Gold Layer Research Articles

Resistivity dependence on nanostructure formation in picosecond ablation of silicon and SERS-based sensing applications

We report on the influence of resistivity in picosecond (ps) laser ablation of silicon (Si) leading to the formation of diverse surface micro- and nanostructures. Subsequently, we investigated their potential in sensing applications based on the surface enhanced Raman scattering (SERS) technique. The varying resistivity (ρ 1: 1–10 Ω cm, ρ 2: 0.01–0.02 Ω cm, ρ 3: 0.001–0.005 Ω cm) Si wafers were subjected to cross patterned ps laser ablation in ambient air. Ladder-like microstructures embedded with numerous nano growths were formed on low resistivity Si (ρ 3) while similar micro- and nanostructures were observed on higher resistivity Si (ρ 2 < ρ 1). The structures were non-plasmonic and anti-reflecting in nature with an optical reflectance of <6% over a broad range of wavelengths (350–1200 nm). Non-plasmonic Si microstructures were subsequently transformed to plasmonic by means of deposition of a thin layer of gold (Au). Additionally, the effect of annealing on the evolution of nanostructures was also investigated. We employed these hybrid substrates for the trace detection of an explosive molecule, ammonium nitrate, and dye, malachite green. Our detailed SERS studies have demonstrated a superior enhancement in the trace detection of analytes for low resistivity Si substrate. However, the annealed hybrid substrates have demonstrated further improvement in the SERS signal (by at least one order of magnitude). These detailed SERS investigations provide us a proof of the sensitivity of different resistivity Si nano/microstructures.

Plasmonically enhanced composite vortex beam generation using ultra-thin dielectric fork gratings

We experimentally demonstrate a simple method for the generation of composite vortex beams using resonant ultra-thin dielectric fork gratings (UFGs) of thicknesses an order of magnitude less than the incident wavelength. The degradation in the diffraction efficiency of these gratings at reduced dielectric thicknesses was computationally shown to be compensated for by introducing a thin continuous gold layer (Au, 30 nm) between the grating and the substrate. At the resonance wavelength, the diffraction efficiency of UFGs with Au was ∼ 4 times higher when compared to that of UFGs without Au, which was attributed to plasmon-induced transmission enhancement. UFGs were fabricated with optimized geometric parameters using electron beam lithography. These gratings showed lattice-plasmon resonance at the wavelength corresponding to the grating vector, resulting in vortex beams with a specific wavelength and polarization selectivity. Further, hybrid UFGs were designed by replacing a central concentric circular region of a UFG with another UFG of a different topological charge. These hybrid UFGs resulted in the formation of composite vortex beams, indicating that the relative spatial phase imparted to the lattice plasmon by hybrid gratings was preserved in the leaked radiation. These results can help in designing integrated, ultra-thin, low aspect ratio optical-phase-singularity structures for enhanced optical sources, detectors, and sensing applications.

Investigation of neural electrode fabrication process on Polycarbonate substrate.

Polycarbonate is a polymer that has been widely used including medical application due to its useful properties. It has high temperature resistance, biocompatibility, transparency and low water absorption rate, which are needful characteristics for packaging material of implantable neural prosthetic devices. In this study, we investigated fabrication of neural electrode with polycarbonate film using standard photolithography process and heated hydraulic press for thermal lamination. First, oxygen plasma surface treatment was performed to increase the adhesion between metal and polycarbonate film. Then thin layer of titanium and gold layer were deposited. Metal layer is patterned through standard photolithography techniques. After completing the metal patterning, thermal lamination was performed with site opened polycarbonate film.

Complete Perovskite Solar Cells with Gold Electrodes Studied in the Visible and Near-Infrared Ranges

