Au Stripes Research Articles

Anomalous influence of electrode width on the critical current of Nb/Au Josephson junctions

Abstract We study the effect of electrodes width on superconducting current transport in Nb-Au-Nb Josephson bridges. The critical current as well as the normal bridge resistance drop with decreasing electrode width on scales of a few μm, which are orders of magnitude larger than the estimated coherence length of Au strip. We consider several physical reasons of such an anomalous influence of the width W of the superconducting electrode on the critical current Ic (AIWIc) and provide model fits for the resistive and superconducting properties of the bridges. {The smooth dependence of the Nb-Au-Nb bridge parameters on the electrode width can be used to optimize the design of superconducting devices for specific applications.

Chiral Kirigami for Bend-Tolerant Reconfigurable Hologram with Continuously Variable Chirality Measures.

Despite the commonality of static holograms, the holography with multiple information layers and reconfigurable grey-scale images at communication frequencies remain a confluence of scientific challenges. One well-known difficulty is the simultaneous modulation of phase and amplitude of electromagnetic wavefronts with a high modulation depth. A less appreciated challenge is scrambling of the information and images with hologram bending. Here, this work shows that chirality-guided pixelation of plasmonic kirigami sheets enables tunable multiplexed holography at terahertz (THz) frequencies. The convex and concave structures with slanted Au strips exhibit gradual variations in geometries facilitating modulation of light ellipticity reaching 40deg. Real-time switching of 3D images of the letter "M" and the Mona Lisa demonstrates the possibility of complex grey-scale information content and importance of continuously variable mirror asymmetry. Microscale chirality measures of each pixel experiences little change with bending while retaining controllable reconfigurability upon stretching, which translates to remarkable resilience of chiral holograms to bending. Simplicity of their design with local chirality measures opens the door to information technologies with fault-tolerant THz encryption, wearable holographic devices, and new communication technologies.

A novel butterfly-shaped core mode-based asymmetric slotted sensor for ultra-high sensitivity in sucrose concentration detection

In this research, we proposed an asymmetric rectangular slotted biosensor using photonic crystal fiber (PCF), which is subject to surface plasmon resonance (SPR). The proposed sensor utilizes only seven air holes, ensuring better fabrication feasibility and their properties are determined through finite element method (FEM)-based numerical analysis. To simplify the manufacturing process and ensure chemical stability, chemically impermeable gold (Au) strips are employed around the perimeter of the structure as the plasmonic material. With effective structural parameters, the maximum amplitude sensitivity for the proposed sensor is 663.13 RIU−1, the maximum wavelength sensitivity is 204,000 nm/RIU, and the maximum wavelength resolution is 4.90 × 10−7RIU for the y-polarized mode. It also shows a high linearity of 0.9849. For the detection of sucrose content, it has a maximum wavelength sensitivity of 207070.71 nm/RIU and a maximum amplitude sensitivity of 662.80 RIU−1. The newly introduced sensor can detect the refractive index (RI) of various analytes across a broad spectrum, ranging from 1.28 to 1.41. This extensive detection range allows the sensor to precisely measure sucrose concentrations up to 40%. This broad range enables the analysis of various analytes like sucrose, viruses, cancer cells, proteins, and numerous others.

Interface engineering by constructing vertical junction for reduced noise and improved sensitivity in 2D photodetector

Two-dimensional (2D) materials have been widely demonstrated as promising candidates for next generation photodetectors, while the noticeable channel current is still a limiting factor for photodetection sensitivity. In this work, the interface engineering has been developed by constructing a vertical pn and Schottky junction in the 2D WS2 channel, resulting in a reduced dark current and noise spectral density, significantly improving the sensitivity. Specifically, the WS2 bottom surface is coupled with p-type tellurium (Te) nanoribbon and gold (Au) stripes, thus a vertical pn and Schottky junction can be constructed at WS2/Te and WS2/Au interface, respectively. In both device architectures, the dark current and electric noise are much suppressed due to the formation of depletion region in WS2 channel. Meanwhile, the out-of-plane built-in electric field at junction can facilitate the separation of photo-excited electron–hole pairs, which subsequently yields a faster temporal response. For the WS2/Au device, the incident light can be reflected by the bottom Au and propagate through the WS2 layer again, further boosting the photo-absorption, thus the photodetection sensitivity. The engineered WS2 photodetectors exhibit the noise spectral density as low as 5.36 × 10−14 A Hz−1/2 and high specific detectivity (D*) up to 1.12 × 1011 Jones, which has one–two orders of magnitude improvement compared to the pristine device. This work provides an effective and universal interface engineering strategy to achieve low noise and high sensitivity in 2D photodetectors.

