Au Multilayers Research Articles

Metamaterial structure design based on genetic algorithm and phase change material GST for multispectral camouflage

This study proposes a multispectral camouflage tunable multilayer film metamaterial (TMFM) with thermal management function based on genetic algorithm (GA), which is composed of ZnS/YbF3/Ge/Ge2Sb2Te5 (GST)/Au multilayer film. Through numerical analysis, we assess its efficacy in visible-infrared compatibility camouflage and radiative heat dissipation. Within the visible light band, different structural colors can be produced by adjusting the thickness of the ZnS film. The average emissivity within the 3–5 μm and 8–14 μm infrared bands is measured at 0.04 and 0.14, respectively. The low emissivity facilitates effective thermal management. Moreover, an average emissivity of 0.52 within the 5–8 μm range is instrumental in achieving efficient radiation heat dissipation. Laser stealth capability is further enhanced, with an emissivity reaching 0.70 at 10.6 μm. Therefore, this metamaterial structure has broad application prospects in both military and civilian industrial fields.

Petroleum coke-derived carbon nanotubes decorated by gold nanoparticles towards highly selective Pb2+ electrochemical sensing

The utilization of petroleum coke with a simple and eco-friendly way is still a challenging task. In this study, an in-situ texturing strategy has been proposed for the preparation of the N-doped carbon nanotubes (N-CNTs), which employs cheap petroleum coke as carbon source and graphitic carbon nitride (g-C3N4) as template and nitrogen source. The synergistic effect between N-CNTs with multilayer adsorption and Au nanoparticles (AuNPs) with remarkable electrocatalytic properties is conducive to constructing a promising N-CNTs/AuNPs nanocomposite as sensing flatform for monitoring the trace amount of heavy metal ions. The sensitivity of N-CNTs/AuNPs-modified glassy carbon electrode (GCE) for lead (II) ion (Pb2+) detection is as high as 26.1 μA·μM−1, which has 42.5 and 3.0-times enhancement compared to bare GCE (0.6 μA·μM−1), and N-CNTs-modified GCE (6.5 μA·μM−1), respectively. Additionally, the corresponding limit of detection of N-CNTs/AuNPs-modified GCE has achieved as low as 0.011 μM (S/N = 3). Encouragingly, the interference of co-existing ions could be negligible, which allows the accurate detection of Pb2+ in real water samples for further practical applications with a satisfactory recovery between 95.7 % and 106.6 %. The exceptional anti-interference performance can be ascribed to the robust chemical interaction between Pb2+ and N-CNTs/AuNPs nanocomposite, which has been proved by the X-ray photoelectron spectroscopy analyses. This work not only opens up a new avenue for the high added-value and efficient utilization of petroleum coke, but also provides valuable insights into harnessing synergistic catalysis of noble metal nanoparticles to improve the electrochemical activity of electrode materials in the electrochemical analysis field.

Estimation of the interfacial Dzyaloshinskii–Moriya interaction in all-metallic multilayer with perpendicular magnetic anisotropy

The interfacial Dzyaloshinskii–Moriya (iDMI) interaction which arises at the interface between a heavy metal (HM) and a ferromagnet (FM) can stabilize chiral Néel type domain walls in ultrathin perpendicularly magnetized multilayers. Dissimilar HMs are required on both bottom and top sides of the FM layer in order to introduce the structural inversion asymmetry which ensures an effective iDMI in the FM layer. HMs like Pt, Ir, Ta etc are very well known for developing large iDMI in the interface with Co, whereas noble metals like Au can produce negligible iDMI. Therefore, a multilayer Pt/Co/Au is chosen to determine the individual iDMI in the Pt/Co interface. Some procedures like field-induced domain wall motion study, spin–orbit torque efficiency estimation study are well established to quantify the effective field due to the iDMI ( HDMI ) which in turn gives the strength of the iDMI ( Deff ). Besides these procedures, a current-induced switching of magnetization was studied to construct a switching phase diagram where the critical current density of magnetization switching has been plotted as a function of the applied in-plane magnetic field. The experimentally constructed diagram and the simulated diagram using a micromagnetic study have revealed the possibility to quantify HDMI . Thus, a systematic and unified estimation of Deff has been done on all-metallic Ta/Pt/Co/Au multilayers.

