Reasonable Electrical Conductivity Research Articles

Insulator-to-metal-like transition in thin films of a biological metal-organic framework

Temperature-induced insulator-to-metal transitions (IMTs) where the electrical resistivity can be altered by over tens of orders of magnitude are most often accompanied by structural phase transition in the system. Here, we demonstrate an insulator-to-metal-like transition (IMLT) at 333 K in thin films of a biological metal-organic framework (bio-MOF) which was generated upon an extended coordination of the cystine (dimer of amino acid cysteine) ligand with cupric ion (spin-1/2 system) – without appreciable change in the structure. Bio-MOFs are crystalline porous solids and a subclass of conventional MOFs where physiological functionalities of bio-molecular ligands along with the structural diversity can primarily be utilized for various biomedical applications. MOFs are usually electrical insulators (so as our expectation with bio-MOFs) and can be bestowed with reasonable electrical conductivity by the design. This discovery of electronically driven IMLT opens new opportunities for bio-MOFs, to emerge as strongly correlated reticular materials with thin film device functionalities.

Effects of Induced Current in Crystals on the Melt Flow and the Melt–Crystal Interface during Industrial 300 mm Czochralski Silicon Crystal Growth under a Transverse Magnetic Field

Due to the high magnetic field intensity during industrial 300 mm silicon crystal growth, typically up to 0.3 T, the crystal’s rotation under this transverse magnetic field (TMF) induces a current that is strong enough to impact both the melt flow and the melt/crystal interface (m/c interface) shape. This paper investigates the influence of TMF-induced current in crystals on the melt flow, temperature distribution, and interface shape through the conduction of three sets of 3D simulations that vary in the electrical conductivity of crystals, TMF intensities, and crystal rotation rates. Combined with experiments, the accuracy of the model has been validated, and a reasonable electrical conductivity of the crystal has been predicted. The study findings reveal a shift in the driving force of forced convection from centrifugal to Lorentz force when the induced current in crystal is augmented. This alteration affects the melt flow and the m/c interface shape. Notably, this study serves as a significant complement to the conventional model, which overlooks the induced current in crystals, enhancing the accuracy and comprehensiveness of the simulation outcomes to provide a robust theoretical underpinning for industrial production.

Enhanced Thermoelectric Performance in Oxide Composites of La and Nb Codoped SrTiO3 by Using Graphite as the Electron Mobility Booster.

Inherent insulating nature of oxides makes it challenging for use in thermoelectric applications that warrant reasonable electrical conductivity. In the present work, we have used graphite (G) to improve the electron transport in La0.07Sr0.93Ti0.93Nb0.07O3 (LSTN) by making composites. Graphite acts as the electron momentum booster in the LSTN matrix, which otherwise suffers from Anderson localization of electrons, causing an order of magnitude increase in weighted mobility and electrical conductivity. As a result, the thermoelectric power factor increases more than 6 times due to graphite incorporation in LSTN. Furthermore, the lattice thermal conductivity is suppressed due to enhanced Umklapp scattering, as derived from the Debye-Callaway model. Hence, we have recorded ∼423% increment in the figure of merit (ZT) in LSTN + G composites. The maximum ZT obtained is 0.68 at 980 K for the LSTN with 1 wt % graphite composite. Furthermore, we have fabricated a four-legged n-type thermoelectric power generator demonstrating a milliwatt level power output, which hitherto remained unattainable for oxide thermoelectrics.

Tuneable synthetic reduced graphene oxide scaffolds elicit high levels of three-dimensional glioblastoma interconnectivity in vitro.