Electron‐Assisted Deposition‐Polymerization in Vacuum of Polymethines with Terminal Allyl Group

AbstractPolymethines containing an allyl group have been synthesized. Their films are produced by physical vapor deposition (PVD) on glass, silicon (Si), gold (Au), polytetrafluoroethylene (PTFE), and nanostructured plastic substrates. Optical spectra recorded during the deposition showed no decomposition of molecules. The influence of dye structure and substrate on the morphology of the deposits is studied using atomic force microscopy (AFM). Depending on the dye structure and the substrate material, various nanostructures are grown. Dichroic nanowires (NWs) are formed by self‐assembly on Au and Si substrates. On the Si surface, NWs grow between the edges of neighboring Au stripes. Several methods are used for the selective opening of the allyl group. Smooth films are produced with optical spectra similar to those deposited by PVD. The morphology of the films is dependent on the activation conditions. The thermal stability of the films exceeds the stability of those deposited via PVD.

Magneto-plasmonic grating-based structure for biosensing application

Gold with satisfactory plasmonic properties can be combined with magneto-optical material to be used as biosensors. In this theoretical work, our suggestion is to use optimized Au strips mounted on a periodic magneto-optical grating, with measurements of the transverse magneto-optical Kerr effect (TMOKE) as the basis for the sensing method. The thickness of the gold strips used is 20 nm after optimizing the structure. Considering the high cost of using gold, since the thickness of the obtained gold layer is small and only placed on the grating, this structure is expected to be economical. Also, in this research, its sensing application has been investigated, and significant results have been obtained.

An asymmetric slotted structured twin core photonic crystal fiber based highly sensitive surface plasmon resonance refractive index biosensor

A butterfly-shaped core photonic crystal fibers with less asymmetric rectangular and circular air holes are proposed, and their properties are numerically analyzed. The sensor construction is reduced to only seven air holes and uses surface plasmons stimulated inside gold (Au) strips for simplicity in manufacture and high sensitivity. Gold is employed as an effective plasmonic metal throughout this design to create resonant effects and is located away from the proposed structure to make production easier. Maximum amplitude sensitivity for the proposed sensor is 228.89 RIU−1, maximum wavelength sensitivity is 88,000 nm/RIU, and maximum wavelength resolution is 1.14 × 10−6RIU−1 for y-polarized mode where the figure of merit is 65.78 RIU−1 with a linearity of 0.9905. The proposed sensor can detect the RI of unspecified analytes between 1.27 and 1.40, allowing for the analysis of many different types of analytes, such as viruses, cancer cells, sugars, proteins, DNA/RNA and many more.

Au-strip structure dependent performance investigation of D-shaped SPR sensors for biosensing applications

Surface Plasmon Resonance (SPR)-based sensing technologies show great promise in diverse applications (e.g. biosensing) as one of the most innovative and exciting label-free sensing techniques in the last few years. In general, SPR-based sensors combine metal and dielectric interfaces, where the oscillation of metal’s free electrons occurs by the incident incoming photons. Thus, the SPR signal strength depends on the metal’s optical properties as well as the surrounding dielectric medium. This work thoroughly investigates the performance of a single mode D-shape SPR-based refractive index (RI) sensor with its gold (Au) strip topology to improve the detection sensitivity. Seven distinct Au strip designs: single-arc, inverted single-arc, multi-arc, inverted multi-arc, half-circle, coil, and sinusoidal wave are introduced to explore sensor performances, which are investigated numerically using Comsol Multiphysics. Systematic investigations are carried out for all seven proposed designs and relative comparisons are made in terms of sensitivity (wavelength and amplitude), resolution, and figure of merit (FoM). Coil and sinusoidal wave-shaped designs show excellent performance among all seven designs with a wide range of analytes’ RI (i.e. 1.31 to 1.39). The maximum wavelength and amplitude sensitivities are found to be 48000 nm/RIU and 18.55 RIU−1 respectively, with a wavelength resolution of 2.08 × 10-6 RIU and a consequent FoM of 141.18 RIU−1 for the sinusoidal wave-shaped Au-strip design. Alternatively, the coil-shaped design shows the maximum wavelength and amplitude sensitivities of 45000 nm/RIU and 32.17 RIU−1 respectively, with a wavelength resolution of 2.22 × 10-6 RIU and a FoM of 85.71 RIU−1. As a wide range of analyte’s RI can be detected by the proposed sinusoidal wave and coil Au-strip-based D-shaped sensors with improved sensitivity, these designs could be effectively used for the detection of different bio-analytes.

