Thick Gold Film Research Articles

Energy–dependent femtosecond LIPSS on germanium and application in explosives sensing

Abstract In this study, we fabricated laser-induced periodic surface structures (LIPSS) on a germanium surface through laser ablation in air using axicon and femtosecond (fs) pulses. This novel approach permitted the nanoscale material processing outcome refinement via an fs Bessel beam. Our investigations aimed at systematically understanding the formation of periodic structures under various experimental conditions, such as (i) different pulse energies ranging from 50 µJ to 1000 µJ at a constant scan speed and (ii) constant energy with different scan speeds (0.1–3 mm s−1). By adjusting the fluences and scan speeds, we were able to identify the parametric space and alter the periodicity of the low-spatial frequency LIPSS and high-spatial frequency LIPSS on germanium, which were analyzed using field emission scanning electron microscopy. An optimal LIPSS formation over a large area of germanium was achieved at an input energy of 250 µJ and a scan speed of 0.75 mm s−1. Additionally, we measured the contact angles of the Ge nanostructures (GeNSs) to demonstrate their hydrophobic nature and non-wetting properties, providing insights into the behavior of LIPSS. Subsequently, the GeNSs were coated with a ∼15 nm thick gold (Au) film using a thermal deposition method. Utilizing these, the surface-enhanced Raman spectroscopy (SERS) technique detected diverse analytes, such as tetryl (an explosive) at a concentration of 50 µM and thiram (a pesticide) at 500 nM. The SERS enhancement factors for tetryl and thiram molecules on GeNSs coated with a 15 nm-thick Au layer were determined to be 2.5 × 104 and 4.2 × 105, respectively.

Characteristics study of a dual-wavelength polarization filter based on gold-filled square lattice photonic crystal fiber

This study proposes a polarization filter based on gold-filled photonic crystal fiber (PCF) with a square lattice structure. Utilizing the finite element method (FEM), the filtering characteristics of the model were numerically simulated. The dispersion relation and loss characteristics of this structure were analyzed, and the optimal structural parameters were obtained through structural adjustments. Furthermore, the performance of the filter was evaluated under a 2% variation in manufacturing tolerances for gold film thickness (), air hole spacing (), and air hole diameters () and (). Results indicated that at the 1310 nm and 1550 nm communication windows, the confinement losses of the filter were 1354.6 dB/cm and 869.04 dB/cm, respectively, while the losses for the -polarization were merely 16.97 dB/cm and 0.98 dB/cm. When the filter length was set to 0.5 mm, the maximum extinction ratios (ERs) for the two windows reached 588.2 dB and 370.6 dB, and the filter bandwidth extended to 640 nm. Moreover, the characteristics of the filter under manufacturing tolerances were computed, revealing that the filter’s performance remained stable and feasible despite manufacturing errors. The proposed rectangular gold-coated PCF is anticipated to have broad applications in optical fiber communication and optical information processing.

[formula omitted] modified U-shaped fiber surface plasmon resonance sensor with high sensitivity

Design of optical fiber structure and sensitive material coating are two effective performance improvement approaches for fiber optic surface plasmon resonance (SPR) sensors. Here, a tungsten diselenide (WSe2) modified U-shaped fiber optic SPR sensor is proposed. It is found that the sensing performances of the proposed U-shaped probe can be controlled with the thickness of gold film, WSe2 layers, and bending radius of the U-shaped fiber. A sensitivity of 27520 nm/RIU (RIU: refractive index unit) is obtained with the optimized U-shaped probe, which is about 11.56-fold and 12.29-fold improvements over the traditional in-line transmission fiber optic SPR sensors without WSe2 coating and with monolayer WSe2, respectively. These results demonstrate a promising approach for sensitivity improvement of fiber optic SPR sensors, and the proposed WSe2 modified U-shaped fiber optic SPR sensor may have prospective potential applications in biological sensing, chemical sensing, and environmental monitoring.

