Concentration Of Au Atoms Research Articles

Synthesis, characterization and application of plasmonic hollow gold nanoshells in a photothermal therapy—New particles for theranostics

This article describes the work on synthesis, surface functionalization and characterization of hollow gold nanoshells (HGNs), and their application in a photothermal tumor therapy. The studied gold nanoshells were synthesized using a method based on a reduction of HAuCl4 onto silver nanoparticle templates. A selected aptamer - AS1411 – selective towards nucleolin, with a terminal thiol group was conjugated to HGNs. Surface functionalization of synthesized nanoparticles was necessary to gain the affinity to tumor cells, thus allowing the selective delivery of the modified nanoparticles to target cells. As expected, an increased selectivity of nanoconjugates towards tumor cells (A375) in a comparison to normal ones (HaCaT) was observed (2.67 times). In the framework of our studies the biological activity of the obtained nanoconjugates was evaluated using MTT assay. For this aim, both normal and tumor cell cultures respresenting skin tissue were exposed to gold nanoparticles solutions. It was found, that HGN-AS1411 conjugates cause less than 10% loss in a cell viability in the case of both cell lines at the highest tested concentration. The potential of the developed nanoconjugates as agents in PTT of skin cancer was investigated in a subsequent stage of our research. It was found, that A375 cell viability amounted to less than 40% for 75μM of nanoconjugates (expressed as a concentration of Au atoms) as a result of the laser irradiation of this cell culture after desired accumulation of the tested nanoconjugates inside A375 cells.

First-principles study of Au-decorated carbon nanotubes

The electronic structures and spin-orbit (SO) coupling of carbon nanotubes with adsorbed Au atoms are investigated based on density functional theory. Three kinds of zigzag single-walled CNT (8,0), (10,0) and (12,0) are selected. The Au atoms prefer to adsorb on the top of C atoms. The adsorption of Au atoms can introduce impurity states in the band gap, modifying the electronic properties of systems. Furthermore, the influence of SO coupling on these impurity states is also explored. Considerable SO splitting (∼130 meV) can be obtained. We find that the SO splitting decreases with the increase of the concentration of Au atoms, which can be ascribed to the interaction between Au atoms, suppressing the SO splitting. Our work provides imperative understanding on the electronic properties and SO coupling effect in Au-decorated CNTs.

Surface Modification on Pd Nanostructures for Selective Styrene Oxidation with Molecular Oxygen

AbstractThe catalytic oxidation based on molecular oxygen (O2) is one of the most preferable choices for oxidation reactions toward atom‐efficient utilization of oxidants, in which heterogeneous catalysts based on palladium (Pd) nanostructures have been commonly used. However, in terms of selective styrene oxidation, it is still a great challenge to balance reactivity and selectivity by employing pure Pd catalysts. Herein, a well‐designed model for seeking a selective oxidation catalyst based on surface lattice engineering is described. In the proposed model, Au atoms are sparsely deposited on the surface of concave Pd nanostructures. As such, the activation degree of adsorbed O2 can be altered by simply tailoring the concentration of Au atoms on surface, suppressing the formation of over‐oxidized byproducts. Moreover, the Pd@Au nanostructures reported here have sufficient plasmonic cross‐sections for light harvesting, which enables light‐driven catalysis through a photothermal effect. Taken together, the Pd@Au0.08 concave nanostructures with an Au/Pd ratio of 8% achieve 87% main product selectivity with a conversion of 44% in the aerobic oxidation of styrene using molecular O2 (1 atm) without additional initiator.