Development of in situ characterization of two-dimensional materials grown on insulator substrates with spectroscopic photoemission and low energy electron microscopy

Ultrathin two-dimensional (2D) materials offer great potential for next-generation integrated circuit and optoelectronic devices. Chemical vapor deposition (CVD)-grown 2D materials provide a way to mass production in industry. However, how to in situ characterize their intrinsic electric/photoelectric properties and carrier dynamics with electron/photoelectron probes is still a problem due to the interference from the conducting substrate. Here, we present a grounding Au grids method to realize in situ characterization of the CVD-grown MoS2 on the insulating thick SiO2 layer covered Si substrate with spectroscopic photoemission and low energy electron microscopy (SPELEEM). Through depositing Au grids afterwards, we have achieved good grounding of MoS2 flakes in the photoemission electron microscopy (PEEM), mirror electron microscopy (MEM), and micro-area low energy electron diffraction (µ-LEED) measurements. We have clarified the false signal caused by stray photoelectrons originated from the Au stripes, and as well as the space charge effects induced by intense photoemission. We have also confirmed that time-resolved PEEM results are not affected by the stray signal, and by adopting a small light spot, both static and time-resolved micro-area photoelectron spectroscopy (µ-PES) can be unaffected by space charge effects. Our results provide a reliable way to in situ investigate 2D materials grown on insulating substrates by probing photoelectrons or backscattered electrons.

Efficient leaching and recovery of metallic gold and copper from integrated circuits with the novel bromotrihalide ionic liquids based on the redox mechanism

In order to develop a safe, closed-loop and eco-friendly process for high efficiency leaching and recovery Au and Cu from integrated circuits (ICs), bromotrihalide ionic liquids (ILs) were synthesized as the perfect substitutes for corrosive or toxic leaching agents. Notably, bromotrihalide ILs showed excellent satisfied thermostability, low viscosity and low water solubility traits in green recovery of metallic Au and Cu. The leaching behavior was explored by studying experimental factors, including solid-to-liquid ratio, temperature and leaching methods. In addition, the corresponding kinetics models were established. It was noteworthy that the maximum Au leaching efficiency of 94.6% and that of Cu 100% were reached in the optimal conditions (20 g/L, 45 °C). It suggested that the leaching process of Au was co-controlled by chemical reaction and diffusion, with a corresponding activation energy of 37.4 kJ/mol. For revealing the redox leaching mechanism, XPS, UV–Vis, SEM, EDS-mapping and ICP spectrometry were conducted, and the leaching pathways of Au were triumphantly investigated via DFT-computed transition state energy barrier and ADCH charge. At last, Au nanoparticles and Cu(II) solution were obtained by selective stripping of Au and Cu. And the recovery efficiencies of Au and Cu were 94.6% and 100%. This work suggests a promising approach to recover the Au and Cu from ICs.

Step‐Edge‐Induced Patterning and Orientation Control of Crystalline Organic Semiconductor Films

AbstractOrientation control over micropatterned crystalline organic semiconductor film is crucial to achieve high device performance with small variation in organic electronics. Here, using Au patterned SiO2 substrates, a method is reported to realize high‐resolution patterning and orientation control of crystalline organic thin films simultaneously. The vacuum deposited N,N‐dioctyl‐3,4,9,10‐perylene tetracarboxylic diimide (PTCDI‐C8) molecules can selectively diffuse to and nucleate on prepatterned Au stripes, resulting in patterned crystalline films with a preferential orientation distribution. Scanning tunneling microscope and high‐resolution atomic force microscope images reveal that the PTCDI‐C8 molecules first assemble on Au with perylene diimide cores in a laying down configuration, providing nucleation sites at the step edges for directional growth along the a‐axis of the molecule crystal. Subsequent deposition of molecules leads to orientated crystalline films growth due to the π packing of the perylene diimide cores, resulting in orientation control on micropatterned crystalline films. The finding provides a new strategy to grow oriented crystalline films for high device performance uniformity.

Design of an all-optical multi-logic operation-integrated metamaterial-based terahertz logic gate.

Terahertz logic gates play a vital role in optical signal processing and terahertz digitization. Herein, a strategy to design an all-optical terahertz logic gate device composed of metamaterials with a semiconductor-metal hybrid is proposed; accordingly, a concrete logic gate composed of Ge embedded-in Au stripe supported by a Si board is presented theoretically. Simulation results reveal the dependence of the terahertz transmission spectra on the different illuminations in the device. Based on the illumination-transmission response, the designed device can realize the NOR or OR Boolean operation. The effects of the width of the Ge-Au stripe as well as the Si board on the transmission spectra and logic performance were also investigated.

