Gold Nanowire Arrays Research Articles

Enhancing four-wave-mixing processes by nanowire arrays coupled to a gold film

We consider the process of four-wave mixing in an array of gold nanowires strongly coupled to a gold film. Using full-wave simulations, we perform a quantitative comparison of the four-wave mixing efficiency associated with a bare film and films with nanowire arrays. We find that the strongly localized surface plasmon resonances of the coupled nanowires provide an additional local field enhancement that, along with the delocalized surface plasmon of the film, produces an overall four-wave mixing efficiency enhancement of up to six orders of magnitude over that of the bare film. The enhancement occurs over a wide range of excitation angles. The film-coupled nanowire array is easily amenable to nanofabrication, and could find application as an ultra-compact component for integrated photonic and quantum optic systems.

<I>In-Situ</I> Fabrication of AAO Template without Oxide Barrier Layer and Its Applications

Porous anodic aluminum oxide (AAO) film is the most widely used template in combination with electrodeposition (ED) method to fabricate one-dimensional nanostructures such as nanowires, nanotubes and nanorods. However, the existing oxide barrier layer after the anodization blocks the application of AAO template in synthesis of nanostructures via direct electrodeposition. In this paper, AAO template without oxide barrier layer was successfully fabricated by stepwise voltage decrement; influence of two types of stepwise voltage decrement on the removal of oxide barrier layer was introduced. Field Emission Scanning Electron Microscopy (FESEM) images indicated that stepwise voltage decrement could make the oxide layer thin effectively. Meanwhile, highly ordered gold nanowire arrays were fabricated by using direct electrodeposition method based on AAO template with the second anodization process with stepwise voltage decrement of 1 V/min, FESEM image showed that as-prepared gold nanowires are uniform in diameter and the diameter is in accordance with the diameter of AAO template pores. XRD pattern revealed that gold nanowires were indexed as face-centered cubic phase.

Growth of E18 Rat Hippocampal Neuronal Cells on Nanostructured Surfaces for Enhanced Electrical Stimulation and Recording

We have prepared gold nanowire arrays inside nanoporous alumina templates with the goal towards neuronal interfacing and electrical recording from neurons. We have investigated biofunctionalization of such gold nanowire arrays (GNWs) and gold nanofilm (GNF) platforms to understand its impact on neuronal attachment and growth. Poly-D-Lysine (PDL) was coated on the nano-templates surfaces for adhesion of neurons which also enhanced the neuronal growth. Optical microscopy and scanning electron microscopy images revealed strong affinity and improved growth of neurons on PDL-coated surfaces. Such results will impact future investigation of stimulation and recording of electrical activity on nanoscale surfaces.

Non-Enzymatic and Highly Sensitive H2O2 Sensor Based on Pd Nanoparticle Modified Gold Nanowire Array Electrode

A non-enzymatic hydrogen peroxide (H2O2) sensor based on a vertically aligned gold nanowire array electrode modified with palladium nanoparticles (PdNP/AuNAE) has been fabricated. PdNP have been deposited onto the AuNAE surface by a hydrothermal reduction method using a borohydride technique. Scanning electron microscope inspection (SEM) has revealed granular Pd particles deposited on the surface of the nanowires. X-ray diffraction (XRD) peak analysis has determined an average crystallite size of 3 to 5 nm for PdNP. The catalytic behavior of PdNP/AuNAE has been studied using amperometry and voltammetry which showed a linear response up to 2 mM of H2O2 with a sensitivity of 530 μA mM−1 cm−2 at 20°C. This electrode can detect 5 μM (S/N = 3) of H2O2 at normal conditions without using any enzyme or mediator. A high selectivity toward H2O2 (up to 97%) has been obtained using this electrode platform in the presence of common electrochemical interferences such as ascorbic acid, uric acid, acetaminophen and dopamine.

