Au Samples Research Articles

Application of thin-film interference coatings in infrared reflection spectroscopy of organic samples in contact with thin metal films

A thin dielectric IR-transparent interlayer is introduced between an IR-transparent medium of incidence and a thin metal film. The interlayer increases the intensity of light on the metal/sample interface at certain wavenumbers. By computations, the reflectivities of the system "calcium fluoride (CaF)-germanium (Ge)-gold (Au) sample" are analyzed as a function of incidence angle and Ge layer thickness. Absorbance spectra with acetonitrile as a sample are recorded for different angles of incidence and polarizations and compared to computations. A characteristic feature of the absorbance spectra is the occurrence of interference fringes distributed between 1000 and 6000 cm(-1), i.e., over the complete mid-IR wavelength range into the near-IR. These fringes could be used in analytical spectroscopy.

Angle resolved total reflection fluorescence XAFS and its application to Au clusters on TiO2(110) (1 * 1)

The bonding features and three dimensional structures of metal clusters on single crystal oxide surfaces can be determined by the polarization dependent total reflection fluorescence XAFS (PTRF-XAFS) method. K-edge XAFS has a cos2 θ polarization-dependence to give successfully three dimensional structure while L3 edge XAFS has a weaker polarization dependence though the L3 edge is suitable for Au and Pt samples. In order to overcome this issue, we have developed an angle-resolved total reflection fluorescence XAFS (ARTRF-XAFS) method to determine more precise three dimensional structures of Au clusters using the L3 edge by increase the number of data points. In this paper we described the methodologies of the ARTRF-XAFS and the results of Au clusters on the TiO2(110) surface.

Bulk gold with hierarchical macro-, micro- and nano-porosity

Millimeter-sized, free-standing gold structures were created with three levels of multiscale porosity. First, macro- and microporosity, which are useful for mass and heat transport within the structure, are formed within an Ag–19at.% Au alloy by salt powder replication during powder densification and by entrapped gas expansion during sintering, respectively. Nanoporosity, which provides high surface area, is then produced by silver dealloying of these Ag–19at.% Au foams. The resulting hierarchical gold structures are annealed at 100–800°C, thus coarsening the ligaments, increasing relative density, and healing cracks produced during dealloying. The first effect weakens the structure, while the other two make it stronger. A bulk Au sample with hierarchical porosity annealed at 600°C shows good compressive ductility and a strength in agreement with models.

An Atomic‐Scale View of Palladium Alloys and their Ability to Dissociate Molecular Hydrogen

AbstractPalladium and its alloys play a central role in a wide variety of industrially important applications such as hydrogen reactions, separations, storage devices, and fuel‐cell components. Alloy compositions are complex and often heterogeneous at the atomic‐scale and the exact mechanisms by which many of these processes operate have yet to be discovered. Herein, scanning tunneling microscopy (STM) has been used to investigate the atomic‐scale structure of Pd–Au and Pd–Cu bimetallics created by depositing Pd on both Au(111) and Cu(111) single crystals at a variety of surface temperatures. We demonstrated that individual, isolated Pd atoms in an inert Cu matrix are active for the dissociation of hydrogen and subsequent spillover onto Cu sites. Our results indicated that H spillover was facile on Pd–Cu at 420 K but that no H was found under the same H2 flux on a Pd–Au sample with identical atomic composition and geometry. In the case of Au, significant H uptake was only observed when larger ensembles of Pd were present in the form of nanoparticles. We report experimental evidence for hydrogen’s ability to reverse the tendency of Pd to segregate into the Au surface at catalytically relevant temperatures and our STM images reveal a novel H‐induced striped structure in which Pd atoms aggregated on top of the surface in regularly spaced rows. These results demonstrate the powerful influence an inert substrate has on the catalytic activity of Pd atoms supported in or on its surface and reveal how the atomic‐scale geometry of Pd–Au alloys is greatly affected by the presence of hydrogen.