Performance improvement of a discrete dynode electron multiplication system through the optimization of secondary electron emitter and the adoption of double-grid dynode structure

The discrete dynode electron multiplication system (DD-EMS) is the core part of commonly used photomultiplier tubes and electron multipliers, and it has a great influence on the signal amplification capability of these devices. In this work, the sputtering time of Mg target during the deposition of the surface MgO layer of the MgO/(MgO–Au)/Au multilayer film as the secondary electron emitter was optimized, and the strategy of double-grid structures applied at the 7th and 8th dynodes was proposed with the intention of improving the gain and stability of nine-stage DD-EMS under electron bombardment to satisfy the requirements of detecting the single photon or single charged particle. The investigation results show that the DD-EMS fabricated by using the MgO/(MgO–Au)/Au film with a Mg target's sputtering time of 3600 s has the highest maximal gain of 1.22 × 106 and the lowest gain attenuation rate of 15.7%/mC under electron bombardment. In addition, the DD-EMS with the double-grid structure has a higher maximal gain of 1.62 × 106 and a lower gain attenuation rate of 11.6%/mC under continuous electron bombardment, which are 32.8% increased and 17.7% reduced respectively in comparison with that of the single-grid structure.

Plasmon-induced hot electron injection and local surface potential modification in WS2/Au-nanogratings

The integration of metal nanostructures and transition metal dichalcogenides (TMDs) can lead to exciton-plasmon coupling, which can provide a platform to investigate intriguing physics and cutting-edge applications. In this work, we fabricated hybrid systems, consisting of WS2 multilayer flakes and Au nanogratings (AuNGs), and investigated their optical and electrical characteristics. WS2 flakes were directly exfoliated on large-area AuNGs, prepared by evaporation of Au thin films on Blu-ray disc templates. The polarization- and angle-dependence of the reflectance spectra of WS2/AuNGs indicated surface plasmon polariton (SPP) excitation and SPP-exciton coupling in the visible wavelength range. The surface potential maps in WS2/AuNGs, acquired by Kelvin probe force microscopy, could visualize how the SPP-exciton coupling affected the creation and redistribution of charge carriers. The SPP-induced hot electron injection from AuNG to WS2 as well as band-to-band excitation in WS2 contributed to the local modification of the potential distribution under light illumination.

Seed-assisted electrodeposition of multilayer Au nanoparticles-assembled films for sensitive surface-enhanced Raman scattering detection

Surface-enhanced Raman scattering (SERS) spectroscopy can be used to realize sensitive rapid detection of molecules. Three-dimensional (3D) SERS substrates can provide more hotspots within the excitation laser beam when compared with the corresponding two-dimensional (2D) SERS substrates. Most of the methods for fabrication of 3D SERS substrates involve complex processes. Therefore, it is significant to develop a simple and effective method for fabrication of 3D SERS substrates. Here, a seed-assisted electrodeposition approach is developed for fabrication of a 3D SERS substrate composed of multilayer Au nanoparticles. Interestingly, it is demonstrated that a uniform film composed of multilayer Au nanoparticles that can serve as a 3D SERS substrate can be achieved directly by one-step electrodeposition on a conductive surface coated with monolayer Au seeds. It is found that a diffusion-controlled growth during electrodeposition narrows the nanoparticle size distribution and results monosized Au nanoparticles. The as-prepared multilayer Au nanoparticles-assembled film shows high SERS sensitivity and good spectral uniformity. For SERS detection of rhodamine 6G, a limit of detection as low as 3.4×10−12 M has been achieved. Moreover, good spectral uniformity (relative standard deviation ∼7.8%) and high substrate-to-substrate reproducibility (relative standard deviation ∼8.6%) have also been demonstrated. The as-prepared multilayer Au nanoparticles-assembled film is used to detect organic pollutants such as dye molecule crystal violet (CV) and methylene blue (MB). Calibration curves with a linear correlation between the logarithmic SERS intensity and logarithmic concentration of CV and MB have been obtained. Limit of detections for CV and MB are 1.2×10−8 M and 9.8×10−10 M, respectively. Therefore, the fabricated 3D SERS substrate has good application prospects in sensitive detection of organic molecules.