Circular Dichroism in the Optical Second-Harmonic Emission of Curved Gold Metal Nanowires

Here we report the experimental observation of circular dichroism in the second-harmonic field (800-400 nm conversion) generated by self-organized gold nanowire arrays with subwavelength periodicity (160 nm). Such circular dichroism, raised by a nonlinear optical extrinsic chirality, is the evident signature of the sample morphology. It arises from the curvature of the self-assembled wires, producing a lack of symmetry at oblique incidence. The results were compared, both in the optical linear and nonlinear regime, with a reference sample composed of straight wires. Despite the weak extrinsic optical chirality of our samples (not observable by our optical linear measurements), high visibility (more than 50%) was obtained in the second-harmonic generated field.

Interactions between E18 Rat Hippocampal Neurons and Au-Nanowire Arrays

The anodization of aluminum templates created nanoporous alumina tubes arranged parallel to each other and electrodeposition using gold solution (AuHCl4) resulted in arrays of gold nanowires (GNWs) inside the pores. For investigation of Au-nano-neuronal interactions, we have cultured embryonic day 18 rat hippocampal neurons on the surface of nanowires. For preliminary understanding of the neuronal growth and connectivity, we studied the images of nano-neuronal interactions by using optical, fluorescence and scanning electron microscopy (SEM). For adhesion of neurons to nanoarrays surfaces, we used bioconjugating protein coating Poly-D-Lysine (PDL). The embryonic hippocampal tissues were dissociated mechanically and cultured on Au-nano templates. We demonstrated well-defined neuronal networks on Au-nanowire (GNW) arrays and on standard glass coverslips. The neurons attached with the nanowires surfaces by an interface of PDL, which is a positively charged poly-peptide and plays a vital role in neurites growth on the nanowire arrays. The pre- and post-synaptic affects of neuronal interactions on the surfaces of nanowires were measured by Ca+ imaging in Keck microscope.

Optical and electrical properties of gold nanowires synthesized by electrochemical deposition

Gold nanowire arrays with different sizes were fabricated by electrochemical deposition in etched ion-track templates. The diameter of the gold nanowires between 30 and 130 nm could be well adjusted by pore sizes in the templates through etching time. Single-crystalline nanowires were achieved by changing the parameters of electrochemical deposition. The morphology and crystal structure of the fabricated gold nanowires were characterized by means of scanning electron microscopy and transmission electron microscopy. The optical properties of the gold nanowire arrays embodied in templates were systematically measured by absorption spectra with a UV/Vis/NIR spectrophotometer. Due to the surface plasmon resonance effect, the extinction peaks of gold nanowire arrays possessed a red-shift with increasing wires diameter and a blue-shift with decreasing angle between incident light and nanowire arrays. The failure current density of the single gold nanowire as a function of diameter was determined and the failure mechanism was also discussed.

Observation of ultra-narrow band plasmon induced transparency based on large-area hybrid plasmon-waveguide systems

We report the observation of an ultra-narrow band plasmon induced transparency resonance which is realized in a large area hybrid plasmon-waveguide system consisting of a gold nanowire array embedded in a slab waveguide. Due to the destructive interference between optical modes supported by the hybrid system, an ultra-narrow plasmon induced transparency resonance with a bandwidth of 8 nm at the wavelength of 966 nm was obtained (i.e., ∼1/120 of the peak wavelength at the incident angle of 60°). The group velocity is estimated to be ∼76, which is promising for miniaturized slow-light components.

Harvesting light at the nanoscale by GaAs-gold nanowire arrays

A nanoscale metal-semiconductor-metal photodetector with a 40 nm-thick GaAs absorbing layer has been studied numerically and experimentally. A gold nanowire array is the top mirror of a Fabry-Perot cavity and forms interdigitated Schottky contacts. Nearly perfect absorption is achieved in TE polarization. It is shown numerically that the gold nanowire array induces light absorption in GaAs nanowires with tiny sections (100 nm × 40 nm). High external quantum efficiency (η > 40 %) is demonstrated.

