Frédéric Leroy

Transition from molecule to solid state: reactivity of supported metal clusters.

The evolution of the adsorption energy of carbon monoxide (CO) molecules on palladium (Pd) clusters as function of Pd particle size from the molecular regime (less than ~100 atoms per particle) to the bulk regime has been revealed. This adsorption energy is retrieved from the residence time of CO molecules on the Pd clusters, measured by a pulsed molecular beam technique, versus temperature. Unprecedented accuracy on the determination of the particle size has been achieved here by using a regular array of metal clusters exhibiting a size dispersion down to the ultimate limit of a Poisson distribution. This allows getting rid of the convolution effects that generally occur when considering particles grown through other techniques.

Effects of near-neighbor correlations on the diffuse scattering from a one-dimensional paracrystal

The one-dimensional paracrystal model is generalized by folding the lattice sites with objects whose scattering lengths or sizes and separation display a spatial correlation from cell to cell. A general theory to calculate the diffuse scattering and the scattering-length autocorrelation function is developed. The investigated models of coupling along the paracrystalline chain are the correlations between (i) the sizes of the scatterers, (ii) the sizes of scatterers and their separations, and (iii) the sizes of scatterers and the fluctuation of their separation distances. In the first case (i), the size of a scatterer is, on average, linked to that of its neighbors. As a result, a continuous transition from the total lack of size correlation (known as decoupling approximation or DA) to the scattering from monodisperse domains (local monodisperse approximation or LMA) is obtained. In the second case of correlation (ii), the mean interobject distance is assumed to depend on the respective sizes of nearest neighbors. Depending on the introduced correlation parameter, aggregation or hard-core-type effects can be accounted for. Surprisingly, in some cases, it is possible to find a peak in the scattering curve without any structure in the total interference function. The size-separation correlations may also dramatically reduce the scattering intensity close to the origin compared to the completely uncorrelated case. The last model (iii) foresees a coupling between the sizes of neighboring objects and the variance of the separation between neighbors. Within this model, on average along the chain, the fluctuations of distances between scatterers become dependent on the respective sizes of neighbors, while the mean distance between objects remains constant.

In-Plane Si Nanowire Growth Mechanism in Absence of External Si Flux.

We report on a new mechanism of nanowire formation: during Au deposition on Si(110) substrates, Au-Si droplets grow, move spontaneously, and fabricate a Si nanowire behind them in the absence of Si external flux. Nanowires are formed by Si dissolved from the substrate at the advancing front of the droplets and transported backward to the crystallization front. The droplet shape is determined by the Si etching anisotropy. The nanowire formation can be tuned by changing experimental parameters like substrate temperature and Au deposition rate.

Synthesis of potent and broad genotypically active NS5B HCV non-nucleoside inhibitors binding to the thumb domain allosteric site 2 of the viral polymerase.

The hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase (RdRp) plays a central role in virus replication. NS5B has no functional equivalent in mammalian cells and, as a consequence, is an attractive target for selective inhibition. This Letter describes the discovery of a new family of HCV NS5B non-nucleoside inhibitors, based on the bioisosterism between amide and phosphonamidate functions. As part of this program, SAR in this new series led to the identification of IDX17119, a potent non-nucleoside inhibitor, active on the genotypes 1b, 2a, 3a and 4a. The structure and binding domain of IDX17119 were confirmed by X-ray co-crystallization study.

Stress effects on solid-state dewetting of nano-thin films

In this paper, we present a brief survey of stress effects on dewetting. For this purpose, i) we develop a simple thermodynamic model to illustrate stress effects; ii) we study stress effects in strained–Silicon–On–Insulator (s–SOI) thin films by means of Low Energy Electron Microscopy, and Atomic Force Microscopy; iii) we discuss some available data. In particular, we show that while for s–SOI the strain only provides a relatively small contribution to the total driving force for dewetting, in some other cases stress can really dominate the driving force for the dewetting.

X-ray scattering from stepped and kinked surfaces : An approach with the paracrystal model

A general formalism of X-ray scattering from different kinds of surface morphologies is described. Based on a description of the surface morphology at the atomic scale through the use of the paracrystal model and discrete distributions of distances, the scattered intensity by non-periodic surfaces is calculated over the whole reciprocal space. In one dimension, the scattered intensity by a vicinal surface, the two-level model, the N-level model, the faceted surface and the rough surface are addressed. In two dimensions, the previous results are generalized to the kinked vicinal surface, the two-level vicinal surface and the step meandering on a vicinal surface. The concept of crystal truncation rod is generalized considering also the truncation of a terrace by a step (yielding a terrace truncation rod) and a step by a kink (yielding a step truncation rod).

Regular arrays of palladium and palladium–gold clusters supported on ultrathin alumina films: stability under oxygen

Grazing Incidence Small Angle X–ray Scattering (GISAXS) studies were conducted to determine the effect of oxygen on regular arrays of mono (Pd)– and bimetallic (Pd–Au) clusters. Unlike bimetallic Pd–Au particles, pure palladium clusters are not stable at a partial oxygen pressure of 10−6 mbar. A comparison of the experimental data with Fourier transforms of known distributions reveals that Pd clusters move and that their aspect ratio increases. These results are explained by the adsorption of oxygen that changes the equilibrium shape of the Pd particles and reduces the adhesion energy. In the case of bimetallic Pd–Au clusters, the presence of Au on the surface of the particle prevents adsorption of oxygen.

Synthesis and antiviral evaluation of 7-fluoro-7-deaza-2-aminopurine nucleoside derivatives.

Three 7-fluoro-7-deaza-2-aminopurine nucleoside derivatives were synthesized and evaluated as potential inhibitors of RNA virus replication, including hepatitis C virus (HCV).

Synthesis and antiviral evaluation of 4-fluoropyrazole-3-carboxamide nucleoside derivatives

A series of novel 4-fluoro-1H-pyrazole-3-carboxamide nucleoside analogues were synthesized and evaluated as potential inhibitors of RNA virus replication, including hepatitis C virus (HCV).

Discovery of benzophosphadiazine drug candidate IDX375: A novel hepatitis C allosteric NS5B RdRp inhibitor

Hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase (RdRp) plays a central role in virus replication. NS5B has no functional equivalent in mammalian cells, and as a consequence is an attractive target for selective inhibition. This paper describes the discovery of a novel family of HCV NS5B non-nucleoside inhibitors inspired by the bioisosterism between sulfonamide and phosphonamide. Systematic structural optimization in this new series led to the identification of IDX375, a potent non-nucleoside inhibitor that is selective for genotypes 1a and 1b. The structure and binding domain of IDX375 were confirmed by X-ray co-crystalisation study.