Complete solar cells with the triple-cation perovskite (FA0.76MA0.19Cs0.05Pb(I0.81Br0.19)3) sandwiched between spiro-OMeTAD (2,2′,7,7′-tetrakis-(N,N-di-4methoxyphenylamino)-9,9′-spirobifluorene) and mesoporous titania layers were examined using femtosecond transient absorption (TA) and steady-state absorption in the visible and near-infrared (NIR) regions. We demonstrate in this paper that the transmission spectroscopic measurements through a gold layer are possible and open the way to investigate the solar cells in working conditions (with applied voltage and/or additional illumination). We show that a gold electrode does not exhibit a significant TA signal itself but causes a difference in the perovskite response at around 800 nm and in the NIR range. The irradiation with a femtosecond laser, 1 Sun stationary illumination, or applied voltage causes significant changes in the TA spectra and kinetics at the TiO2 interface, most probably due to ion segregation or ion rearrangement process. The transmission signal in the NIR range is shown to be dominated by spectral modulation due to light interference; however, the process of hole injection at spiro-OMeTAD interfaces can be extracted. Finally, application of an appropriate forward bias enables the suppression of electron and hole injection to contact materials and results in increased lifetime of charge population in the perovskite.

Surface Functionalisation and Electroless Plating of 3D-Printed Microstructures

A microelectrode with a large surface area is one of the essential components in biosensors, electronic implants, and energy harvesting systems. In particular, enzymatic biofuel cells and biosensors benefit significantly from microelectrodes with a large surface area to volume ratio because of the increased enzyme loading and hence improved the power density of the final devices. Therefore, the fabrication of microelectrodes with a large surface area will advance its application in devices. Projection-microstereolitography (PµSLA) offers the ability to fabricate three-dimensional and geometrically adjustable polymeric microstructures with well-defined complex shapes in microscale. 3D polymeric microstructures produced using PµSLA can be then coated with metal to achieve high conductivity. Microelectrodes have been created via 3D printing of polymeric structures followed by electroless plating. However, the weak adhesion of the metal to the polymer limits the practical use of the produced devices as electrodes. Here, we show the method to introduce thiol groups on the surface of PµSLA-generated polymeric microstructures to improve the adhesion between the polymer surface and gold thin film. Our results demonstrate that thiol groups on the polymer surface provide the anchoring site for gold deposition during electroless plating via gold-sulfur bonding, resulting in strong adhesion between the polymer surface and the gold layer and long-term microelectrode durability. The gold coated 3D microelectrode exhibits excellent electrical conductivity up to 1.4 × 107 S/m (35% of bulk gold). This method can offer exciting potential for constructing microelectrodes for architecture-specific applications in future energy, catalysis, and sensing.

Greatly Enhanced CTC Culture Enabled by Capturing CTC Heterogeneity Using a PEGylated PDMS-Titanium-Gold Electromicrofluidic Device with Glutathione-Controlled Gentle Cell Release.

The circulating tumor cells (CTCs, the root cause of cancer metastasis and poor cancer prognosis) are very difficult to culture for scale-up in vitro, which has hampered their use in cancer research/prognosis and patient-specific therapeutic development. Herein, we report a robust electromicrofluidic chip for not only efficient capture of heterogeneous (EpCAM+ and CD44+) CTCs with high purity but also glutathione-controlled gentle release of the CTCs with high efficiency and viability. This is enabled by coating the polydimethylsiloxane (PDMS) surface in the device with a 10 nm gold layer through a 4 nm titanium coupling layer, for convenient PEGylation and linkage of capture antibodies via the thiol-gold chemistry. Surprisingly, the percentage of EpCAM+ mammary CTCs can be as low as ∼35% (∼70% on average), showing that the commonly used approach of capturing CTCs with EpCAM alone may miss many EpCAM- CTCs. Furthermore, the CD44+ CTCs can be cultured to form 3D spheroids efficiently for scale-up. In contrast, the CTCs captured with EpCAM alone are poor in proliferation in vitro, consistent with the literature. By capture of the CTC heterogeneity, the percentage of stage IV patients whose CTCs can be successfully cultured/scaled up is improved from 12.5% to 68.8%. These findings demonstrate that the common practice of CTC capture with EpCAM alone misses the CTC heterogeneity including the critical CD44+ CTCs. This study may be valuable to the procurement and scale-up of heterogeneous CTCs, to facilitate the understanding of cancer metastasis and the development of cancer metastasis-targeted personalized cancer therapies conveniently via the minimally invasive liquid/blood biopsy.

