Gold Layer Research Articles

Surface Acoustic Wave Resonator Chip Setup for the Elimination of Interfering Conductivity Responses.

A surface acoustic wave (SAW) resonator chip setup is presented that eliminates interfering signal responses caused by changes in the electrical environment of the surrounding media. When using a two-port resonator, applying electrically shielding layers between the interdigital transducers (IDTs) can be challenging due to the limited dimensions. Therefore, a layered setup consisting of an insulating polymer layer and a conductive gold layer was preferred. The SAW resonators were provided with polycarbonate housings, resulting in SAW resonator chips. This setup enables easy application of a wide range of coatings to the active part of the resonator surface, while ensuring subsequent electrical and fluidic integration of the resonator chips into a microfluidic array for measurements. The signal responses of uncoated SAW resonators and those with polymer coatings with and without a gold layer were tested with aqueous potassium chloride (KCl) solutions up to 3 mol/L, corresponding to conductivities up to 308 mS/cm. The use of a polymer coating at the thickness of the first Love mode resonance and a conductive gold layer completely reduced the electrical impact on the SAW resonator signal response, making small signals resulting from changes in viscosity and density of the KCl solutions visible.

Nano-Engineered HfO2-Au photonic sensor for ultra-sensitive refractive index detection

In this study, we introduce a novel hafnium dioxide (HfO2) and thin gold layer based photonic crystal fiber (HfAu-PCF) sensor for refractive index measurement and optimize in the spectrum of 1.3 µm to 1.6 µm. The proposed sensor incorporates a D-shaped geometry for enhanced light-matter interaction, and the core of the fiber is surrounded by periodic air holes to facilitate efficient coupling of the guided mode with surface plasmons. The proposed HfAu-PCF sensor is geometrically optimized using finite element method (FEM) by fine-tuning air hole diameter, core size, layer thickness dimensions of the fiber to achieve performance stability. Leveraging the unique optical properties of HfO2 and Au, the sensor demonstrates superior performance metrics, achieving confinement loss (<10−6 dB/m), propagation constant (β) ∼ 6 × 106, V-Parameter < 2.3, a peak relative sensitivity of 99.05 % across the tested wavelength of 1.3 µm to 1.6 µm. Our findings reveal that choosing suitable parameters could lead to further enhancements in sensitivity, making the sensor for applications in bio-sensing, environmental monitoring, and chemical analysis, etc.

Adaptability of VisCalor versus bulk-fill composites using scanning electron microscope: an in-vitro study

Purpose To evaluate the marginal integrity of two types of bulk-fill composite resins in Class I box-shaped cavities. Materials and methods Forty extracted human sound molars were selected. The teeth were fixed with sticky wax to the base of plastic cylinder and the cylinder was filled with self-curing acrylic resin so that only root was embedded. Simple Class I box-shaped cavities were prepared using a fissure carbide bur with water spray and finished with fine-grained flame burs. The overall dimensions and depth of the cavities were standardized as follows: 4 mm length mesiodistally and 3 mm width buccolingually and up to 4 mm depth. All prepared cavities were bonded using Futurabond M+ one-step self-etch adhesive system. The teeth were randomly divided into two groups (n = 20 teeth each): group I: specimens were restored with VisCalor composite bulk-fill composite resin, which is heated before insertion using a VisCalor dispenser dental device. Group II: specimens were directly restored with X-tra fill bulk-fill composite resin without preheating. After curing, finishing and polishing were performed. Each group was subdivided into two subgroups a and b (n = 10) according to whether subjecting 500 thermocycling fluctuations or not. Each specimen was sectioned buccolingually through the center of the composite resin restoration in two halves, and then cleaned under running tap water and subjected to thorough ultrasonic cleaning to get rid of both soft and hard surface deposits. All sectional samples were fixated in cylindrical carriers, and a thin layer of gold was applied to the surfaces. The marginal adaptation of composite restorations and ultramorphology of adhesive bonds were analyzed at ×50, ×1000 magnification, with a scanning electron microscope. ×50 magnification was utilized to measure the length of margins free gap in enamel and dentin by Autodesk Auto CAD program and expressed in mm/percent. All data of measurements of the length of nongaped margins in enamel and dentin are collected, tabulated, and statistically analyzed. Results Group Ia (VisCalor bulk-fill not thermocycled), recorded the highest mean value of marginal free-gap with 10.26 ± 0.27 mm (93.31%), while group IIb (X-tra-fill bulk-fill thermocycled) recorded the lowest mean value in 7.90 ± 0.26 mm (73.04%) and the difference was statistically highly significant (P = 0.000). In general, group I recorded higher mean values of marginal free gap and adaptation in mm/percent than group II, and the difference was statistically highly significant at P value of 0.000 (9.86 ± 0.55 and 8.23 ± 0.39 mm and 89.15 ± 5.38 and 74.89 ± 3.69%, respectively). Bulk-fill restorations without thermocycling exhibited a higher mean value of marginal free gap and adaptation in mm/percent than the thermocycled one with a significant difference recorded at P value of 0.005. Conclusion Using preheated VisCalor bulk-fill composites could decrease the marginal gap formation improving the continuity at the tooth–restorative material interface than conventional bulk-fill restorations. On the other hand, thermocycling.