Investigation of the surface properties of gold nanowire arrays

Gold nanowire arrays with diameters ranging from 45 to 200 nm were obtained via electrochemical deposition within the ion-track templates. The morphology of gold nanowires was imaged by scanning electron microscopy (SEM). The surface properties were investigated by surface plasmon resonance (SPR) and X-ray photoelectron spectroscopy (XPS). The SPR peaks were observed as the gold nanowire arrays embedded in the templates and their intensity decreased after the sample exposed to the air for a certain time due to the formation of chemisorbed oxygen on nanowire surface. The positive binding energy shifts in Au core level was found when the gold nanowire arrays embodied in template and the initial- and finial-state effects were introduced to explain this phenomenon.

Omnidirectional absorption enhancement in hybrid waveguide-plasmon system

We investigate the omnidirectional absorption enhancement induced by the excitation of the localized surface plasmon in the hybrid system consisting of a gold nanowire array embedded in a slab waveguide. Assisted by the waveguide layer, the hybrid system can support the localized waveguide-plasmon resonances for a wide range of incident angles. Theoretical and experimental results are both presented to demonstrate the omnidirectional absorption enhancement which could find important applications on plasmonic-assisted photovoltaic devices or photodetectors.

Characterization and Application of Surface Plasmon-Enhanced Optical Diffraction from Electrodeposited Gold Nanowire Arrays

Arrays of gold nanowires formed by the process of lithographically patterned nanowire electrodeposition (LPNE) were characterized by a combination of SEM, polarized UV-visible absorption spectroscopy and optical diffraction measurements. A transverse localized surface plasmon resonance (LSPR) was observed for gold nanowire arrays with an absorption maximum (λ(max)) that varied with nanowire width. Transmission optical diffraction measurements were measured with the even and odd diffraction orders creating an alternating, out of phase sinusoidal intensity pattern characteristic of the LPNE nanowire arrays. The intensities of the even diffraction order maxima were the strongest for nanowires with a width of 115 ± 10 nm; nanowires of this width exhibit a λ(max) of 635 ± 10 nm, verifying that the transverse LSPR has enhanced the optical diffraction signal. Real time total internal reflection diffraction intensity measurements were used to monitor in situ the electrodeposition of silver monolayers onto the gold nanowire arrays.

Tuning the optical properties of metamaterials based on gold nanowire arrays embedded in alumina

We fabricated a series of gold nanowires/alumina composite films with different wire lengths. Optical transmission measurements confirmed that the composite films exhibit transverse and longitudinal surface plasmon resonances. We show that the wavelength of the longitudinal resonance is sensitive to nanowire length, while that of the transverse resonance is not. The experimental results are in agreement with the modeled results based on the Maxwell Garnett effective medium theory. Moreover, the window for negative refraction of the samples can be tuned in synchronism with the longitudinal resonance by the nanowire length.

Tunability and linewidth sharpening of plasmon resonances on a periodic gold nanowire array coupled to a thin textured silver film

We theoretically study the plasmon mode spectrum of a multilayer structure consisting of a periodic gold nanowire array and a spatially separated thin silver film with periodic slits. Results show that the plasmon mode spectrum of the multilayer structure depends sensitively on the relative lateral displacement of the Au nanowire array with respect to the textured silver film. This is due to the interaction between the localized surface plasmon (LSP) of the nanowire array and the plasmon modes, including the horizontal LSP and the antisymmetric short-range surface plasmon polariton (SPP), of the textured thin silver film. The strong coupling between the LSP and the antisymmetric short-range SPP results in a redshifted plasmon resonance with a significantly narrow linewidth and a large electromagnetic field enhancement. Moreover, the lateral displacement also has a great influence on the spacer layer controlled dipole-surface interaction. Therefore, this relative lateral displacement provides an efficient way to tune the optical properties of the multilayer structure, and this kind of highly tunable nanostructure can be used as a tunable plasmonic filter or a substrate for LSPs sensor.

Fabrication and optical properties of gold nanowire arrays

In this work the optical properties of arrays of gold nanowires in transmission and attenuated total reflectance (ATR) geometry has been examined further, with a view to maximising the sensitivity by finding optimum nanowire and array dimensions. Gold nanowire arrays were grown by electrochemical deposition into a nano-porous alumina template. The effect of changing the nanowire aspect ratio on the optical properties was investigated.