Light‐Driven Shape Memory of 3D‐Printed PEEK for Programmable Actuations

AbstractRemotely controllable actuation of engineering polymers is highly demanded in the fast‐developing intelligent society. Here, this work demonstrates that the programmable shape memory of 3D‐printed poly(ether ether ketone) (PEEK), which is an excellent engineering material, could be driven by both ultraviolet (UV) light and natural sunlight. The shape recovery ratio reaches 97.6% and could be finely regulated by defining the sample thickness, shape programming, way of placement, and light intensity. Light‐induced continuous, sequential, and programed actuations (shape recovery) are further realized in various 3D‐printed PEEK structures. Meanwhile, the coating of a thin layer of gold is proven to be effective in anti‐UV oxidation and the enhancing of shape recovery. Moreover, natural sunlight during daytime is demonstrated to be able to induce the shape recovery of 3D‐printed PEEK in outdoor environment. The work here can pave the way for the use of PEEK as a smart material in the fields such as aerospace and intelligent industry.

Sensitivity enhancement of microelectromechanical sensors using femtosecond laser for biological and chemical applications

Rapid, selective, and highly sensitive microelectromechanical sensors are a promising technology for biosensing, medical recognition, and the detection of chemical hazards. At the same time, the surfaces of silicon microcantilevers cannot bond with thiols and cannot be functionalized without a bonding layer, such as gold. Therefore, in past literature, the surfaces of silicon microcantilevers have been coated with gold to facilitate their bonding with the thiol functional groups on the probe layers. However, gold coating produces thermal noise in the results owing to the metallic effect. Accordingly, this study aimed to modify the surface of silicon microcantilevers by patterning it using femtosecond laser (FSL) micromachining so that it could bond with the thiol functional groups with high sensitivity. The surface patterning of silicon microcantilevers enhances their physical, micromechanical, and chemical properties, increasing sensitivity by increasing the quality factor, specific surface area, and creating trapping areas on the microcantilever surfaces. The surfaces of the silicon microcantilever were patterned by microgrooves aligned from the free end to the bounded end, with each microgroove comprising submicrogrooves. To demonstrate their use in a biosensing applications, the modified microcantilevers were functionalized to detect severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2; COVID‐19) by immobilizing thiolated oligonucleotides on the surfaces, which worked as the probe layer. The modified biosensor was used to detect low concentrations of SSDNA sequence targets ranging from 300 nM down to 100 pM. The modified silicon‐microcantilever sensors were directly functionalized without a joining layer, such as a gold layer. The results revealed a selective response to SARS‐CoV‐2 SSDNA down to a 9‐nM concentration. To detect hazardous chemicals, the modified microcantilever was functionalized using reduced L‐cysteine to detect Pb2+ at low concentrations down to 100 pM. The results revealed enhanced sensitivity and selectivity and demonstrated that the FSL patterning activated the microcantilevers to bond with probe layers through the interaction of the silanol created on the surface with the functional groups, such as the thiols, on the probe layers. The microcantilevers patterned with 10 microgrooves exhibited higher responses than those patterned with seven microgrooves.

A Broadband Biosensor Using Graphene-Metasurface Based Cross-Polarization Converter

We present the design and analysis of a graphene metasurface-based cross polarization converter operating within the terahertz gap for detecting biomolecules over a broad spectral range, taking the SARS-CoV-2 virus as a specific example. To the best of our knowledge, our design reports the widest band of operation in the THz region of a graphene-based metasensor. Each meta-atom comprises a graphene pattern on silicon dioxide atop a continuous gold layer and exhibits near-unity cross polarization conversion ratio (PCR) and a 90% PCR bandwidth of 0.926 THz within the desired band (1.88 THz-2.81 THz). The proposed device demonstrates additional benefits which include a thin configuration ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /7.84) and compact lattice size ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /10.66), which are significantly better than other recently reported graphene metasurface biosensors. The device provides a sensitivity up to 490 GHz/RIU and a figure of merit (FoM) of 0.377 over a wide span of 0.926 THz within the terahertz gap. The electromagnetic response of this device has been validated via rigorous numerical analyses of simulated outputs as well as by developing a detailed circuit model representation of the same. The device demonstrates angular stability of nearly 40° under oblique incidence of the incident wave.

