Gold Membrane Research Articles

Predicting, Fabricating, and Permeability Testing of Free-Standing Ternary Palladium−Copper−Gold Membranes for Hydrogen Separation

For hydrogen from coal gasification to be used economically, novel separation processes that produce high-purity H2 must be developed. While binary palladium based alloys have shown promising pure hydrogen flux values, the search for optimal binary or ternary alloys is an involved and costly process due to the immense number of alloy variations that can be prepared and tested. In this paper an approach to identify, fabricate, and experimentally verify the hydrogen permeation performance of PdCu and PdAu binary alloys and ternary alloys of PdCuAu at various copper and gold concentrations to produce robust, poison-tolerant, hydrogen selective free-standing membranes is reported. This approach utilizes three primary tasks of (1) materials modeling and composition selection, (2) fabrication of high-performance binary and ternary alloy membranes, and (3) membrane testing and evaluation that are all operating independently and concurrently. For the binary Pd−Cu system, using a pure Pd membrane as the reference, both the theoretically predicted and experimentally measured additions of copper lowered the hydrogen permeability. For the binary Pd−Au system, the addition of gold slightly lowered permeability in the theoretical model but in the experimental testing was enhanced. For the ternary system, both experimental and theoretical permeabilities were depressed, with Cu exhibiting a larger influence on reducing the permeability.

Investigation of mechanical properties of gold thin films using a bulge test technique

A bulge test device has been built, with the aim to perform mechanical tests on membranes with a thickness in the 100 nm to 10 μm ranges, between room temperature and 900 °C.Our set up a differential atmospheric pressure is applied across a membrane, while the deflection is measured using a laser interferometer. We show first results obtained from gold membranes with different thicknesses.

Planarization optimization of RF-MEMS switches with a gold membrane

In this paper, a new process is analysed to improve the contact area between a metallic bridge and a signal line of a capacitive switch thanks to a better membrane planarization. Two planarization methods are investigated: thermal process with hard-bake steps and chemical mechanical polishing planarization. Moreover, two different sacrificial layers are used: polyimide (PMGI) and photoresist (AZ1529). For each sacrificial layer and planarization method, the influence of planarity and roughness on down-state capacitance is evaluated. Results show that down-state capacitance is more sensitive to flatness than roughness. Moreover PMGI is the best sacrificial layer to improve down-state capacitance mainly for high resonance frequency switches due to capacitance surface reduction.

Experimental Validation of Mixed Electromechanical and Electromagnetic Modeling of RF-MEMS Devices Within a Standard IC Simulation Environment

The validity and applicability of a high-level simulation approach of radio-frequency microelectromechanical-system (RF-MEMS) devices, based on a library of analytical compact models of elementary MEMS components, are investigated through an extensive comparison between simulation results and measurements of some representative devices (variable capacitors and series ohmic switches). The in-house developed simulation tool is implemented in a standard IC simulation environment supporting behavioral description capabilities. The devices are built in a silicon substrate technology with suspended gold membranes. We analyze the mechanical, electrical, and RF response of the devices. The RF behavior is modeled by extracting a lumped element network from measured S-parameters (scattering-parameters) to account for parasitic effects and by wrapping this network around the intrinsic MEMS device simulated with the compact models. We show that an accuracy within 5% is obtained in all considered physical domains and conditions, provided that some effective parameters (including the residual air gap in the actuated state and the RF parasitic elements) are properly extracted from measurements and accounted for in the simulations. The main factors limiting the model's predictive capability are due to process nonidealities, such as plate bending due to residual stress gradient, oxide charging, surface roughness, and suspended membrane thickness variations, rather than for instance in-plane geometric process variations.

The surface profile and biocompatibility of hydroxyapatiteblasted gold membrane as a periodontal guided tissue regeneration membrane

AbstractGuided tissue regeneration (GTR) membrane is essential for periodontal surgery, GTR membrane can guide successful bone tissue formation. The aim of this study is to assess morphologic property and biocompatibility of hydroxyapatite (HA) blasted gold membrane as a periodontal GTR membrane. 99.99 gold (LS Nikko, Korea) was rolled to 0.025∼0.050 mm thickness, and then, blasted with hydroxyapatite powder (5 ∼ 25 µm, Ossgen, Korea) onto the rolled gold sheets. Contact angle measurement of non‐blasted and HA‐blasted surface was performed. And, scanning electron microscopy analysis (simple surface profile observation and observation after attachment of human osteosarcoma cell) was performed. In implantation test using adult dog, Ti‐membrane (Implantium, Suwon, Korea) was used as a control group, and HA‐blasted gold membrane was used as a experimental group. Contact angle of HA‐blasted gold membrane was higher than that of non‐blasted gold surface (p < 0.05). In SEM analysis, HA‐blasted gold membrane showed roughened surface and attachment of MG‐63 cell was more than that of non‐blasted gold surface. There were not any specific clinical symptoms and histological signs in implantation test. This result shows that HA‐blasted gold membrane has a possibility as promising periodontal GTR membrane. Copyright © 2010 John Wiley & Sons, Ltd.