Electrochemistry of Molybdenum Single Crystals and Thin Wires in Cyanide and Gold Cyanide Electrolytes

Thin wires of molybdenum coated with gold are used for space applications and the adhesion of the gold layer is decisive for their use. The surface morphology of the wires is determined by the manufacturing process and preferential orientation of single crystal surfaces is expected. In this work three different single crystal surfaces were studied together with a 20 μm molybdenum wire to elucidate the importance of surface morphology on the electrodeposition process for gold. Electrochemical impedance spectroscopy was used to study the molybdenum samples in the absence and presence of gold cyanide complexes. The results show large pseudocapacitance prior to gold deposition, indicating the presence of a thin molybdenum oxide film on the surface. Thus, the electrodeposition takes place on the surface oxide and is afflicted with a nucleation overpotential. The overpotential is only slightly dependent on the single crystal orientation, while it is more negative for the wire. The adhesion of gold on the flat single crystal surfaces is weak but marginally better on the wire. This clearly shows that strong chemical binding to the surface is absent and that other processes, such as physical interlocking of the gold layer is necessary for good adhesion.

Fabricating the Ti-DLC/Au/Si heterostructure films and high-performance NIR photo-detecting

Titanium-doped Diamond-like carbon (Ti-DLC) has been previously used in photodetectors. However, these photodetectors suffer from large dark currents and long response times, limiting their practicality. In this study, we propose a Ti-DLC/Au/Si Schottky junction photodetector. We effectively suppressed the dark current by incorporating a thin layer of gold while enhancing the light current. The results showed the device shows the optimal performance when the gold is at 3 nm and the Ti-DLC thickness is 68 nm, the specific detectivity of the device reaches 1.8 × 1011 Jones and an optical-to-dark ratio exceeding 105 at zero bias voltage, and the response speed is in the range of tens of microseconds, significantly improving its performance. With its ability to suppress dark current, this Schottky junction photodetector holds excellent potential for various applications in the market.

Tuning SERS performance through the laser-induced morphology changes of gold nanostructures

Differently shaped periodic gold nanostructures on the surface of a thin metal film are fabricated utilizing the direct laser writing technique. The variations in the energy of single femtosecond pulses lead to the formation of morphologically distinct hollow nanostructures. The arrays that excite hybridized plasmonic modes are characterized by electron microscopy and assessed for surface-enhanced Raman spectroscopy (SERS). Plasmonic properties are investigated through SERS using the adsorbed 4-mercaptobenzoic acid (4-MBA) molecules. The development of sharp tips in the nanostructures is initiated by the higher-energy laser pulses, while the structure formation principle itself is altered by the thickening of the film. The change in the structure shape and gold layer thickness tune the SERS signal and the enhancement factor (EF), leading to an EF of 107. Such a factor enables the future prospects of the arrays to be applied for single-molecule detection.

