Gold Nanowire Arrays Research Articles

Near field photothermal printing of gold microstructures and nanostructures

We report on a rapid near field photothermal printing (NPTP) approach for fabricating gold microstructures and nanostructures guided by flexible and transparent polymer molds. The optical energy of nanosecond laser pulse is spatially redistributed by a PDMS phase-shifting mask, resulting in selective gold melting in light intensity enhanced areas. The melted gold migrates to cold areas and forms desired structures after cooled down. Using NPTP, we have demonstrated rapid laser printing of periodic gold nanowire array with a 320 nm linewidth, nanosphere arrays with 400 nm in diameter, and nonperiodic structures across a 1 mm2 area with few laser pulses.

Micro-capacitors based on electrochemically grown vertical arrays of gold nanowires as electrodes

This paper describes the development of micro-capacitors with electrodes based on electrochemically grown vertical gold nanowire arrays. A high aspect-ratio anodized aluminum oxide template integrated on silicon dioxide/silicon substrates was exploited for fabricating a vertical array of nanowires with a high surface to volume ratio. Bismuth ferric oxide thin films were deposited to create high dielectric material between the electrodes using room temperature electrodeposition. This nanofabrication process may be compatible with a complementary metal-oxide-semiconductor (CMOS) process, therefore, this capacitor can be used for protecting and regulating the surge voltage biased to the CMOS circuits. This capacitor achieved a high density capacitance of 3.1 μF/m 2 at 1 MHz, which was measured using a parallel plate set-up.

Direct electrochemistry of horseradish peroxidase immobilized on a monolayer modified nanowire array electrode

Vertically aligned nanowire array electrodes (NAEs) were prepared by electrodeposition of gold into an anodic aluminium oxide membrane (AAM), providing an ordered three-dimensional (3D) matrix for immobilization of redox proteins. Third-generation H 2O 2 biosensors were prepared by covalent immobilization of horseradish peroxidase (HRP) on the self-assembled monolayer modified NAEs. Direct electron transfer and electrocatalytic performances of the HRP/NAEs with different nanowire lengths (deposition time of 2, 4 and 5 h) were investigated. Results showed that with longer nanowires, better performances were achieved. The HRP/NAE 5 h (5 h deposition time) exhibited remarkable sensitivity (45.86 μA mM −1 cm −2) towards H 2O 2 with a detection limit of 0.42 μM ( S/ N = 3), linearity up to 15 mM and a response time of 4 s. The ordered 3D gold nanowire array with high conductivity, excellent electron transfer capability and good biocompatibility proved promising for fabricating sensitive, selective, stable and mediator-free enzymatic biosensors.

Gold nanowire array electrode for non-enzymatic voltammetric and amperometric glucose detection

The non-enzymatic voltammetric and amperometric detection of glucose using a gold nanowire array electrode is described. The voltammetric detection of glucose was performed by cyclic and differential-pulse voltammetry. The detection of glucose by partial and direct oxidation of glucose during the anodic and cathodic potential sweeps was shown in cyclic voltammetry. An unusual decrease in overpotential for partial oxidation of glucose on a Au NW array electrode was observed. A linear differential-pulse voltammetric response for partial oxidation of glucose was observed up to a glucose concentration of at least 20 mM with a sensitivity of 41.9 μA mM −1 cm −2 and detection limit below 30 μM (signal-to-noise ratio of 3) for glucose oxidation at low potentials, where the influence of possible intermediates can be avoided. The amperometric response was also linear up to a glucose concentration of 10 mM with a sensitivity of 309.0 μA mM −1 cm −2. The wide dynamic range and high sensitivity, selectivity and stability, as well as good biocompatibility of the Au NW electrode make it promising for the fabrication of non-enzymatic glucose sensors.

