Au Stripes Research Articles

Development of a hydrometallurgical process for the recovery of gold and silver powders from anode slime containing copper, nickel, tin, and zinc

In order to recover gold and silver from anode slimes containing Cu, Ni, Sn, and Zn, an integrated hydrometallurgical process consisting of leaching, solvent extraction, and cementation was developed. All the metals together with 10% of Ag(I) were dissolved by the mixture of HCl and H2O2 at the optimum conditions. Separation of Au (III) together with Sn (II) was performed by Cyanex 272 from the leaching solution with two-stage counter current extraction. Stripping of Au (III) and Sn (II) from the loaded organic phase was sequentially carried out by NH4Cl and NaOH. Cu (II) in the raffinate after Au (III) extraction was separated by LIX 63 with three-stage counter current extraction. Pure Cu (II) solution was recovered from the loaded LIX 63 by stripping with dilute HCl solution. Ag powders with extra high purity were obtained by cementation with copper sheet from the raffinate after Cu (II) separation. Au (III) (99.3%) and 96.8% of Sn (II) were recovered by extraction, and purity of Au (III) and Sn (II) stripping solutions was found to be 99.99%. Au powders with extra high purity were directly synthesized by adding ascorbic acid solution into the NH4Cl stripping solution.

Synthesis of Au(I) complex-based aqueous colloids for sensing of biothiols

The present work represents new facile route for synthesis of luminescent hydrophilic core-shell colloids, where the luminescence results from Au(I) complex (AuCl)2L with cyclic PNNP ligand (L). The synthesis is based on solvent mediated aggregation of (AuCl)2L in aqueous organic solutions. Instability of (AuCl)2L in aqueous organic solutions was minimized by specific hydrophilic shell deposition arisen from electrostatically driven adsorption of polyethylenimine onto (AuCl)2L-based cores. Luminescence of the colloids is stable for week at least due to restricted degradation of the luminescent complex at the interface and high positive exterior charge of the colloids. The sensing properties of the colloids towards thiols results from their complex formation with Au+ ions. The thiol-induced stripping of Au+ ions from the colloids quenches the luminescence. The optimal conditions for fluorescent recognition of cysteine, homocysteine and glutathione with lower detection limits about 1 μM are highlighted in the work.

C60 layer growth on intact and Tl-modified Si(1 1 1)5 [formula omitted] 2-Au surfaces

The Si(1 1 1)5 × 2-Au surface comprises a quasi-one-dimensional surface reconstruction consisting of Au stripes mediated by honeycomb Si chains. In the present study, using STM observations we explored adsorption of thallium (Tl) onto Si(1 1 1)5 × 2-Au surface as well as growth of C60 layers on Tl-modified and intact Si(1 1 1)5 × 2-Au surfaces. Analysis of the results was based on the recently proposed KK model of Si(1 1 1)5 × 2-Au surface [Kwon and Kang, PRL 113 (2014) 086101]. It was found that intact Si(1 1 1)5 × 2-Au surface produces a poor template effect on the overgrown C60 layers which have a close-packed-like structure without distinct ordering. In contrast, the C60 layers grown on the Tl-adsorbed Si(1 1 1)5 × 2-Au surface where Tl atoms occupy various adsorption sites on the honeycomb Si chains have a well-ordered quasi-one-dimensional structure consisting of straight C60 chains. Ordering of the C60 molecules is a result of an intricate interplay between adsorbed C60 molecules with each other and with a substrate surface. Separation between neighboring C60 chains is dictated by the periodicity of the underlying Si(1 1 1)5 × 2-Au template, while the C60-C60 spacing within the chains of ∼12 Å that is ∼3.2a0 reflects the peculiarity of the C60-C60 intermolecular interaction on the Tl-adsorbed Si(1 1 1)5 × 2-Au surface. Structural information on (Au, Tl)/Si(1 1 1) and C60/(Au, Tl)/Si(1 1 1) systems gained in the present study can be useful for the prospective works on elucidating the ways to control electronic properties of the Si(1 1 1)5 × 2-Au surface using atomic and molecular adsorbates.

Fabrication of long range surface plasmon waveguide biosensors in a low-index fluoropolymer

The authors report the fabrication of long-range surface plasmon polariton biosensors consisting of thin narrow Au stripes embedded in a low refractive index fluoropolymer with etched fluidic channels. The fabrication process incorporates a sacrificial SiO2 channel etch stop layer to avoid waveguide damage and prevent channel over-etching, and an Al etch mask to minimize thermal cracking of the fluoropolymer during channel etching. Process details are reported along with fabrication results, and the optical and biosensing performance of the fabricated devices are demonstrated. The biosensors were tested for bulk sensitivity and bovine serum albumin (BSA) protein adsorption producing notable changes for solutions with different refractive indices (increment of 2 × 10−3) and a change in insertion loss of 0.1 dB as a monolayer of BSA forms on the device.

