Au Doping Research Articles

Enhanced photocatalytic activity of Au-doped Au@ZnO core-shell flower-like nanocomposites

We introduce a simple and low-cost three-step hydrothermal and pulsed laser ablation technique for the fabrication of flower-like pure ZnO nanostructures, Au@ZnO core-shell nanocomposites, and Au@ZnO/Au core-shell nanocomposites doped with various concentrations (5, 10, and 15 wt%) of Au nanoparticles without using surfactants or catalysts to enhance the catalytic performance of ZnO under UV–visible irradiation. The decoration of Au nanoparticles on the surface of ZnO promoted the absorption of visible light due to the surface plasmon resonance of Au. Further, we evaluated the photocatalytic performance of the nanocomposites in the degradation of methylene blue (MB). Our findings revealed that the Au@ZnO/Au core-shell nanocomposites with 5 wt% of doped Au NPs demonstrated the highest photocatalytic activity. In addition, radical-scavenging experiments were conducted to determine the main reactive species formed in the reaction mixture, and accordingly, a plausible photocatalytic reaction mechanism for the enhanced photodegradation of MB is presented.

Effect of Au and/or Mo Doping on the Development of Carbon and Sulfur Tolerant Anodes for SOFCs—A Short Review

The presented work is a short review of the research attempts from our group with collaborators, during the last 15 years, which had as main objective to study and improve the electrocatalytic performance of Ni-based electrode materials for the CH4 Internal steam Reforming process (I.S.R.) in Solid Oxide Fuel Cells (SOFCs). In particular, NiO/YSZ and NiO/GDC anode powders were modified with Au and/or Mo nano-particles via different preparation methods. These efforts resulted in anode materials with high tolerance and improved electrocatalytic activity under both carbon forming and sulfur poisoning conditions. The most important findings are being reviewed and critical findings are being highlighted50 as to stress the key differences in the electrocatalytic performance between Ni/YSZ and Ni/GDC. The possible effects of Au and/or Mo addition on the physicochemical and strucutral properties of the cermets are thoroughly discussed as well as active functional layers in the form of anode SOFC electrodes.

Improved unipolar resistive switching characteristics of Au-doped nickel ferrite magnetic thin films for nonvolatile memory applications

Au-doped nickel ferrite (NiFe2O4-Au, NFO-Au) magnetic thin films were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method to explore the effect of Au doping on unipolar resistive switching (RS) behavior. Experimental results reveal that 1% Au doped NFO film demonstrated considerably optimum switching parameters such as lower electroforming voltage, narrow distribution of SET/RESET voltages, good cycle-to-cycle endurance (103 cycles) and long data retention (105 s at 125 °C) as compared to NFO and Au-(0.5% and 2%) doped NFO films. The improved performance is attributed to suppressing of randomness of oxygen vacancies based filament by Au doping. Current transport conduction mechanisms are found to be Ohmic in low resistance state and Schottky emission in high resistance state. Physical model concerns for the rupture and formation of Au atoms assisted conductive filament inside the Au-doped NFO films based on the thermal effect of oxygen vacancies. Magnetic properties correlated with RS were measured and analyzed. The variation of saturation magnetization with different resistance state may be attributed to Au-doping induced different oxygen vacancies concentrations and make the conversion of valence states of Fe3+ and Fe2+ ions in octahedral sites easier. Our results provide a pathway towards the applications in nonvolatile RS memory and magnetoelectronic coupling devices.

