Au L3 Research Articles

X-Ray Nanothermometry of Nanoparticles in Tumor-Mimicking Tissues under Photothermia.

Temperature plays a critical role in regulating body mechanisms and indicating inflammatory processes. Local temperature increments above 42°C are shown to kill cancer cells in tumorous tissue, leading to the development of nanoparticle-mediated thermo-therapeutic strategies for fighting oncological diseases. Remarkably, these therapeutic effects can occur without macroscopic temperature rise, suggesting localized nanoparticle heating, and minimizing side effects on healthy tissues. Nanothermometry has received considerable attention as a means of developing nanothermosensing approaches to monitor the temperature at the core of nanoparticle atoms inside cells. In this study, a label-free, direct, and universal nanoscale thermometry is proposed to monitor the thermal processes of nanoparticles under photoexcitation in the tumor environment. Gold-iron oxide nanohybrids are utilized as multifunctional photothermal agents internalized in a 3D tumor model of glioblastoma that mimics the in vivo scenario. The local temperature under near-infrared photo-excitation is monitored by X-ray absorption spectroscopy (XAS) at the Au L3 -edge (11 919 eV) to obtain their temperature in cells, deepening the knowledge of nanothermal tumor treatments. This nanothermometric approach demonstrates its potential in detecting high nanothermal changes in tumor-mimicking tissues. It offers a notable advantage by enabling thermal sensing of any element, effectively transforming any material into a nanothermometer within biological environments.

Experimental benchmark data for Monte Carlo simulated radiation effects of gold nanoparticles. Part II: comparison of measured and simulated electron spectra from gold nanofoils

Electron emission spectra of a thin gold foil after photon interaction were measured over the energy range between 50 eV and 9500 eV to provide reference data for Monte Carlo radiation-transport simulations. Experiments were performed with the HAXPES spectrometer at the PETRA III high-brilliance beamline P22 at DESY (Hamburg, Germany) for photon energies just below and above each of the gold L-edges, that is, at 11.9 keV, 12.0 keV, 13.7 keV, 13.8 keV, 14.3 keV, and 14.4 keV. The data were analyzed to obtain the absolute values of the particle radiance of the emitted electrons per incident photon flux. Simulations of the experiment were performed using the Penelope and Geant4 Monte Carlo radiation-transport codes. Comparison of the measured and simulated results shows good qualitative agreement. On an absolute scale, the experiments tend to produce higher electron radiance values at the lower photon energies studied as well as at the higher photon energies for electron energies below the energy of the Au L3 photoelectron. This is attributed to the linear polarization of the photon beam in the experiments, something which is not considered in the simulation codes.

Spectroscopic Manifestations and Implications for Catalysis of Quasi-d10 Configurations in Formal Gold(III) Complexes.

Several gold +I and +III complexes are investigated computationally and spectroscopically, focusing on the d-configuration and physical oxidation state of the metal center. Density functional theory calculations reveal the non-negligible electron-sharing covalent character of the metal-to-ligand σ-bonding framework. The bonding of gold(III) is shown to be isoelectronic to the formal CuIII complex [Cu(CF3 )4 ]1- , in which the metal center tries to populate its formally unoccupied 3dx2-y2 orbital via σ-bonding, leading to a reduced d10 CuI description. However, Au L3 -edge X-ray absorption spectroscopy reveals excitation into the d-orbital of the AuIII species is still possible, showing that a genuine d10 configuration is not achieved. We also find an increased electron-sharing nature of the σ-bonds in the AuI species, relative to their AgI and CuI analogues, due to the low-lying 6s orbital. We propose that gold +I and +III complexes form similar bonds with substrates, owing primarily to participation of the 5dx2-y2 or 6s orbital, respectively, in bonding, indicating why AuI and AuIII complexes often have similar reactivity.

Bent crystal Laue analyser combined with total reflection fluorescence X-ray absorption fine structure (BCLA + TRF-XAFS) and its application to surface studies.