Dual-window polarization filtering characteristics of rectangular photonic crystal fibers

This paper presents a photonic crystal fiber (PCF) polarization filter with a square array arrangement of gold film fillings, allowing for filtering at dual wavelengths. The paper analyzes the dispersion characteristics and loss properties of this structure and optimizes the structural parameters through adjustments to achieve the best performance. At 1310 nm, the confinement losses of x and y polarization fundamental modes are 903.54 dB/cm and 30.51 dB/cm, respectively; at 1640 nm, the confinement losses of y and x polarization fundamental modes are 479.02 dB/cm and 88.72 dB/cm, respectively. The corresponding filtering bandwidths are 390 and 350 nm, while the full width half maximum (FWHM) is 59.56 nm, indicating excellent selectivity and resolution of the filter. The performance metrics, such as confinement loss, extinction ratios, and bandwidth, are compared in the paper with those reported for other filters. Additionally, the study also analyzed the filter’s performance under varying manufacturing tolerances of gold film thickness and air hole diameter by 5%, revealing that the filter’s performance remains stable and feasible even in the presence of errors.

Miniature fiber optic SPR high sensitivity humidity sensor based on coated polyvinyl alcohol film

For the measurement of relative humidity, this study employed Surface Plasmon Resonance (SPR) technology, a sensor with a micro-conical fiber structure (sensing length is only 375 μm) was combined with Polyvinyl Alcohol (PVA) to create a humidity sensor that is highly sensitive, compact, dense, and exhibits good linearity. The humidity sensor is based on a gold film (thickness of about 40 nm) on the surface of the miniature fiber optic structure, and by applying PVA coating, the SPR humidity sensor shows resonance peaks in the transmission spectrum in ambient air, and as the number of layers of PVA coating (thickness) is added, the resonance peaks’ positions are red-shifted. The experimental findings demonstrated that this SPR humidity sensor’s sensitivity was 0.162 nm/%RH at an initial resonance wavelength of about 550 nm (one layer) and about 1.542 nm/%RH at an initial resonance wavelength of 656 nm (five layers) in the range of 46 %RH to 93 %RH. The wavelength and the relative humidity had a good linear connection. Temperature tests revealed the sensor has a −0.152 nm/°C temperature sensitivity between 20 °C and 50 °C and has a high linearity (0.999). Therefore, the sensor has potential applications in humidity measurement.

SPR based dual parameter wide range curling pot shaped photonic crystal fiber sensor

This article proposes a curling pot shaped photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR), which utilizes two parallel polished surfaces in the cladding to achieve dual parameter measurements of liquid refractive index (RI) and temperature. The mode characteristics and sensing performance of the designed PCF sensor are studied using the finite element method, and the effects of changes in structural parameters such as pore radius, spacing, and gold film thickness on the resonance spectrum are analyzed. The sensing accuracy of the sensor is insensitive to the change of structural parameters, and it has the characteristics of a wide detection range, high sensitivity, and easy manufacture. When the measured RI is in the range of 1.33∼1.42, the maximum RI sensitivity is 20400 nm RIU−1, and the maximum FOM is 483.3 RIU−1. When the temperature ranges from −10 °C to 100 °C, the maximum sensitivity is 15.4 nm °C−1, and the maximum FOM is 0.43 RIU−1. The tight structure design of the sensor core close to the polishing surface and the anti-spill light design with a uniform arrangement of air holes enhance the SPR effect, which is the essential reason for achieving a wide detection range and high sensitivity.

Tunable chalcogenide solid-core anti-resonant fiber polarization filter based on SPR effect

Based on surface plasmon resonance (SPR), we proposed a tunable chalcogenide solid-core anti-resonant fiber (SC-ARF) polarization filter. The purpose of introducing the SPR, which is excited by coating the inner wall of the cladding tubes with a gold film, is to achieve a discrepancy between the confinement loss of two polarized fundamental modes (FMs). The full-vector finite element method (FV-FEM) evaluates the impact of fiber core radius, cladding tube radius, cladding tube wall thickness, and gold film thickness on the polarization filter characteristics. The results show that when the thickness of the gold film is 30 nm and the fiber length is 4 mm, the filter bandwidth can simultaneously cover the S + C + L optical communication band and reach 248 nm, and the extinction ratio (ER) value reaches -377.46 dB. Moreover, we also confirmed the tuning effect of the gold-coated cladding tube wall thickness on the resonance wavelength. The proposed fiber polarization filter has potential application value in optical fiber communication and transmission.

