Au Nanofilms Research Articles

Antioxidant Activity of Gold Nanofilms Synthesized via Cyclic Voltammetry Technique

Abstract Gold nanoparticles (AuNPs) have attracted much attention as one of the most effective agents with high catalytic activities for radical scavenging reactions. Many studies have investigated its antioxidant activity using various in vitro methods and have shown promising scavenging action. In this research, we demonstrated the synthesis of Au nanofilms (AuNFs) by cyclic voltammetry technique and evaluated for their antioxidant activity. The application of a range of voltage levels was utilized in the synthesis of AuNFs, and their antioxidant potential was subsequently assessed through in vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. All AuNFs exhibited antioxidant activity which increased as the upper potential was reduced from 1,5 V to 0,75 V. The antioxidant activity of AuNFs was shown to increase gradually with longer incubation times before the DPPH assay, indicating a significant impact on their performance. The obtained inhibition percentage was ranging from 8,26% to 22,91%. The highest antioxidant activity could be achieved by synthesizing AuNFs using 0,75V of upper potential and incubating it for 90 minutes prior to DPPH assay. The variations in the applied potential influenced the morphological characteristics of AuNFs, leading to increased surface area, while the duration of incubation was found to enhance the efficacy of the scavenging reaction between the AuNFs and DPPH. In conclusion, this cyclic voltammetry technique was shown to successfully synthesize AuNFs with significant antioxidant activity.

Optical Observations of Sputtered Au-nanostructures and Characterizations

o develop novel optoelectronic devices, controlling and predetermined absorption is necessary. In the current work, the gold nano-islands were sputtered onto quartz surface substrates using a DC sputtering unit with an optimized chamber. The effects of the sputtering time (10, 15, and 20 seconds) on the characteristics of the golden layers deposited on quartz substrates were studied. Au nanofilms were investigated by XRD (X-ray diffraction), UV-Vis (ultraviolet-visible light) diffractometer, and AFM (atomic force microscopy) techniques. The thicknesses of the three films prepared at different sputtering times (10, 15, and 20 seconds) were calculated using the theoretical deposition formula method. The average layer thickness, and hence the size of the golden crystallites, rose from 6.8 to 13.6 nm when the sputtering period was increased. The X-ray spectra revealed a very distinguish peak at (111), pointing that the gold single crystal has fully oriented along [111] and the gold film has a pure crystalline Fcc structure. When deposition times are lengthened, the color of the resulting films changes from blue to green. Nano-films have seen important changes in their surface shape and roughness. The structural layer of Au's surface is remarkably semi-spherical, giving it the appearance of spherolytic and hummock-like. Analyzing the UV-VIS spectra of the precipitated structures using Tauc's paradigm revealed the optical energy gap (non-zero Eg in the range of 2.36 to 2.38 eV) that is associated with the nanostructure's semiconducting properties. In addition, as the sputtering duration increases from 10 to 20 seconds, the wavelengths at which peak values of the surface plasmon resonance occur shift from 610 to 650 nm, and the widths of the peaks rise. The AFM images of the ultra-thin Au layers showed smooth surfaces whose roughness decreases from 1.82 to 0.673 nm with increasing sputtering time from 10 to 20 nm. Solar cells can take advantage of the higher absorption in the blue spectrum region by using a set of depositing parameters and prescribed thicknesses. In addition, the formation of nano-islands can also be used as nucleation sites (seed layer) to promote the growth of various nanostructures to obtain a good aspect ratio and improve the performance of various optoelectronic devices and gas sensors.

Surface effects and symmetry lowering effect on the anisotropic bending and equilibrium of freestanding nanofilms

A self-consistent theory for describing self bending, self equilibrium and symmetry lowering of nanofilms was proposed in this paper. The lowered symmetry and corresponding additional elastic parameter were considered to describe the mechanical properties of nanofilms. A freestanding nanofilm may spontaneously roll into a nanotube due to intrinsic surface stress imbalance. It is not necessarily isotropic for surface stress. The anisotropic surface stress is possible, Si nanofilm with (001) surface may behave (2 × 1) reconstruction, for example. The anisotropic surface stress induces anisotropic bending. And then, the isotropic Stoney formular should be modified to suit the anisotropic surface stress effect. A theory for anisotropic bending should be established. On the other hand, intrinsic surface stress balance induces uniform in-plane deformation of nanofilms. The theory in this paper was used to predict equilibrium strains of Cu, Ni, Ag, Au, Pd and Pt nanofilms, and was used to research Si nanofilm rolling behavior.