PeakForce Quantitative Nanomechanical Imaging for Characterization of the Surface Energy of Nano-Patterned Au Strip

ABSTRACT Precise measurement of the surface energy of nanoscale metal thin films is crucial for the fabrication of reliable miniaturized electronic devices consisting of multi-stacked thin film strips. However, the conventional method utilizing sessile drops to measure the surface energy is not suitable for nanoscale samples owing to the much larger size of the liquid droplets than those of the samples being measured. Herein, nCA-AFM (nano contact angle-atomic force microscopy) based on PF-QNM (PeakForce quantitative nanomechanical mapping) imaging mode is explored as a novel tool to measure the surface energy of nanoscale Au strips. Au strips with thicknesses of 50 and 100 nm were patterned to have widths in a range from 200 to 500 nm. The surface energy of the nano-patterned Au strips measured with PF-QNM methods revealed that grain size is the most important factor determining the surface energy. The sample having different widths with the same grain size showed similar surface energy values, regardless of the sample dimensions. Our results highlight that grain size control is required to achieve the target surface energy of metal strips for applications in nanoscale electronic devices.

Tunable Narrow-Band Filter Based on Long-Range Surface Plasmon Polariton Waveguide Bragg Grating

A narrow-band Bragg grating filter based on a long-range surface plasmon polariton (LRSPP) waveguide is theoretically demonstrated. The three-dimensional Au stripe that is embedded in polymer SU-8 acts as both the waveguide and the heating electrode. With the eigen mode expansion and finite element method optimizations, the proposed filter shows a reflectivity of 0.578 and a 3 dB bandwidth of 1.1 nm. The central wavelength can be tuned from 1549.9 nm to 1544.3 nm by varying temperature from 25 °C to 75 °C, while maintaining the optical return loss at −2.5 dB. This proposed tunable filter has potential in on-chip light signal processing.

Second harmonic generation from GaAs-Au subwavelength relief gratings

We study numerically the second-harmonic generation (SHG) from subwavelength GaAs relief gratings with and without Au nano-stripes on the bottom of grating troughs. The SHG efficiency is calculated by finite element method as a function of grating amplitude, Au-stripes thickness, depth of trough for TE and TM polarized fundamental harmonic. Our results show that a deep subwavelength grating without Au stripes can be considered as a homogeneous film when the grating period is 3.5 times shorter than the wavelength. Such a grating with a certain amplitude enhances the SHG efficiency by about 20 times compared with the efficiency of a crystal with flat surface. The Au-stripes at the grating troughs significantly increase the electromagnetic field concentration in the crystal ridges of the grating due to plasmonic resonance. In this case, the SHG efficiency enhancement is more than 500 times, while the absolute value of SHG efficiency reaches 1.2 × 10−3% when the intensity of pump light is 1 GW/cm2.

TiOx/Ti/TiOx Tri-Layer Film-Based Waveguide Bolometric Detector for On-Chip Si Photonic Sensor

In this article, we experimentally demonstrate an on-chip optical power monitoring at the near-infrared spectral region (1520&#x2013;1600 nm) using the waveguide bolometric detector with a TiO_<i>x</i>/Ti/TiO_<i>x</i> tri-layer film based on the silicon-on-insulator (SOI) platform. For the incident light absorption causing a heat generation, a heavily doped (<inline-formula> <tex-math notation="LaTeX">${n}^{+}$ </tex-math></inline-formula>) Si waveguide is introduced to utilize the mechanism of free-carrier absorption (FCA), and a metal (Au) strip is deposited onto the <inline-formula> <tex-math notation="LaTeX">${n}^{+}$ </tex-math></inline-formula> Si waveguide to further enhance the light absorption. A bolometric material of TiO_<i>x</i>/Ti/TiO_<i>x</i> tri-layer film is integrated for the thermal-to-electrical conversion. As a result, it exhibits superior performances, which are the temperature coefficient of resistance (TCR) of &#x2212;2.296&#x0025;/K and the maximum sensitivity of &#x2212;46.45&#x0025;/mW with a low wavelength-dependency. In addition, a rapid response time is obtained with the rise/fall time of <inline-formula> <tex-math notation="LaTeX">$24.6 ~\mu \text{s}/29.8 ~\mu \text{s}$ </tex-math></inline-formula>, which is enough for a variety of optical sensing applications. This work demonstrates the waveguide-based bolometric photodetection using the FCA effect, for the first time to our knowledge, which can also be simply extended for the operation wavelength range to the mid-infrared (MIR) spectral region for bio/chemical sensing applications.

