Gold decoration of silica by decomposition of aqueous gold(iii) hydroxide at low temperatures.

The decomposition of gold hydroxide to give metallic gold is known to take place around 300 °C in dry environments. However, little information about the gold hydroxide stability in wet environments has been recorded. Here, we present experimental evidence which shows that aqueous/water-enriched gold(iii) hydroxide colloids decompose spontaneously to form gold nanoparticles at temperature values above the freezing point of water. Based on this reaction, we developed a method to decorate silica spheres with gold nanoparticles by precipitation and decomposition of gold(iii) hydroxide onto the silica surface in wet media by a simple one-pot/one-step protocol. The silica|gold nanostructures are prepared in high yield and with a low level of by-products.

Gold-palladium core@shell nanoalloys: experiments and simulations.

In this work, we report a facile synthesis route, structural characterization, and full atomistic simulations of gold-palladium nanoalloys. Through aberration corrected-STEM, UV-vis spectroscopy and EDS chemical analysis, we were able to determine that Au(core)-Pd(shell) bimetallic nanoparticles were formed. Using different computational approaches, we were capable of establishing how the size of the core and the thickness of the shell will affect the thermodynamic stability of several core-shell nanoalloys. Finally, grand canonical simulations using different sampling procedures were used to study the growth mechanism of Pd atoms on Au seeds of different shapes.

Nanodomain induced anomalous magnetic and electronic transport properties of LaBaCo2O5.5+δ highly epitaxial thin films.

A giant magnetoresistance effect (∼46% at 20 K under 7 T) and anomalous magnetic properties were found in a highly epitaxial double perovskite LaBaCo2O5.5+δ (LBCO) thin film on (001) MgO. Aberration-corrected Electron Microscopy and related analytical techniques were employed to understand the nature of these unusual physical properties. The as-grown film is epitaxial with the c-axis of the LBCO structure lying in the film plane and with an interface relationship given by (100)LBCO || (001)MgO and [001]LBCO || [100]MgO or [010]MgO. Orderly oxygen vacancies were observed by line profile electron energy loss spectroscopy and by atomic resolution imaging. Especially, oxygen vacancy and nanodomain structures were found to have a crucial effect on the electronic transport and magnetic properties.

On the atomic structure of thiol-protected gold nanoparticles: a combined experimental and theoretical study.

In the present work new findings on the structure of the S-Au interface are presented. Theoretical calculations using a new semiempirical potential, based on density functional theory and a bond-order Morse potential, are employed to simulate the adsorption process in a more realistic way. The simulation results reveal the formation of gold adatoms on the nanoparticle surface and high surface disorder due to the strong S-Au bond. Experimental data were acquired by aberration (Cs) corrected scanning transmission electron microscopy (STEM) using a high angle annular dark field detector (HAADF) that showed a great similarity with the theory predicted.

Moiré patterns in high resolution electron microscopy images of MoS2.

The contrast observed in the (0001) HREM images of MoS2 are interpreted with a model based on rotational moiré patterns. Computer-simulated images show that rotations of two supercells by angles of 3, 5, 8, and 16 degrees around their centers reproduce the contrast observed in the experimental images. The calculations suggest that these rotations occur between the sulphur layers of the MoS2 structure.