Size-dependent detection sensitivity of spherical particles sitting on a double-bent gold strip array

To achieve a size-dependent detection sensitivity of spherical nanoparticles, we propose a one-dimensional array of double-bent Au strips as a nanoplasmonic sensor and also as a size-filtering device. Electromagnetic simulations and measured absorbance spectra demonstrate that local plasmonic fields developed at the double-bent Au strips differentiate plasmonic responses for 100 nm- and 200 nm-sized spherical particles. Our results highlight the potential of the double-bent Au strip array as a sensing platform providing size-dependent sensitivity for spherical analytes.

Polymer/silica hybrid integration waveguide Bragg grating based on surface plasmon polaritons.

We proposed a device composed of a Bragg grating and a long-range surface plasmon polariton waveguide. The waveguide is formed by embedding a thin Au stripe in negative UV photoresist (SU-8 2005). The corrugated grating structure is created on a silica substrate using contact lithography and inductively coupled plasma etching, which is transferred onto the SU-8 2005 film by a spin coating process, producing a periodic modulation of refractive index along the waveguide. We achieve a transmission peak with an extinction ratio of 17dB and a 3-dB bandwidth of 0.9nm at a wavelength of 1575.2nm. We achieve a reflection peak with a side-mode suppression ratio of 9.7dB, a 3-dB bandwidth of 0.9nm at a wavelength of 1575.2nm when the heating electrode isn't working. The shift of the reflection peak with heating power over the range 0-6mW is approximately 2.9nm. This thermal dependence exhibits an average slope of -0.48 nm/mW.

Ultrathin Au film on polymer surface for surface plasmon polariton waveguide application

Formation of laterally continuous ultrathin gold films on polymer substrates is a technological challenge. In this work, the vacuum thermal evaporation method is adopted to form continuous Au films in the thickness range of 7–17 nm on polymers of Poly(methyl-methacrylate-glycidly-methacrylate) and SU-8 film surface without using the adhesion or metallic seeding layers. Absorption spectrum, scanning electron microscope and atomic force microscope images are used to characterize the Au film thickness, roughness and optical loss. The result shows that molecular-scale structure, surface energy and electronegativity have impacts on the Au film morphology on polymers. Wet chemical etching is used to fabricate 7-nm thick Au stripes embedded in polymer claddings. These long-range surface plasmon polariton waveguides demonstrate the favorable morphological configurations and cross-sectional states. Through the end-fire excitation method, propagation losses of 6-[Formula: see text] wide Au stripes are compared to theoretical values and analyzed from practical film status. The smooth, patternable gold films on polymer provide potential applications to plasmonic waveguides, biosensing, metamaterials and optical antennas.

Guiding Properties of 1.31-and 1.55-μm-Wavelength Surface Plasmon Polaritons on Striped Waveguides on Silicon and Their Wavelength-Selective Detection

We have analyzed the propagation behavior of 1.31-and 1.55-μm-wavelength-band surface plasmon polaritons (SPPs) for three simple Si-based plasmonic waveguides: the Au stripe waveguide, the SiO2 stripe waveguide, and the Au/SiO2 stripe waveguide on a Si substrate. The SPP propagation length in the waveguide varied depending on the waveguide structure and propagation lengths for waveguides with different structural parameters are summarized. The energy that was required for SPP detection after propagation along the waveguides for the 1.31- and 1.55-μm-wavelength bands was calculated for intensity-modulation direct-detection and heterodyne frequency-shift keying systems. The results demonstrate that SPPs can propagate with lower energy consumption than conventional electric wiring below a specific interconnect length. A wavelength-selective structure for SPPs that comprised nano-slits in an Au film on an Si substrate was fabricated. The device can selectively detect 1.31-μm-wavelength SPPs as electrical signals and transmit 1.55-μm-wavelength SPPs. Experimental photoresponses and transmittances were measured and compared with calculated results. Magnitude correlation of the measured and calculated photoresponses and transmittances showed good agreement. Evaluation of the SPP propagation behavior and the wavelength-selective structure are important considerations for the development of optoelectronic integrated circuits that use SPPs and electrons as signal carriers.

Enhanced light absorption in waveguide Schottky photodetector integrated with ultrathin metal/silicide stripe.