Facile Preparation of Au–Ag Composite Nanostructure for High-Sensitive and Uniform Surface-Enhanced Raman Spectroscopy

Preparation of a high-sensitive and uniform surface-enhanced Raman spectroscopy (SERS) active substrate structure usually faces complex processes and high costs. Here, porous Au–Ag composite nanostructures that are conventional fabricated by the deposition of a multilayer Au–Ag, annealing, and dealloying process are proposed for high-performance SERS. By annealing at a suitable temperature, nanopores could be firmly distributed on the surface, which serves as hot spots. The electric field distribution was also performed by the finite difference time domain. The experiment results exhibited excellent uniformity and high sensitivity of SERS detection. The enhancement factor of the R6G molecules detected by the SERS substrate reached 1.37 × 107, and the relative standard deviation was as low as 4.9%. The minimum detection concentration of R6G molecules by the Au–Ag composite nanostructures with bottom Au mirror could reach 10−13 M. The proposed Au–Ag composite nanostructures and the fabrication process have great potential in preparation of a high-sensitive and uniform SERS substrate.

Plasmonic gadolinium oxide nanomatryoshkas: bifunctional magnetic resonance imaging enhancers for photothermal cancer therapy.

Nanoparticle-assisted laser-induced photothermal therapy (PTT) is a promising method for cancer treatment; yet, visualization of nanoparticle uptake and photothermal response remain a critical challenge. Here, we report a magnetic resonance imaging-active nanomatryoshka (Gd2O3-NM), a multilayered (Au core/Gd2O3 shell/Au shell) sub-100nm nanoparticle capable of combining T1 MRI contrast with PTT. This bifunctional nanoparticle demonstrates an r1 of 1.28×108 mM-1 s-1, an MRI contrast enhancement per nanoparticle sufficient for T1 imaging in addition to tumor ablation. Gd2O3-NM also shows excellent stability in an acidic environment, retaining 99% of the internal Gd(3). This report details the synthesis and characterization of a promising system for combined theranostic nanoparticle tracking and PTT.

Highly Porous Gold Electrodes – Preparation and Characterization

AbstractGold screen printed electrodes (Au‐SPEs) were treated electrochemically to produce a micro‐rough pattern increasing the real electrode surface. The procedure based on the Dynamic Hydrogen Bubble Template (DHBT) method included electrochemical deposition of Au layers onto the surface of the Au‐SPEs, followed by a reductive process at −3 V (vs. Ag/AgCl) leading to formation of H2 bubbles, which produced pores in the Au multilayer. The morphology of the micro‐porous Au electrode was characterized by scanning electron microscopy (SEM), surface mapping, surface profilometry, and confocal microscopy. The electrode surface morphology was controlled by the time of the electrode reductive treatment (H2 evolution) and the optimized condition resulting in the best surface structuring was found. Notably, the surface roughness leading to the highest electrode surface area was significantly increased compared to previously reported results with Au‐SPEs.

Mechanism of emitters coupled with a polymer-based hyperbolic metamaterial.

We study a polymer-based hyperbolic metamaterial (HMM) structure composed of three Au-polymer bilayers with a hyperbolic dispersion relation. Using an effective refractive index retrieval algorithm, we obtain the effective permittivity of the experimentally fabricated polymer-based structure. In particular, the unique polymer-based HMM shows the existence of high-k modes that propagate in the metal-dielectric multilayered structure due to the excitation of bulk plasmon-polaritonic modes. Moreover, we compare the experimental luminescence and fluorescence lifetime results of the multilayered Au and a dye-doped polymer (PMMA) to investigate the dynamics of three different emitters, each incorporated within the unique polymer-based HMM structure. With emitters closer to the epsilon-near-zero region of the HMM, we observed a relatively high shortening of the average lifetime as compared to other emitters either close or far from the epsilon-near-zero region. This served as evidence of coupling between the emitters and the HMM as well as confirmed the increase in the non-radiative recombination rate of the different emitters. We also show that the metallic losses of a passive polymer-based HMM can be greatly compensated by a gain material with an emission wavelength close to the epsilon-near-zero region of the HMM. These results demonstrate the unique potential of an active polymer-based hyperbolic metamaterial in loss compensation, quantum applications, and sub-wavelength imaging techniques.