Long-term air-stable Au doping of graphene by layer-by-layer assembly with graphene oxide for flexible transparent electrodes

In order to realize the most suitable hybrid structure for air-stable graphene-based transparent and flexible electrodes, we systematically compared graphene oxide (GO)/Au/graphene and graphene/Au/GO hybrid films fabricated by layer-by-layer assembly. The sheet resistance of graphene/Au/GO was proportional to the concentration of AuCl3 (1–5 mg/ml), which can be understood by a significant blue-shift in the G-band associated with the phonon stiffening. The size and density of formed Au nanoparticles strongly influenced their reduction reaction, which is a crucial factor for maximizing the doping effects. The optimized optical transmittance and sheet resistance of GO/Au/graphene were 94.9% and 198 ± 29 Ohm/sq, respectively. Furthermore, the hybrid films revealed stable doping effects (sheet resistance variation: 23–55%) against ambient conditions after 1 month. The variation in sheet resistance for GO/Au/graphene hybrid films corresponds to 30% with a bending radius of 10 mm after repeated bending tests (bending cycles of 105).

Hydrogen Production by Ethanol Steam Reforming on Ni-Based Catalysts: Effect of the Support and of CaO and Au Doping

Nickel-based catalysts were investigated for hydrogen production by ethanol steam reforming. A suitable support was assessed among the metal oxides TiO2, ZrO2 and CeO2. Alongside catalytic testing with ethanol-water mixture, a series of characterization measurements were carried out: N2-physisorption, XRD, TPR, TPO, CO2-TPD, SEM, AAS and IC. Zirconium and cerium oxides proved to be suitable supports, even if both still suffer from coking phenomena. The effects of doping both by calcium oxide and gold nanoparticles were checked. Doping by calcium oxide prevented deactivation and highly increased the hydrogen yield. Moreover, the addition of gold nanoparticles greatly improved the hydrogen yield. The combination of the two dopants resulted in the best performing catalyst: the basic doping by CaO and the promotion of the water gas shift reaction by gold nanoparticles contributed to the highest hydrogen production.

Facile Synthesis of Cu Doped Au–ZnS Photocatalyst

In this work, we report on the synthesis of of Cu-doped Au–ZnS nanoparticles (Au–Zn1−xCuxS; where x = 0.00, 0.1 and 1%) using a one-pot chemical method that makes use of 1,3-propanediol as a solvent, a reducting agent and a stabilizing layer. The structure and morphology of the as prepared nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectrometry (EDX). Optical extinction measurements showed that the Cu-doped Au–ZnS nanoparticles exhibit a localized surface plasmon resonance (SPR) clearly red-shifted with respect to that of bare Au nanoparticles (AuNPs). In addition, it was found that the optical band gaps of Cu-doped ZnS nanocrystals blue-shifted (i.e., the band gap widening) to shorter wavelength compared to pure ZnS nanocrystals. Photocatalytic activities of Cu-doped Au–ZnS nanocomposites were evaluated by the degradation of 4-Nitrophenol under illumination by solar light. Enhanced performances compared either to undoped Au–ZnS nanocomposites were observed. The effect of various parameters was investigated on the photocatalytic activities of Cu-doped Au–ZnS nanocomposites.

Reducin g Contact Resistance of Carbon Nanotubes by Au Doping

Reducin g Contact Resistance of Carbon Nanotubes by Au Doping

Room-temperature H2S Gas Sensor Based on Au-doped ZnFe2O4 Yolk-shell Microspheres.

Room-temperature type H2S sensing devices that use Au-doped ZnFe2O4 yolk-shell microspheres as the active material have been fabricated using a solvothermal method as well as subsequent annealing and a chemical etching process. The samples are characterized using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the doping of Au does not change the spinel structure of the products, which were yolk-shell microspheres, while the particle size varied with the Au doping concentration. Also, the as-fabricated sensor device exhibited excellent selectivity toward H2S gas at the room temperature; the gas-sensing property of 2 wt% Au-doped ZnFe2O4 microspheres was the best. The Au-doped ZnFe2O4 yolk-shell microspheres can be promising as a sensing material for H2S gas detecting at room temperature.