High-density gold nanowire arrays by lithographically patterned nanowire electrodeposition

Here we describe a new method for preparing multiple arrays of parallel gold nanowires with dimensions and separation down to 50 nm. This method uses photolithography to prepare an electrode consisting of a patterned nickel film on glass, onto which a gold and nickel nanowire array is sequentially electrodeposited. After the electrodeposition, the nickel is stripped away, leaving behind a gold nanowire array, with dimensions governed by the gold electrodeposition parameters, spacing determined by the nickel electrodeposition parameters, and overall placement and shape dictated by the photolithography.

Controlled in situ nanoscale enhancement of gold nanowire arrays with plasmonics

The controlled in situ growth of ordered gold nanoparticles and nanowire arrays has beenstudied by optically tracking changes in the local surface plasmon resonance (LSPR)spectrum. A spectrometer and custom-programmed analysis software track changes inthe LSPR spectrum. The peak position, peak height (i.e. extinction intensity)and peak width (e.g. radius of curvature) were tracked over time to quantify thedynamic growth of gold as soon as the system was exposed to a commercial goldenhancement solution. This enables the controlled dynamic growth of nano-objectswithout the necessity of characterizing the growth and aggregation kinetics of thegold enhancement solution. The result was the successful enhancement of theirelectrically conductive and plasmonic properties, as well as the controlled growth andtransformation of line-patterned nanoparticles into conductive particle-based nanowires.

Optical sensing with simultaneous electrochemical control in metal nanowire arrays.

This work explores the alternative use of noble metal nanowire systems in large-scale array configurations to exploit both the nanowires’ conductive nature and localized surface plasmon resonance (LSPR). The first known nanowire-based system has been constructed, with which optical signals are influenced by the simultaneous application of electrochemical potentials. Optical characterization of nanowire arrays was performed by measuring the bulk refractive index sensitivity and the limit of detection. The formation of an electrical double layer was controlled in NaCl solutions to study the effect of local refractive index changes on the spectral response. Resonance peak shifts of over 4 nm, a bulk refractive index sensitivity up to 115 nm/RIU and a limit of detection as low as 4.5 × 10−4 RIU were obtained for gold nanowire arrays. Simulations with the Multiple Multipole Program (MMP) confirm such bulk refractive index sensitivities. Initial experiments demonstrated successful optical biosensing using a novel form of particle-based nanowire arrays. In addition, the formation of an ionic layer (Stern-layer) upon applying an electrochemical potential was also monitored by the shift of the plasmon resonance.

Hydrogen sensor based on metallic photonic crystal slabs

We present a hydrogen sensor based on metallic photonic crystal slabs. Tungsten trioxide (WO(3)) is used as a waveguide layer below an array of gold nanowires. Hydrogen exposure influences the optical properties of this photonic crystal arrangement by gasochromic mechanisms, where the photonic crystal geometry leads to sharp spectral resonances. Measurements reveal a change of the transmission depending on the hydrogen concentration. Theoretical limits for the detection range and sensitivity of this approach are discussed.

Disposable biosensor based on immobilisation of glutamate oxidase on Pt nanoparticles modified Au nanowire array electrode

Novel electrochemical platform based on Pt nanoparticle modified ordered three-dimensional gold nanowire arrays (PtNP/NAEs) for the amperometric sensing of H 2O 2 and glutamate is developed. Pt nanoparticle (PtNP) is fabricated by electrodeposition onto the 3D nanowires and characterised using scanning electron microscopy (SEM) and cyclic voltammetry. The deposited nanoparticles have an average size of 20 nm. The PtNP/NAE shows a linear response of up to 20 mM for H 2O 2 detection with a sensitivity of 194.60 μA mM −1 cm −2 at 20 °C. It can detect 1 μM (S/N = 3) of H 2O 2 at normal condition without using any enzyme or mediator. Analytical performance of this electrode is tested by immobilising glutamate oxidase (GlutOx) through cross-linking in the matrix of bovine serum albumin (BSA), Nafion and glutaraldehyde. At physiological pH, the biosensor showed the sensitivity of 10.76 μA mM −1 cm −2, with a linear range of up to 0.8 mM.