Au Doping Research Articles

First-principles study of electronic structures and optical properties of Cu, Ag, and Au-doped anatase TiO2

We perform first-principles calculations to investigate the band structure, density of states, optical absorption, and the imaginary part of dielectric function of Cu, Ag, and Au-doped anatase TiO2 in 72 atoms systems. The electronic structure results show that the Cu incorporation can lead to the enhancement of d states near the uppermost of valence band, while the Ag and Au doping cause some new electronic states in band gap of TiO2. Meanwhile, it is found that the visible optical absorptions of Cu, Ag, and Au-doped TiO2, are observed by analyzing the results of optical properties, which locate in the region of 400–1000nm. The absorption band edges of Cu, Ag, and Au-doped TiO2 shift to the long wavelength region compared with the pure TiO2. Furthermore, according to the calculated results, we propose the optical transition mechanisms of Cu, Ag, and Au-doped TiO2. Our results show that the visible light response of TiO2 can be modulated by substitutional doping of Cu, Ag, and Au.

A novel NiO–Au hybrid nanobelts based sensor for sensitive and selective glucose detection

A novel amperometric nonenzymatic glucose sensor based on Au-doped NiO nanobelts has been successfully fabricated and applied to nonenzymatic glucose detection. Its electrochemical behavior towards the oxidation of glucose was compared with NiO nanofibers and Au microparticles prepared with a similar procedure. The NiO–Au hybrid nanobelts modified electrode displays greatly enhanced electrocatalytic activity towards glucose oxidation, revealing a synergistic effect between the matrix NiO and the doped Au. The as-prepared NiO–Au nanobelts based glucose sensor displays significantly lower onset potential, lower detection limit, higher sensitivity, and wider linear range than that of pristine NiO nanofibers modified electrode. Moreover, Au nanoparticles distributed in NiO nanofibers enabled amperometric glucose detection with insignificant interference from ascorbic acid and uric acid. These results indicate that the NiO–Au hybrid nanobelt is a promising candidate in the development of highly sensitive and selective nonenzymatic glucose sensors.

Electron spin diffusion and transport in graphene

We investigate the spin diffusion and transport in a graphene monolayer on SiO${}_{2}$ substrate by means of the microscopic kinetic spin Bloch equation approach. The substrate causes a strong Rashba spin-orbit coupling field $~0.15$ meV, which might be accounted for by the impurities initially present in the substrate or even the substrate-induced structure distortion. By surface chemical doping with Au atoms, this Rashba spin-orbit coupling is further strengthened as the adatoms can distort the graphene lattice from ${\mathit{sp}}^{2}$ to ${\mathit{sp}}^{3}$ bonding structure. By fitting the Au doping dependence of spin relaxation from Pi et al.[Phys. Rev. Lett. 104, 187201 (2010)], the Rashba spin-orbit coupling coefficient is found to increase approximately linearly from 0.15 to 0.23 meV with the increase of Au density. With this strong spin-orbit coupling, the spin diffusion or transport length is comparable with the experimental values. In the strong scattering limit (dominated by the electron-impurity scattering in our study), the spin diffusion is uniquely determined by the Rashba spin-orbit coupling strength and insensitive to the temperature, electron density, as well as scattering. With the presence of an electric field along the spin injection direction, the spin transport length can be modulated by either the electric field or the electron density. It is shown that the spin diffusion and transport show an anisotropy with respect to the polarization direction of injected spins. The spin diffusion or transport lengths with the injected spins polarized in the plane defined by the spin-injection direction and the direction perpendicular to the graphene are identical, but longer than that with the injected spins polarized vertical to this plane. This anisotropy differs from the one given by the two-component drift-diffusion model, which indicates equal spin diffusion or transport lengths when the injected spins are polarized in the graphene plane and relatively shorter lengths when the injected spins are polarized perpendicular to the graphene plane.