Three-dimensional tissue scaffolds have utilised nanomaterials to great effect over the last decade. In particular, scaffold design has evolved to consider mechanical structure, morphology, chemistry, electrical properties, and of course biocompatibility - all vital to the performance of the scaffold and how successful they are in developing cell cultures. We have developed an entirely synthetic and tuneable three-dimensional scaffold of reduced graphene oxide (rGO) that shows good biocompatibility, and favourable mechanical properties as well as reasonable electrical conductivity. Importantly, the synthesis is scaleable and suitable for producing scaffolds of any desired geometry and size, and we observe a high level of biocompatibility and cell proliferation for multiple cell lines. In particular, one of the most devastating forms of malignant brain cancer, glioblastoma (GBM), grows especially well on our rGO scaffold in vitro, and without the addition of response-specific growth factors. We have observed that our scaffold elicits spontaneous formation of a high degree of intercellular connections across the GBM culture. This phenomenon is not well documented in vitro and nothing similar has been observed in synthetic scaffolds without the use of response-specific growth factors - which risk obscuring any potential phenotypic behaviour of the cells. The use of scaffolds like ours, which are not subject to the limitations of existing two-dimensional substrate technologies, provide an excellent system for further investigation into the mechanisms behind the rapid proliferation and success of cancers like GBM. These synthetic scaffolds can advance our understanding of these malignancies in the pursuit of improved theranostics against them.

Effect of Oxygen Partial Pressure on Reactive-Sputtered Ni-YSZ Anode Properties for Low-Temperature Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) is a promising next-generation energy conversion device because of its high efficiency, cleanliness, and fuel flexibility. Recently, SOFC operating at low- to intermediate-temperature (LT to IT) range (< 600 ℃) has been studied to overcome the limitations of conventional SOFC, e.g., thermal stability, cost, and limited application. In lowered temperature range, however, charge transfer and transport rates slow down; therefore, SOFCs design with thin film stacks, namely thin film SOFC (TF-SOFC) fabricated on porous anode support have been usually adopted for sufficient power density even at this temperature regime.TF-SOFC usually uses Ni-YSZ (nickel-yttria-stabilized zirconia) cermet for anode functional layer (AFL) to accommodate the deposition of dense electrolyte layers on anode support with relatively large pores because of its reasonable cost, catalytic activity, and electrical conductivity. While various thin film techniques have been reported for AFL fabrication, e.g., pulsed layer deposition (PLD), RF sputtering, etc. Among such techniques, reactive sputtering method, which uses metal target in controlled gas environment (e.g., oxygen environment for oxide deposition), is a versatile method to deposit various types of thin films with fast speed (up to > 1um/hr), which is beneficial in manufacturabilily regarding the usual thickness range of AFL (a few microns). Furthermore, the reactive co-sputtering method can control anode properties such as composition ratio, deposition speed, and morphology in wide ranges.In this study, we fabricate reactive sputtered Ni-YSZ cermet anodes, as prototypes for AFLs of TF-SOFCs, by using a single metal target with various oxygen partial pressure conditions, and characterize their physical and chemical properties. Oxygen partial pressure significantly affects deposition speed, surface morphology, composition, electrochemical performance and its thermal durability at 450 ℃. The Ni-YSZ anode sputtered at the environment of O2/Ar partial pressure ratio of 0.1 sample shows the lowest activation resistance when applied to LT-SOFC’s anode. It is also shown that excessive O2/Ar partial pressure ratio (> 0.2) significantly reduces the deposition speed by approximately one order of magnitude compare to the lower ratio case.

Conductivity mechanism and dielectric properties of poly (2-aminophenol) with boron nitride and graphite composites

Polyaniline (PANI) is one of the important of the conducting polymers because of its easy synthesis, redox recyclability, reversible proton dopability, environmental stability, cost-effectiveness and reasonable electrical conductivity. PANI and its composites have the most promising applications as conducting materials in optoelectronics and microelectronics devices. Recently, PANI composite studies have increased remarkably in order to overcome the negative properties of polyaniline. In this study, 2-Aminophenol as monomer was polymerized oxidatively in the presence of ammonium persulfate as oxidant to obtain poly(2-aminophenol) (P2AMP). Then, 2-Aminophenol was polymerized in the presence of difference weight percentage (1%, 2%, 5%) of Boron nitride and graphite to obtain its composites (P2AMP-BN and P2AMP-GH), respectively. These composites were characterized by using spectroscopic, morphologic and physical methods.