Tilted fiber Bragg grating sensor based on surface plasmon resonance and electrospinning for glucose detection

A tilted fiber Bragg grating (TFBG) sensor based on surface plasmon resonance (SPR) with electrospinning nanofibers was proposed for the precise detection of glucose. In this design, a 50 nm thick gold film was deposited on the surface of a 10° TFBG. Polyacrylonitrile (PAN) nanofibers were wrapped around the sensor through electrospinning, subsequently serving as a scaffold for the immobilization of glucose oxidase (GOD). Within the dynamic range of 100–500 mg/dL glucose concentrations, the sensor exhibited good response and worked effectively. The experimental results show that the sensitivity and limit of detection (LOD) of the sensor are 12.42 pm/(mg/dL) and 100 mg/dL. Furthermore, the structural characterization was carried out using atomic force microscopy (AFM), scanning electron microscopy (SEM), and Fourier transform infrared spectrometer (FTIR). This sensor exhibits outstanding stability and high sensitivity, providing a new method for diabetes detection.

Highly oriented single-crystalline gold quantum-dot metamaterials as prospective materials for photonics

Miniaturization of optical devices is a modern trend essential for optoelectronics, optical sensing, optical computing and other branches of science and technology. To satisfy this trend, optical materials with a small footprint are required. Here we show that extremely thin, flat, nanostructured gold films made of highly oriented single-crystalline gold quantum-dots can provide elements of topological photonics in visible light and be used as high-index dielectric materials in the infrared part of the spectra. We measure and theoretically confirm the presence of topological darkness and associated phase singularities in studied gold films of thickness of below 10 nm placed on MgO substrates in the red part of the spectrum. At telecom wavelengths, the fabricated gold metasurface behaves as a dielectric with the refractive index of n≈2.75 and the absorption coefficient of k≈0.005.

Quantum-mechanical effects in photoluminescence from thin crystalline gold films.

Luminescence constitutes a unique source of insight into hot carrier processes in metals, including those in plasmonic nanostructures used for sensing and energy applications. However, being weak in nature, metal luminescence remains poorly understood, its microscopic origin strongly debated, and its potential for unraveling nanoscale carrier dynamics largely unexploited. Here, we reveal quantum-mechanical effects in the luminescence emanating from thin monocrystalline gold flakes. Specifically, we present experimental evidence, supported by first-principles simulations, to demonstrate its photoluminescence origin (i.e., radiative emission from electron/hole recombination) when exciting in the interband regime. Our model allows us to identify changes to the measured gold luminescence due to quantum-mechanical effects as the gold film thickness is reduced. Excitingly, such effects are observable in the luminescence signal from flakes up to 40 nm in thickness, associated with the out-of-plane discreteness of the electronic band structure near the Fermi level. We qualitatively reproduce the observations with first-principles modeling, thus establishing a unified description of luminescence in gold monocrystalline flakes and enabling its widespread application as a probe of carrier dynamics and light-matter interactions in this material. Our study paves the way for future explorations of hot carriers and charge-transfer dynamics in a multitude of material systems.

Two-dimensional beam scanning by tunable photonic spin Hall effect

To the best of our knowledge, a novel tunable photonic spin Hall effect is proposed based on a pair of liquid crystal Pancharatnam-Berry (PB) lenses. Owing to the spin-dependent geometric phases, a PB lens focus or defocus the incident light field according to its spin angular momentum. By cascading two PB lenses with a small gap, the focus and defocus effects can be suppressed, and the transmitted light fields with opposite spin will be deflected toward opposite directions when the two PB lenses have a relative lateral displacement. The deflection angles vary linearly with the displacements, thus double-lines two-dimensional continuous beam scanning is achieved with a scanning angle of 39o × 39° and a beam diverging angle of 0.028o × 0.028°. The scanning beam is used to write different patterns on a 200 nm thick gold film. We believe this beam scanning system can find wide applications ranging from laser processing, Lidar, particle manipulation, to free space optical communications.

Convergence and Performance Analysis of a Particle Swarm Optimization Algorithm for Optical Tuning of Gold Nanohole Arrays.

Gold nanohole arrays, hybrid metal/dielectric metasurfaces composed of periodically arranged air holes in a thick gold film, exhibit versatile support for both localized and propagating surface plasmons. Leveraging their capabilities, particularly in surface plasmon resonance-oriented applications, demands precise optical tuning. In this study, a customized particle swarm optimization algorithm, implemented in Ansys Lumerical FDTD, was employed to optically tune gold nanohole arrays treated as bidimensional gratings following the Bragg condition. Both square and triangular array dispositions were considered. Convergence and evolution of the particle swarm optimization algorithm were studied, and a mathematical model was developed to interpret its outcomes.

