of dendrites is important in realizing a reliable lithium metal anode. Dendrite suppression has also become an important topic in overcharging lithium ion batteries with graphite intercalation anodes. It would be highly desirable to find mechanisms that prevent the formation of dendrites during the unintentional deposition of lithium. The morphology of electrodeposited and cycled lithium is a function of the electrolyte and electrochemical conditions. 2,3 Lower deposition rates tend to lead to moss-like lithium deposits and delayed dendrite growth. Higher deposition rates result in longer, entangled dendrites. Reliable suppression of dendrites has so far been achieved by confining the lithium electrode with a solid ceramic electrolyte, adding selected cations to form and electrostatic shield, and co-depositing metals such as sodium or potassium with lithium. The ceramic electrolyte solves the dendrite problem by providing a physical barrier to dendrite growth. While dendrites are known to grow through separators and even polymers, 2,8 the ceramic electrolyte is an effective physical barrier. Given the large inherent volume change in a lithium metal anode, maintaining contact with the metal electrode during discharge is problematic. 9 Ding et al. showed that adding a small concentration of Cs + , whose potential is slightly negative of that of lithium, creates an electrostatic shield that results in a dendrite-free lithium deposit. 11,12 Although dendrite growth can be suppressed or eliminated, knowledge about * Electrochemical Society Student Member. * * Electrochemical Society Fellow. z E-mail: [email protected] the lithium deposition process is important in order to suppress the growth of dendrites under a wide range of conditions. In addition, the recent papers on dendrite-free lithium deposits have coulombic efficiencies less than 100% and often in the 70 to 95% range. 9-12 Tip growth of dendrites can be electrochemically explained to some extent. It is commonly stated that a rupture in the SEI leaves fresh lithium metal exposed, which is the site for preferential plating leading to the formation of a protrusion. 17 Yamaki et al. present a mechanism where the SEI cracks due to stress from lithium being deposited underneath it. The stress caused by the SEI forces the movement of lithium along defects and grain boundaries. Lithium is forced out of the crack in the SEI, extruding a whisker. Continued growth occurs with lithium depositing on the substrate instead of the protruding whiskers for some time. Lithium then deposits on the tip and kink points of the growing whisker. This mechanism explains the morphology observed but it is hard to explain why, after the SEI rupture, lithium would continue to deposit through the SEI instead of on the freshly deposited lithium at the crack. The initial form of the metal deposit can be investigated by examining the morphology at different points in the electrodeposition process. When a potential is applied, nuclei populate the surface and begin to grow. The observed current is a direct result of the growing surface area available for deposition. Eq. 1 shows the basic form for the current, where N is the number of nuclei, k is the deposition rate in mol/(cm 2 s), n is the number of equivalents per mole, and F is Faraday&apos;s constant. i = Ar ea nuclei · N · kn

DOE STI Product/Final Report Number 3 Electrochemical Investigation of Novel Electrolytes for Ambient Temperature Sodium Batteries

The need for low-cost, high-energy density, durable, secondary batteries continues to rise with the demands of the electronics and automobile industries. A room-temperature version of the (high-temperature) ''Zebra Cell'' may provide an interesting technology for portable electronics and transportation. Sodium-based batteries have received attention as an alternative to the lithium-based batteries due to several factors including the absence of dendrite formation during sodium deposition and the abundance of sodium. This work focused on (1) the development of room-temperature ionic liquids (IL) for use in electrochemical devices, including batteries, (2) development and evaluation of secondary sodium batteries using room-temperature ILs, and (3) advancing the fundamental understanding of the electrochemical processes involving ILs and battery technology. Several objectives were accomplished during this program