Four-band highly sensitive tunable absorber based on Al-Cu-Fe quasicrystals

This paper introduces a four-band tunable perfect absorber built on Al-Cu-Fe quasicrystal. The operating frequency range is 4.75 THz to 9.25 THz, which is in the terahertz band. The absorber exhibits multiple narrow bands, polarization incoherence, high sensitivity, and tunability. The structure comprises a gold layer, a silica dielectric layer, and a top layer of Al-Cu-Fe quasicrystal from bottom to top. The Al-Cu-Fe quasicrystal structure at the top consists of a circular ring left after being cut by a 45° rotation of the cruciform and a cruciform design containing a central circular cavity. Simulation results reveal four absorption peaks attributed to cavity resonance and surface plasmon resonance, with absorption efficiencies of 0.998, 0.994, 0.989, and 0.998, respectively. Furthermore, changing the radius of the inner ring in the top layer structure allows for varying the number of absorption peaks. We also propose a new fabrication process for Al-Cu-Fe quasicrystals absorbers. The calculated results demonstrate that the designed absorber, characterized by a simple structure and high sensitivity of 2620 GHz/RIU, holds significant potential for applications in optical switches, optical modulators, biomedicine, and sensing.

Tribological Properties of the Fast Ceramic Conversion Treated Ti-6Al-2Sn-4Zr-2Mo Alloy with a Pre-Deposited Gold Layer

Ceramic conversion treatment (CCT) is an effective way to modify the surface of titanium alloys. However, this process normally needs more than a 100-h treatment at 600–700 °C to form a hard and wear-resistant titanium oxide layer. In this paper, we pre-deposited a thin gold layer on the surface of Ti-6Al-2Sn-4Zr-2Mo (Ti6242) samples before CCT to investigate if Au can speed up the treatment. Treatments at 640/670/700 °C were carried out for 10 or 120 h. After CCT, the surface roughness, surface morphology, microstructure, elemental composition, and phase constituents were characterized. Surface hardness and the nano-hardness depth distribution were measured. Finally, reciprocating sliding tribological tests were carried out to study the friction and wear of the surface layers. Thin gold layers accelerated the CCT significantly with a much thicker oxide layer. The friction of the untreated Ti6242 alloy against the WC ball was unsteady and high, but it was much lower and stable for the CCTed samples pre-deposited with Au because of the formation of titanium oxides and lubrication effect of the gold particles. The wear resistance of the CCTed Ti6242 alloy samples with gold was reinforced significantly. By pre-depositing a thin gold layer on the surface of Ti6242, the treatment time can be cut significantly, and CCT becomes more efficient.

Angle-Resolved Optical Characterization of a Plasmonic Triangular Array of Elliptical Holes in a Gold Layer

Plasmonic arrays are grating-like structures able to couple an incoming electromagnetic field into either localized or propagating surface plasmonic modes. A triangular array of elliptical holes in a gold layer were realized resorting to displacement Talbot lithography. Scanning electron microscopy was used to evaluate the geometrical features and finite time domain simulations were performed to verify the consistency of the design. The optical response was characterized by angle-resolved reflectance and transmittance measurements. The results demonstrate the good quality and uniformity of the array. Furthermore, the study on the dependence of the optical response on both the hexagonal lattice and the elliptical hole-defined symmetry properties was conducted allowing the distinction of their effects on both the localized and propagating plasmonic modes. The results indicate that the localized component of the plasmonic modes is mainly affected by the elliptical shape, while the propagating part is influenced by the hexagonal lattice symmetry.

Silica-coated gold nanoshells: Surface chemistry, optical properties and stability

In this study, we present a comprehensive analysis of the optical properties of colloidal gold nanoshells (NSs) with varying thicknesses of the gold layer and an additional silica layer. Our results demonstrate that the spectral position of the localized plasmon resonance in NSs is very sensitive to the above parameters. Furthermore, we observe that the silica coating has a notable impact on the stability of colloidal systems. We supplement our experimental results with theoretical calculations, revealing the relative contributions of the absorption and scattering to the overall extinction as a function of the gold layer thickness. The calculations also provide an insight into the origin of spectral broadening in the case of clustered NSs. Our findings hold significant potential for the design of hybrid materials intended for diverse applications, including refractive-index sensing, metal-enhanced fluorescent emission (MEF), and surface-enhanced Raman scattering (SERS).