Synthesis and optical limiting studies of Au-doped TiO2 nanoparticles

A series of Au-doped TiO 2 nanoparticles with different Au concentrations were prepared by the sol–gel method using titanium (IV) isopropoxide and tetrachloroaurate (III) trihydrate as precursors. The framework substitution of Au in TiO 2 nanoparticles was established by x-ray diffraction (XRD) and Fourier transform infrared (FT-IR) techniques. X-ray diffraction (XRD) and transmission electron microscopy (TEM) image results confirmed the anatase phase and nanocrystalline nature of TiO 2–Au. The optical properties revealed an extended tailing of the absorption edge toward the visible region upon Au doping. The incorporation of Au in TiO 2 was also confirmed by fluorescence quenching. The increase in Au doping enhanced the ‘red-shift’ in the UV-Vis absorption spectra. The spectral and nonlinear optical properties were studied using fluence-dependent transmittance measurements in order to reveal the optical limiting mechanism. The nonlinear optical response and optical limiting effects of TiO 2–Au nanocomposites dispersed in ethylene glycol were studied at 532 nm using 5 ns Nd:YAG laser pulses. Effective three-photon absorption mechanisms play a major role for good optical limiting characteristics in these nanoparticles and it is seen that the optical nonlinearity enhances with lower threshold as the volume fraction of the Au concentration increased.

First-principles study of the noble metal-doped BN layer

Intriguing electronic and magnetic properties of boron nitride (BN) layer with noble metal (Pd, Pt, Ag and Au) doping are obtained by first-principles calculations. Adsorbed Pd (or Pt) reduces the bandgap of BN sheet owing to the induction of impurity states. The unpaired electrons in the Ag (or Au)-adsorbed and the Pd (or Pt)-substituted BN layers are polarized, and thus, exhibit a magnetic moment of 1.0 μB, leading to these BN configurations to be magnetic semiconductors. The half-metallic feature of the Ag-substituted BN layer, along with the delocalization of spin states, renders this configuration an excellent spin filter material. Thus, these findings offer a unique opportunity for developing BN-based nanoscale devices.

Spin correlations and electron transport in MnBi:Au films

The structural, magnetic, and electron transport properties of Mn55−xAuxBi45 (x = 0, 4.5) thin films prepared by magnetron sputtering have been investigated. The magnetization of the MnBi films decreases and the coercivity increases due to Au doping. The temperature dependence of resistivity between 2 to 300 K shows that the films are metallic but the 4.5% Au-doped film shows a Kondo behavior with resistance minimum at 10.2 K. The magnetoresistance is anisotropic and the positive transverse magnetoresistance is significantly enhanced (16.3% at 70 kOe) by Au doping. We interpret these data in terms of a model in which Au atoms preferentially substitute for Mn atoms on the Mn lattice, and some Mn atoms are displaced to interstitial sites in the NiAs structure. These interstitial Mn atoms are coupled antiferromagnetically to the Mn atoms on the original Mn lattice leading to the large decrease in magnetization, Kondo effect, and the positive magnetoresistance.

The study on structures and properties of Run and Run Au(n=112) clusters by density functional theory

The geometries, the stabilities, and the electronic properties of Run Au and Run (n=112) clusters are systematically investigated by the density functional theory. The results suggest that the lowest energy structures for Run Au clusters can be obtained by substituting one Ru atom in Run+1 clusters with Au atom. The geometries of Run Au clusters are similar to those of Run+1 clusters except local structural distortions. The second-order difference and fragmentation energy show that Ru5, Ru8, Ru5Au, and Ru8Au clusters are the most stable among these studied clusters, the doped Au atoms do not change the relative stabilities of Run clusters; the Au impurities increase the chemical activities of Run clusters, and the value of gap is determined mainly by the electron-pairing effect; the doped Au atoms increase the total magnetic moments of Run Au in most cases.

Influence of Diffusion-Annealing Temperature on the Physico-Mechanical Properties of Au-doped Bi-2223 Superconductors

In order to investigate the influence of Au doping and diffusion-annealing temperature on the mechanical and superconducting properties of Bi-2223, Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors were prepared by standard solid-state reaction methods. Doping of Bi-2223 was carried out by means of gold diffusion during sintering from an evaporated gold film on pellets. The investigation consisted of scanning electron microscopy, dc resistivity and hardness measurements. Electrical-resistivity measurements indicated that the room-temperature resistivity value decreased with decreasing diffusion-annealing temperature from 830 to 500 °C and these samples (G830, G800, G750, G700, G600 and G500) show the resistive behavior above the onset critical transition temperature with the zero-resistivity transition temperatures of 104 K, 80 K, 98 K, 95 K, 102 K and 103 K, respectively. To investigate mechanical properties of the samples, we have measured the diagonal length as a function of test load in the range of 0.245–2.940 N. Mechanical properties (microhardness, Young’s modulus, yield strength and fracture toughness) of the samples are found to be load and diffusion-annealing temperature dependent. In addition, we have calculated the load independent hardness, Young’s modulus, yield strength, and fracture toughness of the samples. The possible reasons for the observed changes in superconducting and mechanical properties due to Au diffusion and diffusion-annealing temperature were discussed.