Engineering the Self-Assembly Induced Emission of Cu Nanoclusters by Au(I) Doping

Aggregation-induced emission (AIE) and self-assembly induced emission (SAIE) effects have been employed to tune the emission properties of metal nanoclusters (NCs). However, it is still not possible to further enhance the photoluminescence quantum yields (PLQYs) and control the emission colors of the NCs using AIE and SAIE. On the basis of our recent work studying the contribution of Cu(I) defects in the SAIE of Cu NCs, in this article, Au(I) was doped into Cu NC self-assembled nanosheets (NSASs) to construct a more stable Au(I)-centered state. As a result, the PLQYs, emission stability, and tunability of emission colors of the Cu NSASs were significantly improved. Detailed studies reveal that the doped Au(I) induces a Au(I)-Cu(I) metallophilic interaction, which leads to a ligand-to-Cu-Au charge transfer, which facilitates the relaxation of excited electrons via a radiative pathway, thereby enhancing the emission intensity. The charge transfer from Cu to Au lowers the energy, thus leading to the red-shift of PL emission. Au(I) is likely doped into the Cu NSASs rather than in individual NCs, because 0.3% Au doping is enough to alter the emission properties. By mixing Au(I)-doped Cu NSASs with different emission colors (due to different Au doping percentages) as color conversion materials on commercially available 365 nm GaN chips, a white light-emitting diode prototype is fabricated.

Quenching effect of exciton energy transfer from CdS:Mn to Au nanoparticles: A highly efficient photoelectrochemical strategy for microRNA-21 detection

A novel and simple photoelectrochemical (PEC) biosensing method for microRNA-21 (miRNA-21) detection is reported based on energy transfer (ET) between CdS:Mn doped structure (CdS:Mn) and Au nanoparticles (AuNPs). In this protocol, TiO2-CdS:Mn hybrid structure was used as a sensing platform for hairpin DNA immobilization. In the absence of miRNA-21, the immobilized DNA was in the hairpin form. In this state, the photocurrent of the electrode was greatly depressed, due to the effective ET effect produced by short interparticle distance between CdS:Mn and AuNPs. In the presence of miRNA-21, the hairpin DNA hybridized with miRNA-21 and changed into a more rigid, rodlike double helix, which forced the AuNPs away from the electrode surface, leading to obvious recover of photocurrent because of the vanished damping effect. Integrating the fine PEC performance of TiO2-CdS:Mn hybrid structure with the significant ET effect between CdS:Mn and AuNPs, the sensitive detection of miRNA-21 was realized in a linear range of 1.0fM to 10.0pM with a low detection limit of 0.5 fM. This method might be aussichtsreich for the detection of miRNAs and other biomarkers.

Influences of metal (Cu, Ag, Au) doping on (AlO)2/(AlO)2− square-planar units

Due to their unique chemical reactivity, transition-metal-doped aluminum oxides have received increased attention. In this work, the influences of metal (Cu, Ag, Au) doping on small (AlO)2 and (AlO)2− rings have been investigated using density functional theory (DFT) and topological analysis of the electron density. The calculated results show that the effects of doping Cu and Ag are similar to those of Au. Thus, Cu and Ag can be used as the substitutions for Au to stabilize the (AlO)2 unit. The doping Cu, Ag, and Au have different influences on (AlO)2 compared to (AlO)2−. Specifically, doping metals enhances the stability of the (AlO)2 unit, whereas it decreases the stability of (AlO)2−. Overall, the effects of metal doping on the (AlO)2− anion are larger than on the neutral (AlO)2 cluster. Finally, the metal-doping decreases the aromaticity of (AlO)2 and (AlO)2− clusters.