Gold nanoparticle membranes as large-area surface monolayers

An aqueous suspension of gold nanoparticles of sizes from 20 to 90 nm can be conjugated with mercaptosuccinic acid and exposed to a second phase of toluene containing an electrostatic coupler, tetraoctylammonium bromide, to organize the gold particles at the interface between water and toluene. The particles have an amphiphilic character similarly to Janus beads. The thus formed membrane can be transferred to a solid surface to yield centimeter-sized densely packed particle layers. We show that by changing the coupler concentration, the particle distances can be tailored, which modifies the optical properties.

A Novel Filter Rating Method Using Less Than 30-nm Gold Nanoparticle and Protective Ligand

This paper describes a novel filter rating method beyond the current 30-nm limit by combining dynamic light scattering and inductively coupled plasma mass spectrometer technique and proposes the use of gold nanoparticle as the standard challenge particle. Furthermore, the effect of protective ligand addition is investigated in order to decrease the adsorbing effect between gold nanoparticle and membrane surface.

Effect of stress on the pull-in voltage of membranes for MEMS application

In this work, the effect of process residual stress has been studied on three different designs of membranes for RF MEMS switch application. Expressions for the pull-in voltage of stressed membranes have been developed by simple modification of existing relation for unstressed membranes. To validate the results, gold membranes have been fabricated and released successfully using silicon dioxide as the sacrificial layer. The theoretical results show a very good match with experimental results. This expression allows the estimation of the pull-in voltage of stressed membranes without the need for numerical simulations. The stress in the membranes can also be extracted from pull-in voltage measurements. Our results show that high spring constant (K) structures are less prone to deflection and change in the pull-in voltage. Also, for a high stress value, the pull-in voltages of the structures become almost independent of the spring constant.

Dot-immunogold filtration assay for rapid screening of three fluoroquinolones

A dot-immunogold filtration assay (DIGFA) was described for simultaneous screening of three fluoroquinolones (FQs): enrofloxacin (ENR), ciprofloxacin (CIP) and norfloxacin (NOR). Colloidal gold particles were used as visible labels, and anti-ENR polyclonal antibodies from mice and rabbits were exploited for gold labelling and membrane coating, respectively. Several parameters affecting DIGFA were optimised, and the operation was validated with pure buffer matrix and spiked eel samples, respectively. The detection limits in eel samples were estimated to be about 20 µg kg−1 for ENR and CIP, and 50 µg kg−1 for NOR. With pretreated nitrocellulose membranes, the determination could be completed within 30 minutes, and the results could be read just by the naked eye without the help of any equipment.

Fabrication of Reliable RF MEMS Switches in CPW Configuration

This paper describes a new fabrication technique for RF MEMS switches where the coplanar waveguide (CPW) is fabricated in a basin. A planar profile and good coverage at the edges in a basin is achieved by spinning and baking the sacrificial positive photoresist (PPR) in multiple steps to fill the basin. The basin structure allows an increase in the length of the membrane resulting in lower pull-in voltage and better isolation. The PPR is removed using Piranha solution (H2SO4:H2O2::3:1). Structures with the gap of about 2.5 µm and the thickness of the gold membrane varying from 1µm to 2.5 µm have been successfully realized.

Gold nanotube membranes functionalised with fluorinated thiols for selective molecular transport

Gold nanotube membranes were prepared by electroless deposition of gold within the pores of polycarbonate track-etched membranes. This approach provides control over the pore size of the membrane, with pore sizes being reduced to molecular dimensions. The effect of the surface chemistry on the transport properties of these gold nanotube membranes has been explored through functionalisation with self-assembled monolayers. The transport properties and the selectivity of fluoro-derivatised membranes (1H,1H,2H,2H-perfluorodecanethiol) towards hydrophobic and hydrophilic molecules was compared with a membrane modified with an analogous alkanethiol; 1-decanethiol.