Ceria supported group IB metal catalysts for the combustion of volatile organic compounds and the preferential oxidation of CO

Catalytic combustion of volatile organic compounds (VOC) and preferential oxidation of CO (PROX) were investigated over IB metal/ceria catalysts prepared by deposition–precipitation (DP) or coprecipitation (CP). The activity towards the deep oxidation of VOC was in the order: Au/CeO2≥Ag/CeO2>Cu/CeO2≫CeO2. The same trend was also found in the PROX reaction in terms of total conversion of O2, which includes O2 consumed both for CO and H2 oxidation. A different behaviour was observed in the CO conversion to CO2, that is the desired PROX reaction. For this reaction, in fact, Au and Cu catalysts gave high CO conversions, Au/CeO2 at low temperature (maximum of 84.3% for AuDP at 70°C) and Cu/CeO2 at higher temperature (maximum of 96.8% for CuCP at 150°C), whereas Ag catalysts always exhibited very low CO conversions (maximum of 16.7% for AgCP at 80°C). Both for PROX and VOC combustion the Au sample prepared by DP was more active than the CP one, whereas a reverse behaviour was found on Ag and Cu catalysts.On the basis of characterization data (XRD, H2-TPR, surface area measurements, H2–D2 isotopic exchange, N2O and H2–O2 chemisorption) it was proposed that a higher atomic radius of the IB metal and the presence of smaller crystallites of both IB metal and ceria result in a larger enhancement of mobility/reactivity of surface ceria oxygens, involved in both investigated reactions through a Mars–van Krevelen mechanism. The very low PROX activity of Ag/CeO2 samples was related to the low capacity of silver to activate the CO molecule.

Effect of Defects Buried in Pentacene/Alkanethiol Self-Assembled Monolayer/Au Film on Its Electronic Properties Visualized by Scanning Tunneling Microscopy/Spectroscopy

We have used scanning tunneling microscopy/spectroscopy to visualize the spatial correlation between buried structural defects and observed electronic properties in organic device structures. As a typical structure of an organic field-effect transistor, we have prepared pentacene/alkanethiol self-assembled monolayer (SAM)/Au samples with or without defects associated with a gap state at the molecule/Au interface. The effect of the defects, which were hidden behind the pentacene overlayers, on the electronic properties of the SAM was clearly observed. The method used in this study has potential for evaluating the nanoscale correlation between electrical properties and hidden defects inside organic devices.

Grain refinement of coarse grained gold by combined thermo-mechanical process of severe plastic deformation and low temperature annealing

A high purity gold composed of coarse grains (d = 1.7 mm) was repeatedly thermo-mechanically processed by multi directional forging (MDF) at room temperature and annealing at warm temperature range. The effects of small addition of Ca (180 at. ppm) to Au on the static recrystallization (SRX) behavior and ultrafine grain evolution were investigated. Extensive SRX was observed in the MDFed Au sample to cumulative strain of ΣΔϵ = 1.2 even at 453 K. After 2 cycles of the repeated TMP, fine grains of about d = 10 μm was obtained in the Au sample. The Au-Ca alloy MDFed to ΣΔϵ = 1.2, however, was hardly SRXed even by annealing at 543 K. Subsequently, the fine-grained Au and Au-Ca alloy were further MDFed to ΣΔϵ = 8.0 at maximum at room temperature. By the prolonged MDF, average (sub)grain size of about 200 nm was achieved in the Au sample. The hardness increased with increasing cumulative strain. Although the tensile strength was also raised with cumulative strain, large loss of ductility did not appear.

Magnetic Properties and Magnetoresistance of CdMnS: Au Based Structures Prepared by Co-evaporation

Polycrystalline CdMnS and CdMnS: Au films with hexagonal structure on Si(111) substrates are prepared by co-evaporation, and exhibit ferroelectric and ferromagnetic properties, respectively Under optimized growth conditions, CdMnS: Au samples with an average crystallite size of 90 nm and Mn concentration of 5.0 at. % are obtained, and an all-semiconductor spin valve device of Co/Au/CdMnS: Au/CdMnS/Pt is fabricated. Electrical measurement of the device reveals the clear dependence of resistance on applied magnetic field, with a relative magnetoresistance of 0.06% and a switching field of 100 Oe at 77 K.