Developing age-hardenable Al-Zr alloy by ultra-severe plastic deformation: Significance of supersaturation, segregation and precipitation on hardening and electrical conductivity

The aluminum-zirconium (Al-Zr) alloys are of interest because of their superior thermal stability and good electrical conuctivity, but their main drawback is their rather low hardness (<75 Hv) even after severe plastic deformation (SPD). These alloys, which are actually composites of Al and Al3Zr intermetallics (D023 tetragonal structure), do not show age-hardening behavior due to the immiscibility of Zr in Al. In this study, ultra-SPD with shear strains up to 40,000, realized by high-pressure torsion (HPT), is employed to generate supersaturated solid solution in an Al-Zr alloy. Subsequent aging leads to unusual precipitation of AlZr precipitates at grain boundaries (Bf orthorhombic structure) and of coherent metastable Al3Zr precipitates within grain interiors (L12 cubic structure). It is found that the supersaturation of Zr in Al by ultra-SPD is controlled by an ultrafast dynamic diffusion which is comparable to surface diffusion, while the formation of precipitates by static aging is controlled by lattice and pipe diffusions. These microstructural features provide exceptional increase in hardness up to 148 Hv, great thermal stability up to 523 K and reasonable electrical conductivity up to 35 %IACS. Detailed analysis shows that ~30% of this hardening is caused by precipitation strengthening, while extra hardening is achieved due to nanograin formation, grain-boundary segregation and dislocation accumulation. This study introduces a rational approach to produce novel age-hardenable Al alloys with high thermal stability and reasonable electrical conductivity by application of ultra-SPD.

The Influence of the Continuous Casting Conditions on the Properties of High-Strength Two-Phase CuMg Alloys.

Constant tendency toward the improvement of the material properties nowadays creates opportunities for the scientists all over the world to design and manufacture new alloys almost every day. Considering the fact that companies all over the world desire alloys with the highest values of mechanical properties often coexisting with a reasonable electrical conductivity made it necessary to develop new materials based on Cu, such as CuMg alloys. However, before such new material may be mass produced it must undergo a series of tests in order to determine the production technology, its parameters and influence on the chemical composition, microstructural properties, and both mechanical and physical properties of CuMg alloys. The research tests have shown that with the increase of the casting feed the Brinell’s hardness of each material slightly increases (by 5 HB2.5/62.5). There is little to none impact of the casting feed on the electrical conductivity, values of which are between 20.6 and 21.4 MS/m (around 40% IACS-International Annealed Copper Standard) depending on the Mg content. The conducted scanning electron microstopy (SEM) analysis has shown that the magnesium precipitations are evenly distributed among the volume of the alloy, however, a significant difference in the density and shape of the Cu + Cu2Mg aggregates was noticed regarding various casting feed. Static compression test proved that these alloys may be subjected to strain hardening as the hardness of the material after compression increases by approximately 40 HB2.5/62.5.

Electrical conductivity of tremolite under high temperature and pressure: implications for the high-conductivity anomalies in the Earth and Venus

We measured the electrical conductivity of tremolite over a range of pressures (1.0, 1.5, and 2.0 GPa) and temperatures (648–1373 K). At temperatures lower than 1173 K, the electrical conductivity of tremolite was ~ 0.001 S/m, but once the dehydroxylation reaction took place at 1173 K, we observed a significant increase in the electrical conductivity. The electrical conductivity continued to increase until it reached its maximum value of ~ 1 S/m at a temperature of 1373 K, which we attributed to dehydroxylation in the tremolite samples. The electrical behavior was altered by the physical breakdown of the tremolite structure, rather than the oxidation process. The decomposition of tremolite resulted in the creation of diopside, enstatite, and quartz. To explain some anomalous conductivity measurements, we propose that iron-free amphibole experiences a dehydroxylation mechanism that differs from the dehydroxylation mechanism observed in iron-bearing amphiboles. Our conductivity analyses indicate that the observed increase in the electrical conductivity in deep subduction regions (at depths of ~ 180 km) is driven by the dehydroxylation of tremolite and by the mixing of lherzolite and tremolite in the upper mantle. Using our data and previously published temperature gradient data, we were able to extrapolate reasonable electrical conductivity values for the surface and interior of Venus.