Gold Nanowire Arrays as a Platform for Salivary and ISF Cortisol Evaluation

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Direct Electrodeposition of Porous Gold Nanowire Arrays for Biosensing Applications

Nanochannel alumina templates are used as templates for fabrication of porous gold nanowire arrays by a direct electrodeposition method. After modification with glucose oxidase, a porous gold nanowire-array electrode is shown to be an excellent electrochemical biosensor for the detection of glucose. The picture shows an SEM image of a nanowire array after removal of the alumina template by acid dissolution. We report the fabrication of porous gold nanowire arrays by means of a one-step electrodeposition method utilizing nanochannel alumina templates. The microstructure of gold nanowires depends strongly on the current density. The formation of porous gold nanowires is attributed to disperse crystallization under conditions of low nucleation rate. Interfacial electron transport through the porous gold nanowires is studied by electrochemical impedance spectroscopy. Cyclic voltammetric studies on the porous gold nanowire arrays reveal a low-potential electrocatalytic response towards hydrogen peroxide. The properties of the glucose oxidase modified porous gold nanowire array electrode are elucidated and compared with those of nonporous enzyme electrodes. The glucose oxidase modified porous gold nanowire-array electrode is shown to be an excellent electrochemical biosensor for the detection of glucose.

Structural characterisation of gold nanowire arrays

This study is devoted to a thorough crystallographic and microstructural characterisation of gold nanowire arrays. The nanostructures were produced by directional solid-state decomposition of the Fe–Au eutectoid. The system structure and microstructure were investigated using differential thermal analysis (DTA), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM) and scanning Auger electron microscopy (SAEM). The most relevant sample features, with particular attention to the microstructure evolution, morphology and crystallography of the gold nanoarrays, are critically discussed. Gold nanofibres exhibit a faceted morphology with an average width of 20 nm, length of 100 nm and inter-wire distance of 250 nm. HRTEM analysis revealed that the obtained nanostructures are single crystalline and that the fibre-matrix crystallographic orientation relationship is of the Nishiyama–Wassermann type.

Microtubule‐Based Gold Nanowires and Nanowire Arrays

Biological structures are attractive as templates to form nanoscale architectures for electronics because of their dimensions and the ability to interact with inorganic materials. In this study, we report the fabrication and electrical properties of microtubule (MT)-templated Au nanowires, and methods for assembling Au nanowire arrays based on these templates. The adsorption of MTs on silicon substrates is an effective means for preserving the conformation of the MT and provides a convenient platform for electrical measurements. To improve the metallization of MTs, a photochemical route for gold reduction is adapted, which leads to continuous coverage. The conductivity values measured on micrometer-long nanowires are similar to those reported for other biotemplated gold nanowires. A protocol for fabricating arrays of MT-templated gold nanowires is demonstrated.

Mesoporous Titania Thin Film with Highly Ordered and Fully Accessible Vertical Pores and Crystalline Walls

We report the preparation of mesoporous titania thin films with the R$\bar 3$m pore structure derived from the Im$\bar 3$m self-assembled ordering of the titania species and an EO(106)PO(70)EO(106) triblock copolymer. The films were spin-cast and then aged at 18 degrees C at a relative humidity of 70 %, which led to the orientation of the Im$\bar 3$m structure with the [111] direction perpendicular to the substrates. The [111] body-diagonal channels became vertical channels upon calcination at 400 degrees C, thus leading to thin films with vertical channels. The pores are ordered over a large area of up to 1 mum(2). The titania films can be formed on various types of substrates. By using a titania film formed on a Pt-coated Si wafer as a template, we produced by an electrochemical-deposition technique arrays of gold nanowires, whose morphology suggests that most of the pores of the titania thin films are accessible. The pore structure of vertical channels is stable up to 600 degrees C, at which temperature the wall materials crystallize into anatase.

Ultra-Low-Voltage Schottky-Barrier Field-Enhanced Electron Emission From Gold Nanowires Electrochemically Grown in Modified Porous Alumina Templates

Superior field emission (FE) action has been observed from a tailored array of gold nanowires (AuNWs) grown in porous anodic alumina (PAA) templates. The turn-on voltage was found to be 0.2 V, which is far less than the values reported earlier for diamond-coated cathodes and carbon nanotubes (CNTs). Furthermore, the FE current was unaffected by the ambient gas pressure. Such a low-voltage FE is attributed here to the formation of a Schottky barrier at the interface of gold and amorphous alumina scales that remain on the AuNWs.