We investigate the light absorption enhancement in waveguide Schottky photodetector integrated with ultrathin metal/silicide stripe, which can provide high internal quantum efficiency. By using aab0-quasi-TE hybrid modes for the first time, a high absorptance of 95.6% is achieved in 5 nm thick Au stripe with area of only 0.14 μm2, without using resonance structure. In theory, the responsivity, dark current, and 3dB bandwidth of the corresponding device are 0.146 A/W, 8.03 nA, and 88 GHz, respectively. For most silicides, the quasi-TM mode should be used in this device, and an optimized PtSi device has a responsivity of 0.71 A/W and a dark current of 35.9 μA.

Nanoscale Schottky contact surface plasmon "point detectors" for optical beam scanning applications.

We propose and investigate a Schottky contact detector where the contact metal is a nanoscale metal stripe waveguide supporting surface plasmons with strong localization along the Schottky contact. We consider Au for the metal stripe, p-doped silicon for the semiconductor, operation in the infrared (at λ0=1550 nm), and internal photoemission as the sub-bandgap detection mechanism. We find that the main surface plasmon mode of operation of the Au stripe exhibits diverging real and imaginary parts of neff with decreasing stripe dimensions, commensurate with increasing confinement. The mode fields are tightly confined to the immediate vicinity of the stripe within a very small area. Coupling efficiencies, responsivities, dark currents, and minimum detectable powers are computed. An application envisaged for such nanoscale "point detectors" is optical beam scanning, motivated by the very small area of the photodetector stripe mode relative to, e.g., a Gaussian beam (∼500× smaller), such that its field distribution approximates a Dirac delta function in comparison, and by the photocurrent originating primarily from selective absorption of the photodetector stripe mode. The proposed application was verified through numerical simulation, demonstrating that a nanoscale "point detector" can scan a tightly focused Gaussian beam (2.5 μm diameter at λ0=1550 nm) with good resolution and signal to noise.

Bloch Long-Range Surface Plasmon Polaritons on Metal Stripe Waveguides on a Multilayer Substrate

We propose and demonstrate a thin Au stripe on a truncated 1D dielectric photonic crystal covered with Cytop as a waveguide for Bloch long-range surface plasmon polaritons. High-quality mode outputs were observed and a mode power attenuation of 12–17 dB/mm measured at λ0 = 1310 nm for propagation in the plane of the truncated photonic crystal and within its stopband. The truncated 1D photonic crystal advantageously enables the use of a large range of materials for the substrate, breaking free from the constraint of material symmetry to support long-range plasmons. An input grating coupler implemented as a periodic array of nanoscale Au ridges on a Au stripe was used to excite the mode via perpendicularly incident p-polarized light. The output was provided by adding a second grating coupler near the end of a waveguide to diffract light upward or by polishing the output facet and allowing the mode to radiate into a free-space beam. Advantageously, grating coupling eliminates the need for high-quality end fa...

Facile three-dimensional nanoarchitecturing of double-bent gold strips on roll-to-roll nanoimprinted transparent nanogratings for flexible and scalable plasmonic sensors.

We develop scalable 3D plasmonic nanoarchitectures comprising a double-bent nanoscale Au strip array integrated within the transparent nanograting framework, which can be continuously fabricated on a large-area flexible substrate via roll-to-roll nanoimprint lithography and angled Au deposition, realizing localized surface plasmon resonance with higher sensitivity in a smaller footprint.

Heating effects of low power surface plasmon resonance sensors

We present here a study of the possible local heating effects in surface plasmon resonance sensors using low power lasers (∼mW/mm2). By measuring the increase of electrical resistivity in an Au stripe while exciting SPR and performing numerical simulations we determine upper limits to the local heating that result of the order of ∼0.1K and ∼1K for laser power densities of 1.5mW/mm2 and 15mW/mm2 respectively.

Bulk sensing using a long-range surface-plasmon triple-output Mach–Zehnder interferometer

A triple-output Mach–Zehnder interferometric sensor operating with long-range surface plasmon–polaritons at free-space wavelengths near 1310 nm was constructed by etching a microfluidic channel through the top cladding (Cytop) of one arm of the interferometer to expose the Au stripe embedded therein. Optical bulk (refractometric) sensing was conducted by sequentially flowing sample solutions with different refractive indices through the microfluidic channel and measuring the optical powers of the three outputs, which responded sinusoidally and were separated by ∼2π/3 rad as expected in theory. Three detection schemes are analyzed and compared, demonstrating that the device benefits from a 3× larger dynamic range and the ability to suppress common perturbations relative to its single-output counterpart, thus improving the detection limit. The device is promising for biosensing applications.