Modeling and analysis of discrete particle detection in wide-field surface plasmon resonance microscopy

Wide-field surface plasmon resonance microscopy (WF-SPRM), based on Kretschmann’s configuration, is a powerful technique for detecting nano-objects in solution. In this study, key parameters for building a highly sensitive WF-SPRM are optimized, including laser wavelength, prism refractive index, numerical aperture of the objective, and gold layer thickness. A medium model describes the surface plasmon resonance (SPR) sensor principle, treating molecules bound on the sensor surface as an effective medium with an effective refractive index and thickness. On the other hand, the SPR discrete particle model is introduced to describe the detection principle for discrete particles. Theoretical, numerical, and experimental analyses are conducted, and the calculated intensity profiles of single and double nanoparticles from the discrete particle model describe the experimental profiles well. Furthermore, the influence of coating the gold layer with a dielectric layer on the SPR sensitivity is investigated for varying refractive indices.

Adjustable graphene disk‐based THz absorber for biomedical sensing: Theoretical description

AbstractAs a basic building block, the THz wave absorber has intense imaging, sensing, and nondestructive testing applications. There are several methods for tuning THz absorbers, including electricity modulation, light modulation, mechanical tuning, using phase change materials, liquid crystal, flexible materials, MEMS technology, and thermally tuning vanadium dioxide. The choice of tuning method depends on the specific application and the desired performance characteristics of the THz absorber. In this work, we report a theoretical description of mechanically tunable THz absorber based on overlapping periodic arrays of graphene nano‐disks. The basis of this work is based on the movement of a dielectric surface covered on both sides with graphene disks. This surface moves on a fixed plane while the distance between these two surfaces is free space. Also, the fixed surface consists of a relatively thick layer of gold at the bottom, dielectric on it, and graphene disk patterns on the dielectric. Now, by moving the movable surface in the horizontal direction, it is possible to adjust the amount of absorption in different frequencies of the terahertz (THz) band. Additionally, an equivalent RLC circuit model is developed and theoretical results match with simulated data. The proposed mechanically tunable THz absorber can be exploited in various emerging applications such as sensing due to its capability of covering all of the THz gap and beyond with multiple absorption peaks.

Adjustable THz Absorber Exploiting Nested Graphene Disk-Ring

This work introduces a THz dual-band absorber with the capability of being tuned via external stimulation. A nested disk-ring graphene pattern is proposed on top of the lossless substrate while the other side of the substrate is coated by a thick layer of gold. The proposed absorber is modeled using an equivalent circuit model (ECM) and also simulated by the full wave method. A perfect match between the circuit model and numerical full wave simulation highlights the developed circuit modeling. Since the circuit modeling can reduce CPU time and need memory considerably. The impedance-matching concept interpretations are discussed in detail. Ample simulation results show the dual-band operation of the proposed absorber at 2THz and 10THz, while an interesting tuning capability is provided by changing chemical potentials. Such a simple and adjustable wave absorber is in demand for numerous applications ranging from medical imaging to indoor communication.

Photocatalytic Oxidization Based on TiO2/Au Nanocomposite Film for the Pretreatment of Total Phosphorus (TP)

Phosphorus, an essential rare element in aquatic ecosystems, plays a key role in maintaining ecosystem balance. However, excess phosphorus leads to eutrophication and algal proliferation. To prevent eutrophication, the pretreatment and measuring of the concentration of total phosphorus (TP) is crucial. Compared to conventional TP pretreatment equipment (autoclave), a lab-on-a-chip detection device fabricated using micro-electromechanical system technology and titania (TiO2) as a photocatalyst is more convenient, efficient, and cost-effective. However, the wide bandgap of TiO2 (3.2 eV) limits photocatalytic activity. To address this problem, this paper describes the preparation of a TiO2/Au nanocomposite film using electron-beam evaporation and atomic-layer deposition, based on the introduction of gold film and TiO2 to a quartz substrate. The photocatalytic degradation properties of TiO2/Au nanocomposite films with thicknesses of 1, 2, 3, and 4 nm were assessed using rhodamine B as a pollutant. The experimental results demonstrate that the deposition of gold films with different thicknesses can enhance photocatalytic degradation efficiency through synergetic reactions in the charge separation process on the surface. The optimal photocatalytic efficiency is achieved when the deposition thickness is 2 nm, and it decreases with further increase in the thickness. When the photocatalytic reaction time is 15 min, the lab-on-a-chip (LOC) device with a 2-nm-thick gold layer and autoclave exhibits a similar TP pretreatment performance. Therefore, the proposed LOC device based on photocatalytic technology can address the limitations of conventional autoclave equipment, such as large volumes, long processing times, and high costs, thereby satisfying the growing demand for on-site evaluation.

