Characterization of nano‐organized multilayers constituted by successive inorganic (gold) and organic (alkylthiols) layers

Nanostructured multilayers constituted by alternate metallic (gold) and organic (alkyldithiol) layers, and grafted onto glass or silicon substrates are prepared and analysed. Such complex layers could be of interest as a new type of surfaces but also as localized dissipative zones particularly in the field of adhesion science. The formation and the structure of these model systems are examined using a number of techniques such as atomic force microscopy (AFM), wetting analysis (contact angles), X‐ray photoelectron spectroscopy (XPS) and conductivity measurements. It is shown that, in terms of electrical conductivity, gold layers exhibit a percolation transition from an insulating granular structure to a conductive worm‐like structure at a threshold thickness of about 5 nm. XPS (and wettability) analyses clearly indicate that the fractional coverage of the gold surface is about 30% with alkyldithiol and that these molecules are either grafted in a stand‐up position or in the form of a loop. Moreover, a partial electrical connection between two successive gold layers is observed, confirming that the confined organic layer of alkyldithiol between them is too loosely organized to play the role of an insulating barrier. Copyright © 2007 John Wiley & Sons, Ltd.     

Etude en RMN du carbone 13 de dicoumarols substitués

The ¹³C n.m.r. spectrum of the bridge substituted dicoumarols are interpreted in order to obtain structural information for quantitative structure-activity relationships. The results are in agreement with those obtained by ¹H n.m.r. These dicoumarols exhibit double restricted rotation around both bridge bonds.     

The diameter of domination k-critical graphs

A graph is k-domination-critical if γ(G) = k, and for any edge e not in G, γ(G + e) = k ? 1. In this paper we show that the diameter of a domination k-critical graph with k ≧ 2 is at most 2k ? 2. We also show that for every k ≧ 2, there is a k-domination-critical graph having diameter [(3/2)k ? 1]. We also show that the diameter of a 4-domination-critical graph is at most 5.     

Electrochromism in WO3 thin films. I. LiClO4-propylene carbonate-water electrolytes

The performances of electrochromic cells containing evaporated amorphous WO₃ thin films as electrochromic material in 1M LiClO₄-propylene carbonate-water electrolytes are presented. Much attention has been paid to some parameters such as the thickness of the layer, the overpotential applied to WO₃ electrode during the electrochemical coloration and the amount of water contained in the electrolyte (from 50 ppm to 10% in weight). Simultaneous electrical and optical in situ measurements have been carried out to study electrochromism. The optical data were stored into a microprocessor and restituted after treatment. The method used here gave us the possibility to rapidly test electrochromic materials.     

A novel femtosecond-laser formation of CdS nanocrystallites in zirconia matrices

A novel method for direct laser writing of two-dimensional cadmium sulfide (CdS) semiconductor nanoparticle microstructures is reported. A two photon or a higher-order multiphoton absorption process, originating from femtosecond laser pulses, was used to decompose CdS precursors dispersed in a zirconia thin film previously dip-coated on a glass substrate. The kinetics of nanoparticle formation as a function of laser power were monitored in situ by photoluminescence spectroscopy. Raman spectroscopy was also performed to characterize the structural changes of the zirconia matrix under irradiation and to verify the formation of CdS nanoparticles. Results show that CdS nanoparticles were formed by two-photon absorption (TPA) with or without the help of an additional carbazole photoinitiator.     

Structure and growth kinetics of the oxidation process of Fe(001) whisker surfaces over a 10-decade pressure range

Fe(001) surfaces of whiskers of good crystalline quality were oxidized in a pressure range from 10^? 7 mbar to 1 bar at different temperatures. Epitaxial Fe₃O₄ and FeO thin films with negligible strain were grown depending on the oxidation temperatures. The kinetics of the oxide thickness growth was measured and compared with the predictions of the Fromhold–Cook theory for oxidation of metals. Some discrepancies were found and a possible explanation is presented.     

Regular path decompositions of odd regular graphs

Kotzig asked in 1979 what are necessary and sufficient conditions for a d‐regular simple graph to admit a decomposition into paths of length d for odd d>3. For cubic graphs, the existence of a 1‐factor is both necessary and sufficient. Even more, each 1‐factor is extendable to a decomposition of the graph into paths of length 3 where the middle edges of the paths coincide with the 1‐factor. We conjecture that existence of a 1‐factor is indeed a sufficient condition for Kotzig's problem. For general odd regular graphs, most 1‐factors appear to be extendable and we show that for the family of simple 5‐regular graphs with no cycles of length 4, all 1‐factors are extendable. However, for d>3 we found infinite families of d‐regular simple graphs with non‐extendable 1‐factors. Few authors have studied the decompositions of general regular graphs. We present examples and open problems; in particular, we conjecture that in planar 5‐regular graphs all 1‐factors are extendable. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 114–128, 2010     

The feasibility of Al-based oxide precipitation in Fe–10%Cr alloy by ion implantation

This paper reports the feasibility of nano-oxide precipitate formation in Fe–Cr alloy by ion implantation synthesis. High contents of Al⁺ and O⁺ ions were implanted into thin films of high purity Fe–10%Cr alloy at room temperature and were studied by transmission electron microscopy (TEM) and atom probe tomography (APT). In contrast, to the common two-stage implantation/annealing scheme of precipitate ensemble synthesis by ion beams, cluster formation took place at the implantation stage in our study, requiring no subsequent high-temperature annealing. The post-implantation microstructural examination revealed in the as-implanted thin foil an array of precipitates with diameters in the range of 3–30?nm. The precipitate number density distribution was found to depend on the foil thickness. The precipitate enrichment with both Al and O was confirmed by the energy-filtered TEM analysis. Judging from the electron diffraction pattern and high-resolution TEM analysis, the crystal lattice of precipitates corresponds to some cubic modification of aluminium-rich oxide or pure aluminium oxide. The precipitate lattice alignment with the host matrix was revealed for at least a part of precipitates. The analysis of APT data using cluster detection algorithm indicates the presence of local zones enriched in Al and O, even in those areas of as-implanted samples where no clusters were visible by TEM.