Coefficient de diffusion dans une chaîne linéaire de Heisenberg à haute température

For a linear Heisenberg chain, the knowledge of the 16th order moment for spin 1/2, allows a better description of the time-dependent spin pair correlation function at infinite temperature. The diffusion coefficient D is calculated and compared to the value obtained by a simulation technique (S = ∞). The ratio D/(J/ħ) √(16 S(S + 1)/ 3) depends little on the spin value.Pour une chaîne linéaire de Heisenberg la connaissance des moments jusqu'à l'ordre 2 n = 16 pour des spins S = 1/2, permet d'améliorer la description des fonctions de corrélation de spin à haute température. Nous avons calculé le coefficient de diffusion D. La comparaison avec les résultats obtenus par simulation montre que le rapport D/J/ħ √(16 S(S + 1))/3 dépend peu de la valeur du spin

Polarimetry of light scattered by surface roughness and textured films and periodic structures in nanotechnologies: a new challenge in instrumentation and modeling

Exhaustive studies in the literature detail the Mueller matrices properties through decomposition, optical entropy and depolarization formalism. It has been applied for many years in rather different fields. In radar polarimetry, mathematical basis of depolarizing systems, have been first developed. In the visible range optics, standard diattenuation and retardance, decomposition is currently used in turbid organic media. The optical entropy concept, developed by S.R. Cloude, provides a very powerful analysis technique yielding important surface parameters such as depolarization, correlation and roughness. Complementary applications exist in scatterometry, for thin periodic grating films. With high capability polarimeters, such as the next generation of angle resolved polarimeters instruments, Polarimetry opens new fields of investigation for nanotechnologies materials as well as for gratings and photonics structures analysis: a program presently developed through a national consortium ANR08-NANO-020-03. With this instrumentation progress, simulation remains a key point to overpass as a challenge between future instruments. The theories for surfaces spectral power density (PSD) and the random coupled wave approximation (RCWA) in periodic structures are widely described in the literature. The implementation of some of these codes is described here for surface analysis and lithography scatterometry structures: grating overlay or double patterning

Polarisation dynamique dans un système de heisenberg unidimensionnel, le tanol

Overhauser experiments were performed on single crystals of the nitroxyde free radical TANOL. The enhancement of the nuclear polarisation is strongly anisotropic. For some orientations of the crystal in the magnetic field, enhanced signals of complex shape are observed. The experimental results are interpreted with a model including 10 nuclear réservoirs, connected to each other by cross-relaxation terms and connected to the electronic spins by hyperfine couplings. A quantitative agreement is obtained for the global nuclear polarization enhancement for the different orientations. It is shown that one can induce a situation where polarizations of opposite signs coexist within the same molecule. The unidimensionality of exchange interactions in TANOL plays a crucial role. When account is taken of the pair-correlations between two electronic spins of the same exchange chain, one can establish that the previously unknown direction of these chains is along the c axis.On a effectué des expériences d'effet Overhauser sur un monocristal du radical libre nitroxyde TANOL. L'augmentation de la polarisation nucléaire est fortement anisotrope. Pour certaines orientations du cristal dans le champ magnétique on observe des signaux polarisés de forme complexe. Ces faits expérimentaux sont interprétés à l'aide d'un modèle qui considère 10 réservoirs nucléaires, connectés entre eux par les termes de cross-relaxation nucléaire, et couplés aux spins électroniques par les interactions hyperfines. Un accord quantitatif est obtenu pour l'augmentation globale de la polarisation nucléaire aux différentes orientations. Il est montré que l'on peut créer une situation où des polarisations de signes opposés coexistent au sein d'une même molécule. Le caractère unidimensionnel des interactions d'échange dans le TANOL joue un rôle très important. En tenant compte des corrélations électroniques croisées entre deux spins appartenant à la même chaîne d'échange, on établit que la direction de ces chaînes, qui était jusqu'alors inconnue, est suivant l'axe c

Growth mechanism investigation of SnO2 thin films deposited by aerosol pyrolysis for biosensor applications: Importance of the thickness

International audienceTransparent conductive oxide films are suitable sensitive layers for gas sensors and biosensors, provided that their intrinsic properties are controlled, notably considering their thickness dependence. The present paper reports on a study of the variation of some physical properties of polycrystalline Sb doped SnO2 films according to the film thickness. Films were deposited onto Si and glass substrates by aerosol pyrolysis. Their thickness was varied in a range of 20-280 nm. The electrical resistivity, the roughness, the optical constant, the microstructure and the texture were investigated. Correlated evolutions of the resistivity and the surface roughness are found in relation with the evolutions of both the microstructure and the texture. Two main successive growth steps were evidenced which are delimited by a critical film thickness. Below this thickness of approximately 100-120 nm, a strong dependence of physical properties with the thickness is evidenced whereas for thicker films no significant change is evidenced. A two-step growth model is proposed to explain this behaviour. This mechanism growth is to be considered in view of the integration of SnO2 films as sensitive layers in biosensors. Notably, in the case of biosensors based on the label-free electrochemical detection of biomolecules, it is recommended to use films with thicknesses ranging above the critical thickness value of 100-120 nm in order to obtain optimized, reproducible and comparable responses of biosensors. (c) 2012 Elsevier B.V. All rights reserved

Analysis of textured films and periodic Grating Structures with Mueller Matrices: A new Challenge in Instrumentation with the generation of angle-resolved SE polarimeters

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Observation of HfO2 thin films by deep UV spectroscopic ellipsometry

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Crystalline Structure of HfZrO Thin Films and ZrO2 / HfO2 bi-Layers Grown by AVD for MOS Applications

International audienceThe downscaling in CMOS transistors requires the introduction of new materials with a higher dielectric constant. The electrical properties of HfxZryOz films and ZrO2 / HfO2 bi-layers grown by Atomic Vapor Deposition were analyzed for their integration as gate oxides. While crystallinity of those layers was found to be dependent on their zirconium concentration, the electrical performance was shown to depend mainly on the growth temperature of the high-k films