Nonlinear optical response of a gold surface in the visible range: A study by two-color sum-frequency generation spectroscopy. I. Experimental determination

International audienceWe experimentally determine the effective nonlinear second-order susceptibility of gold over the visible spectral range. To reach that goal, we probe by vibrational two-color sum-frequency generation spectroscopy the methyl stretching region of a dodecanethiol self-assembled monolayer adsorbed on a gold film. The sum-frequency generation spectra show a remarkable shape reversal when the visible probe wavelength is tuned from 435 to 705 nm. After correcting from Fresnel effects, the methyl stretching vibrations serve as an internal reference, allowing to extract the dispersion of the absolute phase and relative amplitude of the effective nonlinear optical response of gold in the visible range. Published by AIP Publishing. https://doi

Effect of Nitrogen on Properties of Na2O-CaO-SrO-ZnO-SiO2 Glasses

Glasses in the Na2O-CaO-SrO-ZnO-SiO2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the aim of increasing the mechanical properties of a series of these Zn-based GPC glasses by doping with nitrogen to give overall compositions of: 10Na2O-10CaO-20SrO-20ZnO-(40-3x)SiO2-xSi3N4 (x is the no. of moles of Si3N4). The density, glass-transition temperature, hardness, and elastic modulus of each glass were found to increase fairly linearly with nitrogen content. Indentation fracture resistance also increases with nitrogen content according to a power law relationship. These increases are consistent with the incorporation of N into the glass structure in threefold coordination with silicon resulting in extra cross-linking of the glass network. This was confirmed using 29Si MAS-NMR which showed that an increasing number of Q2 units and some Q3 units with extra bridging anions are formed as nitrogen content increases at the expense of Q1 units. A small proportion of Zn ions are found to be in tetrahedral coordination in the base oxide glass and the proportion of these increases with the presence of nitrogen

Structure-Property Correlation in Sodium Borophosphate Glasses Modified with Niobium Oxide

Bulk glasses of the series (100−x)[0.4Na2O-0.2Nb2O5-0.4P2O5]-xB2O3 with x = 0–48 mol% B2O3 were prepared by slow cooling in air. Their glass transition temperature increases within the range of 0–16 mol% B2O3, but further additions of B2O3 result in its decrease. Their structure was investigated by Raman, 11B, and 31P MAS NMR spectroscopy. The relative number of BO4 units decreases with increasing B2O3 content, while the number of BO3 units increases up to 59 % at x = 48. The upfield shift of a broad resonance peak in the 31P MAS NMR spectra is ascribed to an increasing connectedness of the structural network with increasing B2O3 content. A strong Raman band at 916–929 cm−1 shows the presence of NbO6 octahedra in the structural network of these glasses. With the B2O3 addition, a decrease in DC conductivity is observed, which is attributed to the decrease in the concentration of Na+ ions

The structure and properties of zinc aluminophosphate glasses

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Le pouvoir alimentaire mondial en question

Cyclope pocheNational audienceLe pouvoir alimentaire, qui consiste à utiliser la fourniture d'aliment pour faire pression sur un partenaire ou un adversaire, est-il en voie de disparition ? Un grand nombre de pays, souvent les plus pauvres, se trouvent en état de dépendance alimentaire vis-à-vis de quelques grandes puissances agro-alimentaires. Le nombre de mal-nourris va-t-il nettement diminuer ou seulement se stabiliser ? La dépendance alimentaire va-t-elle s'aggraver ? Quels sont les facteurs de déstabilisation de la situation alimentaire mondiale ? Les mesures spectaculaires comme embargos et boycotts font-elles partie du passé ? Quel peut être le rôle spécifique de l'Europe en matière de politique agricole et de coopération face à la stratégie récemment réaffirmée des Etats-Unis ? C'est à ces questions cruciales que l'ouvrage tente de répondre

Structure and properties of glasses in ZnO–P2O5–TeO2 system

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Glass-forming ability, structure and physical properties of ZnO–In2O3–P2O5 glasses

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