Magnetic Properties of Fe<SUB><I>x</I></SUB>Pt<SUB><I>y</I></SUB>Au<SUB>100−<I>x</I>−<I>y</I></SUB> Nanoparticles

Fe(x)Pt(y)Au(100-x-y) nanoparticles of size 3.5 nm were prepared by polyol reduction of platinum acetylacetonate and gold acetate and the thermal decomposition of iron pentacarbonyl. The as-synthesized nanoparticles with disordered fcc structure were then heat treated to transform to the L1(0) structure with high magnetocrystalline anisotropy. By tuning the stoichiometry of the Fe(x)Pt(y)Au(100-x-y) nanoparticles, the phase transition temperature was reduced by more than 200 degrees C. After the annealing 500 degrees C, for instance, the highest coercivity of 18 kOe was obtained from the Fe51Pt36Au13 nanoparticles which is substantially higher compared to 2 kOe for Fe51Pt49 nanoparticles annealed at the same temperature. In addition to the high coercivity, the saturation magnetization value obtained from Fe51Pt36Au13 nanoparticles was 47 emu/g which is similar to that for the Fe51Pt49 nanoparticles, indicating that there is no trade-off between the coercivity and the saturation magnetization upon Au doping.

Effect of Au Doping and Defects on the Conductivity of Single-Walled Carbon Nanotube Transparent Conducting Network Films

We examined the electrical conductivity and transmittance of six types of SWNT network films, developed for potential use in transparent conductive films, to investigate the effect of Au doping on single-walled carbon nanotube (SWNT) defects: (i) SWNT network films without Au doping (as-produced (AP-SWNTs), purified (P-SWNTs), and cut (C-SWNTs)) and (ii) Au-doped films of AP-SWNTs (Au/AP SWNTs), P-SWNTs (Au/P-SWNTs), and C-SWNTs (Au/C-SWNTs). The density of SWNT network films was varied systematically by controlling the SWNT concentration and mediating defect formation. The electrical conductivity of each SWNT film was found to be significantly enhanced upon Au doping, with a negligible loss of optical transmittance. The effects of Au doping differed depending on the type of nanotube network present: the electrical conductivity of Au/C-SWNTs was found to be similar to that of Au/AP-SWNTs for a given transmittance, whereas the conductivity of C-SWNTs is much lower than that of the AP-SWNTs prior to Au dopi...

First-principles study of the doping effects in bilayer graphene

We used first-principles calculations to study the doping effects in bilayer graphene, focusing on Au substitute doping in the upper layer of graphene. We found that Au doping in the upper layer maintains the lattice structure of the lower graphene layer. Our study on binding energy shows that the Au-doped bilayer structure is stable with Au atom tightly confined in a small region between the upper and lower layers. Charge density analysis indicates that charge is transferred from the Au donor to the carbon atoms in the lower layer, increasing the carrier density in the lower graphene.

The effect of low levels of dopants upon the formation and properties of beta-phase molybdenum nitride

The addition of 1 wt% Pd, Au, Ni and Cu dopants has been demonstrated to strongly alter the morphology of beta-phase molybdenum nitride prepared by treatment of MoO 3 with a 3/1 H 2/N 2 mixture at 750 °C. Furthermore, the addition of Pd significantly enhances the surface area and the formation of the nitride phase. It is proposed that the facile formation of molybdenum bronzes in this system is important in this respect. The dopants have also been observed to modify the denitridation characteristics of the beta-phase, with an overall reduction of the proportion of NH 3 formed upon using a 3/1 H 2/Ar mixture with respect to the undoped sample.