Cyanide-free electrolyte for Au/Co-Au nano-multilayer electrodeposition utilising 5,5-dimethylhydantoin as a complexing agent.

A novel cyanide-free electrolyte was used in electrodepositing Au/Co–Au nano-multilayers. Firstly, an optimised electrolyte for Au–Co alloy electrodeposition was obtained from orthogonal experiments. The effect of current density and potential values on the deposited composition was investigated. Results showed that low current density and over-potential value promoted Au deposition. A large current density and high over-potential value resulted in high cobalt concentration. The co-deposition of gold and cobalt in this study system was canonical. When the electrode potential was positive (−0.6 V, −0.7 V vs. saturated calomel electrode (SCE)), only gold was deposited; when the potential was negative (−0.8 V vs. SCE), gold and cobalt were co-deposited. Using an optimised cyanide-free electrolyte produced Au/94.07 at% Co–Au multi-layers with a gold layer of approximately 20 nm and a 94.07 at% Co–Au alloy layer of approximately 90 nm in the 5,5-dimethylhydantoin-containing, cyanide-free system.

Hot deformation behavior and related microstructure evolution in Au−Sn eutectic multilayers

Hot compression was performed on a multilayered Au−20Sn eutectic alloy to investigate the deformation behavior and microstructure evolution. During hot compression, microstructural spheroidization was initiated from plastic instability regions, and it was preferentially activated in vertical lamellae with a growth direction parallel to the compressive direction. Continuous dynamic recrystallization associated with lattice dislocations was the mechanism in both AuSn and Au5Sn multilayers. After spheroidization, strain accumulations were weakened in both of the equiaxed phases, and the deformation mechanism was substantially replaced by grain boundary sliding and migration. Based on these findings, hot rolling was conducted on an as-cast Au−20Sn alloy and a foil with a thickness of ~50 μm was successfully prepared. The present study can promote the development of Au−20Sn foils, and provide insights into the deformation behavior and microstructure evolution of multilayered eutectic alloys.

Fully resolved currents from quantum transport calculations

We extract local current distributions from interatomic currents calculated using a fully relativistic quantum mechanical scattering formalism by interpolation onto a three-dimensional grid. The method is illustrated with calculations for Pt$|$Ir and Pt$|$Au multilayers as well as for thin films of Pt and Au that include temperature-dependent lattice disorder. The current flow is studied in the "classical" and "Knudsen" limits determined by the sample thickness relative to the mean free path $\lambda$, introducing current streamlines to visualize the results. For periodic multilayers, our results in the classical limit reveal that transport inside a metal can be described using a single value of resistivity $\rho$ combined with a linear variation of $\rho$ at the interface while the Knudsen limit indicates a strong spatial dependence of $\rho$ inside a metal and an anomalous dip of the current density at the interface which is accentuated in a region where transient shunting persists.

Single-hemisphere photoelectron momentum microscope with time-of-flight recording.

Photoelectron momentum microscopy is an emerging powerful method for angle-resolved photoelectron spectroscopy (ARPES), especially in combination with imaging spin filters. These instruments record kx-ky images, typically exceeding a full Brillouin zone. As energy filters, double-hemispherical or time-of-flight (ToF) devices are in use. Here, we present a new approach for momentum mapping of the full half-space, based on a large single hemispherical analyzer (path radius of 225 mm). Excitation by an unfocused He lamp yielded an energy resolution of 7.7 meV. The performance is demonstrated by k-imaging of quantum-well states in Au and Xe multilayers. The α2-aberration term (α, entrance angle in the dispersive plane) and the transit-time spread of the electrons in the spherical field are studied in a large pass-energy (6 eV-660 eV) and angular range (α up to ±7°). It is discussed how the method circumvents the preconditions of previous theoretical work on the resolution limitation due to the α2-term and the transit-time spread, being detrimental for time-resolved experiments. Thanks to k-resolved detection, both effects can be corrected numerically. We introduce a dispersive-plus-ToF hybrid mode of operation, with an imaging ToF analyzer behind the exit slit of the hemisphere. This instrument captures 3D data arrays I (EB, kx, ky), yielding a gain up to N2 in recording efficiency (N being the number of resolved time slices). A key application will be ARPES at sources with high pulse rates such as synchrotrons with 500 MHz time structure.

