Properties Of Au Research Articles

Local order and dynamic properties in liquid Au-Ge eutectic alloys byab initiomolecular dynamics

We report the results of first-principles molecular dynamics simulations for liquid and undercooled eutectic Au${}_{72}$Ge${}_{28}$ alloys at various temperatures. In comparison with the parent Au${}_{81}$Si${}_{19}$ liquid, we find a much less pronounced chemical short-range order in Au${}_{72}$Ge${}_{28}$, mainly due to the increasing influence of Ge-Ge nearest neighbor packing. In addition, a structural analysis using three-dimensional pair-analysis techniques evidences an icosahedral short-range order and its evolution with temperature, closer to that of pure Au than to that of Au${}_{81}$Si${}_{19}$. We use such differences to understand the dynamic properties of both systems and to discuss disparities in other properties of Au${}_{72}$Ge${}_{28}$ and Au${}_{81}$Si${}_{19}$ alloys.

DI-JET MEASUREMENTS IN HEAVY-ION COLLISIONS AT STAR

Jets are produced from hard scatterings in the early stages of heavy-ion collisions. It is expected that these high-pT partons travel through the hot and dense medium before fragmenting. Therefore they are expected to suffer energy loss in the QGP via gluon radiation and elastic collisions along their path. Measurements of fully reconstructed jets help understand the effect of the energy loss on the jet structure and energy profile. A data-driven characterization of the background in Au + Au is needed in order to compare the results to p + p . The full azimuthal coverage of STAR Time Projection Chamber and Electromagnetic Calorimeter allows measurements of fully reconstructed di-jets, defined by jets that match the online trigger and recoil jets on the away side. A tight selection of the trigger jets allows for a selection of those coming from the surface. Hence, the population of jets on the recoil side is biased towards a maximal energy loss because of the extreme in-medium pathlength. We present measurements of di-jets, exploring their structure and properties in Au + Au and p + p at [Formula: see text] in the STAR experiment.

Geometrical, electronic, and magnetic properties of Au n V (n = 1–8) clusters: A density functional study

The geometrical, electronic, and magnetic properties of small Au n V (n = 1–8) clusters have been investigated using density functional theory at the PW91 level. An extensive structural search indicates that the V atom in low-energy Au n V isomers tends to occupy the most highly coordinated position and the ground-state configuration of Au n V clusters favors a planar structure. The substitution of a V atom for an Au atom in the Au n +1 cluster transforms the structure of the host cluster. Maximum peaks are observed for the ground-state Au n V clusters at n = 2 and 4 for the size dependence of the second-order energy differences, implying that the Au2V and Au4V clusters possess relatively higher stability. The energy gap of the Au3V cluster is the largest of all the clusters. This may be ascribed to its highly symmetrical geometry and closed eight-electron shell. For ground-state clusters with the same spin multiplicity, as the clusters size increases, the vertical ionization potential decreases and the electron affinity increases. Magnetism calculations for the most stable Au n V clusters demonstrate that the V atom enhances the magnetic moment of the host clusters and carries most of the total magnetic moment.

Adsorbate and defect effects on electronic and transport properties of gold nanotubes

First-principles calculations have been performed to study the effects of adsorbates (COmolecules and O atoms) and defects on electronic structures and transport properties ofAu nanotubes (Au(5, 3) and Au(5, 5)). For CO adsorption, various adsorptionsites of CO on the Au tubes were considered. The vibrational frequency of theCO molecule was found to be very different for two nearly degenerate stableadsorption configurations of Au(5, 3), implying the possibility of distinguishingthese two configurations via measuring the vibrational frequency of CO inexperiments. After CO adsorption, the conductance of Au(5, 3) decreases by0.9G0 and the conductance of Au(5, 5) decreases by approximately0.5G0. For O-adsorbed Au tubes, O atoms strongly interact with Au tubes, leading to around2G0 of drop in conductance for both Au tubes. These results may have implicationsfor Au-tube-based chemical sensing. When a monovacancy defect is present,we found that, for both tubes, the conductance decreases by around1G0. Another type of defect arising from the adhesion of one Au atom is also considered. For thiscase, it is found that, for the Au(5, 3) tube, the defect decreases the conductance by nearly1G0, whereas for Au(5, 5), the decrease in conductance is only0.3G0.