High-Performance MEMS Oxygen Sensors Based on Au/TiO2 Films

High-performance microelectromechanical system (MEMS) oxygen sensors were realized by successful preparation of Au nanofilms over TiO2 thin films through successive sputtering on commercial MEMS microhotplates. Oxygen sensing performance of 3 and 6 nm thick Au over TiO2 thin films were compared with that of pure TiO2 thin films. It was shown that 6 nm thick Au over TiO2 thin films have the best sensitivity toward oxygen. The prepared TiO2 thin films were characterized using SEM, EDS, XPS, and a gas testing instrument. The results show that Au decoration has little influence on the surface morphologies of TiO2 thin films. However, Au decoration has a strong influence on the surface properties of the composite films. The favorable performance of 6 nm Au-doped TiO2 thin films is attributed to factors such as catalytical performance, height of Schottky contact, and number of oxygen vacancies. This work makes contributions to low power consumption and high-performance oxygen sensors for Internet of Things applications.

Poisson’s ratio determination of Au nanofilms by piezoresistive measurements

Poisson’s ratio determination of Au nanofilms by piezoresistive measurements

Ultrahigh strain rate-activated superplastic forming of aluminum and gold nanometals

Commonly, the increased free surface of nanometals results in completely different mechanical behaviors from their bulk counterparts. At present, studies on the plasticity behavior of nanometals is widely carried out under quasi-static states. Understanding the plasticity mechanism of nanometals during a high-speed forming process is largely unexplored. This study explored the rate dependence of the forming behaviors of Al and Au nanofilms using laser-induced ultrahigh strain rate forming processes. The results showed that the superplastic behavior of the nanofilms can be activated above a critical value of the strain rate (>2.0E8 s−1). The Al nanofilm exhibited a maximum vertical strain of ∼ 567% at a strain rate of 8.1E8 s−1, and that of the Au nanofilm was ∼ 620% at a strain rate of 8.8E8 s−1. The superplastic forming mechanism mediated by interstitials was revealed for the first time. Further, the potential contribution of the interstitial-mediated plasticity mechanism in breaking through grain size limit and constitutive model modification was discussed. The discovery of this particular mechanism supplements the deformation mechanism diagram and constitutive relationship of nanometals, and is thus of great significance to the study of material responses in extreme conditions and manufacturing process analysis and optimization.

Microstructure and thermal stability of glance angle deposited Au nanofilms

Gold nanoarray films prepared by glancing angle deposition are a new type of material with broad application prospects. Microstructure and thermal stability are of fundamental pertinence for corresponding practical applications, but there is a lack of systematic research at present. In this paper, pure Au nanofilms were prepared by glancing angle magnetron sputtering deposition. The three-dimensional morphology, texture, density, resistivity, and other parameters of the samples were quantitatively characterized with an atomic force microscope, an X-ray diffractometer, and a four-probe film resistance meter. Accordingly, the influence of the deposition glancing angle on the microstructure parameters was analyzed. Then the thermal stability of the film microstructure was studied. The microstructure of the Au films can be divided into three types in accordance with the oblique angle. When the glancing angle reached 60°, nanoparticle arrays began to form, whereas above 80°, nanorod arrays with a loose structure were formed. At 200 °C, the nanoparticle arrays degraded obviously in the form of surface flattening. For the nanorod arrays, the degradation temperature increased to 250 °C. In this process, the lateral size of the nanorods increased and their areal density decreased. The reason for the difference of thermal stability is that they have various microstructure features. Moreover, this structural distinction makes the micro mechanisms in the degradation process completely different.