High performance ammonia gas sensor based on GaN honeycomb nanonetwork

In this work, we have demonstrated a FET-like ammonia (NH3) gas sensor fabricated on a unique structure namely GaN honeycomb nanonetwork (GaN-HN) which is in-plane electrically conductive together with large surface-to-volume ratio. Utilizing ohmic contact Ti/Al/Ti/Au multilayers as the source and the drain terminals and Pt nanonetwork layer as the gate terminal, the FET-like NH3 gas sensors were fabricated by a two-mask photolithography process. The fabricated NH3 gas sensors have high selectivity, fast response/recovery, and a wide detection range up to 5000 ppm. The response and recovery time for 5 ppm NH3 gas are 23 s and 101 s at a moderate operating temperature of 120 °C. Interestingly, this sensor is capable to detect trace NH3 gas and the low limit of detection (LOD) is as small as 0.31 ppm. Its absorption activation energy Ea is also investigated by the transient-state study.

Ultra-high sensitivity SPR fiber sensor based on multilayer nanoparticle and Au film coupling enhancement

• Electric field intensity of multilayer of GNPs coupled with gold film was studied. • The RI sensitivity of the double-layer gold nanospheres sensor was 15747 nm/RIU. • The RI sensitivity of the double-layer gold nanorods sensor was 25642 nm/RIU. • The LOD of double-layer gold nanospheres biosensor is 10 ng/mL. • The LOD of double-layer gold nanorods biosensor is 4.6 ng/mL. The main challenge for all biosensors is how to measure the biological samples at very low concentrations. In this paper, a surface plasmon resonance (SPR) fiber biosensor using multi-layer gold nanoparticles (Au NPs)/Au film coupling to enhance sensitivity was proposed. The coupling effect between such longitudinally aligned multilayer nanoparticles increases the intensity of the local electromagnetic field and the depth of propagation to the outside. We used the finite element method to analyze the local enhancement effect of multi-layer Au nanospheres and Au nanorods, and the fabricated double-layer Au NPs (Au nanospheres and Au nanorods)/Au film coupling enhancement sensors. These two sensors’ refractive index sensitivities are 15,747 nm/RIU and 25,642 nm/RIU, respectively. By changing biomolecules immobilized on the sensor’s surface, the highly sensitive double-layer Au nanoparticle/Au film fiber sensor enables high-precision measurement of different biomarkers at low concentration. For detection of human IgG, the detection limit of gold nanosphere sensor is 10 ng/mL and gold nanorod sensor is 4.6 ng/mL.

A molecularly imprinted polymer combined with dual functional Au@Fe3O4 nanocomposites for sensitive detection of kanamycin

Based on molecular imprinting and nanotechnology, a highly specific and sensitive electrochemical aptasensor was proposed for assaying kanamycin (KAN). First, chitosan-graphene (CG) composite multilayer films and Au nanoparticles (AuNPs) were applied to modify a glassy carbon electrode (GCE) for augmented “electron antennae». Then, we constructed a KAN sensor using functional monomer of 3-aminophenylboronic acid (3-APBA) as trap. Au@Fe3O4 nanocomposites, Fe3O4 nanoparticles (Fe3O4NPs) loaded with AuNPs, were dual functionally modified with β-cyclodextrin-ferrocene (Fc/β-CD-SH) and KAN aptamers (APT/Fc/β-CD-SH/Au@Fe3O4) were applied as the tracing tag. The KAN aptamer acted as the bind unit to specifically identify the KAN captured by the imprinted cavities on the MIP modified electrode surface, while the Fc/β-CD-SH was used as a signal unit for KAN quantification. The presented assay exhibited a good linear relationship between KAN concentration (10–500 nM) and the strength of the electrochemical signal, with a detection limit of 1.87 nM and a correlation coefficient of 0.98. The selectivity, stability and reproducibility of the proposed sensor were acceptable. Furthermore, it was used successfully to detect KAN in different aqueous solution, such as in spiked milk, the proposed sensor could be applied for specifically, sensitively and rapid determination for antibiotic contamination in food, water and biological samples.

