Influence of electrode structure on the performance of a direct methanol fuel cell

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin film and a traditional catalyst layer. A decal transfer method was used to apply the thin film to the Nafion(R) membrane. Results show that the performance of a cell with the hydrophilic thin film is obviously enhanced. A cell with the optimal thin film electrode structure operating at I M CH3OH, 2 atm oxygen and 90degreesC yields a current density of 100 mA/cm(2) at 0.53 V cell voltage. The peak power density is 120 mW/cm(2). The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin film was employed. (C) 2002 Elsevier Science B.V. All rights reserved.

Structure and properties of samarium overlayer and Sm/Rh surface alloy on Rh(100)

The structure and properties of Sm overlayer and Sm/Rh surface alloy have been investigated with Auger electron spectroscopy (AES), low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption spectroscopy (TDS). The growth of Sm on Rh(100) at room temperature (RT) appears following the Stranski-Krastanov growth mode and only the trivalent state Sm is observed from XPS results. Thermal treatment of the Sm film at 900 K leads to the formation of ordered surface alloy which shows the c(5 root2 x root2)R45 degrees and c(2 x 2) LEED patterns. Annealing the Sm film at temperature above 400 K makes the binding energy (B.E.) of Sm 3d(5/2) shift to higher energy by 0.7 eV, which indicates charge transfer from Sm to Rh(100) substrate, causing the increase of CO desorption temperature.

Development of block copolymer lithography for device structure fabrication

This thesis investigated well-ordered block copolymer (BCP) thin film characteristics and their use for nanoscale pattern formation using a series of polystyrene-block-polymethylmethacrylate (PS-b-PMMA), polystyrene-blockpolydimethylsiloxane (PS-b-PDMS) and polystyrene-block-poly(ethylene oxide) (PS-b-PEO) systems of various molecular weights. BCP thin films, which act as an ‘on-chip’ etch mask and material templates, are highly promising self-assembling process for future scalable nanolithography. Unlike conventional BCP processing methods, the work in this thesis demonstrates that well-ordered patterns can be achieved in a few seconds compared to several hours by use of a non-conventional microwave assisted technique. As a result, well-ordered BCP nanoscale structures can be developed in industry appropriate periods facilitating their incorporation into current technologies. An optimised and controlled plasma dry etch process was used for successful pattern transfer to the underlying silicon substrate. Long range ordered BCP templates were further modified by selective metal inclusion technique to form a hard mask template towards fabrication of high aspect ratio nanopillars and nanowires. The work described here is centred on how these templates might be used to generate function at substrate surfaces. Herein we describe a number of innovations which might allow their successful uptake in a number of applications.

Observation of C60 film formation on a highly oriented pyrolitic graphite substrate via scanning tunnelling microscopy

We have investigated the early stages in the adsorption process of C60 molecules on a highly oriented pyrolitic graphite (HOPG) substrate. C60 powder was thermally evaporated in UHV of 10−8 Pa conditions onto a freshly cleaved HOPG surface. We did not observe individual fullerenes on the substrate for the case of short deposition times and low evaporation rates. However, small islands of C60 molecules with an fcc structure could be observed when the deposition rate was about 0.2 nm/min and the total thickness was above 1 nm. The islands did not grow in the vicinity of the HOPG steps. The typical lateral dimensions of these islands were of the order of a few hundred square nanometers, having thickness of up to five monolayers. We modified the shapes and positions of these islands by the STM tip, using a small (less than 1 V) bias voltage.

Investigation of dead-layer thickness in SrRuO3/Ba0.5Sr0.5TiO3/Au thin-film capacitors

Thin-film capacitors, with barium strontium titanate (BST) dielectric layers between 7.5 and 950 nm in thickness, were fabricated by pulsed-laser deposition. Both crystallography and cation chemistry were consistent with successful growth of the BST perovskite. At room temperature, all capacitors displayed frequency dispersion such that epsilon (100 kHz)/epsilon (100 Hz) was greater than 0.75. The dielectric constant as a function of thickness was fitted, using the series capacitor model, for BST thicknesses greater than 70 nm. This yielded a large interfacial d(i)/epsilon (i) ratio of 0.40 +/-0.05 nm, implying a highly visible parasitic dead layer within the capacitor structure. Modeled consideration of the dielectric behavior for BST films, whose total thickness was below that of the dead layer, predicted anomalies in the plots of d/epsilon against d at the dead-layer thickness. In the capacitors studied here, no anomaly was observed. Hence, either (i) 7.5 nm is an upper limit for the total dead-layer thickness in the SRO/BST/Au system, or (ii) dielectric collapse is not associated with a distinct interfacial dead layer, and is instead due to a through-film effect. (C) 2001 American Institute of Physics.