Simulation research of localized surface plasmon sensor based on gold nanocone hexagonal array structure

The sensor based on gold nanocone hexagonal array structure was designed. Gold nanocone array was positioned above a gold film and separated by silica dielectric spacer layer. Finite-difference time-domain simulation was used to discuss theoretically the influence of gold film and dielectric layer thickness on the structure performance. The formation mechanism of three resonance peaks was studied through the electric field distribution. With the increase of the dielectric thickness, the absorption went upwards first and then went downwards. The refractive index sensitivity of the structure and figure of merit (FOM) at the dipole resonance peak can reach 450 nm/RIU and 4.3, respectively. At the peak caused by the plasmon resonance between the gold nanocone array and the gold film, the sensitivity is 275 nm/RIU while the FOM value is 18.3. The results provide a valuable insight into the application of metal nanoarrays in sensors.

Quasi-bound states in the continuum in a metal nanograting metasurface for a high figure-of-merit refractive index sensor.

In this work, we investigate the bound states in the continuum (BICs) in a gold nanograting metal-insulator-metal metasurface structure at oblique angles of incidence. The nanograting metasurface consists of a gold nanograting patterned on a silicon dioxide dielectric film deposited on a thick gold film supported by a substrate. With rigorous full-wave finite difference time domain simulations, two bound states in the continuum are revealed upon transverse magnetic wave angular incidence. One BIC is formed by the interference between the surface plasmon polariton mode of the gold nanograting and the FP cavity mode. Another BIC mode is formed by the interference between the metal-dielectric hybrid structure guided mode resonance mode and the FP cavity mode. While true BIC modes cannot be observed, quasi-BIC modes are investigated at angles of incidence slightly off from the corresponding true BIC angles. It is shown that quasi-BIC modes can suppress radiation loss, resulting in narrow resonance spectral linewidths and high quality-factors. The quasi-BIC mode associated with the surface plasmon polariton mode is investigated for refractive index sensing. As a result, a high sensitivity refractive index sensor with a large figure-of-merit of 364 has been obtained.

Measurements of the amplitude-dependent microwave surface resistance of an Au/Nb bilayer

Surface properties are critical to the capabilities of superconducting microwave devices. The native oxide of niobium-based devices is thought to consist of a thin normal conducting layer. To improve understanding on the importance of this layer, an attempt was made to replace it with a more easily controlled gold film. A niobium sample host microwave cavity was used to measure the surface resistance in continuous wave operation at and . Sample conditions studied include temperatures ranging from to with RF magnetic fields on the sample surface ranging from to the maximum field before the superconducting properties were lost (quench field). The nominal film thickness of the gold layer was increased from to in five steps to study the impact of the normal layer thickness on surface resistance on a single niobium substrate. The film was found to reduce the surface resistance of the sample and to enhance the quench field. With the exception of the final step from a gold film to , the magnitude of the surface resistance increased substantially with gold film thickness. The nature of the surface resistance field-dependence appeared to be roughly independent from the gold layer thickness. This initial study provides new perspectives and suggests avenues for optimizing and designing surfaces for resonant cavities in particle accelerators and quantum information applications.

Refractive index SPR sensor with high sensitivity and wide detection range using tapered silica fiber and photopolymer coating.

This paper introduces a surface plasmon resonance (SPR) sensor using tapered silica fiber and photopolymer coating for enhanced refractive index (RI) detection. Tapering the silica fiber to a diameter of 10 µm ensures the evanescent wave leaks into a 1.8-µm thick photopolymer film, which increases the average waveguide RI and broadens the RI detection range accordingly. A 50-nm thick single-side gold film is coated on the photopolymer film, exciting SPR and causing less light transmission loss than a double-side gold film. The method avoids the complex microfabrication processes of conventional polymer optical fiber SPR sensors, while the waveguide RI can be controlled by altering the curing time of the photopolymer during fabrication. The sensor has an overall sensitivity of 3686.25 nm/RIU, enabling RI detection of 1.333 - 1.493. Moreover, the sensor has an ultrahigh sensitivity of 6422.9 nm/RIU in the RI range of 1.423 - 1.493. The temperature response is about 1.43 nm/°C at 20 - 50 °C, which has little impact on RI detection. Finally, we demonstrate that the sensor can grade the severity of hepatic steatosis by measuring the RIs of cytoplasm/triglyceride emulsions with superior sensing performance.