A bent crystal Laue analyser (BCLA) is an X-ray energy analyser used for fluorescence X-ray absorption fine-structure (XAFS) spectroscopy to separate the fluorescence X-ray emission line of a target atom from the elastic scattering X-rays and other fluorescence emission lines. Here, the feasibility of the BCLA for total reflection fluorescence XAFS (TRF-XAFS), which has a long X-ray footprint on the substrate surface owing to grazing incidence, was tested. The focal line of the BCLA was adjusted on the X-ray footprint and the XAFS signal for one monolayer of Pt deposited on a 60 nm Au film with high sensitivity was obtained. Although range-extended XAFS was expected by the rejection of Au fluorescence arising from the Au substrate, a small glitch was found in the Au L3 edge because of the sudden change of the complex refraction index of the Au substrate at the Au edge. This abnormal spectrum feature can be removed by reflectivity correction using Au foil absorption data. BCLA combined with TRF-XAFS spectroscopy (BCLA + TRF-XAFS) is a new technique for the in situ surface analysis of highly dispersed systems even in the presence of a liquid overlayer.

Gold Catalysts Synthesized Using a Modified Incipient Wetness Impregnation Method for Propylene Epoxidation

AbstractPropylene epoxidation in the presence of oxygen and hydrogen were measured for a series of Au/TS‐1 catalysts prepared by a modified incipient wetness impregnation (mIWI) method. This method enables precise control of the Au : Ti ratio in the Au/TS‐1 catalysts. The optimized Au/TS‐1 catalyst exhibited 12 % propylene conversion, 87 % PO selectivity, and 25 % hydrogen efficiency. The particle size of gold nanoparticles prepared by the modified IWI was between 2 and 3 nm, as demonstrated by XRD patterns, STEM images, and X‐ray absorption spectroscopy at the Au L3 edge. XPS spectra showed that the surface species on the catalysts were similar. UV‐Vis spectra suggested that in the modified IWI method, the chlorine ligands in Au(Cl)4− were replaced by hydroxyl groups, which contributes to form small gold nanoparticles. Kinetic studies showed that the active sites of Au(mIWI)/TS‐1 are similar to the Au(DP)/TS‐1 prepared by deposition precipitation.

Direct synthesis of H2O2 in AuPd coated micro channels: An in-situ X-Ray absorption spectroscopic study

For the first time, we perform in-situ X-Ray Absorption Spectroscopy on both Au L3 and Pd K edges during the direct synthesis of hydrogen peroxide in a high-pressure gas-liquid-solid microreactor using SiO2 supported Pd, Au and AuPd catalysts under relevant reaction conditions. The catalysts were coated on the walls of 320 µm ID micro capillaries, used in this work both as microreactors and as spectroscopic cells, ensuring safety of operation, ease of portability and absence of reactor effects during the measurements. XANES analysis revealed that the fresh Pd and AuPd catalysts contained a mix of Pd/PdO phases which was readily reduced in H2 atmosphere. The presence of only metallic Pd under reaction conditions for both catalysts proved that metallic Pd is the active phase for this reaction. Au was present in its metallic form in both Au and AuPd under all conditions tested. Unlike the AuPd, monometallic Pd showed an increase in the Pd-Pd distance under reaction conditions, attributed to the formation of Pd-hydride. We propose that the absence of Pd-hydride in the AuPd catalysts reduces further hydrogenation of H2O2 to water, thereby explaining the increased selectivity to H2O2 observed with AuPd catalysts.

Deactivation of a Single-Site Gold-on-Carbon Acetylene Hydrochlorination Catalyst: An X-ray Absorption and Inelastic Neutron Scattering Study

