LEED,AES and work function measurements on clean and cesium covered polar faces of GaP

After argon bombardment and annealing both the (111) and (1̄1̄1̄) faces of GaP show a (1 × 1) LEED pattern. The stabilization of the polar termination is probably obtained by charging of surface states. Measurements of the work function, the Auger spectrum and the LEED pattern during cesium deposition at room temperature suggest disordered cesium adsorption limited to a monolayer.     

Chelate-Controlled Asymmetric Synthesis of 2-Substituted 2,3-Dihydropyridin-4(1H)-ones: Synthesis of D- and L-aminodeoxyaltrose derivatives

Asymmetric methylation and phenylation of the chiral pyridinium salt 7 , as well as methylation of chiral pyridinium salt 18 , with Grignard reagents occurred in good yield and with good-to-excellent diastereoselectivities (Schemes 2 and 3, resp.). These results are best explained by assuming chelate control to govern the asymmetric alkylation/arylation process. The minimum-energy conformations of the out-of-plane twisted pyridinium salts 7 and 18 , as determined by the ‘Molecular Simulations Cerius-Dreiding II’ program, are in good agreement with the postulated asymmetric chelate-control mechanism.     

The magnetic form factors of 15N, 17O and 39K

The elastic magnetic form factors and magnetic moments of light nuclei with simple closed-shell ±1 configurations are investigated. Core-polarization and meson-exchange current corrections are treated consistently to second order in perturbation theory. The effect of the Δ-isobar currents is small compared with the quenching by “tensor correlations”, i.e. the admixture of multi-?ω configurations into the ground-state wave function. Pionic exchange currents are found to enhance the form factors and provide a partial cancellation of the large second-order effects. We find good agreement with experiment for ¹⁵N and ³⁹K, but more modest results for ¹⁷O near 0.9 fm^?.     

Orienting the Demixion of a Diblock‐copolymer Using 193 nm Interferometric Lithography for the Controlled Deposition of Nanoparticles

DUV interferometric lithography and diblock copolymer self‐organization have successfully been combined to provide a simple and highly collective nanopatterning technique enabling the organization of nanoparticles over several orders of magnitude, from nanometre to millimetre. The nanostructural changes at the surface of the polymer film after thermal annealing have been monitored by AFM and the process parameters optimized for obtaining a long‐range organization of the lamellar domains. In particular, the impact of the annealing conditions and geometric parameters of the substrate patterns have been investigated. The nanopatterns resulting from the lamellar demixion of (PS‐b‐MMA) were used for a controlled deposition of nanoparticles. The affinity of the hydrophobic particles for the PS block was demonstrated, opening new doors towards the preparation of high‐density arrays of nanoparticles with potential applications in data storage.

     

Un problème d'optimisation de forme pour la contrôlabilité exacte de l'équation des ondes 2D

We consider the wave equation defined on $\Omega ?{\mathbb{R}}^2$ and $\omega ?\Omega$. We designate by $v_{\omega }$ the distributed control of minimal $L^2(\omega \times (0,T))$ norm obtained with the Hilbert Uniqueness Method which stabilizes the system at time $T>0$. This Note addresses the question of the optimal position of ω in order to minimize $J:\omega \to 6v_{\omega }{6}_{L^2(\omega \times (0,T))}$. Assuming $\omega \in C^{1,1}(\Omega )$, we express the shape derivative of J as a curvilinear integral on ?ω (independently of any adjoint solution) leading to a descent algorithm. A numerical application is given. To cite this article: A. Münch, C. R. Acad. Sci. Paris, Ser. I 343 (2006).     

Surface structure of (10(-)10) and (11(-)20) surfaces of ZnO with density functional theory and atomistic simulation

We have calculated the stability of two of the low-index surfaces known to dominate the morphology of ZnO as a function of stoichiometry. These two surfaces are (10(-)10) and (11(-)20). In each case, two terminations only are stable for a significant range of oxygen and hydrogen chemical potential: the pure stoichiometric surface and a surface covered in a monolayer of water. The mode by which the water adsorbs is however different for the two surfaces considered. On the (10(-)10) surface the close proximity of the water molecules means hydrogen bonding can occur between adjacent chemiabsorbed water molecules and hence there is little difference in the stability of the hydrated and hydroxylated surface, and in fact the most stable surface occurs with a combination of dissociated and undissociated water adsorption. In the case of the (11(-)20) surface, it is only when full dissociation has occurred that a hydrogen-bonding network can form. Our results also show good agreement between DFT and atomistic simulations, suggesting that potential based methods can usefully be applied to ZnO.     

Huge excitonic effects in layered hexagonal boron nitride

The all-electron GW approximation energy band gap of bulk hexagonal boron nitride is shown to be of indirect type. The resulting computed in-plane polarized optical spectrum, obtained by solving the Bethe-Salpeter equation for the electron-hole two-particle Green function, is in excellent agreement with experiment and has a strong anisotropy compared to out-of-plane polarized spectrum. A detailed analysis of the excitonic structures within the band gap shows that the low-lying excitons belong to the Frenkel class and are tightly confined within the layers. The calculated exciton binding energy is much larger than that obtained by Watanabe et al. [Nat. Mater. 3, 404 (2004).] based on a Wannier model assuming h-BN to be a direct-band-gap semiconductor.     

Chlorofluoroiodomethane as a potential candidate for parity violation measurements

CHFClI is among the more favorable molecules for parity violation (PV) measurements in molecules. Despite the fact that calculated PV effects are two orders of magnitude smaller than in some organometallic compounds, CHFClI displays interesting features which could make possible a new experimental PV test on this molecule. Indeed, ultrahigh resolution spectroscopy using an ultrastable CO(2) laser is favored by several intrinsic properties of this molecule. For example, the high vapor pressure of CHFClI allows investigation by supersonic beam spectroscopy. Indeed, the spectroscopic constants have been accurately determined by microwave and millimetre wave spectroscopy. This is important for the subsequent selection of an appropriate absorption band of CHFClI that could be brought to co?ncide with the absorption of CO(2). Partially resolved (+)- and (-)-CHFClI enantiomers with respectively 63.3 and 20.5% ee's have been recently prepared and analyzed by molecular recognition using chiral hosts called cryptophanes. Finally, the S-(+)/R-(-) absolute configuration was ascertained by vibrational circular dichro?sm (VCD) in the gas phase.     

Bounded type Siegel disks of finite type maps with few singular values

Let U be an open subset of the Riemann sphere \(\hat {\mathbb{C}}\). We give sufficient conditions for which a finite type map f: U → \(\hat {\mathbb{C}}\) with at most three singular values has a Siegel disk compactly contained in U and whose boundary is a quasicircle containing a unique critical point. The main tool is quasiconformal surgery à la Douady-Ghys-Herman-?wi?tek. We also give sufficient conditions for which, instead, Δ has not compact closure in U. The main tool is the Schwarzian derivative and area inequalities à la Graczyk-?wi?tek.