THE INFLUENCE OF THE STRUCTURAL PARAMETERS OF THE MATERIALS OF THE SENSITIVE ELEMENT OF THE OPTICAL SENSOR ON ITS SENSORY PROPERTIES

The sensor element of an optical sensor based on surface plasmon resonance is investigated in the paper. In particular, the influence of the components of the sensor element on its sensor properties by modeling design options. The Kretschmann configuration was chosen as the model, which is a glass prism with a multilayer nanoscale structure applied to one face. It was established that the material of the prism affects only the resonance angle of the structure. The thickness of nanoscale gold and silver films varied from 1 to 100 nm. The minimum value of the coefficient was obtained when the thickness of the gold and silver nanoscale films was 50 nm and 45 nm, respectively. The thickness of the silicon dioxide film varied from 10 to 150 nm. In the Au – SiO2 structure, the addition of silicon dioxide improved the optical properties of the multilayer structure. The minimum value of the reflection coefficient has decreased, but the thickness of the silicon dioxide is 3 nm. When the thickness of the dielectric layer increases, the optical properties of the structure deteriorate. The structure of the sensitive element, which uses a nanosized silver film, almost does not change its optical properties when adding a layer of SiO2, its thickness can reach 50 nm.

Electrical and Mechanical Behavior of Aerosol Jet–Printed Gold on Alumina Substrate for High‐Temperature Applications

There is a growing interest in the development of microelectronics that can perform reliably and robustly at temperatures above 300 °C. Such devices require stable thermal properties, low thermal drift, and thermal cycling resistance. Conventional hybrid circuit technology demonstrates high‐temperature packages, but the high costs and lead time are significant drawbacks. In contrast, additive manufacturing processes, including aerosol jet printing (AJP), offer cost and time benefits, as well as 3D structures and embedded features. However, the properties and reliability of additive packaging materials at extreme temperatures are not well known. Herein, the reliability at temperatures up to 750 °C in terms of electrical performance and mechanical strength of aerosol jet printed gold thick films onto ceramic substrates are assessed. Thermal coefficient of resistance of printed gold films is measured. The electrical resistance stability and leakage current of printed gold structures are also characterized during over 100 h of aging at temperatures up to 750 °C. Finally, the mechanical adhesion strength of the printed gold films is evaluated after aging for 100 h at temperatures up to 750 °C. The adhesion of the printed gold to the ceramic substrates remains high after aging, very stable resistances and minimal leakage currents have been observed.

A surface plasmon resonance haemoglobin concentration sensor based on D‐type optical fibre with a graphene‐gold surface architecture

AbstractIn this study, a surface plasmon resonance sensor for detecting haemoglobin concentration based on a D‐type optical fibre with a graphene‐gold surface architecture is proposed. The graphene‐gold surface architecture included a 50 nm thick gold film and monolayer graphene film, which were decorated on a 10 mm long D‐type sensing region. The proposed sensor worked in wavelength interrogation mode, with the light wavelength ranging from 400 to 1100 nm. The authors realised the D‐type optical fibre surface polishing process, the gold film vacuum coating process, and the chemical‐vapour‐deposited graphene's wet transfer process. Furthermore, the fabricated sensors were used to detect the refractive index (RI) of haemoglobin samples, which varied from 1.331 to 1.346. Experiment results show that the fitted RI sensitivity of the sensor decorated with gold and graphene reaches 1874.41 nm/RIU, 4.995% higher than that of the sensor decorated only with gold. The concentration sensitivity of the sensor coated with gold and graphene film is 4.96 nm/(g/dL), and the proposed sensor can provide a resolution of 20.2 mg/dL for haemoglobin concentration detection.

Gold film effect on temperature compensation of a POF sensor with different structures.

In this paper, temperature compensation of plastic optical fiber (POF) is studied and gold absorbability is utilized. Gold film is modified on the surface of POF by magnetron sputtering. The temperature output characteristics of different structures such as ordinary (POF-N), side-polished (POF-SP), U-shaped (POF-U), and narrow groove structure (POF-NGS) are tested, and the effects of gold film thickness, polishing area, and sputtering sequence on the temperature output characteristics are also investigated. The power change of the sensor at different temperatures is recorded. The experimental results show that when the temperature is between 25°C and 50°C and the sputtering gold film thickness is 50nm, the temperature stabilities of POF-N, POF-U, POF-SP, and POF-NGS are 1.02µW/°C, 0.77µW/°C, 0.18µW/°C, and 0.35µW/°C, respectively. The compensation effect is enhanced as the gold film thickness increases. When the thickness is 100nm, the temperature stability of POF-NGS is 0.06µW/°C. The proposed temperature compensation method is competitive and straightforward.