Integration of amorphous ferromagnetic oxides with multiferroic materials for room temperature magnetoelectric spintronics

A room temperature amorphous ferromagnetic oxide semiconductor can substantially reduce the cost and complexity associated with utilizing crystalline materials for spintronic devices. We report a new material (Fe0.66Dy0.24Tb0.1)3O7-x (FDTO), which shows semiconducting behavior with reasonable electrical conductivity (~500 mOhm-cm), an optical band-gap (2.4 eV), and a large enough magnetic moment (~200 emu/cc), all of which can be tuned by varying the oxygen content during deposition. Magnetoelectric devices were made by integrating ultrathin FDTO with multiferroic BiFeO3. A strong enhancement in the magnetic coercive field of FDTO grown on BiFeO3 validated a large exchange coupling between them. Additionally, FDTO served as an excellent top electrode for ferroelectric switching in BiFeO3 with no sign of degradation after ~1010 switching cycles. RT magneto-electric coupling was demonstrated by modulating the resistance states of spin-valve structures using electric fields.

Tetrahedral amorphous carbon prepared filter cathodic vacuum arc for hole transport layers in perovskite solar cells and quantum dots LEDs

ABSTRACT (ta-C) films coated through the filtered cathodic vacuum arc (FCVA) process as a hole transport layer (HTL) for perovskite solar cells (PSCs) and quantum dot light-emitting diodes (QDLEDs). The p-type ta-C film has several remarkable features, including ease of fabrication without the need for thermal annealing, reasonable electrical conductivity, optical transmittance, and a high work function. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy examinations show that the electrical properties (sp3/sp2 hybridized bond) and work function of the ta-C HTL are appropriate for PSCs and QDLEDs. In addition, in order to correlate the performance of the devices, the optical, surface morphological, and structural properties of the FCVA-grown ta-C films with different thicknesses (5 ~ 20 nm) deposited on the ITO anode are investigated in detail. The optimized ta-C film with a thickness of 5 nm deposited on the ITO anode had a sheet resistance of 10.33 Ω−2, a resistivity of 1.34 × 10−4 Ω cm, and an optical transmittance of 88.97%. Compared to the reference PSC with p-NiO HTL, the PSC with 5 nm thick ta-C HTL yielded a higher power conversion efficiency (PCE, 10.53%) due to its improved fill factor. Further, the performance of QDLEDs with 5 nm thick ta-C hole injection layers (HIL) showed better than the performance of QDLEDs with different ta-C thicknesses. It is concluded that ta-C films have the potential to serve as HTL and HIL in next-generation PSCs and QDLEDs.

Sc and Ta-doped SrCoO3-δ perovskite as a high-performance cathode for solid oxide fuel cells

Sealing and stability is the challenge for solid oxide fuel cells (SOFCs) at high temperature. It is crucial to operate SOFCs at a low temperature to avoid these issues. Thus, it is necessary to improve the sluggish oxygen reduction reaction (ORR) activity of cathode. The SrCoO3-δ perovskite with a cubic phase is identified as a potential cathode material for SOFCs due to its high oxygen permeability and reasonable electrical conductivity. However, it readily decomposes into the orthorhombic structured brownmillerite Sr2Co2O5 or hexagonal Sr6Co5O15 during high-temperature sintering resulting in the loss of a significant amount of lattice oxygen. Herein, we partially replace Co with Sc and Ta at SrCoO3-δ to stabilize its cubic perovskite structure and restrain the lattice oxygen loss, thus improving the oxygen-ionic conductivity, and the structural and chemical stability. The synthesized SrSc0.175Ta0.025Co0.8O3-δ (SSTC) cathode achieves a remarkably high ORR performance and an area-specific resistance obtained in this study reaches as low as 0.233, 0.033, and 0.004 Ω cm2 at 500, 600, and 700 °C, respectively. The new Sc and Ta-doped SrCoO3-δ perovskite cathode even present a better ORR activity than the previously reported Sc and Nb-doped SrCoO3-δ cathode. The reason for the improved performance by Ta doping is possible that Ta–O bond is stronger than Nb–O bond and the electronegativity of Ta5+ is lower than that of Nb5+, resulting in a lower valence state of cobalt and a higher oxygen vacancies concentration.