Ultrathin MEMS thermoelectric generator with Bi2Te3/(Pt, Au) multilayers and Sb2Te3 legs

Multilayer structure is one of the research focuses of thermoelectric (TE) material in recent years. In this work, n-type 800 nm Bi2Te3/(Pt, Au) multilayers are designed with p-type Sb2Te3 legs to fabricate ultrathin microelectromechanical systems (MEMS) TE devices. The power factor of the annealed Bi2Te3/Pt multilayer reaches 46.5 μW cm−1 K−2 at 303 K, which corresponds to more than a 350% enhancement when compared to pristine Bi2Te3. The annealed Bi2Te3/Au multilayers have a lower power factor than pristine Bi2Te3. The power of the device with Sb2Te3 and Bi2Te3/Pt multilayers measures 20.9 nW at 463 K and the calculated maximum output power reaches 10.5 nW, which is 39.5% higher than the device based on Sb2Te3 and Bi2Te3, and 96.7% higher than the Sb2Te3 and Bi2Te3/Au multilayers one. This work can provide an opportunity to improve TE properties by using multilayer structures and novel ultrathin MEMS TE devices in a wide variety of applications.

Plasmon charge transfer dynamics in layered Au–ZnO nanocomposites

Understanding the charge transfer dynamics at the interface of metals and semiconductors has received much attention in efficient plasmonic induced photonic devices. Here, we present ultrafast charge transfer dynamics in Au–ZnO nanocomposite systems by exciting them in interband and intraband levels of Au with pump energies higher (2.48 eV) and lower (1.96 eV) than the threshold energy for interband transition (2.4 eV), using the femtosecond time-resolved pump-probe technique. The spectral responses for both the excitations exhibit different behaviors, and these variations are quantitatively interpreted in terms of pump-induced changes in the dielectric constant of Au. It is found from the temporal dynamics that the electron–phonon component in the Au–ZnO system decays relatively faster (∼3 ps in the multilayer Au–ZnO) than that observed in the Au sample (∼7 ps in Au) for both the pump energies. The transfer of highly energetic hot electrons from Au nanoparticles to ZnO across the Schottky barrier results in an accessible optical response for wide bandgap ZnO in the visible to infrared range via plasmon charge collection. The calculated charge transfer rate in the Au–ZnO system is found to be (>1011 s−1). Our results demonstrate the pump excitation dependent ultrafast plasmon charge behavior in an optically active Au–ZnO system that can be attractive for efficient plasmonic-based hybrid photonic devices.

Quantification of atomic force microscopy tip and sample thermal contact.

A thermal conduction measurement device was fabricated, consisting of a silicon dioxide membrane with integrated thermal sensors (Pt resistance heater/thermometer and Pt-Au thermocouples) using MEMS technology. Heat transfer between the heated device and a number of unused atomic force microscope and scanning thermal microscope probes was measured. Changes in thermal conduction related to changes in the tip shape resulting from initial contact were observed. The sensors were fabricated by electron beam lithography and lift-off followed by local subtractive processing of a Pt-Au multilayer to form Pt heater-resistance thermometer elements and Pt-Au thermocouples. Thermal isolation from the silicon substrate was provided by dry release of the supporting 50 nm thick SiO2 membrane using an isotropic SF6 inductively coupled plasma etch. The high thermal isolation of the sample combined with the sensitivity of the temperature sensors used allowed the detection of thermal conduction between the tip and the sample with high precision. The measured temperature range of the Pt resistor was 293-643 K. The measured thermal resistance of the membrane was 3 × 105 K/W in air and 1.44 × 106 K/W in vacuum. The tip contact resistance was measured with a noise level of 0.3g0T at room temperature, where g0 is the thermal resistance quantum.