Single-site Au species supported on carbon have been shown to be the active sites for acetylene hydrochlorination. The evolution of these single-site species has been monitored by Au L3 X-ray Absorption Spectroscopy (XAS). Alternating between a standard reaction mixture of HCl/C2H2 and the single reactants, has provided insights into the reaction mechanism and catalyst deactivation processes. We demonstrate that oxidative addition of HCl across an Au(I) chloride species requires concerted addition with C2H2, in accordance with both the XAS measurements of Au oxidation state and the reaction kinetics being 1st order with respect to each reactant. The addition of excess C2H2 changes the Au speciation and results in the formation of oligomeric acetylene species which were detected by inelastic neutron scattering. Catalyst deactivation at extended reaction times can be correlated with the formation of metallic Au particles. The presence of this Au(0) species generated during the sequential gas experiments or after prolonged reaction times, results in the analysis of the normalised near edge white line intensity of the Au L3 X-ray absorption spectrum alone becoming an unsuitable guide for identifying the active Au species, affecting the strong correlation between normalized white line height and VCM productivity usually observed in the active catalyst. Thus, a combination of scanning transmission electron microscopy and detailed modelling of whole XAS spectrum was required to distinguish active Au(I) and Au(III) species from the spectator Au(0) component.

A Demonstration of Pt L3-Edge EXAFS Free from Au L3-Edge Using Log–Spiral Bent Crystal Laue Analyzers

Pt-Au nanostructures are important and well-studied fuel cell catalysts for their promising catalytic performance. However, a detailed quantitative local structure analysis, using extended X-ray absorption fine structure (EXAFS) spectroscopy, have been inhibited by interference between Pt and Au L3-edges. In this paper, Pt L3-edge XAFS analysis, free of Au L3 edge, is demonstrated for a Pt-Au reference sample using a low-cost log–spiral bent crystal Laue analyzer (BCLA). This method facilitates the EXAFS structural analysis of Pt-Au catalysts, which are important to improve fuel cell catalysts.

Ionization cross sections of the Au L subshells by electron impact from the L3 threshold to 100 keV

We measured the cross sections for Au Lα, Lβ, Lγ, Lℓ and Lη x-ray production by the impact of electrons with energies from the L3 threshold to 100 keV using a thin Au film whose mass thickness was determined by Rutherford Backscattering Spectrometry. The x-ray spectra were acquired with a Si drift detector, which allowed to separate the components of the Lγ multiplet lines. The measured Lα, Lβ, , L, , , and Lη x-ray production cross sections were then employed to derive Au L1, L2 and L3 subshell ionization cross sections with relative uncertainties of 8%, 7% and 7%, respectively; these figures include the uncertainties in the atomic relaxation parameters. The correction for the increase in electron path length inside the Au film was estimated by means of Monte Carlo simulations. The experimental ionization cross sections are about 10% above the state-of-the-art distorted-wave calculations.

Electrochemical Photocurrent X-Ray Spectroscopy: A Novel Analytical Surface Technique

X-ray absorption spectroscopy (XAS) is a powerful tool for characterizing the chemical nature and environment of atoms in molecules. However, in situ techniques are limited to transmission and fluorescence techniques and are not surface sensitive. A novel in situ technique that uses synchrotron radiation to produce photoelectrons was developed to provide information on the surface and near surface regions. The results obtained from this technique, Electrochemical Photocurrent X-ray Spectroscopy (EPXS) were compared transmission and fluorescence X-ray absorption spectroscopy (XAS). Surface sensitive information was obtained by collecting X-ray induced photocurrent from a polarized electrode. An Au working electrode in 0.1 N H2SO4 was polarized to 300 mVSCE and exposed to high energy X-rays. The photocurrent response was recorded during Au L3 edge scans while X-ray fluorescence yield data was collected concurrently. The photocurrent data showed good agreement with fluorescence data and transmission data collected on Au foils (Figure 1). Investigations using electrochemical impedance spectroscopy and cyclic voltammetry we conducted to insure the photocurrent response was not due to double layer charging or solution radiolysis. Minor differences in peak characteristics were observed between photocurrent and fluorescence data. We believe this to be due to the surface sensitivity of the photocurrent technique. A comparison of the surface sensitivity of fluorescence and photocurrent techniques was accomplished by evaluating signal response to X-ray beam intensity changes. The results show that the photocurrent technique, as expected, was more surface sensitive than fluorescence. Current work is focusing on EXAFS analysis of photocurrent spectra to quantify the techniques surface sensitivity. This novel technique has the potential to provide information on electron distribution on conductive surface atoms and changes in charge of surface atoms as a function of electrochemical potential. It could significantly impact fields where measurements of surface electron distribution during electrochemical charge transfer are of primary importance, such as corrosion, catalysts and semiconductor research. Figure 1- XAS spectrum of Au foil using transmission (left) and a spectrum of Au in 0.1N H2SO4 polarized to 300 mVSCE using the photocurrent technique. Figure 1