Non-Destructive Scientific Analysis of the Gold Fabric Excavated of Cheongsong Shim’s Grave

Using non-destructive analytical methods, we identified the material characteristics of two gold fabric artifacts excavated from the Cheongsong Sim clan (Bugeum Wonsam, Jikgeum Chima), including the artifact condition, fiber type, surface contamination, and metallic threads. We found that the artifacts were buried and had turned brown; thus, we were unable to determine their original color. The fiber type was determined to be silk from cocoons, based on scanning electron microscopy, Fourier transform infrared (FT-IR) analyses of Amide I, II, III, and IV peaks, and color reactions Further, the FT-IR and X-ray fluorescence (XRF) analyses identified the white and black stains as natural resin hydrolyzed substances, such as lipids and proteins, that occurred as microbial decomposition due to body decay. Finally, the XRF analyses identified the thin gold layer of the metallic yarn as gold (Au). According to the FT-IR data and the color reaction to the metallic yarn medium, the adhesive component of the medium was a product of-Amides I, II, III, and 3000 cm-1 within Amides A and B (an animal type), respectively. Thus, the medium was identified as Hanji (Korean paper), which is made from domestically produced Broussonetia kazinoki fibers.

Optically Transparent Gold Nanoparticles for DSSC Counter-Electrode: An Electrochemical Characterization.

A gold nanoparticles transparent electrode was realized by chemical reduction. This work aims to compare the transparent gold nanoparticles electrode with a more commonly utilized gold-film-coated electrode in order to investigate its potential use as counter-electrode (CE) in dye-sensitized solar cells (DSSCs). A series of DSSC devices, utilizing I−/I3− and Co(III)/(II) polypyridine redox mediators [Co(dtb)3]3+/2+; dtb = 4,4′ditert-butyl-2,2′-bipyridine)], were evaluated. The investigation focused firstly on the structural characterization of the deposited gold layers and then on the electrochemical study. The novelty of the work is the realization of a gold nanoparticles CE that reached 80% of average visible transmittance. We finally examined the performance of the transparent gold nanoparticles CE in DSSC devices. A maximum power conversion efficiency (PCE) of 4.56% was obtained with a commercial I−/I3−-based electrolyte, while a maximum 3.1% of PCE was obtained with the homemade Co-based electrolyte.

Dual polarized surface plasmon resonance refractive index sensor via decentering propagation-controlled core sensor

Refractive index (RI) is a unique attribute of bio-analytes which highly relies upon their concentrations or the activity/infectivity of the microbes. In this paper, a dual-polarized surface plasmon resonance (SPR) RI sensor based on a decentered propagation-controlled core photonic crystal fiber (PCF) has been studied. Fine-tuned light guidance is realized by scaling down the core air holes. The external surface of the fiber is metalized with a thin gold layer that maximizes the chemical stability by reducing the chances of oxidation. The deposition of the core from the central position reduces the core to analyte distance resulting in efficient coupling as well as greater sensitivity. Finite element method (FEM) based numerical investigation warrants promising sensing performances in wavelength and amplitude interrogation methods. The proposed sensor is viable for the RI range from 1.33 to 1.39, where it demonstrates the highest wavelength sensitivities of 13,700 and 15,400 nm/RIU and highest amplitude sensitivities of 852 RIU-1 and 654 RIU-1 in x-and y-polarized modes, respectively. It also exhibits high sensor resolutions of 7.30 × 10−6 RIU and 6.49 × 10−6 RIU, and high figure of merits of 216 and 256 RIU-1 for x and y-polarized modes, respectively. Along with the liberty of selecting light sources, the highly sensitive nature of the sensor will enable accurate detections of different organic compounds and bio-molecules.

Structural characterization of Au/Cr bilayer thin films using combined X‐ray reflectivity and grazing incidence X‐ray fluorescence measurements

