Silver-Platinum nanoparticles and nanodroplets supported on silica surfaces: structure and chemical ordering

Stable and metastable metallic nanoparticles exhibit unique properties compared to the bulk, with potentially important applications for catalysis. This is in particular the case for the AgPt alloy that can exhibit the ordered L1$_1$ structure (alternation of pure Ag and Pt (111) planes) in nanometer size particles. However, for such small systems, the interfaces play an important role. Therefore, the support used to elaborate the nanoparticles in ultrahigh vacuum experiments may influence their properties, even in the case of weakly interacting substrates like amorphous carbon or silica. This work focuses on the AgPt nanoparticles deposited on silica, and investigates the effect of the support disorder and roughness on the structure and chemical ordering, in particular at the interface with the substrate, by Monte Carlo calculations of the atomic density profiles with semi-empiric potentials

Tuning growth from clusters to continuous ultrathin films: Experiments and molecular dynamics simulations of Pd plasma sputter deposition

Plasma sputter deposition experiments and simple molecular dynamics calculations are performed for highlighting the effects of plasma ions and kinetic energy of palladium atoms on the morphology of thin films. A transition between cluster and continuous film growth is observed. It is attributed to the kinetic energy of the depositing sputtered palladium atoms and to high binding energy trapping sites resulting from the effects of ions incident on the surface during deposition. These high binding energy trapping sites act as additional nucleation centres that are allowed to be visited by the diffusing Pd atoms

XMCD studies of Co and Co Pt nanoparticles prepared by vapour deposition

International audienc

Caractérisation structurale et contraintes résiduelles de films d'AIN par diffraction des rayons X

L'état mécanique des couches minces influence considérablement leurs propriétés macroscopiques et notamment leur comportement tribologique. Ainsi, outre les caractéristiques structurales, la détermination des microdéformations et des contraintes résiduelles apparaît comme essentielle. Cette étude porte donc sur la caractérisation par diffraction des rayons X de l'état microstructural et mécanique de couches de nitrure d'aluminium élaborées par deux types de procédé : la nitruration d'aluminium par plasma induit par laser et le dépôt par pulvérisation cathodique. Les résultats montrent l'absence d'orientation préférentielle et de contraintes résiduelles dans les couches d'AIN laser-plasma, alors que les dépôts présentent une direction de croissance privilégiée et de fortes contraintes d'origine thermique.The mechanical state in thin films considerably influences their macroscopic properties, especially their tribological behaviour. It is the reason why microstrains and residual stresses determination is very important. This paper deals with the characterization by X-ray diffraction of the microstructural and mechanical state of aluminum nitride layers elaborated by two kinds of processing : laser induced plasma aluminum nitriding and magnetron sputtering deposition. Results show no preferential orientation and residual stresses in laser-plasma AIN films while deposits offer preferential growth direction and high stresses from thermal ones

Real-time icosahedral to fcc structure transition during CoPt nanoparticle formation.

Nucleation and growth of supported CoPt nanoparticles were studied in situ and in real time by combined grazing incidence small-angle x-ray scattering (GISAXS) and grazing incidence x-ray diffraction (GIXD). GISAXS provides morphological features of nanoparticles as a function of size, shape and correlation distance between particles, while GIXD allows the determination of the atomic structure. We focus on the formation of ultrasmall CoPt nanoparticles, in the 1–4 nm size range at 500○C. The structural analysis method based on the Debye equation is coupled with cluster model calculations performed by Monte Carlo simulations using a semi-empirical tight-binding potential to interpret diffraction spectra and structural transitions. Our results show that the cluster structure evolution during the growth is size-dependent and composition-dependent, yielding an icosahedral to fcc structure transition

Trends in anomalous small-angle X-ray scattering in grazing incidence for supported nanoalloyed and core-shell metallic nanoparticles

As atomic structure and morphology of particles are directly correlated to their functional properties, experimental methods probing local and average features of particles at the nanoscale elicit a growing interest. Anomalous small-angle X-ray scattering (ASAXS) is a very attractive technique to investigate the size, shape and spatial distribution of nanoobjects embedded in a homogeneous matrix or in porous media. The anomalous variation of the scattering factor close to an absorption edge enables element specific investigations. In the case of supported nano-objects, the use of grazing incidence is necessary to limit the probed depth. The combination of grazing incidence with the anomalous technique provides a powerful new method, anomalous grazing incidence small-angle X-ray scattering (AGISAXS), to disentangle complex chemical patterns in supported multi-component nano-structures. Nevertheless, a proper data analysis requires accurate quantitative measurements associated to an adapted theoretical framework. This paper presents anomalous methods applied to nanoalloys phase separation in the 1–10 nm size range, and focuses on the application of AGISAXS in bimetallic systems: nanocomposite films and core-shell supported nanoparticles

Reversed size-dependent stabilization of ordered nanophases

Increasing nanoparticle size usually increases the stability of ordered phases within them. In contrast, the authors show here that the L11 ordered phase only forms in AgPt nanoparticles smaller than 2.5 nm because the segregation of a monolayer Ag shell constrains the nanophase which becomes unstable at larger sizes

Controlling Structure and Morphology of CoPt Nanoparticles through Dynamical or Static Coalescence Effects

International audienc