Bulk Sensing Using a Long-Range Surface-Plasmon Dual-Output Mach–Zehnder Interferometer

Optical bulk (refractometric) sensing of sample solutions is demonstrated using dual-output Mach-Zehnder interferometers built from long-range surface-plasmon polariton waveguides operating at a free-space wavelength of 1375 nm. The device of interest was constructed by embedding Au stripes in Cytop claddings and etching a fluidic channel through the top cladding of one arm of the interferometer to expose the Au stripe. Bulk sensing was carried out by flowing sequentially a series of solutions of different refractive index through the microfluidic channel. The optical powers of the two outputs responded sinusoidally and were complimentary, as expected in theory. Three detection schemes aiming at improving the detection limit are analyzed showing that the device benefits from a 2× larger dynamic range, and has the ability to suppress common perturbations, relative to a single output. A detection limit of ~4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> RIU is demonstrated, which can be further improved by lengthening the sensing channel. The device is promising for application as a biosensor.

UV-Written Long-Period Grating Based on Long-Range Surface Plasmon-Polariton Waveguide

This letter proposes a long-period grating based on coupling between the long-range surface plasmon mode and a cladding mode of a thin Au film stripe fully buried in polymer SU-8. Periodical surface corrugation and accompanied refractive index variation on the SU-8 upper-cladding were induced by ultraviolet-written technique. This configuration along the Au stripe gives rise to the observation of strong resonance in a 3-mm long periodic grating. A rejection band with a contrast of −23.5 dB at the wavelength 1561 nm was achieved, which can be tuned by $\sim 30$ nm with a temperature change of 6 °C. The grating offers potential applications in surface plasmon waveguide circuits and biosensors.

Parity-time symmetry-broken Bragg grating operating with long-range surface plasmon polaritons

A parity-time symmetry-broken Bragg grating concept, comprising step-in-width IR-140 doped PMMA stripes covering step-in-width Au stripes on a fused silica substrate and operating with long-range surface plasmon polaritons, is reported. The design methodology is outlined, structures are modelled using a combination of modal analysis and the transfer matrix method, and reflectance and transmittance responses are computed. The design robustness with respect to deviations in the dimensions due to fabrication error is also investigated. The structure is capable of producing a reflectance contrast ratio of 1 over optical bandwidths of 879.96–880.04 nm.

Stress engineering of high-quality single crystal diamond by heteroepitaxial lateral overgrowth

A method for lateral overgrowth of low-stress single crystal diamond by chemical vapor deposition (CVD) is described. The process is initiated by deposition of a thin (550 nm) (001) diamond layer on Ir-buffered a-plane sapphire. The diamond is partially masked by periodic thermally evaporated Au stripes using photolithography. Lateral overgrowth of the Au occurs with extremely effective filtering of threading dislocations. Thermal stress resulting from mismatch of the low thermal expansion diamond and the sapphire substrate is largely accommodated by the ductile Au layer. The stress state of the diamond is investigated by Raman spectroscopy for two thicknesses: at 10 μm where the film has just overgrown the Au mask and at 180 μm where the film thickness greatly exceeds the scale of the masking. For the 10-μm film, the Raman linewidth shows spatial oscillations with the period of the Au stripes with a factor of 2 to 3 reduction relative to the unmasked region. In a 180-μm thick diamond film, the overall su...

Transmission of long-range surface plasmon-polaritons across gap in Au waveguide

Optical loss induced by the arbitrary structure discontinuity in the Au stripe that supports long-range surface plasmon-polaritons (LRSPPs) propagation is investigated in this paper. A broad range of arbitrary gap sizes, 4 to 20 μm, is reported for 25 nm thick Au stripe with different widths embedded in 5 μm thick optically symmetric polymer SU-8. The simulations and experimental data find a high tunneling efficiency of the long-range mode power transmission of larger than 50% over a 10 μm gap at a wavelength of 1550 nm. Accordingly, a thermally activated in-line Mach–Zehnder interferometer switch based on the guiding of LRSPPs along Au stripe with gaps is designed and fabricated. Switching characteristics are analyzed upon heating one arm of the interferometer through the passage of current therein. The fabricated switch exhibits an extinction ratio of 17 dB with a driving power of 13 mW. The results prove that LRSPPs are insensitive to technological imperfections and waveguide interruptions, which is of benefit to active plasmonic device applications.

Long-range surface plasmon Y-junctions for referenced biosensing

Long-range surface plasmon Y-junctions are demonstrated as sensors for the detection of bulk refractive index changes in solution and for protein binding. Using a fully-cladded Au stripe waveguide as a reference channel, common drift and noise in the system can be eliminated, relaxing the need for precise optical alignments. The performance of the structure is discussed theoretically, then bulk sensing is carried out experimentally with five solutions of different refractive indices, and protein sensing is demonstrated through physisorption of bovine serum albumin on a carboxyl-terminated Au stripe. The Y-junction biosensor demonstrated a very good ability to perform drift and noise suppression for fast and accurate biosensing.