Covellite CuS as a matrix for “invisible” gold: X-ray spectroscopic study of the chemical state of Cu and Au in synthetic minerals

Geological processes leading to formation of sulfide ores often result in precipitation of gold-bearing sulfides which can contain high concentrations of this metal in “invisible” (or “refractory”) state. Covellite (CuS) is ubiquitous mineral in many types of the ore deposits, and numerous studies of the natural ores show that covellite can contain high concentrations of Au. At the same time, Au-bearing covellite withstands cooling in contrast to other minerals of the Cu–Fe–S system (chalcocite, bornite, chalcopyrite), where Au exsolves at low temperatures. This makes covellite a convenient model system for investigation of the chemical state (local environment and valence) of the “invisible” Au in copper-sulfide ores (copper-porphyry, epithermal, volcanogenic massive sulfide, SEDEX deposits). Therefore, it is necessary to determine the location of Au in the covellite matrix as it will have important implications for the methods employed by mineral processing industry to extract Au from sulfide ores. Here we investigate the chemical state of Cu and Au in synthetic covellite containing up to 0.3wt.% of Au in the “invisible” state. The covellite crystals were synthesized by hydrothermal and salt flux methods. Formation of the chemically bound Au is indicated by strong dependence of the concentration of Au in covellite on the sulfur fugacity in the experimental system (d(log C(Au))/d(log f(S2))∼0.65). The Au concentration of covellite grows with increasing temperature from 400 to 450°C, whereas further temperature increase to 500°C has only minor effect. The synthesized minerals were studied using X-ray absorption fine structure spectroscopy (XAFS) in high energy resolution fluorescence detection (HERFD) mode. Ab initio simulations of Cu K edge XANES spectra show that the Cu oxidation state in two structural positions in covellite (tetrahedral and triangular coordination with S atoms) is identical: the total loss of electronic charge for the 3d shell is ∼0.3 for both positions of Cu. This result is confirmed by theoretical analysis of electron density performed using quantum theory of atoms in molecules (QTAIM). Modeling of the Au L3 edge EXAFS/XANES spectra showed that Au in covellite exists in the form of the isomorphous solid solution formed by substitution for Cu atoms in triangular coordination with the Me–S distance in the first coordination shell increased by 0.18Å relative to the pure CuS structure. The “formal” oxidation state of Au in covellite is +1. The Bader partial atomic charge for Au in covellite is lower than the charge of Cu (+0.2e vs. +0.5e) indicating that the degree of covalency for the Au-bearing covellite is higher than that of pure CuS. The analysis of electronic density of states shows that this structural position of Au results in strong interactions between hybridized Au s,p,d, S p, and Cu p,d orbitals. Such chemical bonding of Au to S and Cu can result in the formation of Au-bearing solid solution with other minerals in the Cu–Fe–S system.

Double Jahn-Teller Distortion in AuGe Complexes Leading to a Dual Blue-Orange Emission.

