Thick Gold Film Research Articles

Gold plating of AlSi10Mg parts produced by a laser powder-bed fusion additive manufacturing technique

Laser powder-bed fusion (LPBF) method is one of the most important additive manufacturing (AM) technologies. AM-LPBF parts frequently need post-printing coatings for electrical and thermal conductivity enhancement, or matching decoration considerations. The current study presents a methodology for surface finishing of AM-LPBF AlSi10Mg artifacts coated with electroless gold. For this purpose, gold was deposited on AM-LPBF AlSi10Mg disk-shaped specimens and coins, resulting in an appearance similar to the original objects. The gold coating was characterized as a function of deposition time and gold film thickness. Mass and dimension measurements, optical profilometry, light microscopy observation, XRD analysis and a FIB-SEM technique were applied to characterize the coated samples. The roughness of the plated specimens was slightly reduced as the thickness of the gold film was increased. AM-LPBF AlSi10Mg disk-shaped specimens were coated successfully for the first time by electroless gold plating technique. The developed surface finish technique can be used for various applications, including 3D-printed replicas of ancient prestige artifacts and coins for museum exhibitions.

Hollow hanging-core fiber SPR sensor for microfluidic chip with large size channel

We propose and demonstrate a surface plasmon resonance (SPR) sensor based on a hollow hanging-core fiber (HHCF). The diameter of the air hole in the HHCF is 130 μm, which ensures the infiltration of the liquid samples. We deposit the gold film on the surface of the hanging-core, and an evanescent field near the hanging-core will excite the SPR. The relationship between the gold film thickness and the testing sensitivity is studied. The experimental results show that the thicker the gold film, the longer the resonance wavelength, and the higher the testing sensitivity. The testing sensitivity is in the range of 1440 nm/RIU to 2010 nm/RIU, when the gold film thickness range is 30−70 nm with the sample refractive index range of 1.333−1.433. Due to the unique structure of the HHCF, the proposed SPR sensor has the advantage of being applied in a microfluidic chip system.

High-Temperature Electronics Packaging for Simulated Venus Condition

Abstract An electronic packaging technology that survives the simulated Venusian surface temperature of 465°C and 96 bar pressure in carbon dioxide (CO2) and nitrogen environments, without the corrosive trace gases, was developed. Alumina ceramic substrates and gold conductors on alumina were evaluated for electrical and mechanical performance. The most promising die-attach materials are thick-film gold and alumina-based ceramic pastes. Alumina, sapphire, silicon, and silicon carbide dies were attached to the alumina substrates using these die-attach materials and exposed to 96 bar pressure in a CO2 environment at 465°C for 244 h. The ceramic die-attach material showed consistent shear strengths before and after the test. An alumina ceramic encapsulation material was also evaluated for thermomechanical stability. The devices on the packaging substrates were encapsulated by a ceramic encapsulation with no significant increase in cracks and voids after the Venusian simulator test. Wire pull strength tests were conducted on the gold bond wire to evaluate mechanical durability before and after the Venusian simulator exposure. The average gold bond wire pull strengths before and after exposure were 5.78 g-F and 4 g-F for 1-mil gold bond wires, respectively, meeting the minimum MIL-STD-885 2011.9 standard. The overall wire bond daisy chain resistance change was .47% after the Venus simulator test, indicating a promising wire bond integrity. A titanium package was fabricated to house the ceramic packaging substrate and a two-level metalized feedthrough was fabricated to provide electrical interfaces to the package.

Time-fractional subdiffusion model for thin metal films under femtosecond laser pulses based on Caputo fractional derivative to examine anomalous diffusion process

In this paper, the non-Fourier effects are examined in thin metal films exposed to femtosecond laser pulses. For the first time, the time-fractional subdiffusion model is presented based on the Caputo fractional derivative to examine the anomalous diffusion process in nano-scale metal films. The fractional heat conduction equation is solved numerically, using the finite difference method based on implicit scheme and the numerical results are compared to experimental data. The comparison implies that the numerical results well coincide with experimental data, proving the accuracy and suitability of fractional model to capture thermal behaviors of thin metal films heated by short-pulse laser. Furthermore, the results of time-fractional model are compared to other models including parabolic and hyperbolic two-step models. Having compared, one can be found is that the fractional model is more reliable than other models, because its results are well matched with experimental data. The use of Fourier's law in parabolic and hyperbolic two-step model leads to deviation from experimental data which can be addressed upon applying the proposed time-fractional model in this work. Moreover, the presented time-fractional model can be effectively utilized for studying the heat transport in thin metal films under laser pulses as well as the laser heating process and its applications in engineering. Ultimately, the effect of changes in various parameters such as order of fractional derivative, laser pulse duration, metal materials (gold and chromium), gold film thickness, relaxation time and absorption depth of laser pulses are investigated on temperature response of thin metal films.