Quad-band terahertz metamaterial absorber using three parallel gold strips surrounded by two identical gold ring arcs

Quad-band terahertz metamaterial absorber with near-perfect absorption is given in this paper. It is designed by a patterned Au layer and a continuous Au film separated by an insulating dielectric layer, of which the patterned Au layer is consisted of three parallel Au strips (a longer and two shorter) surrounded by two Au ring arcs of the same size. Four separated terahertz absorption peaks with narrow bandwidths and large absorptance are realized. The first three absorption peaks are due to the fundamental modes of the Au strips and the Au ring arcs, while the fourth absorption peak is ascribed to the excitation of three-order resonance in the Au ring arcs. The field distributions of the four absorption peaks are presented to verify their physical mechanisms. The influence of geometrical dimensions of the proposed configuration on the performance of the quad-band light absorption is discussed. Moreover, considering the potential sensing applications, the sensing performance of the proposed absorption device is also explored. The suggested scheme could provide considerable application prospects in selective thermal radiation, spectral imaging, sensing, detecting, electromagnetic stealth, etc.

Universal Design of Ultra-Broadband and Ultra-Compact High Order Mode Pass Filters Based on Enhanced Absorption in Ultrathin Metal Layers

In hybrid plasmonic Si waveguides integrated with ultrathin Au stripes, mode hybridization effects between quasi-TE modes of different orders and various bound modes are first presented. Enabled by nearly complete mode-selective absorption attributed to the enlarged mode propagation attenuation (MPA) coefficient for lower-order quasi-TE modes under circumstances of mode hybridizations, multi-segment tapered structures are theoretically proposed to constitute high order mode (HOM) pass filters. It is believed that these innovative observations would have potential applications in the ultra-compact on-chip mode division multiplexing (MDM) systems, and provide inspirations for the development of multimode photonics.

Au-strip's shape dependent performance of D-shaped SPR based sensors

D-shaped Surface Plasmon Resonance (SPR) based sensors show great promise for detecting different analytes with improved sensitivity and resolution. This work focuses on the investigation of the effect of gold (Au) strip's shape on the performance of D-shaped SPR sensor having a single mode germanium (Ge) core and microfluidic channel for analytes. Three different designs of Au strips namely, flat (design A), parabolic (design B), and combined (design C) having mixing of small flat and parabolic strips are considered here. The detailed numerical investigations are performed for all the designs using the finite element method. The highest wavelength and amplitude sensitivities are found to be 44 μm/RIU and 115.85 RIU−1, respectively at a resolution of 2.27 × 10−06 for the parabolic-shaped Au strip (i.e., design B). Alternately, design A shows reduced wavelength and amplitude sensitivities of 13 μm/RIU and 51.43 RIU−1, respectively with a resolution of 7.69 × 10−06. Similarly, design C reveals the wavelength and amplitude sensitivities of 14 μm/RIU and 45.01 RIU−1, respectively with a resolution of 7.14 × 10−06. Thus, the sensitivity of D-shaped SPR based sensors could be tuned significantly by modifying only the shape of the metal strip. This analysis would be useful in designing highly sensitive SPR based sensors.

Fabrication of Bloch Long Range Surface Plasmon Waveguides Integrating Counter Electrodes and Microfluidic Channels for Multimodal Biosensing

We report the fabrication of a novel multimodal biosensor combining plasmonic and electrochemical detection. The plasmonic sensors are based on monitoring the propagation of Bloch long-range surface plasmon polaritons (LRSPPs) along thin narrow Au stripes, integrating grating couplers as input/output means. The electrochemical sensors use the same Au stripes as working electrodes with nearby Pt stripes integrated on-chip as counter electrodes. The structures are fabricated on a truncated 1D photonic crystal comprised of a 15-period stack of alternating layers of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> . The Au and Pt stripes are fabricated using bilayer lift-off photolithography, and the gratings are fabricated using e-beam lithography. The structures are arranged into arrays targeting multichannel biosensing. The wafer is covered with CYTOP as the upper cladding with etched microfluidic channels providing access to the sensing surfaces and is wafer-bonded to a Borofloat silica wafer to encapsulate the fluidic channels and enable edge (in-plane) fluidic interfacing. The wavelength response of the grating-coupled plasmonic waveguide sensors is presented along with surface sensing results. Cyclic voltammetry measurements using the Au and Pt stripes as the working and counter electrodes are also presented. [2021-0103]