Gold thin‐film mirrors are widely used as X‐ray reflective optics to manipulate X‐rays especially in synchrotron beamlines. Application of a thin underlying buffer layer of chromium enhances the adhesion of gold film to the substrate material and provides long term structural stability. In the present work, Au/Cr bilayers deposited using the DC magnetron sputtering technique with different thickness values on a Si substrate are studied to better understand the correlation between micro‐structure properties and residual stress. In order to obtain precise structural properties of Cr binding layer and gold layer, as well as in‐between nanoscaled interfacial structure, nondestructive probing is carried out by simultaneously utilizing synchrotron‐based combined X‐ray reflectivity (XRR)–grazing incidence X‐ray fluorescence (GIXRF) techniques. It has been clearly observed that when thickness of Cr layer is relatively small, a composite interlayer structure is formed at the Au/Cr boundary and at the Cr/Si interface boundary due to the interdiffusion of two layer mediums. However, when the thickness of the Cr layer is relatively larger (~90 Å), emergence of such an interlayer medium does not take place. The grazing incidence X‐ray diffraction (GIXRD) measurements have also been performed to investigate crystalline structure and residual stress of the gold layer medium. Our results show that relatively large residual stress exists in the Au layer if thickness of Cr layer is small. The surface roughness morphology of the top gold layer obtained from the atomic force microscopy measurements showed the partial agreement with the results obtained from the XRR‐GIXRF technique.

Electrical conduction and noise spectroscopy of sodium-alginate gold-covered ultrathin films for flexible green electronics

Green electronics is an emerging topic that requires the exploration of new methodologies for the integration of green components into electronic devices. Therefore, the development of alternative and eco-friendly raw materials, biocompatible and biodegradable, is of great importance. Among these, sodium-alginate is a natural biopolymer extracted from marine algae having a great potential in terms of transparency, flexibility, and conductivity, when functionalized with a thin gold (Au) layer. The electrical transport of these flexible and conducting substrates has been studied, by DC measurements, from 300 to 10 K, to understand the interplay between the organic substrate and the metallic layer. The results were compared to reference bilayers based on polymethyl-methacrylate, a well-known polymer used in electronics. In addition, a detailed investigation of the electric noise properties was also performed. This analysis allows to study the effect of charge carriers fluctuations, providing important information to quantify the minimum metallic thickness required for electronic applications. In particular, the typical noise behavior of metallic compounds was observed in samples covered with 5 nm of Au, while noise levels related to a non-metallic conduction were found for a thickness of 4.5 nm, despite of the relatively good DC conductance of the bilayer.

Analysis of Dual-Band Plasmonic Nanoantenna with Ultra-Thin Circular Gold Layers in Visible Region

Aperture-based plasmonic nanoantenna design with dual-band resonance obtained in the region very close to the green wavelength in the spectrum between 400 nm and 700 nm, which can be used in non-invasive biological sensing applications in the future, is presented. In this circular aperture-based nanoantenna design, the effect of changing the material thickness and dielectric medium parameters on the antenna response is investigated. In the nanoantenna design using a double-layer conductive gold layer, both of thickness values are reduced to 5 nm. It is observed that this thickness value exhibits a very strong transmittance response compared to the thicker gold layer values used in the visible region. In this nanoantenna, which exhibits dual band properties at 508 and 551 nm wavelengths, the strongest transmittance peaks are obtained for 5 nm thickness of gold, 100 nm thickness of magnesium fluoride and the 100 nm radius of the circular aperture. In order to contribute to spectroscopic sensing applications, hot spots locations and near field enhancement distribution maps are also examined.

Sensitivity-Tunable Temperature SPR Sensor Based on Side-Opening Grapefruit Fiber With Liquid Mixture

We demonstrate a sensitivity-tunable temperature SPR sensor based on side-opening grapefruit fiber. The opening sections of the fiber are coated with gold layer and then filled with a liquid mixture of ethanol and chloroform as the sensing medium. The variation of the temperature will lead to different coupling efficiencies between the core-guided mode and the plasmonic mode, and then resulting in the change of loss spectra of the fiber that will be detected. Simulation results indicate that the temperature sensitivity of the sensor is 19.9 nm/°C at 10°C when the volume fraction of ethanol in the mixture is 0.1. Moreover, by adjusting the volume fraction, the sensitivity of proposed sensor can achieve the upper limit for a certain temperature range without the excitation of higher order plasmonic modes.