Surface segregation of AuCu3 by He+ and Au+ irradiation

Surface segregation is a significant phenomenon due to its influence on many surface processes, such as corrosion, oxidation and catalysis. Defects and vacancies produced by ion irradiation in alloys used in reactors or other radiation environments may also induce surface segregation. In this work, we deposit AuCu3 film on a Si(111) substrate by magnetic sputtering. He+ and Au+ produced by pelletron are used to simulate radiation fields in reactors, and surface segregation induced by ion irradiation is investigated. SRIM software is used to simulate ion range and displacements produced in sample. Rutherford backscattering spectrometry is used to determine concentration changes near the surface of sample before and after irradiation. The results show that two kinds of ion irradiations lead to different surface segregation trends. When irradiated by 2 MeV He+, Au elements are segregated at the surface of sample. Oppositely, when irradiated by 1 MeV Au+, Cu elements are observed at the surface of sample. After analysis and discussion, we consider that this phenomenon is induced by different vacancy distributions by He+ and Au+ irradiation. 2 MeV He+ produced Au and Cu vacancies are distributed in whole film from surface to substrate smoothly, except very near the surface the concentration of vacancies has an obvious reduction. As a result, a gradient of the vacancy concentration is formed between the surface and the interior of the film. As the concentration of vacancies on the surface is lower than in interior, it would lead to vacancy diffusion from interior to surface, equivalent to diffusions of Cu and Au atoms along the opposite directions. Because of lighter atomic mass, Cu atom has a faster diffusion rate than Au atom. As a result, the concentration of Au atoms near the surface increases. Unlike He+, Au+ produces a mass of vacancies near the surface of the film, consistent with the Bragg peak by energy deposition of Au+, but decreases rapidly inside the film. It leads to a gradient of the vacancy concentration from surface to interior of the film. When vacancies diffuse from surface to interior, Cu and Au atoms diffuse from interior to surface, the lighter Cu atom concentration increases faster than Au atom concentration. Our research results explain the different segregation trends by light ion with higher energy and heavy ion with lower energy. It may help to understand the surface segregation of alloys used in complex irradiation field.

Au 4f spin-orbit coupling effects in supported gold nanoparticles.

Using X-ray photoelectron spectroscopy we examine the Au 4f spin-orbit components in Au 4f spectra of nanosized Au particles on a TiO2 support. In general, the peak ratios of the Au 4f7/2 and 4f5/2 excitations are found to deviate from the statistical ratio of 4 : 3 and their linewidths (FWHM) are not equal. We reveal that both the FWHM and the Au 4f7/2-to-4f5/2 peak ratios increase appreciably as the Au atomic concentration on the surface of the TiO2 support and the size of Au nanoparticles decrease. On the contrary, the Au 4f spin-orbit splitting remains essentially unchanged. Our findings are discussed in terms of alterations in the electronic band structure.

Point Defect Configurations of Supersaturated Au Atoms Inside Si Nanowires

Aberration-corrected scanning transmission electron microscopy (STEM) is used to reveal individual Au atom configurations inside Si nanowires grown by Au-catalyzed vapor-liquid-solid (VLS) molecular beam epitaxy (MBE). We identify a substitutional and three distinct interstitial configurations, one of which has not been previously identified. We confirm the stability of the observed point defect configurations by density functional theory (DFT) calculations. The observed number densities of the various configurations are in accord with their calculated formation energies. The concentration of Au atoms is larger than the solubility limit, but the effect may be caused by the STEM beam.

Compositional changes in the surface layers of the Cu 3Au(1 0 0) below the bulk transition temperature

The surface compositional changes in the surface layers of Cu 3Au(1 0 0) have been studied by medium-energy ion-scattering spectroscopy (MEIS). Using 100 keV N + ions in a MEIS experiment, single atomic layer depth resolution was obtained. At a temperature starting at about 500 K, the Au atoms in the surface layer of Cu 3Au(1 0 0) apparently began to move to the second layer with increasing temperature. The atomic concentration of Au in the first layer as measured by MEIS then decreased from 50% at room temperature (RT) to 32% at 720 K. This decrease in the atomic concentration of Au atoms in the first layer was continuous, rather than abrupt at the critical temperature. Moreover, it was found that the compositional change between the first and the second layers was reversible at temperatures up to 720 K. The atomic concentration of Au atoms in the third layer remained constant over the temperature range from RT to 720 K. The difference between this result, where the first layer Au concentration decreases, and the previous low-energy ion-scattering spectroscopy (LEIS) measurements which show a relatively constant Au concentration, lies in the production of surface vacancies and adatoms at elevated temperatures. These defects have no significant effect on yield in LEIS experiments but are seen using MEIS.

Concentration-Dependent Surface-State Shifts: Au on Cu(001)

AbstractHigh-resolution angle-resolved photoemission has been used to investigate the behavior of the Cu(001) surface state as a function of Au coverage and substrate temperature. Binding-energy shifts of this state are dependent on the concentration of Au atoms substituted into the top surface layer of the Cu(001) substrate. The results demonstrate the use of surfacelocalized Tamm states as a specific probe of the chemical environment in the surface plane.