A first principle simulation of competitive adsorption of SF6 decomposition components on nitrogen-doped anatase TiO2 (101) surface

Gas insulated switchgear has been widely used in modern electric systems due to its significantly excellent performances such as compact structure and low land occupation as well as the security stability. However, inside defects caused during manufacture process can lead to partial discharge which might develop into serious insulation failure. Online monitoring method on basis of gas sensors is considered a promising way of detecting partial discharge for alarm ahead of time. Research has found that TiO2 nanotubes sensors show good response to SO2, SOF2, SO2F2, the decomposition components as a result of partial discharge. In order to investigate the gas-sensing mechanism of nitrogen-doped TiO2 prepared via plasma treatment methods to SO2, SOF2, and SO2F2, the adsorption structures of both three gas molecules and anatase TiO2 (101) surface were built, and DFT calculations were then carried out for calculation and analysis of adsorption parameters. Adsorption property comparison of anatase TiO2 (101) surface after nitrogen doping with Au doping and without doping shows that nitrogen doping can obviously enhance the adsorption energy for SO2 and SOF2 adsorption and no charge transfer for SO2F2 adsorption, further explaining the adsorption mechanism and doping influence of different doping elements.

Free-standing conductive thin films from gold-carbon nanotube composites

We report on the development of a method of formation of free-standing gold-carbon nanotube (CNT) composites. It is based on a quick and simple decoration of CNT films with the application of chloroauric aqueous solution. Flexible and conductive macroassemblies of any size and shape can be created with ease. Addition of as little as 1% of Au by weight allowed for reduction of resistance by more than a quarter. Higher Au doping resulted in further decrease of resistance, but not so significant. From the practical point of view, these composites are a new type of materials with high electrical conductivity, but also offer resistance to corrosion.

Gold-Hyperdoped Black Silicon With High IR Absorption by Femtosecond Laser Irradiation

Gold (Au)-doped-textured silicon (Si) material with a thermostable absorption below bandgap (>50%) is obtained by femtosecond laser irradiation. Although the concentration of Au impurity (1019 cm−3 ) in textured Si is at least four orders of magnitude greater than the solid solubility of Au in crystalline Si, the sheet carrier density (approximately 1010 cm−2) in Au-doped Si is very low due to a self-compensation effect of Au impurity in Si material. The infrared absorption of Au-doped Si is related to laser-induced-structural defects and sub-band absorption of deep energy levels of Au in Si, which is determined by temperature-dependent Hall Effect measurement. Besides supersaturated doping of Au, a gold silicide phase is formed at textured Si surface.

Enhancing the sensing performance of SnO2 inverse opal thin films by In and Au doping

SnO2 is an important n-type semiconductor sensing material. However, there are some drawbacks in the traditional SnO2 based gas sensors, such as high operating temperature, low gas response, long response/recovery time and poor selectivity. In this paper, In and Au doped SnO2 inverse opal thin films (IOFs) were prepared by employing a monolayer PMMA sphere template. The ordered macroporous structure of IOFs with large surface areas benefited the enhancement of the sensing performance. The response of the SnO2 IOFs to 100ppm ethanol had been enhanced from 6 to 308 by 5% In doping. Moreover, the optimum operating temperature was decreased from 350°C to 250°C, and the response/recovery time was shortened obviously by 0.25% Au doping. The 0.25%Au-SnO2:5%In IOFs based sensor exhibited high response, low operating temperature, high response speed, good selectivity and repeatability to ethanol, which had a promising application in ethanol detection. The XPS characterizations indicated that the doping of In and Au contributed to the increase of the adsorbed oxygen amounts which benefited the enhancement of the sensing performance.

The impact of Au doping on the charge carrier dynamics at the interfaces between cationic porphyrin and silver nanoclusters

We explore the impact of Au doping on the charge transfer dynamics between the positively charged porphyrin (TMPyP) and negatively charged silver nanoclusters (Ag29 NCs). Our transient absorption (TA) spectroscopic results demonstrate that the interfacial charge transfer, the intersystem crossing and the triplet state lifetime of porphyrin can be tuned by the doping of Au atoms in Ag29 NCs. Additionally, we found that the electrostatic interaction between the negative charge of the cluster and the positive charge on the TMPyP is the driving force that brings them close to each other for complex formation and subsequently facilitates the transfer process.

Air and thermally stable perovskite solar cells with CVD-graphene as the blocking layer.