Microstructure-dependent electrochemical properties of chemical-vapor deposited poly(3,4-ethylenedioxythiophene) (PEDOT) films

Conductive polymer electrodes hold exceptional promise in energy conversion technologies and bioelectronics due to the inherent mechanical flexibility and synthetic tunability of physical, chemical, and electronic properties. Solution-processing is favorable to retain low-cost but can often result in heterogeneity of physical and electronic structure due to non-conjugated side chains and polyionic dopants creating insulating domains. Such a complex landscape limits control and systematic understanding of fundamental properties including electrical and ionic transport and rates of electron transfer central to overall device efficiencies. Oxidative chemical vapor deposition (oCVD) offers a promising route to simultaneously synthesize and deposit conductive polymer films at low temperatures (<150°C) with controllable microstructure. Herein we use the oCVD technique to synthesize and deposit different paracrystalline films of poly(3,4-ethylenedioxythiophene). Using grazing incidence wide-angle x-ray scattering, we demonstrate three different orientations of the π-π packing direction, relative to the surface normal, to yield thin films with face-on, edge-on, and isotropic character. These different microstructures have direct impact on the electrochemical conditioning of the redox properties of the films. We show that electrochemical properties, as defined by energy and power density, are highest for crystalline materials with edge-on orientation to facilitate ion transport while still retaining reasonable electrical conductivity.

Hard/Soft Template Synthesis of Mesoporous TiO2/Carbon Supports for Fuel Cells

Mesoporous carbons (MC) are attractive catalyst supports for polymer electrolyte membrane fuel cells (PEMFCs) applications because of their low cost, high surface area, good electrical conductivity, and high chemical stability under normal operating conditions.[1] However, carbon corrosion in the cathode compartment can result in a significant reduction in the catalyst electrochemical active surface area (ECSA), that it will negatively impact in the fuel cell performance.[2] Hence, alternative catalyst substrates with a greater chemical stability under acidic and oxidizing conditions have captured significant attention in recent years. [3,4] Among the most promising materials for PEMFCs are carbon nanotubes (CNTs), graphene, and hybrid core/shell metal oxide/mesoporous carbons (MOx/MC). Unfortunately, CNTs and graphene are still too expensive for this application, while studies on hybrid supports, in the case of metal oxides, were limited to low metal oxide contents due to the reduction on surface area observed after the deposition of metal oxide nanoparticles.[5,6] For that reason, the use of ordered mesoporous carbons obtained by carbonization of polymeric materials synthesized in the presence of soft-templates such as surfactants or polyelectrolytes[7] or silica nanoparticles as hard-templates[1] is quite attractive. It can contribute to produce chemically stable materials with an adequate surface area and pore size distribution, and these properties can be modified by merely varying the synthesis and carbonization conditions.[1,4,7] In this study, the effort was oriented to develop mesoporous carbons (MC), and hybrid TiO2/MC catalyst supports with high surface area and tailored micro-mesoporous structure. Carbon materials were obtained by carbonization of a resorcinol-formaldehyde resin synthesized in the presence of silica nanoparticles and poly(diallyldimethylammonium) chloride, a polyelectrolyte as soft template. The deposition of TiO2 nanoparticles was carried out using a sol-gel method that has shown to result in the formation of core/shell TiO2/carbon nanocomposite structures with low TiO2 segregation.[5,6] Both, MC and TiO2/MC substrates were decorated with Pt or PtRu catalyst nanoparticles using standard impregnation methods. The materials were characterized using standard methods (XRD, XPS, TEM, SEM, TGA, ICP-OES, and Raman spectroscopy). The catalytic activity of Pt and PtRu nanoparticles toward the oxygen reduction reaction (ORR), and the oxidation of methanol (MOR) was investigated using a number of electrochemical techniques in a three-electrode cell configuration. The improvement in the catalytic activity of Pt toward the ORR and the chemical stability were both assigned to the high BET surface area of the starting carbon materials (> 500 m2/g) that allowed working with high TiO2 loadings while still keeping a reasonable electrical conductivity. The high TiO2 content seems to improve the catalyst distribution on the support, and the contact between the TiO2 and Pt nanoparticles. Preliminary results for the oxidation of methanol on PtRu/TiO2/MC also show a significant improvement when compared to Pt/MC and Pt/TiO2/MC, but the changes are less significant when compared with PtRu/MC, however more studies are underway to confirm these findings. REFERENCES Forouzandeh F.; Banham D.W.; Feng F.; Li X.; Ye S.; Birss V., ECS Transactions 58 (1) 1739-1749 (2013).Shao Y.Y, Yin G.P., Zang , Gao Y.Z., Electrochim. Acta 51, 5853 (2006).Wang Y-J, Wilkinson D.P., Zhang J., Chem. Rev. 111 (12) 7625-7651 (2011).Bruno M., Viva F.A., Carbon Materials for Fuel Cells BT - Direct Alcohol Fuel Cells: Materials, Performance, Durability and Applications, in: H.R. Corti, E.R. Gonzalez (Eds.), Springer Netherlands, Dordrecht, pp. 231–270 (2014).Odetola C.; Trevani L.; Easton E., Power Sources 294, 254–263 (2015).Odetola C., Easton E.B., Trevani L., J. Hydrogen Energy 41, 8199–8208 (2016)Bruno M.; Viva F.; Petruccelli M.; Corti H., Power Sources 278, 458–463 (2015).