The tetrahedral AuI complexes [Au(GeCl3 )L3 ] (L=PMe3 (1), PMe2 Ph (2), PMePh2 (3), PPh3 (4)) were synthesized by in situ treatment of the [Au(GeCl3 )(tht)] complex with three equivalents of the corresponding tertiary phosphine. The crystal structures of complexes 1 and 3 have been determined through X-ray diffraction studies and show [GeCl3 ]- fragments bonded to the corresponding [Au(PR3 )3 ]+ units through covalent bonds, leading to a tetrahedral coordination environment for gold. Complexes 3 and 4 show dual phosphorescence in the solid state at 77 K and, in the case of complex 4, an interesting room-temperature mechanochromism effect is observed. Correlated MP2, SCS-MP2, SCS-CC2, and ONIOM MP2/UFF calculations suggest the existence of two largely distorted and thermally connected triplet excited states (T1 and T2 ) for a model system of complex 4. The AuP3 + moiety can be distorted in two different planes leading to the two triplet excited states T1 and T2 , leaving the GeCl3 - unit almost unaltered. The emissions of these phosphorescent AuI GeII complexes is mainly ascribed to a metal (gold)-centered (3 MC) transition with some contribution from the [GeCl3 ]- fragments.

Induced Spin Polarization in the Au Layers of Fe/Au Multilayer in an Antiparallel Alignment State of Fe Magnetizations by Resonant X-ray Magnetic Scattering at the Au L3Absorption Edge

A double periodic Fe1/Au/Fe2/Au multilayer with different Fe thicknesses was epitaxially grown on the MgO(001) substrate to investigate the magnetic structure of the Au spin polarization in an antiparallel alignment state of the Fe magnetizations. The establishment of the antiparallel alignment state at zero applied field was confirmed from the comparison of the magnetization curve measurement and simulation in the applied field along the [110] direction of the MgO substrate. Existence of the Au spin polarization orthogonal to the applied magnetic field was confirmed with resonant X-ray magnetic scattering (RXMS) measurements near the Au L3 absorption edge. Analysis of the RXMS pattern indicated that the magnetic depth profile of the spin polarization in the interior region of the Au layer was approximated to a square-wave shape, which suggests a ferromagnetic nature of the Au spin polarization sandwiched by the Fe layers.

Structure and nonlinear optical studies of Au nanoparticles embedded in lead lanthanum borate glass

Metal nanoparticles of gold in various proportions were prepared by melt-quenching technique without any assistance of reducing agent. X-ray absorption near edge structure analysis shows that measurements at the Au L3 edge were made on lanthanum lead borate doped with gold. X-ray absorption near edge structure shows that the oxidation state of Au and the analysis show the presence of gold nanoparticles. Electron microscopy and energy dispersive absorption X-ray spectroscopy confirm the size of Au nanoparticle inside the lead lanthanum borate glass. Nonlinear optical studies of Au doped oxide glass are performed using nanosecond laser pulse excitation. Z-scan experiments with 532nm wave-length pulses are used to excite glass samples which show that optical limiting effect of these as-prepared glasses doped with Au nanoparticle was also studied.

Charge and Induced Magnetic Structures of Au Layers in Fe/Au Bilayer and Fe/Au/Fe Trilayer Films by Resonant X-ray Magnetic Reflectivity at the Au L3Absorption Edge

It is known that spin polarization induced in the Au layers of Fe/Au multilayers which show interlayer exchange coupling consists of an interface-concentrated component and a uniformly extended interior component. To investigate the origin of the interior component, magnetic depth profiles of spin polarization induced in the Au layers of Fe (15 A)/Au (50 A) bilayer and Fe (15 A)/Au (50 A)/Fe (15 A) trilayer films were investigated with resonant X-ray magnetic reflectivity (RXMR) measurements at the Au L3 absorption edge. After the determination of charge structures, the spin attenuation length for the interior component of the bilayer sample was evaluated to be longer than 15 A from the analysis of the RXMR pattern. The RXMR pattern of the trilayer sample was not sufficiently reproduced if the magnetic structure of the trilayer sample was assumed to be a simple sum of the magnetic structure obtained from the bilayer sample. Results were discussed based on the quantum well model.