Extraction enhancement in organic light emitting devices by using metallic nanowire arrays

The extraction efficiency of organic light emitting devices is enhanced by depositing metallic nanowires on the glass surface and indium tin oxide (ITO) anode. For the aluminum tris-(8-hydroxyquinoline) (Alq3) based devices, a 100nm-width and 450nm-period gold nanowire array increases light extraction up to 46% from glass substrate and 80% from the organic layer. Such metallic nanowire arrays double the brightness with small absorption, only 10% lower than ITO glass. In addition, colors of the devices can be selected by the period of nanowire array. We demonstrated blue to red light emission by using single Alq3-based device.

Preparation and Optical Properties of Gold Nanowire Arrays

Gold nanowires with diameters (d) between,15 run and 200 urn and with length/diameter ratio of 700 were prepared in ion-track templates with electrode position method. The morphology and crystal structure of the gold nanowires were Studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The 200 nm (d) gold nanowires preferred orientation along the [100] direction were formed at the deposition voltage of 1.5 V (Without reference electrode). The optical properties of gold nanowire arrays embedded in ion-track templates were studied by UV-Vis spectrophotometer. There was a strong absorption peak at 539 nm for 45 nm (d) gold nanowire arrays. With the diameter of gold nanowires increasing, the absorption peak shifted to the longer wavelength. At last, the result was discussed combined with surface plasmon resonance of gold nanoparticles.

Ultrafine Single‐Crystalline Gold Nanowire Arrays by Oriented Attachment

Ultrafine single-crystalline gold nanowires (see figure) are synthesized by oriented attachment of nanoparticles in the solution phase. An amine capping agent is preferentially removed from the {111} planes, which causes the wires to form by fusion along these planes. Such nanowires can be used as the fundamental building blocks for nanoelectronics, and will enable basic studies on electric transport in one-dimensional structures to be carried out.

Direct electrochemistry of hemoglobin in gold nanowire array

Gold nanowire array has been proven to be efficient support matrixes for the immobilization of hemoglobin (Hb). The vertically oriented nanowire array provides an ordered well-defined 3D structure with nanowire density ∼5×108cm2. The adsorption of ferritin onto the nanowire surface was visualized by transmission electron microscopy. When Hb was adsorbed, UV–vis absorption and Fourier transform infrared (FT–IR) spectra show no obvious denaturation of Hb in the nanowire array. The Hb-modified nanowire array exerted direct electron transfer and gave a well-defined, nearly reversible redox couple with formal potential of −0.225V. The quantity of electroactive Hb varied with the changing of the morphology of the electrode and found to increase with the increasing of the nanowire length. Comparisons of voltammetric and quartz crystal microbalance measurements show that 70% of the Hb molecules adsorbed are electroactive when the length of the nanowire was 2μm. Both of the Hb-modified nanowire array and the unmodified nanowire array demonstrate good electrocatalytic reduction ability for hydrogen peroxide. With the adsorption of glucose oxidase onto the bare nanowire surface, sensitive and selective glucose biosensors can be fabricated.

Combining Atomic Layer Deposition with a Template-Assisted Approach To Fabricate Size-Reduced Nanowire Arrays on Substrates and Their Electrochemical Characterization