Carbon Helical Nanorobots Capable of Cell Membrane Penetration for Single Cell Targeted SERS Bio‐Sensing and Photothermal Cancer Therapy

AbstractPenetration of cell membrane at micro/nano‐scale with untethered probe is of great scientific significance, yet still challenging. Here, a carbon nanocoil based magnetic nanorobot, which can precisely target single cell and perform cell membrane penetration, is reported. The nanorobots are as‐synthesized by chemical vapor deposition with high yield, followed by physical deposition of Ni and Au nanofilms. Rotating electromagnetic fields are used to steer the nanorobots to navigate following any pre‐designed path. The helical nanorobots can realize mechanical perforation of the plasma membrane and even nuclear envelope with precise position at the subcellular level. With the aid of the externally deposited Au nanofilm, surface enhanced Raman scattering bio‐sensing signals can be collected from cellular plasma and nucleus. Furthermore, the nanorobots demonstrate capability of efficient photothermal therapy against targeted cancer cells and serve as an integrated theranostic platform, providing promising prospects in future precision medicine.

Laser Annealing of Gold Thin Films as a Platform for Plasmonic Sensing Applications

The future of the plasmonic devices is heavily challenged by the nanoconstruction schemes of metals which often require rather fast, low-cost, and high-throughput fabrication techniques. Laser annealing is considered to be an unrivaled tool for surface manipulation of thin metallic films, especially with functional plasmonic devices of pre-determined morphology. Herein, a commercial CW CO2 laser, wavelength of 10.6 µm and optimum power of 15W, has been used for surface reconstruction of thin Au films, with an initial film thickness of 15 nm (±3 nm) sputtered on quartz substrates, as plasmonic sensing platforms. The effect of two main laser parameters on the Au film morphology have been explored namely power density and scanning speed. Thermal annealing of Au nanostructured films by the electrical furnace is also been studied. UV-Visible (UV-Vis) spectroscopy characterization measurements is utilized to monitor the the plasmonic induced optical absorption changes with different experimental conditions. Surface annealed Au nanofilms were then used as a plasmonic sensing substrate to detect the size and density variation of Ag NPs, fabricated by pulsed Nd: YAG laser ablation, ith pulse duration of 7 nsec, in DI water with a wavelength of 1064 nm and different laser energies, imbedded in a solution-processed thin dielectric material (CeO2 NPs) to form a composite film. Our plasmonic sensing structure shows a remarkable detection to variable concentrations of Ag NPs reflected by a significant red-shift in the plasmonic resonance absorption of Au nanostructures with laser ablation energy at a fixed number of pulses of 50 (1Hz).

Au-on-Ag nanostructure for in-situ SERS monitoring of catalytic reactions

Dual-functionality Au-on-Ag nanostructures (AOA) were fabricated on a silicon substrate by first immobilizing citrate-reduced Ag nanoparticles (Ag NPs, ∼43 nm in diameter), followed by depositing ∼7 nm Au nanofilms (Au NFs) via thermal evaporation. Au NFs were introduced for their catalytic activity in concave-convex nano-configuration. Ag NPs underneath were used for their significant enhancement factor (EF) in surface-enhanced Raman scattering (SERS)-based measurements of analytes of interest. Rhodamine 6G (R6G) was utilized as the Raman-probe to evaluate the SERS sensitivity of AOA. The SERS EF of AOA is ∼37 times than that of Au NPs. Using reduction of 4-nitrothiophenol (4-NTP) by sodium borohydride (NaBH4) as a model reaction, we demonstrated the robust catalytic activity of AOA as well as its capacity to continuously monitor via SERS the disappearance of reactant 4-NTP, emergence and disappearance of intermediate 4,4′-DMAB, and the appearance of product 4-ATP throughout the reduction process in real-time and in situ.