Structure and the Metal Support Interaction of the Au/Mn Oxide Catalysts

Gold catalysts with loading 1 and 10 wt % were prepared by deposition−precipitation method with urea over mesoporous manganese oxide, obtained through a surfactant-assisted procedure by using cetyltrimethylammonium bromide (CTAB), followed by treatment with sulphuric acid. For comparison, Au(10 wt %) was also deposited over commercial CeO2 and SiO2 supports. The materials were characterized by XRD and EXAFS at the Mn K and Au LIII edges and XPS. Moreover, the analyses were performed on the samples treated under 1%CO/He, at 250 °C for 90 min. The structural and surface results of the as prepared manganese oxide confirmed the formation of γ-MnO2 along with some amorphous Mn3O4 upon treatment of the precursor oxide with sulphuric acid. The CO treatment induces the formation of reduced phases, Mn3O4 (Hausmannite) and Mn2O3 (Bixbyite). Gold particles have a positive effect in promoting the reduction of manganese oxide and this effect is more pronounced in the Au(10 wt %) catalyst, which exhibits an enhanced CO oxidation activity with respect to both the Au(1 wt %) sample and the metal-free manganese oxide. The higher efficiency of Au(10 wt %) catalyst is attributed to a strong metal−support interaction between gold nanoparticles and support, as demonstrated by the presence of a component Au−O at 2.1 Å in the Fourier transform of the EXAFS signal of both the fresh and the CO-treated samples.

Critical current densities and flux creep rate in Co-doped BaFe2As2 with columnar defects introduced by heavy-Ion irradiation

We report the formation of columnar defects in Co-doped BaFe2As2 single crystals with different heavy-ion irradiations. The formation of columnar defects by 200MeV Au ion irradiation is confirmed by transmission electron microscopy and their density is about 40% of the irradiation dose. Magneto-optical imaging and bulk magnetization measurements reveal that the critical current density Jc is enhanced in the 200MeV Au and 800MeV Xe ion irradiated samples while Jc is unchanged in the 200MeV Ni ion irradiated sample. We also find that vortex creep rates are strongly suppressed by the columnar defects. We compare the effect of heavy-ion irradiation into Co-doped BaFe2As2 and cuprate superconductors.

Measurement of the Casimir effect under ultrahigh vacuum: Calibration method

In this article, the authors present a strategy to measure the Casimir effect with an atomic force microscopy in an ultrahigh vacuum system. The key parameters including the absolute distance, the contact potential difference, and the calibration factor of the probe are determined by electrostatic interaction without contact. The strategy has been developed with the main purpose of performing a reliable relative measurement, that is, comparison of the Casimir force between different surfaces. As an example of the method, the authors estimate the accuracy and the precision of measurements performed on a Au sample.

Rates of Chlamydia trachomatis and Neisseria gonorrhoeae in Chilean adolescents

Chlamydia trachomatis and Neisseria gonorrhoeae are common sexually transmitted diseases among young women and little has been doing to study them in Chilean adolescents. Determine the rates of C trachomatis and N gonorrhoeae in Chilean young women. Urine samples were obtained from 203 sexually active females under 25 year-old, who attended hospitals from either high or low-income areas in Chile's capital, Santiago. C trachomatis and Ngonorrhoeae were detected by nucleic acid amplification testing. Seven percent of samples were positive for C trachomatis. AU samples were negative for N gonorrhoeae. Among pregnant women, 19% of samples were positive for C trachomatis, while non-pregnant women were positive on 5.5% (p =0.04). Systematic use of barrier contraception was referring by 12% of women. AU of the latter was free of C trachomatis. No association was observing between age, number of sexual partners, age of first sexual intercourse, and presence of uro-gynecological symptoms, socioeconomic status and the rate of C trachomatis. Seven percent of this group of Chilean young women was infected with C trachomatis. The figure rises to 19% if pregnant. Surveillance and screening programs should been implemented to prevent sequels on this vulnerable population.