A Large Detection-Range Plasmonic Sensor Based on An H-Shaped Photonic Crystal Fiber.

An H-shaped photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor is proposed for detecting large refractive index (RI) range which can either be higher or lower than the RI of the fiber material used. The grooves of the H-shaped PCF as the sensing channels are coated with gold film and then brought into direct contact with the analyte, which not only reduces the complexity of the fabrication but also provides reusable capacity compared with other designs. The sensing performance of the proposed sensor is investigated by using the finite element method. Numerical results show that the sensor can work normally in the large analyte RI (na) range from 1.33 to 1.49, and reach the maximum sensitivity of 25,900 nm/RIU (RI units) at the na range 1.47–1.48. Moreover, the sensor shows good stability in the tolerances of ±10% of the gold-film thickness.

An Au Nanofilm-Graphene/D-Type Fiber Surface Plasmon Resonance Sensor for Highly Sensitive Specificity Bioanalysis

A highly sensitive Au-graphene structure D-type fiber surface plasmon resonance biosensor is presented in this study to specifically detect biomolecules. The method of growing graphene is employed directly on the copper, and then a gold film of optimum thickness is sputtered, and the copper foil is etched to obtain the structure. This method makes the contact closer between the gold layer and the graphene layer to improve surface plasmon resonance performance. The performance of this type of surface plasmon resonance (SPR) sensor has been previously verified both theoretically and experimentally. With the proposed Au-graphene structure D-type fiber biosensor, the SPR behaviors are obtained and discussed. In the detection of ethanol solution, a red shift of 40 nm is found between the refractive index of 1.3330 and 1.3657. By calculation, the sensitivity of the sensor we designed is 1223 nm/RIU. Besides, the proposed sensor can detect the nucleotide bonding between the double-stranded DNA helix structures. Thus, our sensors can distinguish between mismatched DNA sequences.

Study of surface plasmon resonance effect on P3HT: PCBM/Au nano film

Surface plasmon resonance (SPR) plays a vital role in improving the efficiency of organic solar cells, sensitivity of biosensor and effectiveness of spectroscopy. SPR characteristics depend on the thickness of coated metallic film, sensing medium and also refractive index of the material of prism used. Due to cost effectiveness and easy preparation method, the organic solar cells paid considerable interest among the many researchers. In present paper, we have theoretically study the variation of thickness of P3HT-PCBM: Au composite film on the reflectance of medium because the poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) used as a most efficient organic cell. He-Ne Laser wavelength of 632.8 nm used for Kretschmann-Raether experimental setup for theoretical investigation.The reflectance becomes zero at 15 nm thickness of P3HT-PCBM film and 48 nm thickness of nano gold film. The result shows strong dependence of reflectance on thickness of P3HT-PCBM: Au Solar cell. The localized surface plasmon resonance in nanostructure gold film is responsible for this unusual effect. Gold is utilized as the metal layer in most cases because it is highly chemically stable, inert in nature and higher sensing resolution at visible wavelength range as compared to other metals.

Optimization of metallic nanoapertures at short-wave infrared wavelengths for self-induced back-action trapping.