Achieving current rectification ratios ≥ 105 across thin films of coordination polymer.

Downsizing coordination polymers (CPs) to thin film configurations is a prerequisite for device applications. However, fabrication of thin films of CPs including metal-organic frameworks (MOFs) with reasonable electrical conductivity is challenging. Herein, thin film fabrication of a Cu(ii)-CP employing a layer-by-layer method is demonstrated whereby a self-assembled monolayer on Au was used as the functionalized substrate. Growth of the Cu(ii)-CP at the solid-liquid interface generated open-metal Cu(ii) sites in the thin film which were susceptible to activation by molecular dopant molecules. A significant enhancement in in-plane electrical conductivity and an unheralded cross-plane current rectification ratio (exceeding 105 both at room-temperature and at an elevated temperature) were achieved. Such a remarkable rectification ratio was realized, similar to those of commercial Si rectifier diodes. This phenomenon is attributed to the formation of an electronic heterostructure in the molecularly doped thin film. Molecular doping additionally transformed the interfacial properties of thin films from hydrophilic to highly hydrophobic.

High-performance copper reinforced with dispersed nanoparticles

Copper (Cu) has high electrical conductivity and is widely used for many industrial applications. However, pure Cu is very soft and improving the mechanical properties of Cu comes at the great expense of electrical and thermal conductivity. In this work, high-performance Cu with superior mechanical properties and reasonable electrical/thermal conductivity was fabricated using a scalable two-step method. First, Cu micro-powders with uniformly dispersed tungsten carbide (WC) nanoparticles were created by a molten salt-assisted self-incorporation process. A bulk nanocomposite was then obtained by melting the powders under pressure. The as-solidified Cu with 40 vol% uniformly dispersed WC nanoparticles exhibits high hardness, a yield strength over 1000 MPa, a Young’s modulus of over 250 GPa, and reasonable electrical and thermal conductivity.

(Invited) Moving Electrons and Holes through Porous MOFs and MOF-Supported Catalysts

Porous, thin-film, water stable metal-organic frameworks (MOFs) are potentially highly attractive as electrocatalysts as they can present reactant-accessible catalysts at high areal concentration on electrode surfaces. Indeed, such films, if constructed from molecular catalysts, can present the equivalent of several hundred monolayers or more of catalyst -- amounts that can translate into decreases of hundreds of millivolts in kinetic overpotential relative to overpotentials for otherwise equivalent solution-phase electrocatalysts present at millimolar concentrations. Similar conclusions can be reached for catalysts consisting of MOF-node-supported, metal-oxygen or metal-chalcogen clusters. Required for efficacious electrocatalysis, however, is reasonable electrical conductivity, where the basis for conductivity may be site-to-site redox hopping or may instead operationally resemble band-like electronic conductivity. For electrode-supported MOF films having thicknesses of around a micron, site-to-site charge hopping rates on the order of 105 sec-1 should be sufficient to sustain catalytic currents of tens of mA/cm2. Alternatively, MOF electronic conductivities on the order of 10-2 Siemens/cm (roughly seven and a half orders of magnitude less than the conductivity of copper) should be sufficient to sustain catalytic currents of tens of mA/cm2 with only marginal iR penalties. Thus, in comparison to many applications, the degree of conductivity required for MOF thin-film mediated electrocatalysis is modest. This presentation will describe some approaches to rendering highly-porous MOF films sufficiently electrically conductive to support electrocatalysis. Included will be examples of highly anisotropic electrical conductivity, underscoring the role that MOF topology can play in defining both hopping-like and band-like conductivity. Also included may be examples of intentional chemical modulation of MOF conductivity. Based on these and other examples, some potentially transferrable principles for designing electrocatalysis-competent, conductive MOFs will be proffered.