Prevalencia de Chlamydia trachomatis y Neisseria gonorrhoeae en adolescentes chilenas

Chlamydia trachomatis and Neisseria gonorrhoeae are common sexually transmitted diseases among young women and little has been doing to study them in Chilean adolescents.Determine the rates of C trachomatis and N gonorrhoeae in Chilean young women.Urine samples were obtained from 203 sexually active females under 25 year-old, who attended hospitals from either high or low-income areas in Chile's capital, Santiago. C trachomatis and Ngonorrhoeae were detected by nucleic acid amplification testing.Seven percent of samples were positive for C trachomatis. AU samples were negative for N gonorrhoeae. Among pregnant women, 19% of samples were positive for C trachomatis, while non-pregnant women were positive on 5.5% (p =0.04). Systematic use of barrier contraception was referring by 12% of women. AU of the latter was free of C trachomatis. No association was observing between age, number of sexual partners, age of first sexual intercourse, and presence of uro-gynecological symptoms, socioeconomic status and the rate of C trachomatis.Seven percent of this group of Chilean young women was infected with C trachomatis. The figure rises to 19% if pregnant. Surveillance and screening programs should been implemented to prevent sequels on this vulnerable population.

Influence of the preparation method on the morphological and composition properties of Pd–Au/ZrO 2 catalysts and their effect on the direct synthesis of hydrogen peroxide from hydrogen and oxygen

Bimetallic Pd–Au samples supported on zirconia were prepared by different methods and tested for the direct synthesis of hydrogen peroxide under very mild conditions (room temperature and atmospheric pressure), outside the explosion range and without halides addition. Further catalytic tests were performed at higher pressure using solvents expanded with CO 2. Samples were characterized by N 2 physisorption, metal content analysis, XRD, HRTEM combined with X-ray EDS, TPR, and FTIR. The effect of the addition of gold to Pd in enhancing the yield of H 2O 2 is sensitive to the preparation method: the best catalytic results were obtained by depositing gold by deposition–precipitation (DP) and by introducing in a second step Pd by incipient wetness impregnation. The origin of the differences between samples is discussed. The role of Au in the catalytic reaction seems to be a complex one, changing the chemical composition of the metallic particles, their morphology, and charge of the exposed Pd sites.

Thermal noise as a spectroscopic tool to determine transport properties

The utilization of thermal fluctuations or Johnson/Nyquist noise as a spectroscopic method to determine transport properties in conductors or semiconductors is developed. The autocorrelation function is obtained from power spectral density measurements thus enabling electronic transport property calculation through the Green–Kubo formalism. This experimental approach is distinct from traditional numerical methods such as molecular dynamics simulations, which have been used to extract the autocorrelation function and directly related physics only. This work reports multi-transport property measurements consisting of the electronic relaxation time, resistivity, mobility, diffusion coefficient, electronic contribution to thermal conductivity and Lorenz number from experimental data. Double validation of the experiment was accomplished through the use of a standard reference material and a standard measurement method, i.e. four-probe collinear resistivity technique. Thermal noise measurements resulted in a 1.1 and 5% agreement with the reference material and four-probe values, respectively. Additional measurements were also taken on nanoscale Au and Cu thin films. Specifically, the validated spectroscopic methodology was applied to 30 nm Au and Cu thin films to obtain transport property data that was again compared to four-probe resistivity measurements. Comparative analysis of the resistivity data showed agreement within 13.6 and 4.8% for the Au and Cu samples, respectively, thus lending further credibility to the experimental method and theory.

Sputtering of neutral clusters from silver–gold alloys

Polycrystalline Ag, Ag 20Au 80, Ag 40Au 60, Ag 80Au 20 and Au samples were bombarded with 15 keV Ar + at 60° incidence and the resulting secondary neutral yield distribution was studied by non-resonant laser postionisation mass spectrometry. Neutral clusters containing up to 21 atoms were observed for the targets. The yield of neutral clusters, Ag m Au n− m , containing n atoms, Y n , was found to follow a power in n, i.e. Y n ∝ n − δ , where the exponent δ varied from 3.2 to 4.0. For a fixed n, the cluster yields showed a variation with number of gold atoms similar to that expected for a binomial distribution. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a gold rich surface.