Fs Laser Patterning of Amorphous As2S3 Thin Films.

This study investigates the morphological changes induced by femtosecond (fs) laser pulses in arsenic trisulfide (As2S3) thin films and gold-arsenic trisulfide (Au\As2S3) heterostructures, grown by pulsed laser deposition (PLD). By means of a direct laser writing experimental setup, the films were systematically irradiated at various laser power and irradiation times to observe their effects on surface modifications. AFM was employed for morphological and topological characterization. Our results reveal a clear transition threshold between photoexpansion and photoevaporation phenomena under different femtosecond laser power regimes, occurring between 1 and 1.5 mW, irrespective of exposure time. Notably, the presence of a gold layer in the heterostructure minimally influenced this threshold. A maximum photoexpansion of 5.2% was obtained in As2S3 films, while the Au\As2S3 heterostructure exhibited a peak photoexpansion of 0.8%. The study also includes a comparative analysis of continuous-wave (cw) laser irradiation, confirming the efficiency of fs laser pulses in inducing photoexpansion effects.

Enhancement in the magneto-optical effect induced by combining multiple modes in a gold film–supported hybrid periodic gold/magnetic nanorod array

In this study, the possibility of enhanced transverse magneto-optical Kerr effect (TMOKE) and performance monitoring of a hybrid nanostructure developed by sandwiching a ferromagnetic film within a gold layer and square periodic nanorod arrays, is theoretically investigated. Based on the findings, the TMOKE signal can be enhanced approximately 33 times when compared to the referenced planar film, which is elucidated by the hybrid of modes in the magnetic film region. In addition, a high level of environmental sensor performance is simultaneously achieved by recording the wavelength resonance positions with the variation of refractive index, which is compatible with gaseous medium from 1 to 1.01, indicating that the structure of the proposal will have applications in environmental monitoring.

Dual layer chessboard metasurface sandwiched by a spin-on-carbon for spectral modulation.

Metasurfaces, composed by metals and dielectrics in periodical order with subwavelength pitches, are of great importance for their unique ability to abruptly manipulate optical fields. So far, all the reported metasurfaces are constructed by thermally deposited metals and dielectric films, based on semiconductor processes which are expensive and time-consuming. Inspired by the outstanding dry etch property of spin-on-carbon (SOC) as the interlayer material in CMOS technology, this paper proposes to utilize the SOC as the dielectric layer in a chessboard metasurface with dual layer of gold to form an array of local surface plasmonic resonators (localized surface plasmon resonance). Finite difference and time domain (FDTD) method is used to investigate the spectral characteristics in reflectance of the metasurface in both visible and short wavelengths of infrared light. Electron beam lithography is applied to generate the nanoscale chessboard pattern on ZEP520A, followed by a conventional oxygen-based plasma etch to form high aspect ratio nanopillar arrays in SOC with the feature width under 50 nm, and ended by a thermal deposition of gold to form self-aligned dual layer local surface plasmonic resonators (LSPRs). The measured reflectance spectra agree with the simulated. A wealth of optical properties, such as coupling induced modulations of spectra by LSPRs, are revealed and analyzed. These special modes result in tunable structural colors and wavelength-selective antireflection ability. To the best of our knowledge, this is the first time that SOC is applied in the construction of metasurfaces, which has great potential for next generation nanophotonic devices.