Facile Fabrication of Ultrathin Pt Overlayers onto Nanoporous Metal Membranes via Repeated Cu UPD and in Situ Redox Replacement Reaction

Ultrathin Pt films from one to several atomic layers are successfully decorated onto nanoporous gold (NPG) membranes by utilizing under potential deposition (UPD) of Cu onto Au or Pt surfaces, followed by in situ redox replacement reaction (RRR) of UPD Cu by Pt. The thickness of Pt layers can be controlled precisely by repeating the Cu-UPD-RRR cycles. TEM observations coupled with electrochemical testing suggest that the morphology of Pt overlayers changes from an ultrathin epitaxial film in the case of one or two atomic layers to well-dispersed nanoislands in the case of four and more atomic layers. Electron diffraction (ED) patterns confirm that the as-prepared NPG-Pt membranes maintain a single-crystalline structure, even though the thickness of Pt films reaches six atomic layers, indicating the decorated Pt films hold the same crystallographic relationship to the NPG substrate during the entire fabrication process. Due to the regular modulation of Pt utilization, the electrocatalytic activity of NPG-Pt exhibits interesting surface structure dependence in methanol, ethanol, and CO electrooxidation reactions. These novel bimetallic nanocatalysts show excellent electrocatalytic activity and much enhanced poison tolerance as compared to the commercial Pt/C catalysts. The success in the fabrication of NPG-Pt-type materials provides a new path to prepare electrocatalysts with ultralow Pt loading and high Pt utilization, which is of great significance in energy-related applications, such as direct alcohol fuel cells (DAFCs).

Structure dependent electrooxidation of small organic molecules on Pt-decorated nanoporous gold membrane catalysts

We describe the electrocatalytic properties of self-supported Pt-decorated nanoporous gold (Pt-NPG) membranes towards the electrooxidation of formic acid and some other small organic molecules. By effectively enhancing the Pt utilization and providing a unique surface structure, the electrooxidation of formic acid on Pt-NPG was found to be highly sensitive to its surface structure. An unparalleled increase by nearly two orders of magnitude in catalytic activity was achieved on NPG electrodes decorated with sub-monolayer Pt atoms, as compared to the commercial Pt/C catalyst under the same testing conditions.

Electrokinetically driven fluidic transport in integrated three-dimensional microfluidic devices incorporating gold-coated nanocapillary array membranes

Electrokinetically driven fluid transport was evaluated within three-dimensional hybrid nanofluidic-microfluidic devices incorporating Au-coated nanocapillary array membranes (NCAMs). Gold NCAMs, prepared by electroless gold deposition on polymeric track-etched membranes, were susceptible to gas bubble formation if the interfacial potential difference exceeded approximately 2 V along the length of the gold region. Gold membranes were etched to yield 250 microm wide coated regions that overlap the intersection of two orthogonal microfluidic channels in order to minimize gas evolution. The kinetics of electrolysis of water at the opposing ends of the gold region was modeled and found to be in satisfactory agreement with experimental measurements of the onset of gas bubble formation. Conditions to achieve electrokinetic injection across Au-coated NCAMs were identified, with significant reproducible injections being possible for NCAMs modified with this relatively thin gold stripe. Continuous gold films led to suppressed injections and to a variety of ion enrichment/depletion effects in the microfluidic source channel. The suppression of injections was understood through finite element modeling which revealed the presence of a significant electrophoretic velocity component in opposition to electroosmotic flow at the edge of the Au-dielectric regions.

Membrane-sealed hollow microneedles and related administration schemes for transdermal drug delivery

This paper presents fabrication and testing of membrane-sealed hollow microneedles. This novel concept offers the possibility of a sealed microneedle-based transdermal drug delivery system in which the drug is stored and protected from the environment. Sealed microneedles were fabricated by covering the tip openings of out-of-plane silicon microneedles with thin gold membranes. In this way a leak-tight seal was established which hinders both contamination and evaporation. To allow drug release from the microneedles, three different methods of opening the seals were investigated: burst opening by means of pressure; opening by applying a small voltage in the presence of physiological saline; and opening as a result of microneedle insertion into the skin. It was found that a 170 nm thick gold membrane can withstand a pressure of approximately 120 kPa. At higher pressures the membranes burst and the microneedles are opened up. The membranes can also be electrochemically dissolved within 2 min in saline conditions similar to interstitial fluid present in the skin. Moreover, through in vivo tests, it was demonstrated that 170 nm thick membranes break when the microneedles were inserted into skin tissue. The proposed concept was demonstrated as a feasible option for sealing hollow microneedles. This enables the realization of a closed-package transdermal drug delivery system based on microneedles.