Revealing the Details of the Surface Composition of Electrochemically Prepared Au@Pd Core@Shell Nanoparticles with in Situ EXAFS

Carbon supported Au@Pd core@shell nanoparticles were prepared using two methods based on displacement of a Cu-under potential deposited (upd) layer; the standard method, in which a single Cu-upd layer is formed and then displaced, and a Cu-upd-mediated deposition method, wherein the Pd displaces the Cu-upd layer during the Cu deposition. The resulting materials were characterized using in situ extended X-ray absorption fine structure as a function of the applied potential in an electrochemical cell at both the Au L3 and Pd K absorption edges. This detailed structural analysis shows that the standard, single Cu-upd layer method results in the formation of Pd clusters or islands on the Au core rather than a complete monolayer shell, while the Cu-upd-mediated method produces a mixed/alloyed PdAu shell.

Features of the microstructure of gold nanoparticles inside cavities of cucurbit[7]uril according to XAFS spectra

The Au L3 X-ray absorption fine structure (XAFS) spectra have been measured for gold nanoparticles with the calibrated size dAu ∼ 1 nm in the cavities of cucurbit[7]uril molecules. The features of their electronic structure and microstructure have been characterized. It has been found that gold clusters in cavities of cucurbit[7]uril are characterized by smaller (by 0.01–0.02 A) interatomic distances and a noticeably larger (by a factor of 3 at 12 K) Debye-Waller factor as compared to bulk gold. Analysis of the experimental results and their comparison with the model calculations show that the special properties of atoms on the surface of small metal (gold) particles are not determined by their position at the vertices and edges of small clusters; they are likely attributed to the structural disorder, deformations, and stresses, which increase with a decrease in the size of the particles.

Depth Profile of Induced Magnetic Polarization in Au Layers of Fe/Au(001) Metallic Superlattice by Resonant X-ray Magnetic Scattering at High Angle Region

Spin polarization of 5d conduction electrons induced in the Au layers of antiferromagnetically coupled Fe/Au metallic superlattice was investigated by resonant X-ray magnetic diffraction at the Au L3 absorption edge. Superlattice reflections around the Au 002 Bragg peak were measured in the magnetic saturation state with circularly polarized synchrotron radiation X-rays of 11921 eV. The magnetic diffraction profile was extracted with the combination of helicity switching and reversing the direction of magnetic field applied along the line of intersection between the film surface and the scattering plane. The depth distribution of resonant magnetic scattering length in the Au layers was estimated from the magnetic diffraction profile. Both resonant magnetic diffraction from the Au layer and non-resonant magnetic diffraction from the Fe layer were considered in the analysis. We demonstrated that the depth distribution of the Au magnetic scattering length was expressed with sum of the interface-concentrated ...

The structure of AuPd nanoalloys anchored on spherical polyelectrolyte brushes determined by X-ray absorption spectroscopy

Well-defined and facetted bimetallic gold-palladium nanoalloys have been synthesized and anchored in spherical polyelectrolyte brushes (SPB) as composite particles (AuPd@SPB). These particles are better catalysts in aqueous phase than the pure metals. The atomistic arrangement of these nanoalloys has been analysed by extended X-ray absorption fine structure (EXAFS) spectroscopy at the Au-L3 and the Pd-K absorption edge. The samples with high amounts of gold appear as almost statistically mixed random alloys. Alloy compositions with less gold show slight enrichment of Pd at the surface of the particle. In addition, signals of non-metallic palladium appear at the Pd-K edge which indicate the presence of the Pd2+ species in addition to metallic palladium. The relation of these structural features to the catalytic activity is discussed.

Electroless nanoworm Au films on columnar porous silicon layers

A characterization study of nanoworm Au thin films fabricated onto Si (100) using an intermediate columnar porous silicon (PSi) layer is presented. The Au thin films are resistant to peeling in different buffers and solvents. Adhesion arises from the presence of a diffused Au nucleation layer in the channeled PSi, which can be observed even at short electroless Au deposition times. For longer deposition times, a gold surface film grows from piled and aggregated Au crystals, providing high surface area. X-ray absorption spectroscopy studies revealed differences in the Au L3 absorption edge that can be ascribed to the induced nanoworm structure. The optical behavior of the Au grown on the surface has also been studied by light reflectance spectroscopy and related to the characteristic Au intra-band absorption. Such surfaces could enhance the performance of electric or optical devices with sensitivity limited by surface area availability.