This paper presents simulation results for double nanohole and inverted bowtie nanoapertures optimized to resonate in the short-wave infrared regime (1050 nm and 1550 nm). These geometries have shown great promise for trapping nanoparticles with applications in optical engineering, physics, and biology. Using a finite element analysis tool, we found that the outline length for inverted bowtie nanoapertures in a 100 nm thick gold film with a 20 nm gap dimension having an optimized transmission resonance for 1050 nm and 1550 nm optical wavelengths is 106.5 nm and 188.5 nm, respectively. With the same gap size, the radii of the circles for the double nanohole nanoapertures are 72 nm and 128 nm. The near-field enhancements of the two structures are almost the same, while the double nanohole geometries have a 20% larger full width at half-maximum than the inverted bowtie. Next, by studying the effect of changing the inner radii of the inverted bowtie corners, we found that the difference between 2 nm and 6 nm corner radii can blue-shift the optical resonance by up to 45 nm. As a result of not having any inner corners, the double nanohole structure requires less precise fabrication and therefore could potentially have a higher successful yield of nanoapertures during the manufacturing process. Lastly, we will show experimental results that confirm the optical resonance of the nanoapertures at 1550 nm. These results will enable better performance and signal-to-noise ratio in nanoaperture trapping for the short-wave infrared wavelength regime.

Sensitivity enhancement of an SPR biosensor with a graphene and blue phosphorene/transition metal dichalcogenides hybrid nanostructure.

A novel surface plasmon resonance (SPR) biosensor based on Ag-Au bimetallic films with a hybrid structure of blue phosphorene (BlueP)/transition metal dichalcogenides (TMDCs) and graphene is presented. In order to improve the sensitivity, the thickness of silver and gold films is optimized to achieve minimum reflectivity and an adequate level of sensitivity; further, sensitivity for the monolayer BlueP/MoS2 and graphene structure is enhanced by 19.73%, with respect to a traditional sensor. Besides, the effect of layers of different Blue/TMDCs heterostructures to the sensitivity of the SPR biosensor is investigated, and the highest sensitivity with 335.4°/RIU for the bilayer BlueP/WS2 is obtained. Furthermore, distributions of the electric field and the changes of resonance angle to the refractive index of the sensing medium and prism in the visible regime are illustrated at optimal configuration. In virtue of highly sensitive characteristics, the proposed sensor structure will be a much better option to be employed for further biological detection.

The plasmonic nanoparticles with controlled optical properties

The gold and silver plasmon nanoparticles have been synthesized on the c-sapphire and p-silica substrates by the pulsed laser deposition method. It has been demonstrated that the variation of the thickness of as-grown gold and silver films permits producing the plasmon nanoparticles with different size and density. It provides the retuning of the frequency of surface plasmon resonance in wide spectral region.

Synthesis of gold nanoparticles by annealing its thin film under a layer of fluoropolymer coating

Gold thin films were deposited on the substrate of silicon and fused silica by method of Vacuum Gas Jet Deposition. Obtained films were coated with a fluoropolymer and annealed in a rarefied inert gas atmosphere at the temperature of 400 °C. The film morphology and composite were studied by the scanning electron microscopy. Optical properties of obtained coatings and composites were investigated. The influence of the fluoropolymer coating on formation of gold nanoparticles in the result of annealing of its thin films is established. The critical gold film thickness coated with fluoropolymer is determined, below which the presence of fluoropolymer lends to the formation of spherical nanoparticles during annealing of the composite in a studied range of parameters.

Gold-nanoisland-decorated titanium nanorod arrays fabricated by thermal dewetting approach

Solid-state dewetting is a simple and versatile technique for fabricating plasmonic-nanostructure-decorated platforms. However, understanding of the optical properties of these platforms and the effect of the three-dimensional (3D) morphology of the underlying substrate on the dewetting of metallic thin films is still needed for developing effective platforms for further applications. Herein, the authors report gold (Au)-nanoisland-decorated 3D titanium dioxide (TiO2) nanorod (TiNR) arrays fabricated through the thermal dewetting approach. It is demonstrated that the plasmonic behavior of the fabricated platforms can be manipulated by controlling both the initial gold film thickness and annealing temperature. Furthermore, the fabricated platforms exhibited Raman signal enhancement of up to ∼102 for the probe molecule methylene blue. The surface characteristics of the fabricated platforms were evaluated for biological interactions. For this purpose, osteogenic cells (Saos-2) were seeded on the samples. It was found that the cell behavior was improved on the anisotropic micro–nano pattern of TiNRs and gold-coated TiNR films because of features such as topography and surface chemistry. The authors’ results clearly offer simple but important guidance for the creation of surface-enhanced Raman spectroscopy platforms and tissue-integration devices as biomaterials for real-life applications.