Near-field distribution of optical transmission of periodic subwavelength holes in a metal film

Optical transmission of a two-dimensional array of subwavelength holes in a metal film has been numerically studied using a differential method. Transmission spectra have been calculated showing a significant increase of the transmission in certain spectral ranges corresponding to the excitation of the surface polariton Bloch waves on a metal surface with a periodic hole structure. Under the enhanced transmission conditions, the near-field distribution of the transmitted light reveals an intensity enhancement greater than 2 orders of magnitude in localized (similar to 40 nm) spots resulting from the interference of the surface polaritons Bragg scattered by the holes in an array.

Studies on polypyrrole film in room temperature melt

A bluish-black shining free standing polypyrrole film (PPy) of electronic conductivity 130 S cm-1 has been prepared by electrochemical oxidative polymerization of pyrrole on Pt/transparent glass conducting electrode resistance 15 O cm-1, using a room temperature melt as an electrolyte, composed of 1:3 stoichiometric ratio of cetyl pyridinium chloride and anhydrous aluminum chloride at 0.58 V versus Al wire as a reference electrode. The film possessed a charge transfer resistance of 132 O, and showed two absorption peaks at 457 and 1264 nm in the UV-vis–NIR diffused reflectance spectra. The morphology of the film was hexagonal. The potential step technique suggested a layered structure. This thin film can easily be peeled off from the electrode surface after three cycles and can be used for various applications like dissipation of electrostatic charge, battery electrode materials, solid electrolytic capacitor, electrochromic windows and displays, microactuators etc. It was also characterized by IR, thermal and SEM studies.

Fast imaging of an atmospheric pressure glow discharge in he with a polymer film

To visualize the development of an atmospheric pressure glow discharge in He and the influence of polymer film on the discharge, short exposure time images were recorded using a gated intensified charge coupled detector. If the polymer film is stretched in the middle of the gap, a discharge region on each side of the polymer is created with the characteristic structure of a glow discharge. In this case, strongly asymmetric discharge current pulses can be generated depending on the frequency and the applied voltage.

Light emission from gold and silver thin films in a scanning tunneling microscope: role of contamination and interpretation of grain structure in photon maps

Scanning tunnelling microscope (STM) tip-induced light emission from Au and Ag has been studied. Thin film samples similar to100nm thick were prepared by thermal evaporation at 0.5nm/s onto a room-temperature glass substrate to produce grains of 20-50nm in lateral dimension at the surface. Light emission from the samples in the STM was quasi-simultaneously recorded with the topography, at 1.8V tip bias and 3-40nA current, alternating pixel by pixel at the same bias. Typically, a surface scan range of 150 nm x 150 nm was surveyed. Au, W and PtIr tips were used.

Influence of test methodology and probe geometry on nanoscale fatigue mechanisms of diamond-like carbon thin film

The aim of this paper is to investigate the mechanism of nanoscale fatigue using nano-impact and multiple-loading cycle nanoindentation tests, and compare it to previously reported findings of nanoscale fatigue using integrated stiffness and depth sensing approach. Two different film loading mechanism, loading history and indenter shapes are compared to comprehend the influence of test methodology on the nanoscale fatigue failure mechanisms of DLC film. An amorphous 100 nm thick DLC film was deposited on a 500 μm silicon substrate using sputtering of graphite target in pure argon atmosphere. Nano-impact and multiple-load cycle indentations were performed in the load range of 100 μN to 1000 μN and 0.1 mN to 100 mN, respectively. Both test types were conducted using conical and Berkovich indenters. Results indicate that for the case of conical indenter, the combination of nano-impact and multiple-loading cycle nanoindentation tests provide information on the life and failure mechanism of DLC film, which is comparable to the previously reported findings using the integrated stiffness and depth sensing approach. However, the comparison of results is sensitive to the applied load, loading mechanism, test-type and probe geometry. The loading mechanism and load history is therefore critical which also leads to two different definitions of film failure. The choice of exact test methodology, load and probe geometry should therefore be dictated by the in-service tribological conditions, and where necessary both test methodologies can be used to provide better insights of failure mechanism. Molecular dynamics (MD) simulations of the elastic response of nanoindentation is reported, which indicates that the elastic modulus of the film measured using MD simulation was higher than that experimentally measured. This difference is attributed to the factors related to the presence of material defects, crystal structure, residual stress, indenter geometry and loading/unloading rate differences between the MD and experimental results.