The poor air and thermal stability of organic-inorganic halide perovskite solar cells have hindered their real applications. Here we report the insertion of a chemical vapor deposited graphene between the Au electrode and spiro-OMeTAD in planar perovskite solar cells to block the diffusion of air and Au into the perovskite layer, where the single layer graphene is transferred into the devices by a simple laminated process. After ageing in 45% humidity air for 96 h or thermal annealing at 80 °C for 12 h, more than 94% PCE of the devices with graphene can be maintained, which is much better than that of devices without graphene (∼57%). The improved stability of devices with the graphene layer is attributed to the reduction of carrier recombination from decomposition of the perovskite layer in air or Au doping into the perovskite layer under annealing treatment. Therefore, graphene is a promising ultra-thin barrier against air and metal diffusion, and has potential applications in photovoltaic devices, integrated circuit chips and light emitting diodes.

The effect of nano-sized metallic Au addition on structural and magnetic properties of Bi1.8Sr2 AuxCa1.1Cu2.1Oy (Bi-2212) ceramics

In this paper, we present the superconducting properties of nano-sized metallic Au doped Bi-2212 ceramics. Polycrystalline samples of Bi1.8Sr2AuxCa1.1Cu2.1Oy (x=0.0, 0.05, 0.1 and 0.2) superconductor have been synthesized by the conventional solid state reaction method. The phases as well as electric and magnetic properties have been characterized by XRD, SEM, DC resistivity, and magnetic hysteresis measurements (M-H). It has been observed that Tc (offset) values increase gradually as nano-sized Au content is increased. X-ray diffraction results indicated that nano-sized Au doping with x range from 0 to 0.2 did not provide its incorporation with any elements in the unit cell of the Bi-2212 matrix. M-H measurements were performed at T=10K. In addition, Jc values of the samples were calculated from their magnetic hysteresis loops using the Bean's model. It has been observed that the enhancement of Jc was as high as 4.3×104A/cm2 in 1.95T at 10K for Bi1.8Sr2 Au0.2Ca1.1Cu2.1Oy sample with x=0.2 Au addition when compared to the undoped sample that is considered as important for the enhancement of flux pinning in high magnetic fields.

Synthesis and Characterization of PEGylated Luminescent Gold Nanoclusters Doped with Silver and Other Metals

Doping of fluorescent noble metal nanoclusters is being pursued to manipulate the structure of such materials along with improving physicochemical characteristics such as long-term stability and photoluminescence quantum yield. Here, we synthesize metal-doped and alloyed ultrasmall gold nanoclusters (AuNCs) directly in water using a facile one-step coreduction reaction with bidentate dithiolane PEGylated ligands that terminate in different functional groups including a methoxy, carboxy, amine, and azide. Two primary types of cluster materials were the focus of synthesis and characterization: first, a series of doped/alloyed Ag-doped AuNCs, where the ratio of Au:Ag was varied across a wide range including 99:1, 98:2, 90:10, 80:20, 50:50, 20:80, 10:90, and 2:98 along with pure AuNC and AgNC controls; second, doped Au:D NCs, where D included Pt, Cu, Zn, and Cd. Physical characterization of the modified AuNCs included TEM analysis of size, XPS/EDX analysis of dopant content, and a detailed analysis of photoph...

Geometric, stability, and electronic properties of gold-doped Pd clusters (Pd n Au, n = 3~20)

The structure, stability, and electronic properties of Pd n Au (n = 3~20) clusters are studied by density functional theory. The results show that the clusters studied here prefer three-dimensional structures even with very small atom number. It is found that the binding energies of Pd n Au clusters are higher than the corresponding pure Pd n clusters with the same atom number. Most Pd n Au clusters studied here are magnetic with magnetic moments ranging from 1.0 to 7.0 μ B. The dissociation energies of Pd atoms are lower than the doped gold atom, that is the doped Au atom will increase the mother clusters stability and activity.