Elastic Modulus Measurement of AU Nanofilms by Subtracting the Polymeric Substrate Influence

Elastic Modulus Measurement of AU Nanofilms by Subtracting the Polymeric Substrate Influence

Plasmon enhanced upconversion emission in Tm3+/Yb3+/lithium niobate single crystal

Light conversion efficiency, as the core issue of luminescence applications, has become the focus of upconversion (UC) study. Here, we have coated Au nano-films in different thicknesses on c-cut Tm3+/Yb3+/lithium niobate (LN) single crystal wafers, and discovered the luminescence intensity could be drastically enhanced by 15.1 and 26.5 folds for blue and red emission, respectively, in a proper Au thickness. Compared to the Au-free sample, optical measurements demonstrate a moderate enhancement of local optical power density. However, considering the non-linear relationship between the coating thickness and the enhancement factor, we attribute the drastic UC enhancement to the size-dependent localized surface plasmon resonance (LSPR); and accordingly, adopt an analytical optical absorption model to calculate the electron density of Au coating, which manipulates the resonance intensity and enhancement factor. The above explanation is further verified by the variation of LSPR frequency. These findings interpret the interaction between nano-scale Au coating and crystal surface, and demonstrate the feasibility and superiority of LSPR-enhanced UC luminescence in crystalline materials.

Nonlinear terahertz effects of gold nanofilms

Nonlinear interaction between strong-field terahertz electromagnetic waves and matters will become one of the next hot research frontiers in nonlinear optics. However, the lack of strong terahertz radiation sources and appropriate nonlinear terahertz materials have impeded its progress. Here we systematically have investigated the strong-field terahertz nonlinear effects of gold (Au) nanofilms on different substrates, including SiO2, high-resistivity Si and SiO2-high-resistivity Si hybrid substrates. The strong-field terahertz waves are emitted from lithium niobate crystals via tilted pulse front technique, and obvious nonlinear transmission responses are observed along with varying the incident field strengths for all the Au samples on the three types of the substrates. The nonlinear behavior is enhanced when the gold nanofilm thickness increases, which can be qualitatively understood by introducing the quantum tunneling effect and carrier multiplication theory generated at the Au nano-slits under the illumination of the strong-field terahertz pulses. Our demonstrations not only open a new paradigm for nonlinear terahertz investigations and future high-speed terahertz devices, but also provide an effective platform for exploring extreme terahertz sciences.

Atomistic investigations of melting characterization in metallic nanostructures

Melting temperatures, for bulk materials at constant pressure, remain constant for given materials. In case of nanomaterials however, melting temperature is subject to changes in the shape and size of the material. In this work, the liquid Sshell nucleation and the liquid skin nucleation and growth models, along with empirical relations, are used to predict the melting temperatures of Pt, Au and Ag nanowires and nanofilms. The melting temperatures are calculated taking into account the phenomenon of surface melting and the criteria of stability of the surface liquid layer. For platinum and gold, which are susceptible to surface melting, the liquidus and solidus curves are built, that characterize nanowire melting.

Equilibrium segregation in the stressed Ni(111)(Au) nano-films on inert substrate

Based on the network model and the regular solution model, the equilibrium surface and interface segregations are investigated for the Ni(111)2 at%(Au) nano-films under diffusion-induced stress and intrinsic stress. The size effect with respect to the film thickness, the interlayer interactions and the heteroepitaxial strain in the film are taken into account. The equilibrium layer concentration in the film with the lowest Gibbs free energy of the system is obtained according to the coordinate descent method. The influences of diffusion-induced stress and intrinsic compressive/tensile stress, temperature and bulk concentration on the equilibrium layer concentration of segregation in the film are quantitatively evaluated.

Studying time-dependent contribution of hot-electron versus lattice-induced thermal-expansion response in ultra-thin Au-nanofilms

Through the femtosecond-time-resolved study of photoacoustic pulse generation in ultra-thin gold nanofilms, we observed a time delay of 0.5–0.7 ps in the formation of thermal-expansion pulses after photoexcitation. Our observation indicates that lattice anharmonicity dominates over hot electron pressure in the thermal expansion of Au nanofilms under ultrashort-pulsed photoexcitation.