Catalytic activities and properties of Au(III)/Schiff-base complexes in methanol oxidative carbonylation

Several Au(III)/Schiff-base complexes were studied and proven to be effective catalysts for oxidative carbonylation of methanol to generate dimethyl carbonate (DMC). Effects of Schiff-base ligands, promoters, and promoter mole ratio to Au(III)/Schiff-base complexes on catalytic activity were studied. When the reaction was carried out at a methanol/Au(III) molar ratio of 5060:1, an [AuCl 2(phen)]Cl/KI (phen = 1,10-phenanthroline) ratio of 1:4, a CO/O 2 pressure of 2:1, and a temperature of 120 °C for 3 h, the conversion, selectivity, and TOF value of the model reaction were 10.8%, 98%, and 138.9 h −1, respectively. The catalyst was characterized by FTIR, UV–vis, 1H NMR, and cyclic voltammetry. The oxidation state of gold during the reaction and the role of KI were discussed using data on electrochemical experiments and ESI-MS. [AuI 2(phen)] + was considered an intermediate in the reaction. A plausible Au(III)/Au(I) catalytic cycle mechanism was proposed.

Simultaneous low extinction and high local field enhancement in Ag nanocubes**Project supported by the National Natural Science Foundation of China (Grant Nos. 60736041 and 10874238), and the National Key Basic Research Special Foundation of China (Grant No. 2007CB613205).

We theoretically investigate surface plasmon resonance properties in Au and Ag cubic nanoparticles and find a novel plasmonic mode that exhibits simultaneous low extinction and high local field enhancement properties. We analyse this mode from different aspects by looking at the distribution patterns of local field intensity, energy flux, absorption and charge density. We find that in the mode the polarized charge is highly densified in a very limited volume around the corner of the nanocube and results in very strong local field enhancement. Perturbations of the incident energy flux and light absorption are also strongly localized in this small volume of the corner region, leading to both low absorption and low scattering cross section. As a result, the extinction is low for the mode. Metal nanoparticles involving such peculiar modes may be useful for constructing nonlinear compound materials with low linear absorption and high nonlinearity.

Geometries, stabilities, and electronic properties of Pt-group-doped gold clusters, their relationship to cluster size, and comparison with pure gold clusters

A systematic study of bimetallic Au(n)M(2) (n = 1-6, M = Ni, Pd, and Pt) clusters is performed by using density functional theory at the B3LYP level. The geometric structures, relative stabilities, HOMO-LUMO gaps, natural charges and electronic magnetic moments of these clusters are investigated, and compared with pure gold clusters. The results indicate that the properties of Au(n)M(2) clusters for n = 1-3 diverge more from pure gold clusters, while those for n = 4-6 show good agreement with Au(n) clusters. The dissociation energies, the second-order difference of energies, and HOMO-LUMO energy gaps, exhibiting an odd-even alternation, indicate that the Au(4)M(2) clusters are the most stable structures for Au(n)M(2) (n = 1-6, M = Ni, Pd, and Pt) clusters. Moreover, we predict that the average atomic binding energies of these clusters should tend to a limit in the range 1.56-2.00 eV.

Bulk Properties in Au+Au Collisions at [formula omitted] in STAR Experiment at RHIC

One of the primary goals of high-energy heavy-ion collisions is to establish the QCD phase diagram and search for possible phase boundaries. The planned RHIC energy scan program will explore this exciting physics topic using heavy-ion collisions at various center of mass energies. The first test run with Au+Au collisions at s N N = 9.2 GeV took place in early 2008. We present the results on identified particle ratios, azimuthal anisotropy parameters ( v 1 and v 2 ) and HBT at midrapidity using data from this run. These results are compared to data for both lower and higher center of mass energies at the AGS, SPS and RHIC. These new data demonstrate the capabilities of the STAR detector for exploring the QCD phase diagram.

Properties of GaN(SiC)-(Ti, Zr)B x contacts subjected to rapid thermal annealing

The effect of rapid thermal annealing on the structural and physical properties of Au-(Ti, Zr)Bx- GaN(SiC) contacts and diode structures on their basis is investigated. The Xraydiffraction investigations and the layerbylayer Auger analysis showed that th e phase composition and structure of the GaN and SiC contacts are retained to the temperatures as high as 900 and 1000°C, respectively. The stability of interphase boundaries is confirmed by almost constant physical properties of contacts before and after the rapid thermal treatments. The Schottkybarrier height ϕb amounts to 0.89-0.9 eV for the contacts with GaN and 0.79- 0.83 eV for SiC; the ideality factor n of the I-V characteristic amounts to n = 1.2 for the Au-TiBx(ZrBx)- nGaN(SiC) contacts and n ≈ 1.12 for the Au-ZrB x -nn + �4 HSiC contacts. The structural investigations indicate that there are glassforming boron and metal oxides at an interphase boundary, which form a thin amorphous vitreous layer resistant against rapid thermal annealing and represent the diffusion barrier for the interphase transport.