Morphology and optical properties of films based on CVD graphene and nanostructured gold

In the work presented, the polymer-graphene-gold composites obtained by the methods of chemical vapor deposition and pulsed laser ablation (PLA) are studied. The morphological and optical properties of the given samples are studied in detail. It is shown that with an increase in the number of laser pulses in the PLA method, the metal coating transforms from separate small gold particles to a continuous cover with the presence of large nanoparticles. It is shown that a change in the gold film thickness influences significantly the efficiency of plasmon attenuation of a signal: with an increase in the average mass thickness, the effect increases and reaches its maximal value at film thickness of 6 nm. It is shown that the most intense plasmon absorption occurs in the wavelength range from 550 to 750 nm. A further increase in the thickness of metal coating decreases sample transparency in the studied range and does not affect the intensity of plasmon absorption and scattering.

Gold Nanopost-Shell Arrays Fabricated by Nanoimprint Lithography as a Flexible Plasmonic Sensing Platform.

Plasmonic noble metal nanostructured films have a huge potential for the development of efficient, tunable, miniaturized optical sensors. Herein, we report on the fabrication and characterization of gold-coated nanopost arrays, their use as refractometric sensors, and their optimization through photonics simulations. Monolithic square nanopost arrays having different period and nanopost size are fabricated by nanoimprint lithography on polymer foils, and sputter-coated by gold films. The reflectivity of these gold nanopost-shell arrays present dips in the visible range, which are efficient for refractometric sensing. By finite-difference time-domain (FDTD) simulations we reproduce the experimental spectra, describe the electric fields distribution around the nanopost-shells, and then explain their good sensitivity, around 450 nm/RIU. Furthermore, we determine by simulations the influence of several geometrical parameters, such as array period, nanopost width, gold film thickness, and nanopost side coverage on both reflectivity spectra and sensing capabilities. Fully coated nanoposts provide an extremely deep reflectivity minimum, approaching zero, which makes the relative reflectivity change extremely high, more than two orders of magnitude higher than for partially coated nanoposts. These results contribute to the understanding of the plasmonic properties of metal coated nanopost arrays, and to the development of efficient platforms for sensing and other surface plasmon based applications.

Surface Plasmon Resonance Induced High Sensitivity Temperature and Refractive Index Sensor Based on Evanescent Field Enhanced Photonic Crystal Fiber

An ultra high-sensitivity temperature and refractive index (RI) sensor based on surface plasmon resonance (SPR) effect in D-shape high birefringence photonic crystal fiber (PCF) is presented and discussed by the finite element method (FEM). The designed PCF is polished to enhance the interaction of the evanescent field with the external medium, ultimately improving the sensing performance. The influence of three different plasma materials, gold, silver and aluminum, on the sensing performance was investigated. Finally, the chemically stable plasma material gold is selected to coat on flat surface of D-shape PCF for SPR sensing, realizing the sensitive real-time monitoring of RI and temperature. The sensing performance was greatly improved, with a wide RI (1.43 to 1.50) and temperature (36 $^{\circ }$ C to 86 $^{\circ }$ C) detection range, and the corresponding maximum sensitivity was 44850 nm/RIU and −16.875 nm/ $^{\circ }$ C, respectively. Furthermore, the sensitivity is not particularly sensitive to the sizes of the designed air holes, which leads to a sensor with high structure tolerance. Numerical results show that the coating thickness not only affects the sensitivity but also the detection range of the sensor, so we can tune the RI and temperature detection range by adjusting the gold film thickness to meet specific detection requirements. The sensor with enhanced sensitivity, tunable detection range, and high fabrication tolerance has a wide application prospect in the field of life science research, chemical production, and environmental monitoring.

Enhanced terahertz conductivity in ultra-thin gold film deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS)-coated Si substrates