We report a combinational method to fabricate well-aligned size-reduced gold nanowire (Au NW) arrays on a Si substrate over large areas (>1.5 cm2). In this method, we employ a SiO2 atomic layer deposition (ALD) technique to reduce the pores of a porous anodic alumina (PAA) template which serves as a template for the electrodeposition of Au NW arrays and is directly integrated on the Si substrate. Unlike conventional method that simultaneously reduces the pore size and the interpore spacing by decreasing the applied potential during PAA anodization, our method allows for independently tuning these parameters. By using the ALD-reduced PAA template, we can fabricate the size-reduced Au NW arrays directly on the Si substrate with the average diameter reduced from ∼79 to ∼33 nm while their nanowire density and interwire spacing remain constant. The ALD technique enables the fine-tuning of the pore size or the nanowire diameter at an angstrom scale. Electrochemical characterization of the size-reduced Au NW arrays as nanoelectrodes is performed. The double-layer charging current (noise of the nanoelectrodes) decreases with the reduction of the nanowire diameter. Our method could be used to fabricate nanowire arrays with large spacing and small diameters via high voltage anodization and subsequent ALD reduction on the PAA template. This type of nanowire arrays might have potential applications in electrochemical and field-emission devices.

Controlling the interaction between localized and delocalized surface plasmon modes: Experiment and numerical calculations

We study the fundamental optical effects originating from the resonant excitation of localized and delocalized surface plasmon modes supported by a multilayer metallic photonic crystal slab. The optimized model system consists of a periodic gold nanowire array and a spatially separated homogeneous silver film. We show that the spacer layer controlled dipole-surface interaction reveals a pronounced period dependence when an ordered nanowire arrangement is employed. Our analysis demonstrates that strong coupling gives rise to the formation of hybridized plasmon modes. Moreover, the magnetic activity of the metallic multilayer structure is theoretically analyzed. The presented effects provide interesting tools for the optimization of future plasmonic nanodevices and metal-based metamaterials.

Template Synthesis of Arrays of One-dimensional Gold Nanowires Standing on a Carbon Film

Abstract Arrays of 1D gold nanowires with a diameter of 3–5 nm standing on a carbon film were fabricated on the basis of template-assisted electrodeposition by using an alumina membrane with surfactant-templated silica-nanochannels as the template.

Surface Plasmon Resonances of Free‐Standing Gold Nanowires Fabricated by Nanoskiving

Down to the wire: A top-down technique that combines photolithography, thin-film metal deposition, and thin-film sectioning has been developed to fabricate patterned arrays of gold nanowires of uniform, controllable length, width, and height. A systematic study of the dependence of the surface plasmon resonance (see picture) on the geometry of these wires is presented. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z600394_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Surface enhanced Raman scattering on gold nanowire arrays: Evidence of strong multipolar surface plasmon resonance enhancement

The SERS efficiency of gold nanowires arrays elaborated by electron beam lithography and lift-off technique efficiency is investigated by depositing a molecular probe (BPE) trans-1,2-bis(4-pyridyl)ethylen on the arrays and using an excitation wavelength of 632.8 nm. The observation of the dependence of the Raman enhancement versus the nanowire length is clearly demonstrated and remarkably a maximum enhancement is observed. For such arrays, we also show clearly that odd multipolar localised surface plasmon modes (up to seventh-order) exhibits a stronger efficiency than the first dipolar order in SERS process.

Metallic Photonic Crystals Based on Solution-Processible Gold Nanoparticles

We demonstrate the fabrication of metallic photonic crystals, in the form of a periodic array of gold nanowires on a waveguide, by spin-coating a colloidal gold suspension onto a photoresist mask and subsequent annealing. The photoresist mask with a period below 500 nm is manufactured by interference lithography on an indium tin oxide (ITO) glass substrate, where the ITO layer has a thickness around 210 nm and acts as the waveguide. The width of the nanowires can be controlled from 100 to 300 nm by changing the duty cycle of the mask. During evaporation of solvent, the gold nanoparticles are drawn to the grooves of the grating with apparently complete dewetting off the photoresist for channels less than 2 microm in width, which therefore form nanowires after the annealing process. Strong coupling between the waveguide mode and the plasmon resonance of the nanowires, which is dependent on the polarization and incidence angle of the light wave, is demonstrated by optical extinction measurements. Continuity of the nanowires is confirmed by conductivity properties. Simplicity, high processing speed, and low cost are the main advantages of this method, which may have a plethora of applications in telecommunication, all-optical switching, sensors, and semiconductor devices.