Highly sensitive temperature sensor based on nematic liquid crystal channel waveguide on silicon

This paper presents a highly sensitive hybrid plasmonic liquid crystal channel-based temperature sensor. The proposed structure has V-groove waveguide channel infiltrated with nematic liquid crystal (NLC) material of type E7 and coated by a gold (Au) layer to excite the surface plasmon resonance at the metal/dielectric interface. The NLC refractive indices depend on the temperature which affects the resonance wavelength where coupling occurs between the core and surface plasmon modes. The full vectorial finite element method is employed to evaluate the sensing performance of the reported sensor. The numerical results show that the suggested sensor can achieve an average temperature sensitivity of 24.5 nm/°C over a temperature range from 15 to 40 °C. The obtained wavelength sensitivity is higher than those of most similar temperature sensors based on silica-silicon or silicon-on-insulator technology in literature. In addition, the average amplitude sensitivity and figure of merit of the presented sensor are 0.135 °C− 1 and 0.43 °C− 1, respectively. Moreover, the introduced structure is complementary metal-oxide-semiconductor compatible with simple design and good fabrication tolerance of ± 5% where the temperature sensitivity is better than 23 nm/°C.

High-Temperature Melt Stamping of Polymers Using Polymer/Nanoporous Gold Composite Stamps.

Parallel lithographic deposition of polymers onto counterpart substrates is a widely applied surface manufacturing operation. However, polymers may only be soluble in organic solvents or are insoluble at all. Solvent evaporation during stamping may trigger hardly controllable capillarity-driven flow processes or phase separation, and polymer solutions may spread on the counterpart substrates. Solvent-free stamping of melts prevents these drawbacks. Here, a stamp design for the deposition of melts is devised, which intrinsically circumvents ink depletion. The stamps' topographically patterned contact surfaces with protruding contact elements contacting the counterpart substrates consist of a nanoporous gold layer with a thickness of a few micrometers. The nanoporous gold layer is attached to a molten polymer layer, which is support for the nanoporous gold layer and ink reservoir at the same time. The nanoporous gold layer in turn stabilizes the topography of the stamps' contact surfaces. As examples, arrays of submicron microdots of polystyrene and poly(vinylidenefluoride-trifluoroethylene) (PVDF-TrFE) are manufactured. The P(VDF-TrFE) microdots are partially crystalline, ferroelectric, and can be locally poled. It is envisioned that the methodology reported here can be automatized and may be extended to functional low-molecular-mass compounds, such as active pharmaceutical ingredients.

Dynamically tunable photonic spin Hall effect based on insulating-metallic phase transition of Vanadium Dioxide

The photonic spin Hall effect (PSHE) can manifest as the spin-dependent splitting (perpendicular to the plane of incidence) of a light beam, i.e., transverse beam shift. Introducing dynamically tunable PSHE into post-fabricated systems has great potential for the new type of photonic devices and its tuning range can be manipulated with different reconfigurable methods. Most of these methods are based on modifying the refractive index of bulk or interface materials. However, the perturbation on the refractive index is usually small, leading to difficulty in enhancing PSHE. Fortunately, the changes in the refractive index of Vanadium Dioxide (VO2) with insulating-metallic phase transition can be larger in several orders than that of other materials, making it possible for enhancing PSHE to have greater tuning range. Here, to explore the dynamically tunable PSHE based on the insulating-metallic phase transition of VO2, the transverse beam shift (as an indicator of PSHE) was calculated with a full wave theory at a wavelength of 1550 nm in a layered structure. Without a gold layer, only the PSHE of the H-polarized beam shows significant tunability in the insulating-metallic phase transition of VO2. With the Au layer, the PSHE of the H- and V-polarized beam is enhanced around the Brewster and Brewster-like (originating from the destructive interference between the nanosized layers) angle, respectively. For H- and V-polarized beams, the tuning range of PSHE is mainly determined by the insulating phase of VO2 and can be enhanced with the Au layer. Finally, as an example, the enhanced tuning range makes the output of a two-digit binary code conversion based on PSHE easier to recognize. These results offer us possible ways to control the tuning range of PSHE in post-fabricated systems and provide more potential for new applications.