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

Thermal Stability of Fluorocarbon Films Deposited from Pentafluoroethane/Argon Plasmas

Plasma deposited fluorocarbon films have received considerable attention recently as potential interlevel dielectrics for future generation integrated circuits (ICs). 1,2 Apart from their low dielectric constant (&lt;2.6), they also possess other favorable characteristics such as low moisture absorption, high chemical inertness, and plasma-assisted conformal step coverage. In this study, the effect of applied power and substrate temperature on the chemical structure, chemical composition, and thermal stability of the plasma-deposited fluorocarbon films was investigated by means of X-ray photoelectron spectroscopy (XPS), IR spectroscopy, and thermogravimetric analysis (TGA). The monomer studied, pentafluoroethane (CF 3 CHF 2 ), was selected because of its shorter atmospheric lifetime relative to that of pure fluorocarbon gases. Experimental A parallel-plate radio frequency (rf) plasma reactor was used for the deposition of fluorocarbon films from pentafluoroethane/argon mixtures. Details of the reactor setup and operation are given elsewhere, 7 so only a brief description is presented here. The distance between the 4 cm diam, parallel-plate, stainless steel disk electrodes was fixed at 2.9 cm for all experiments. RF power at 13.56 MHz from an ENI power systems HF-300 rf generator was coupled to the top electrode using a Heathkit SA-2060A antenna tuner. Substrates were placed on the grounded electrode whose temperature was regulated with a Syskon RKC temperature controller. Depositions were carried out at substrate temperatures of 120, 180, and 210ЊC, and a constant operating pressure of 1 Torr. The flow rates of pentafluoroethane and argon were set at 20 and 75 sccm, respectively, for all depositions. In some cases, films deposited at a specific substrate or deposition temperature were heated to 200ЊC in the reactor immediately after deposition and held there for 2 h in vacuum. In the following discussions, this heat-treatment of the deposited films in vacuum is referred to as postdeposition annealing. In this study, films deposited onto both the temperature-controlled, grounded electrode and the powered electrode without temperature control, were characterized by various analytical techniques including TGA, IR, XPS, and mass spectrometry. IR spectra of the deposited films were collected in reflection mode at a grazing angle of 70Њ using a Nicolet Magna-IR 560 Fourier transform infrared (FTIR) spectrometer. All spectra were recorded at a resolution of 4 cm Ϫ1 and averaged over 512 scans. In order to improve the signal-to-noise ratio, fluorocarbon films were deposited onto silicon substrates that had been sputter coated with a 300 nm layer of aluminum. Films deposited on the powered electrode were analyzed directly on the stainless steel powered electrode. XPS was used to obtain the chemical composition and bonding structure of polymer films. Spectra were collected using a PHI model 1600 XPS system equipped with a monochromator. The sample was exposed to monochromatized Al K␣ X-rays, and the ejected photoelectrons were detected by a multichannel hemispherical detector that provided high-energy sensitivity and resolution. Chamber pressure was typically below 5 ϫ 10 Ϫ9 Torr during analysis. High-resolution spectra were collected for C 1s, O 1s, N 1s, and F 1s Fluorocarbon films were deposited from pentafluoroethane/argon mixtures in a parallel-plate reactor at a pressure of 1 Torr and substrate temperatures between 120 and 210ЊC. Films deposited on substrates placed on the heated, grounded electrode as well as films formed on the powered electrode were analyzed using infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). Polymer deposition rates decreased with an increase in substrate temperature indicating that reactant adsorption is the rate-limiting step. Films deposited on the powered electrode had an O/C ratio of 0.14, which was significantly higher than that of films deposited on the grounded electrode at elevated temperatures. Likewise, IR spectra of films on the powered electrode also showed significant contributions from CϭO related groups. TGA data indicated that the powered electrode films had ϳ3% weight loss at 250ЊC, while films deposited on the grounded electrode had ϳ1% weight loss at 250ЊC. The thermal stability of films deposited on the grounded electrode was significantly enhanced when deposited at higher substrate temperatures. XPS analyses indicated a decrease in the F/C ratio of the deposited films with an increase in substrate temperature. TGA analyses indicated that weight loss below 250ЊC was due primarily to the outgassing of low-molecular weight species from the fluorocarbon films. The higher weight loss region between 320 and 425ЊC was ascribed to polymer degradation due to scission of main chain C-C bonds and to evolution of HF and CO 2