Sputtering of clusters from copper–gold alloys

Polycrystalline Cu, Cu 20Au 80, Cu 40Au 60, Cu 80Au 20 and Au samples were bombarded with 15 keV Ar +, and the resulting secondary neutral yield distribution was studied by non-resonant laser post-ionisation mass spectrometry. Neutral clusters containing up to 15 atoms were observed for the targets. The yield of neutral clusters, Cu m Au n − m , containing n atoms, Y n , was found to follow a power in n, i.e. Y n ∝ n - δ , where the exponent δ varied from 5.2 to 10.1. For a fixed n, the cluster yields showed a variation with number of copper atoms, m, much greater than expected for a binomial distribution suggesting that the clusters are not formed randomly above the surface and a component of preformed cluster emission occurs. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a copper rich surface.

Production of X-rays by cosmic-ray muons in heavily shielded gamma-ray spectrometers

Cosmic-ray (CR) muons both directly and indirectly contribute to the spectra of heavily shielded High Purity Germanium (HPGe) detectors, even in deep underground laboratories. Heavy elements are frequently used as the detector components or are occasionally placed close to the detector endcap, and their characteristic X-rays induced by cosmic-ray muons contribute to the low-energy region of the HPGe detector spectra. We study the production of X-rays in tungsten, gold and lead by cosmic-ray muons on the ground level, by means of a coincidence system consisting of a plastic scintillation detector and an extended range HPGe detector placed inside a 12-cm-thick lead shield. In this typical low-background arrangement, the shield with total mass of 725kg acts as a source of secondary particles induced by CR muons. X-rays that originate from direct interactions of muons with the target material, the yield of which may be reliably estimated by Monte Carlo simulations, are excluded by this experimental setup, and only X-rays of W, Pb and Au samples produced by all secondaries from muon interactions with the lead shield are present in the HPGe spectra. The production rate of Kα X-rays per unit mass of all the elements studied (74<Z<82) is found to be close to 7×10−4g−1s−1. This corresponds to a high effective cross-section for this production of 17(3) barns. Unexpectedly, the results do not show any significant dependence on Z in the Z=74–82 region.

Impact of Annealing on the Conductivity of Amorphous Carbon Films Incorporating Copper and Gold Nanoparticles Deposited by Pulsed Dual Cathodic Arc

AbstractThe influence of annealing in argon at 300 °C on the conductivity, phase stability and electronic structure of hydrogen‐free amorphous carbon (a‐C) films containing copper (a‐C:Cu) and gold (a‐C:Au) nanoclusters was investigated. The motivation of this work is twofold: (1) to study the thermal stability of a‐C:Cu and a‐C:Au films and (2) to point out the relevance of X‐ray absorption near edge structure (XANES) technique to study the structural evolution of metal‐doped a‐C nanocomposites. The films were produced at room temperature using a selective‐bias pulsed dual‐cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas grazing incidence X‐ray diffraction (GIXRD) was used to monitor phase transformation and identify the dispersion or agglomeration of the crystallites within the carbon matrix. XANES spectra at the C‐K was used to investigate the effect of annealing in argon on the electronic structure of the a‐C matrix, while Cu K and Au L‐edges were investigated on a‐C:Cu and a‐C:Au samples, respectively, to study the nanocluster evolution. XANES showed that the a‐C host matrix increased its graphitic character and that stress was relieved upon annealing. No relevant changes were observed in the Au arrangements in a‐C:Au films. In the case of the a‐C:Cu samples, the Cu‐K XANES spectra indicated the formation of Cu2O crystals which correlated well with GIXRD spectra and the decrease in conductivity.

New Pd–Pt and Pd–Au catalysts for an efficient synthesis of H 2O 2 from H 2 and O 2 under very mild conditions

Bimetallic Pd–Pt and Pd–Au samples supported on sulfated zirconia were successfully tested for the direct synthesis of hydrogen peroxide under very mild conditions (1 bar and 293 K) and outside the explosion range. The effect of the addition of Pt to Pd in enhancing the yield of hydrogen peroxide is sensitive to the Pt amount: only using a low Pt content it is possible to improve H 2O 2 selectivity (from 55% to 70%) and productivity with respect to the monometallic sample. The addition of gold in 1:1 amount to palladium improved both the productivity and even more the selectivity of the process, producing a hydrogen peroxide concentration already useful for industrial applications and maintaining a stable selectivity (62%) after 12 h of time on stream.