Photocatalytic performances of mesoporous TiO2 films doped with gold clusters

We report on the single-pot fabrication of ordered mesoporous crystallized titania films doped with gold. Au is incorporated in TiO2 films by adding to the coating solution precursors such as AuCl3 or monodisperse Au113+ nanoclusters, and Au nanoparticles are formed by calcination. A systematic study is performed to correlate structure, Au doping and photocatalytic activity of such films. Two-dimensional small angle X-ray scattering (2D-SAXS), transmission electronic microscopy (TEM), scanning electronic microscopy (SEM) and porosimetry–ellipsometry show that the films retain their mesoporous order even for doping levels as high as 1% Au : Ti atomic ratio. Wide angle X-ray scattering (WAXS), and cyclovoltammetry (CV) show that Au113+ nanoclusters promote the formation of the TiO2 (B) phase in competition with the anatase phase. AuCl3 stabilizes instead only the anatase phase. The highest photocatalytic activity is exhibited by films where Au113+ is employed as a precursor, which we attribute to the combination of the mixed anatase/TiO2 (B) phase, of Au nanoparticle doping and of a well-ordered mesoporous TiO2 matrix.

Enhancing electrochemical and electrocatalytic activities of polyaniline via co-doping with poly(styrene sulfonate) and gold

Polyaniline (PANI), polyaniline doped with poly(styrene sulfonate) (PANI–PSS), polyaniline doped with gold (PANI–Au) as well as polyaniline co-doped with poly(styrene sulfonate) and gold (PANI–Au–PSS) have been prepared using the interfacial polymerization method under similar conditions. The morphology and chemical structure of the products were examined by scanning electron microscopy, UV–vis adsorption spectroscopy and Fourier transform infrared spectroscopy. Electrochemical techniques were used to study their electrochemical and electrocatalytic activities. The results demonstrate that PANI has the highest electrochemical activity in acidic solutions among the investigated species, while with the pH values increasing from pH 6.98 to 9.18, PANI–PSS and PANI–Au–PSS exhibit much better electrochemical activity than PANI and PANI–Au, indicating that PSS plays a vital role in improving the electroactivity of PANI in neutral and basic solutions. The doping of Au alone with PANI is not the same effective as the PSS in the enhancement of electrochemical and electrocatalytic activities, whereas the co-use of Au and PSS has a synergistic contribution on the improvement of electrocatalytic activity of PANI, and therefore the ternary PANI–Au–PSS composite exhibits the strongest electrocatalytic ability to the oxidation of ascorbic acid and the reduction of hydrogen peroxide in neutral solutions.

Electrical Transport in Oxide Glasses Containing Gold Nanoparticles

Abstract Gold doped ruby glasses are classical examples of metal-glass nanocomposites that have been investigated for their striking optical properties. For their multifunctional applications, we have explored the nature of the electrical response of two oxide glasses containing a small amount (<0.1mol%) of gold. Gold-doped lithium borate (LBO) and lanthanum borogermanate (LBGO) glasses are studied using ac conductivity as a function of frequency and temperature in relation to their structure as determined by electron microscopy. For ionically conducting LBO, Au doping produces a noticeable increase of the electrical conductivity. For poorly conducting LBGO, gold doping introduces a dielectric loss peak indicative of dipolar relaxation. The heat treatment of both glasses introduces a new mechanism of dc conduction or dipolar loss, which has about one third the activation energy of the untreated samples. This unexpected behavior is attributed to an ionic-to-electronic conductivity transition in gold doped glasses.

Synchrotron Photoluminescence Spectroscopy of Boron Nitride Nanotubes with Different Metal Impurities

AbstractIn this paper, the impurity influences of BNNTs on photoluminescence (PL) analysis have been investigated systematically. Similar PL spectra were obtained from bulk disk of the cold-pressed BNNTs and dispersed individual BNNTs deposited on CaF2 substrate. Metal impurities such as Fe and Au do not affect PL emissions of the BNNTs strongly possibly because Au doping creates sever structural damages but do not change the electronic structure.