Origin of the Modified Electronic Properties of Au Formed on Pentacene

Origin of the Modified Electronic Properties of Au Formed on Pentacene

Synthesis and adsorption properties for Au(III) of alkoxycarbonyl thiourea resin

A novel alkoxycarbonyl thiourea resin(ATR) was synthesized by monomer polymerization of oxydiethane-2,1-diyl dicarbonisothiocyanatidate and polyethylene polyamine, and characterized by FT-IR. The adsorption properties of ATR were investigated by batch test. The adsorption capacities for Au(III), Ag(I), Cu(II), Zn(II), Fe(III), Ca(II) and Mg(II) are 4.65, 0.40, 0.90, 0.86, 0.0080 and 0.016 mmol/g, respectively, when the adsorption condition is as follows: contact time 24 h, temperature 30 °C, initial concentration of Au(III) 5.08 mmol/L and that of other metals 0.10 mol/L, and concentration of acid 1.0 mol/L. The adsorption capacity for Au(III) increases with the increase of contact time, temperature and initial concentration of Au(III). The capacity after five adsorption-desorption cycles remains 90% that of the first time, and the separation factors of ATR for binary metal ion solutions are larger than 995, indicating that ATR is of good regeneration property and selectivity. XPS results show that the functional atoms of ATR supply electrons for Au and coordinate with Au during the adsorption.

A novel glucose biosensor based on immobilization of glucose oxidase in chitosan on a glassy carbon electrode modified with gold–platinum alloy nanoparticles/multiwall carbon nanotubes

A novel glucose biosensor was constructed, based on the immobilization of glucose oxidase (GOx) with cross-linking in the matrix of biopolymer chitosan (CS) on a glassy carbon electrode (GCE), which was modified with gold–platinum alloy nanoparticles (Au–PtNPs) by electrodeposition on multiwall carbon nanotubes (CNTs) in CS film (CNTs/CS). The properties of Au–PtNPs/CNTs/CS were characterized by scan electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectra (EIS). Primary study indicated that Au–PtNPs/CNTs had a better synergistic electrocatalytic effect on the reduction of hydrogen peroxide than did AuNPs/CNTs or PtNPs/CNTs at a low applied potential window. With GOx as a model enzyme, a new glucose biosensor was fabricated. The biosensor exhibited excellent performances for glucose at a low applied potential (0.1 V) with a high sensitivity (8.53 μA mM −1), a low detection limit (0.2 μM), a wide linear range (0.001–7.0 mM), a fast response time (<5 s), and good reproducibility, stability, and selectivity. In addition, the biosensor was applied in the determination of glucose in human blood and urine samples, and satisfied results were obtained.

Template-directed synthesis, characterization and electrical properties ofAu–TiO2–Au heterojunction nanowires

The feasibility of synthesizing metal–oxide–metal (MOM) heterojunction nanowires in theAu–TiO2–Au system is demonstrated. The synthesis method presented here entailssequential electroplating of Au and electro-deposition of amorphous titanium oxide(TiOx) inside nanoholes of anodic aluminium oxide (AAO) templates. This is followed by dissolving thetemplate, and heat-treating the released nanowires, which results in the crystallization of the amorphousTiOx segment intonanocrystalline TiO2. Detailed transmission electron microscopy (TEM) investigation has revealed that the nanocrystallineTiO2 is orthorhombic (columbite) phase primarily. This synthesis method has the potential to providebetter control over the characteristics and architectures of the resulting MOM nanowires. TheAu–TiO2–Au nanowires were incorporated into single-nanowire devices,fabricated using a direct-write method. Nonlinear current–voltage(I–V) responses were obtained for individual MOM nanowires. The heterojunctions in suchMOM nanowires are likely to offer certain advantages over all-oxide nanowires, making theMOM nanowires potentially useful as one-dimensional building blocks in themultifunctional nanoelectronics of the future.

Ferromagnetic behaviour in semiconductors: a new magnetism in search of spintronic materials

The future of the spintronic technology requires the development of magnetic semiconductor materials. Most research groups have focused on diluted magnetic semiconductors because of the promising theoretical predictions and initial results. In this work, the current experimental situation of ZnO based diluted magnetic semiconductors is presented. Recent results on unexpected ferromagnetic-like behaviour in different nanostructures are also revised, focusing on the magnetic properties of Au and ZnO nanoparticles capped with organic molecules. These experimental observations of magnetism in nanostructures without the typical magnetic atoms are discussed. The doubts around the intrinsic origin of ferromagnetism in diluted magnetic semiconductors along with the surprising magnetic properties in absence of the typical magnetic atoms of certain nanostructures should make us consider new approaches in the quest for room temperature magnetic semiconductors.