Home Is Where the Self Is: Monodrama, Journey-Play Structure, and the Modernist Fairy Tale

The first decade of the twentieth century witnessed the creation of two of the most beloved works of children’s literature ever produced. L. Frank Baum’s 1900 novel The Wizard of Oz and Maurice Maeterlinck’s 1908 play each gave rise to many adaptations, including, well beloved film versions, and both have become a deeply ingrained part of the cultural memory and construction of childhood in both Europe and the United States. And while these works are deeply original in content and detail, the structure of these works harkens back to the form of the journey play (traceable, on some level, back to the medieval morality play Everyman), a form that had undergone a considerable revival in the second half of the nineteenth century in the work of writers such as Henrik Ibsen and August Strindberg. This article explores the structural and conceptual links between Baum and Maeterlinck’s children’s classics, Ibsen’s Norwegian folk play Peer Gynt, and August Strindberg’s Lucky Per’s Journey and The Road to Damascus, Part I. In these works, the protagonists, disenchanted with their homes or current situations, set out on an epic journey in which they come upon characters and situations that act as commentary upon their situations before the journey. Ultimately, the characters return to where they started, with the journey seeming to have been a dream or merely a pointless excursion. But in these journeys of self-discovery, the protagonist that emerges at the end has undergone a significant transformation, a process at the heart of all of these works.

CHARACTERIZATION OF THE AU SURFACE-STRUCTURE OF AL-L-AU LIGHT-EMITTING TUNNEL-JUNCTIONS

Visible light is emitted from the Au-air interface of Al-I-Au thin-film tunnel junctions (deposited over a thin layer of CaF2 on glass) as a result of the decay of surface plasmon polaritons (SPPs). We show the surface topography of such a Au film and relate its large-scale features to the outcoupling of fast SPP's to photons. The absence of short-scale roughness features is explained by thier disappearance through surface diffusion. To confirm this a controlled sequence of 5-nm, 20-ms scanning tunneling microscope (STM) W tip crashes has been used to produce indentations 3 nm deep with a lateral dimension of 5-7 nm on a Au crystal in air at room temperature. Four sequences of indentations were drawn in the form of a square box. Right from the start, feature decay is observed and over a period of 2 h a succession of images shows that the structure disappears into the background as a result of surface diffusion. The surface diffusion constant is estimated to be 10(-18) cm2 s-1. The lack of light output via slow mode SPPs is an inevitable consequence of surface annealing.

Structure and Catalytic Activity of Gold in Low-Temperature CO Oxidation

Structures and catalytic activities of Au thin films supported at anatase TiO(2)(101)) and a Au substrate are studied by using density functional theory calculations. The results show that O(2) can hardly adsorb at flat and stepped Au thin films, even supported by fully reduced TiO(2)(101) that can highly disperse Au atoms and offer strong electronic promotion. Interestingly, in both oxide-supported and pure Au. systems, wire-structured Au can adsorb both CO and O(2) rather strongly, and kinetic analysis suggests its high catalytic activity for low-temperature CO oxidation. The d-band center of Au at the catalytic site is determined to account for the unusual activity of the wire-structured film. A generalized structural model based on the wire-structured film is proposed for active Au, and possible support effects are discussed: Selected oxide surfaces can disperse Au atoms and stabilize the formation of a filmlike structure; they may also serve as a template for the preferential arrangement of Au atoms in a wire structure under low Au coverage.

Nanotech thin film photovoltaics

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia de Electrónica e Telecomunicações

Molecular mobility, composition and structure analysis in glycerol plasticised chitosan films

This study was developed with the purpose to investigate the effect of polysaccharide/plasticiser concentration on the microstructure and molecular dynamics of polymeric film systems, using transmission electron microscope imaging (TEM) and nuclear magnetic resonance (NMR) techniques. Experiments were carried out in chitosan/glycerol films prepared with solutions of different composition. The films obtained after drying and equilibration were characterised in terms of composition, thickness and water activity. Results show that glycerol quantities used in film forming solutions were responsible for films composition; while polymer/total plasticiser ratio in the solution determined the thickness (and thus structure) of the films. These results were confirmed by TEM. NMR allowed understanding the films molecular rearrangement. Two different behaviours for the two components analysed, water and glycerol were observed: the first is predominantly moving free in the matrix, while glycerol is mainly bounded to the chitosan chain. (C) 2013 Elsevier Ltd. All rights reserved.