The effect of Au diffusion on some physical properties of Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors

Abstract We have investigated the effect of the gold diffusion on the crystal structure and superconducting properties of Bi-2223 superconducting samples employing X-ray diffraction (XRD), scanning electron microscopy (SEM), critical transition temperature, critical current density, and room temperature resistivity measurements. Doping of Bi-2223 was carried out by means of gold diffusion from an evaporated gold film on pellets during sintering. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters and grain size, respectively. Au doping of the samples increased the critical transition temperature and the critical current density from 100 ± 0.2 to 104 ± 0.2 K and from 40 to 125 A cm−2, in comparison with those of undoped samples. The gold diffusion in Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy has been studied over the temperature range of 500–830 °C using the technique of successive removal of thin layers and measurement of the sample's conductivity at room temperature. The temperature dependence of the Au diffusion coefficient in the range of 500–830 °C was described by the relation D = 5 × 10−4 exp (−1.09 eV/kBT). The possible reasons for the observed improvements in microstructure and superconducting properties due to Au diffusion were discussed.

EDXRF measurements on gold diffusion-doped Bi 1.8Pb 0.35Sr 1.9Ca 2.1Cu 3O y

Gold (Au) diffusion in superconducting Bi 1.8Pb 0.35Sr 1.9Ca 2.1Cu 3O y was investigated over the temperature range 500–800 °C by the energy dispersive X-ray fluorescence (EDXRF) technique. It is found that the Au diffusion coefficient decreases as the diffusion-annealing temperature decreases. The temperature dependences of Au diffusion coefficient in grains and over grain boundaries are described by the relations D 1=6.7×10 −5exp(−1.19 eV/k BT) and D 2=9.7×10 −4exp(−1.09 eV/k BT), respectively. The diffusion doping of Bi-2223 by Au causes a significant increase of the lattice parameter c by about 0.19%. For the Au-diffused samples, dc electrical resistivity and transport critical current density measurements indicated the critical transition temperature increased from 100 to 104 K and the critical current density increased from 40 to 125 A cm −2, in comparison with those of undoped samples. From scanning electron microscope (SEM) and X-ray diffraction (XRD) measurements it is observed that Au doping of the sample also improved the surface morphology and increased the ratio of the high- T c phase to the low- T c phase. The possible reasons for the observed improvement in microstructure and superconducting properties of the samples due to Au diffusion are also discussed.

Selective promotion of different modes of methanol adsorption via the cation substitutional doping of a ZnO [formula omitted] surface

We used density functional theory to examine how doping the surface of an oxide (i.e., substituting a cation in the surface layer of the metal oxide with a different cation) modifies its chemical properties. As an example, we used the ZnO ( 10 1 ¯ 0 ) surface doped with Na, K, Au, Ag, Cu, Ti, Al, or Mg and the adsorption of methanol to probe the chemistry of the doped surface. We calculated the binding energies of the possible adsorption products. When we say that methanol preferred to form a certain product, we mean that the product had the lowest energy of formation from gas-phase methanol and the surface. We found that on a surface doped with Na or K, CH 3OH preferred to dissociate into adsorbed formaldehyde and two hydroxyls on the surface. On the Ti- or Al-doped surfaces, methanol dissociated by forming a methoxy radical bound to the dopant and a hydroxyl on an oxygen atom near the dopant. On the undoped oxide or on ZnO doped with Au, Cu, Ag, or Mg, methanol preferred to adsorb molecularly. The Au, Cu, Ag, or Mg dopants exhibited no significant preference for one adsorption mode over the others. Our most important qualitative conclusion is that doping can significantly alter the chemistry of an oxide surface, offering an avenue for designing catalysts that have better performance than undoped oxides.

Effect of Ag and Au doping on the photocatalytic activity of TiO2 supported on textile fibres

ABSTRACTA simple method to develop TiO2, Ag or Au-doped TiO2 thin films on cotton textiles for advanced applications, is reported. The homogeneous TiO2 thin films have been deposited on cotton textiles by using sol-gel method at low temperature (100° C), whereas Ag and Au nanoparticles were then deposited on the pre-existent TiO2 films by photoreduction. The Ag/TiO2 covered cotton fibres show multichromic behaviour (grey colour under visible light and brown colour upon ultraviolet light exposure) as well as photoactivity. The Au-TiO2 film coated the cotton textile produces a purple colour with excellent self cleaning properties. The original and treated fibres have been characterized by several techniques (SEM, HRTEM, FTIR, Raman, UV–vis spectroscopy and XRD).