A tribological study of kinetically influenced ultrathin Au and Cu metal overlayers grown on dendrimer mediated Si

Evidence is presented here for deposition kinetic energy influences on the wear properties of Au and Cu films deposited by evaporation and sputtering on clean and poly(amidoamine) (PAMAM) dendrimer modified SiOx substrates. Ramped load nanoscratch tests show increased resistance to wear in the presence of the dendrimer monolayer. Nanoscratch profiles indicate that the critical load to failure (scratch bearing capacity) is increased in the presence of a dendrimer interlayer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis of the wear tracks show that following film failure plowing is the predominant mechanism of wear for sputtered or evaporatively deposited Au. No obvious changes in the wear properties (a pure cutting mechanism) of Cu thin films are observed upon changing the kinetic energy of the incoming metal.

Understanding preparation variables in the synthesis of Au/Al 2O 3 using EXAFS and electron microscopy

The catalytic performance of Au/Al 2O 3 catalyst is highly sensitive to preparation procedure. EXAFS and TEM characterization of key steps in the preparation in conjunction with activity measurements result in deeper insights into precautions needed and the complex manner residual chloride impacts catalytic activity. Chloride affects the morphological (Au particle size), chemical (reducibility) as well as the catalytic (poisoning) properties of Au. Alternate preparation procedures to the conventional calcination of a catalyst prepared with deposition–precipitation at neutral pH were explored to increase Au loadings. It was found that low temperature H 2 reduction of a catalyst prepared at low pH but washed with NaOH is an effective preparation method.

Measurement and interpretation of the mid-infrared properties of single crystal and polycrystalline gold

The contribution of electron–phonon scattering and grain boundary scattering to the mid-IR ( λ = 3.392 μm) properties of Au has been assessed by examining both bulk, single crystal samples—Au(1 1 1) and Au(1 1 0)—and thin film, polycrystalline Au samples at 300 K and 100 K by means of surface plasmon polariton excitation. The investigation constitutes a stringent test for the in-vacuo Otto-configuration prism coupler used to perform the measurements, illustrating its strengths and limitations. Analysis of the optical response is guided by a physically based interpretation of the Drude model. Relative to the reference case of single crystal Au at 100 K ( ε = −568 + i 17.5), raising the temperature to 300 K causes increased electron–phonon scattering that accounts for a reduction of ∼40 nm in the electron mean free path. Comparison of a polycrystalline sample to the reference case determines a mean free path due to grain boundary scattering of ∼17 nm, corresponding to about half the mean grain size as determined from atomic force microscopy and indicating a high reflectance coefficient for the Au grain boundaries. An analysis combining consideration of grain boundary scattering and the inclusion of a small percentage of voids in the polycrystalline film by means of an effective medium model indicates a value for the grain boundary reflection coefficient in the range 0.55–0.71.

Silica-Supported Au and Pt Nanoparticles and CO Adsorption

ABSTRACTThe understanding of the surface properties of metal nanoparticles is essential for exploiting their unique catalytic properties. This paper reports findings of the preparation of silica-supported Pt and Au nanoparticles and the FTIR characterization of CO adsorption on the supported nanoparticles. The nanoparticles were prepared by both a traditional impregnation method and molecular-capping based synthesis method. By comparing the spectroscopic characteristics of CO adsorption on these catalysts, similarities and differences in CO stretching bands have been identified. The findings are significant because important insights have been gained into the surface binding properties of Au and Pt nanoparticle catalysts.

졸-겔법에 의한 Au 미립자 분산 ZrO2박막의 제조와 특성

졸-겔법에 의한 Au 미립자 분산 ZrO₂박막의 제조와 특성

A study on the photo-induced crystallization properties in Au+-doped silicate glasses

We report the photo-induced crystallization behaviour of Au+-doped silicate glasses fabricated by Ti: sapphire femtosecond pulsed laser and successive heat treatment. Absorption spectra showed gold nanoparticles precipitated near the f ocal point of the laser beam. We also demonstrate that the size distribution of nanoparticles can be controlled by the laser irradiation conditions. Gold nanop articles-doped glasses reveal stronger optical limiting effects for nano-second laser pulses, and optical nonlinearities of the composite glass were also affec ted by laser irradiation conditions.