Various material properties change considerably when material is thinned down to nanometer thicknesses. Accordingly, researchers have been trying to obtain homogeneous thin films with nanometer thickness but depositing homogeneous few nanometers thick gold film is challenging as it tends to form islands rather than homogenous film. Recently, studies have revealed that treating the substrate with an organic buffer, (3-mercaptopropyl) trimethoxysilane (MPTMS) enables deposition of ultra-thin gold film having thickness as low as 5 nm. Different aspects of MPTMS treatment for ultra-thin gold films like its effect on the structure and optical properties at visible wavelengths have been investigated. However, the effect of the MPTMS treatment on electrical conductivity of ultra-thin gold film at terahertz frequency remains unexplored. Here, we measure the complex conductivity of nanometer-thick gold films deposited onto an MPTMS-coated silicon substrate using terahertz time-domain spectroscopy. Following the MPTMS treatment of the substrate, the conductivity of the films was found to increase compared to those deposited onto uncoated substrate for gold films having the thickness less than 11 nm. We observed 5-fold enhancement in the conductivity for a 7 nm-thick gold film. We also demonstrate the fabrication of nanoslot-antenna arrays in 8.2-nm-thick gold films. The nanoslot-antenna with MPTMS coating has resonance at around 0.5 THz with an electric field enhancement of 44, whereas the nanoslot-antenna without MPTMS coating does not show resonant properties. Our results demonstrate that gold films deposited onto MPTMS-coated silicon substrates are promising advanced materials for fabricating ultra-thin terahertz plasmonic devices.

Gold-Film-Thickness Dependent SPR Refractive Index and Temperature Sensing with Hetero-Core Optical Fiber Structure

A simple hetero-core optical fiber (MMF-NCF-MMF) surface plasmon resonance (SPR) sensing structure was proposed. The SPR spectral sensitivity, full width of half peak (FWHM), valley depth (VD), and figure of merit (FOM) were defined to evaluate the sensing performance comprehensively. The effect of gold film thickness on the refractive index and temperature sensing performance was studied experimentally. The optimum gold film thickness was found. The maximum sensitivities for refractive index and temperature measurement were obtained to be 2933.25 nm/RIU and −0.91973 nm/°C, respectively. The experimental results are helpful to design the SPR structure with improved sensing performance. The proposed SPR sensing structure has the advantages of simple structure, easy implementation, and good robustness, which implies a broad application prospect.

Fabrication of flexible and economical plasmonic biosensor using gold nanograting imprinted on hot-melt adhesive film for label-free sensing of immunoglobulin proteins

We report here, the fabrication of plasmonic nanograting patterned on hot-melt adhesive (HMA) film via thermal nanoimprint lithography. A soft polymer stamp textured with nanograting pattern was used as a mold to imprint nanograting structure on HMA film overlaid on a flexible polyethylene terephthalate substrate. Thereafter, a 50 nm thickness of gold film was evaporated over surface of the nanograting to prepare a plasmonic sensing layer. The surface plasmon resonance excitation on gold coated nanograting was characterized with the reflectance measurement under the normal incidence of light, which was further verified with theoretical calculations. The bulk refractive index sensitivity of our prepared sensor was obtained 886 ± 55 nm/refractive index unit (RIU). Additionally, a label-free detection of specific target analytes was shown by recording the specific interactions between rabbit immunoglobulin (R-IgG) and anti R-IgG proteins. A surface mass detection limit of 162 pg mm−2 was found in the detection of 100 nM anti R-IgG proteins. Thus, our proposed plasmonic sensor based on low-cost HMA represents another promising thermoplastic material for nanostructure fabrications that have potential applications in the development of affordable, flexible, label-free, and highly sensitive optical/biological sensor.

Design and Optimization of Sensing Layer for Terminal Reflective SPR Optical Fiber Hydrogen Sensor

Based on the principle of surface plasmon resonance(SPR), the terminal reflective optical fiber hydrogen sensor structure has been obtained. By simulating, gold is selected as plasma coating material. The performance of the sensor of has been further studied with different thickness of gold film and hydrogen sensitive film. This work can provide theory support for the design of optical fiber surface plasmon resonance hydrogen sensor.

Improving sensitivity of existing surface plasmon resonance systems with grating-coupled short-range surface plasmons

Here we show that surface plasmon resonance sensors that typically use 760 nm wavelength Kretschmann–Raether coupling to a 50 nm thick gold film can have 3 times higher surface sensitivity by using local resonances from periodically arranged short-range modes in the same configuration. Considering shot noise, the resolution was found to improve fourfold. This was calculated by matching the design wavelength and minimum angle as calculated by rigorous coupled wave analysis, giving a period of 250 nm in a 10 nm thick gold film and a gap length of 40 nm. Finite-difference time-domain simulations were used to confirm that the short-range modes correspond to localized surface plasmon resonances. The present short-range plasmon approach can be used to improve the sensitivity in monitoring biomolecule interactions.