Geoffroy Prévot

Ostwald-Driven Phase Separation in Bimetallic Nanoparticle Assemblies

The compositional stability of bimetallic nanoparticles (NPs) is crucial for many applications. We have studied the coarsening of amorphous carbon-supported Au-Pd NPs during annealing at 873 K. Using scanning transmission electron microscopy and energy-dispersive spectroscopy measurements, we show that, despite a complete miscibility of the two metals, the particle assembly undergoes a phase separation during annealing, which leads to two distinct populations: Au-rich NPs with a mean radius of 3.5 nm and large Pd-rich NPs with a mean radius of 25 nm. Thermodynamic calculations and kinetic Monte Carlo simulations explain this behavior that is driven by the competition between surface and mixing energy and by the different mobilities of the two atomic species.

Si Nanoribbons on Ag(110) Studied by Grazing-Incidence X-Ray Diffraction, Scanning Tunneling Microscopy, and Density-Functional Theory: Evidence of a Pentamer Chain Structure

We report a combined grazing incidence x-ray diffraction (GIXD), scanning tunneling microscopy (STM), and density-functional theory (DFT) study which clearly elucidates the atomic structure of the Si nanoribbons grown on the missing-row reconstructed Ag(110) surface. Our study allows us to discriminate between the theoretical models published in the literature, including the most stable atomic configurations and those based on a missing-row reconstructed Ag(110) surface. GIXD measurements unambiguously validate the pentamer model grown on the reconstructed surface, obtained from DFT. This pentamer atomistic model accurately matches the high-resolution STM images of the Si nanoribbons adsorbed on Ag(110). Our study closes the long-debated atomic structure of the Si nanoribbons grown on Ag(110) and definitively excludes a honeycomb structure similar to that of freestanding silicene.

Resolving the Controversial Existence of Silicene and Germanene Nanosheets Grown on Graphite

The highly oriented pyrolytic graphite (HOPG) surface, consisting of a dangling bond-free lattice, is regarded as a potential substrate for van der Waals heteroepitaxy of two-dimensional layered materials. In this work, the growth of silicon and germanium on HOPG is investigated with scanning tunneling microscopy by using typical synthesis conditions for silicene and germanene on metal surfaces. At low coverages, the deposition of Si and Ge gives rise to tiny and sparse clusters that are surrounded by a honeycomb superstructure. From the detailed analysis of the superstructure, its comparison with the one encountered on the bare and clean HOPG surface, and simulations of the electron density, we conclude that the superstructure is caused by charge density modulations in the HOPG surface. At high coverages, we find the formation of clusters, assembled in filamentary patterns, which indicates a Volmer-Weber growth mode instead of a layer-by-layer growth mode. This coverage-dependent study sets the stage for revisiting recent results alleging the synthesis of silicene and germanene on the HOPG surface.

Transition from silicene monolayer to thin Si films on Ag(111): comparison between experimental data and Monte Carlo simulation

Scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low energy electron diffraction have been used to follow the growth of Si films on Ag(111) at various temperatures. Using a simple growth model, we have simulated the distribution of film thickness as a function of coverage during evaporation, for the different temperatures. In the temperature regime where multilayer silicene has been claimed to form (470–500 K), a good agreement is found with AES intensity variations and STM measurements within a Ag surfactant mediated growth, whereas a model with multilayer silicene growth fails to reproduce the AES measurements.

Publisher’s Note: Si Nanoribbons on Ag(110) Studied by Grazing-Incidence X-Ray Diffraction, Scanning Tunneling Microscopy, and Density-Functional Theory: Evidence of a Pentamer Chain Structure [Phys. Rev. Lett. 117 , 276102 (2016)]

This corrects the article DOI: 10.1103/PhysRevLett.117.276102.