Conducting and stretchable nanometer-thin gold/thiol-functionalized polydimethylsiloxane films

Future low-voltage dielectric elastomer transducers (DETs), based on nanometer-thin elastomer membranes, will rely on soft and compliant electrodes with reasonable electrical conductivity and sound adhesion to the elastomer. State-of-the-art adhesion promoters, including nanometer-thin Cr/Ti films, result in defects for applied areal strains larger than 3% and lead to increases in the stiffness of DETs. To generate forces in the Newton range, these low-voltage DETs have to be stacked in thousands of layers. Herein, we present a compliant electrode, which consists of gold bonded covalently to thiol-functionalized polydimethylsiloxane (SH-PDMS) films. The membranes were fabricated using molecular beam deposition and in situ and/or subsequent ultraviolet light (UV) radiation. Peel-off tests demonstrate the expected strong binding of Au to the SH-PDMS network, with this highly stretchable Au/SH-PDMS layer capable of withstanding strains of at least 60%, without losing conductivity. Optical micrographs show signs of cracks for strained pure Au and Au/Cr electrodes but not for the Au/SH-PDMS layer. The mechanical properties and adhesion forces of Au/SH-PDMS were extracted by means of atomic force microscopy (AFM), using a spherical Au tip coated with methyl groups (CH3). The elastic modulus of ( 12 ± 9 ) MPa increased slightly against the 20-nm-thin Au/PDMS example, but it can be tailored by the cross-linking density of Au/SH-PDMS via the UV irradiation dose. Unloading nanoindentation curves revealed pull-off forces between the CH3-functionalized AFM tip and the Au/SH-PDMS layer at the time of separation. For Au/SH-PDMS, the spectral distribution of pull-off forces exhibits repulsive forces with the CH3 groups of the PDMS network as well as adhesive forces resulting from interactions with the nanometer-sized Au clusters. This approach provides the means to bind gold clusters homogenously within the SH-PDMS film. Such compliant electrodes are the prerequisite for fabricating low-voltage DETs that can be stretched by more than 50%.

Sb doped SnO2 as a stable cathode catalyst support for low temperature polymer electrolyte membrane fuel cell

In this work the feasibility of a corrosion resistant non-carbon noble metal support for PEMFC cathode catalysts has been investigated and compared with a traditional carbon black support. We developed an antimony doped tin oxide (ATO) material which has reasonable electrical conductivity (0.7 S/cm) and surface area (50 m2/g). ATO and carbon black (CB) supported Platinum (Pt) electrocatalysts have been prepared by modifying the well-known polyol process. Electrochemical characterizations of the supported catalysts were done to measure the ECSA via cyclic voltammetry, ORR activity via RDE, Pt corrosion via load cycling, support corrosion via potential cycling and finally the catalysts were processed to MEAs for single cell performance tests. ATO supported catalyst showed improved corrosion resistance properties in 0.5 M H2SO4 in three electrode system. However, lower performance than CB supported catalyst has been found after processing to MEAs for single cell tests at defined operating conditions. Electrochemical Impedance Spectroscopy has also been used as a diagnostic tool to asses MEA performance.

Optically transparent composite diamond/Ti electrodes

It is important for electro-optical applications of nanocrystalline diamond (NCD) films to achieve high optical transparency with low electrical resistivity. However, currently fabrication of highly transparent NCD films with reasonable electrical conductivity remains a challenge – any increase in conductivity simultaneously reduces transparency. Here, we report on fabrication of highly conductive and yet highly transparent electrodes based on boron-doped nanocrystalline diamond (B-NCD) films and Ti grids. We studied B-NCD films with variable boron content and thickness to determine preferable electrical and optical characteristics. Composite electrodes with a sheet resistance of 200 Ω/sq and optical transparency of 80% have been obtained by the integration of a thin nanostructured Ti-grid, sandwiched between the glass substrate and B-NCD layer.