Erect Au Nanocones Drawn from Au Nano-Films by Nano-Size Au-Si Eutectic Clamping with High Adhesion to Substrates

Erect Au nanocones with high adhesion to substrates are obtained by simply drawing from Au nano-films through Au-Si eutectic welding. Nanocones with diameters ranging from about 5 to 150 nm and length ranging from about 60 to 600 nm can be observed on both Au and Si substrate surfaces. Nano-scale Au-Si eutectics formed at the rough Au–silicon film interface under annealing at 450 °C and the subsequent cooling process facilitate the formation of nano-bonding points and draw Au nanocones from Au nano-film by mechanical separation. Erect Au nanocones adhered to Au or Si substrates shows higher light enhancement than itself, observed by FDTD simulation. This method provides new strategy for the fabrication of SERS detectors, solar cells et al. with high stability.

Thermally-induced nonlinear optical properties of Al-alloyed Au nano-films

The thermally-induced nonlinear optical properties of Al-alloyed Au nano-films were investigated in the cw regime using z-scan technique. The films were fabricated by thermal evaporation on glass substrates at room temperature. Alloying was obtained through the spontaneous intermixing of sequentially deposited Au and Al nano layers. The observed enhancement in the measured nonlinear refractive index (n2) of the alloyed films compared to pure Au structure is attributed to increase in the number of free electrons supplied by the Al sites near the Fermi level in the composite films which favor polarizability. A discussion of this output is presented.

Electrochemical Sensing of Arsenic Using Physically Vapor Deposited Au Nanofilm Electrodes: Flow Cell Configuration

There is a current need for an inline arsenic sensing system that can continuously sample aquifer water quality for well drilling and ground water monitoring applications. Concentrations of arsenic oxyanions above 10 μg/L in drinking water are considered dangerous by the World Health Organization [1]. Levels above this in daily consumption can lead to renal toxicity and a condition known as Arsenicosis, which produces lesions on the skin. We are currently developing an Au thin film, As stripping voltammetry flow cell sensing to meet this challenging need. Our findings show that use of gold (Au) nanofilm electrodes physically vapor deposited (PVD) onto porous carbon papers can detect concentrations below 10 μg/L of arsenite, As (III), in water. The nanofilms were characterized by SEM, X-ray diffraction and with X-ray fluorescence with a measured loading of approximately 13 μg of Au per 1 cm2 of carbon paper in each electrode. The PVD method increases the manufacturability of aqueous arsenic sensors because it is facile, scalable, and uses much less Au than screen printing methods. Linear stripping voltammetry (LSV) was used in a three-electrode configuration to create a calibration curve for standard additions of 5, 10, 25, 50 and 75 μg/L As (III). The resulting plot of peak area versus concentration resulted in a linear correlation. The capacitance of PVD deposited Au nano films was significantly less than that of Au nanoparticles on XC72 carbon, produced via solution precipitation methods. The lower capacitance enables the detection of low concentrations of As without the need for the application of more complex pulse voltammetry methods.

Optimal Conditions for the Deposition of Gold Nanofilms on a Silicon by Galvanic Replacement Method

The formation conditions of gold nanofilms on silicon (Si) substrate by galvanic replacement in a dimethyl sulfoxide (DMSO) solvent and their subsequent use for the fabrication of Si nanostructures by metal-assisted chemical etching (MACE) method were under study. It was found that the average size and number of Au nanoparticles increase with an increase in the reducible metal ion concentration from 2 to 8 mM HAuCl4 in DMSO, whereas the distribution of Au nanoparticles in height remains low for all concentrations of the reducible metal. In the temperature range 40 - 70°C, a different morphology of the deposited Au nanofilms observed. In particular, at 40 °C, the film is porous mainly homogeneous, whereas at a temperature of 50°C the film is rougher. The subsequent rise in temperature from 60°C to 70°C results in the formation of Au nanofilm with a discontinuous morphology. It was established that regardless of the morphology of deposited Au nanofilms, the Si nanostructures maintain a vertical orientation to the plane of the Si substrate during MACE-etching. The produced Si nanostructures were 1.5 - 2.5 μm in height and their average diameter ranged from 100 to 300 nm.