Graphene-Based Metasurface for Tunable Absorption and Transmission Characteristics in the Near Mid-Infrared Region

This article reports a graphene-based metasurface to work at terahertz domain as a wideband tunable absorber along with a property of electromagnetic transmittivity. This indeed for the first time claims the widest possible absorption band produced by a graphene metasurface-based rasorber operating in terahertz frequencies (2.24–4.67 THz). Each unit cell comprises stacked graphene, silicon dioxide, and slotted gold layer featuring 99.9% absorptivity as well as 34.01% transmittivity across the respective bands. The other novel feature lies in its ultrathin characteristics ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\mathrm {g}}$ </tex-math></inline-formula> /10.70), which is improved by more than a factor of 4 relative to its closest competitor, and also in the compactness in periodicity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\mathrm {g}}$ </tex-math></inline-formula> /12.49), which is identically improved by a factor of 6. The design is executed using an extensive analysis of simulated results. The lack of experimental facility at those frequencies accessible to the authors in their country has been compensated by verifying the simulated prediction using a circuit model developed inhouse. A new biasing scheme for achieving tunable absorption has been illustrated. This work also promises some features, i.e., polarization-insensitive transmission and absorption together with angularly stable characteristics of the incident wave up to 40°. The proposed structure should find potential applications in terahertz, including communication security, satellite communication systems, and stealth applications.

Field enhancement in hydrogen storage by periodic layered structures

This paper investigates, through the field enhancement factor, the increase of hydrogen adsorption around the interface between a layer of hydrogen and a periodic layered structure under different incidence angles of an applied transverse magnetic polarized electromagnetic field. This periodic layered structure is composed of n-binary unit cells based on alternating a thin layer of gold with a thin layer of a metamaterial with equal negative relative permittivity while the relative permeability of the first and the second material's unit cell is considered equal to 1 and -1, respectively. We apply the effective medium theory to replace this layered structure with a single slab of a homogeneous material with an effective permittivity tensor and an effective permeability tensor. We use the Transfer Matrix Method to analyze the reflectivity spectra at the hydrogen/slab interface for adjustable layers’ thicknesses and then we derive the field enhancement factor. We obtain a significant increase of the field enhancement factor of the structure in comparison with the field enhancement factor around the interface between a layer of hydrogen and a structure composed of one gold layer.

Au-Based Thin-Film Metallic Glasses for Propagating Surface Plasmon Resonance-Based Sensor Applications.

We deposited Au–Cu–Si, an Au-based thin-film metallic glass (TFMG) of ∼50 nm thickness, as the activation layer for propagating surface plasmon resonance (PSPR)-based sensors on a BK7 glass substrate to substitute the commonly used gold layer. The film composition was tuned to yield the maximum Au content (∼65 at %), while the structure remained amorphous. The results showed that the Au-based TFMG could support surface plasmon resonance and gave rise to the extinction in the angle-resolved reflection spectrum. Using deionized water and ethyl alcohol with the refractive index difference of ∼0.03 as the analytes, the angle shift given by Au-based TFMG was 4° compared to 5° given by the Au film. Hence, Au-based TFMG is feasible to be used as the activation layer in PSPR-based sensors. Compared to the Au film, Au-based TFMG has the advantages of being less expensive, lacking grain boundary scattering, better adhesion to the substrate, and higher resistance to scratch and corrosion because of its amorphous structure with excellent mechanical properties.

An investigation on the performance of gold layer based cyanide-free HAuCl4 electroplating process under different power conditions

Gold electroplating experiment was carried out by cyanide-free chloroauric acid-based (HAuCl4-based) electroplating process in this paper. Smooth, uniform and golden thick gold layers can all be obtained after 6 h under DC, UD and PR condition. With the changing of power, the macroscopic characteristics and structure of gold layers change obviously. Sample has the best luster under PR condition. SEM images show that microstructure of gold layers vary at different power condition. AFM images show that gold layer under PR condition has the lowest surface roughness. After polishing, samples obtained under DC and UD condition have different densities of pores, while the pores are almost invisible under PR condition. XRD tests show under DC power supply, sample has no obvious orientation. The texture coefficient of (220) crystal plane of gold plating under UD condition can reach to 62.5%, and that of (200) crystal plane under PR condition can reach up to 98.9%. Texture of each sample calculated by XRD data can be verified by EBSD. Gold layer under PR condition has the highest hardness, which can reach up to 98.05 × 10−2 GPa. Gold layer under PR condition possess a number of advantages over the other powers. For pure hard gold, HAuCl4-based baths is a suitable alternative to cyanide-based baths.