Mediated catalysis of Paracoccus pantotrophus cytochrome c peroxidase by P. pantotrophus pseudoazurin: kinetics of intermolecular electron transfer

This work reports the direct electrochemistry of Paracoccus pantotrophus pseudoazurin and the mediated catalysis of cytochrome c peroxidase from the same organism. The voltammetric behaviour was examined at a gold membrane electrode, and the studies were performed in the presence of calcium to enable the peroxidase activation. A formal reduction potential, E (0)', of 230 +/- 5 mV was determined for pseudoazurin at pH 7.0. Its voltammetric signal presented a pH dependence, defined by pK values of 6.5 and 10.5 in the oxidised state and 7.2 in the reduced state, and was constant up to 1 M NaCl. This small copper protein was shown to be competent as an electron donor to cytochrome c peroxidase and the kinetics of intermolecular electron transfer was analysed. A second-order rate constant of 1.4 +/- 0.2 x 10(5) M(-1) s(-1) was determined at 0 M NaCl. This parameter has a maximum at 0.3 M NaCl and is pH-independent between pH 5 and 9.

Compressive Stress Accumulation in Composite Nanoporous Gold and Silicone Bilayer Membranes: Underlying Mechanisms and Remedies

AbstractThis paper outlines a simple method to fabricate a bilayer membrane consisting of a thin nanoporous gold layer infused with uncured polydimethylsiloxane. The fabrication technique offers excellent adhesion due to mechanical interlocking between porous layer and elastomer, and excellent electrical conductivity up to 25% strain, despite a very low effective elastic modulus (∼1.35 MPa) due to cracks in the embedded gold layer. Initially freestanding circular membranes displayed significant out of plane buckling, and created difficulties in extraction of membrane mechanical properties. The underlying mechanisms of compressive stress accumulation that lead to membrane buckling and remedies to prevent it are discussed.

Measurement of Mechanical Properties and Residual Stresses of Bridged Gold Films and Circular Gold Membranes

In order to measure the mechanical properties of gold films on silicon substrate, two types of specimens, i.e., bridged films and circular membranes, are manufactured. Using a wedge tip, the bridged gold films are indented so that the films are pushed off, which is called as V-peel test. The load-deflection curves obtained by the V-peel test are analyzed with the concept of geometrically nonlinear beam by using the minimum potential energy theory together with Ritz method. Thus, Young’s modulus and residual stress of the bridged gold films are obtained. Blister test is also conducted to measure the Young’s modulus and residual stress of a circular gold membrane, of which deformation is measured by Twyman-Green interferometer. By gradually increasing the external pressure applied on the membrane, the interfacial fracture toughness between the gold membrane and silicon substrate is measured based on the concepts of interfacial fracture mechanics.

Simultaneous Excitation of Propagating and Localized Surface Plasmon Resonance in Nanoporous Gold Membranes

Materials multifunctionality for optical sensing of adsorbates has obvious advantages-in addition to the potential for greater sensitivity, the different length scales associated with a variety of optical phenomena allow a greater variety of adsorption characteristics to be examined. Here, we show that ultrathin (approximately 100 nm) nanoporous gold membranes possess features of both planar metal films that exhibit propagating SPR excitations and nanofeatured metals that exhibit localized SPR excitations. This is the first report of such multifunctionality in an optically active metal. We give illustrative examples of using this material to probe biorecognition reactions and to probe the structure evolution of a layer-by-layer deposition of charged dendrimers. Our results are consistent with the very different lengths of the tail of the evanescent field decays associated with each of these plasmon excitation modes.

Vertical nanopatterning of 6H-SiC(0001) surfaces using gold-metal nanotube membrane lithography

Large-area membranes consisting of arrays of gold metal nanotubes were used as shadow masks to generate vertical nanopatterned 6H-SiC(0001) substrates. The gold membranes are formed by a replication technique based on electrochemical deposition of anodic aluminium oxide membranes or silicon substrates containing lithographically generated etch pits. Using the gold metal membranes as masks in reactive ion etching, spatially well-resolved protrusions in the SiC substrate were etched, arranged in periodic and non-periodic two-dimensional arrays. Final vertical morphological reorganizations were obtained in a hot-wall reactor under hydrogen flow. The obtained large-area networks of nano-objects have many potential applications in magnetism, electronics and biology.