Out- versus in-plane magnetic anisotropy of free Fe and Co nanocrystals: tight-binding and first-principles studies

We report tight-binding (TB) and Density Function Theory (DFT) calculations of magnetocrystalline anisotropy energy (MAE) of free Fe (body centerd cubic) and Co (face centered cubic) slabs and nanocrystals. The nanocrystals are truncated square pyramids which can be obtained experimentally by deposition of metal on a SrTiO$_3$(001) substrate. For both elements our local analysis shows that the total MAE of the nanocrystals is largely dominated by the contribution of (001) facets. However, while the easy axis of Fe(001) is out-of-plane, it is in-plane for Co(001). This has direct consequences on the magnetic reversal mechanism of the nanocrystals. Indeed, the very high uniaxial anisotropy of Fe nanocrystals makes them a much better potential candidate for magnetic storage devices.Comment: 8 pages, 7 figure

Experimental and theoretical analysis of hydrogen bonding in two-dimensional chiral 4′,4′′′′-(1,4-Phenylene)bis(2,2′:6′,2″-terpyridine) self-assembled nanoarchitecture

ABSTRACT: The two-dimensional self-assembly of 4′,4⁗- (1,4-phenylene)bis(2,2′:6′,2″-terpyridine) molecules is exper- imentally and theoretically investigated. Scanning tunneling microscopy (STM) shows that this molecular building block forms a compact chiral supramolecular network on graphite at the 1-octanol/graphite interface. The molecules adopt a side- by-side arrangement inside the organic domains. In contrast, the molecules are arranged perpendicularly at the domain boundary. Detailed theoretical analysis based on the density functional theory (DFT) shows that these arrangements are stabilized by double and single hydrogen bonds between pyridine groups. Only the molecular peripheral pyridine groups are involved in the hydrogen bonds stabilizing the long-range ordered molecular nanoarchitectures

Engineering porous and compact two-dimensional nanoarchitectures on surfaces taking advantage of bisterpyridine-derivatives self-assembly

International audienceThe self-assembly of two bis-terpyridine derivatives is experimentally investigated at the nanometer scale. Scanning tunneling microscopy (STM) reveals that two-dimensional compact and porous nanoarchitectures can be engineered by changing the length of terpyridine spacer; i.e. a benzene ring or a quaterthiophene (4T) unit. In both cases the molecular nanoarchitecture appears to be stabilized by double hydrogen-bonds between molecular terpyridine groups. The STM images suggest however that terpyridine groups adopt different conformations, s-cis and s-trans as well as s-trans and s-trans conformations, in the two self-assembled organic layers

Hypoxia and antitumor CD8(+) T cells: An incompatible alliance?

T Lymphocytes face pathologically low O2 tensions within the tumor bed at which they will have to function in order to impact on the malignancy. Recent studies highlighting the importance of O2 and hypoxia-inducible factors for CD8(+) T-cell function and fate must now be integrated into tumor immunology concepts if immunotherapies are to progress. Here, we discuss, reinterpret, and reconcile the many apparent contradictions in these data and we propose that O2 is a master regulator of the CD8(+) T-cell response. Certain T cell functions are enhanced, others suppressed, but on balance, hypoxia is globally detrimental to the antitumor response

La tolérance aux fautes dans un système temps-réel à contraintes strictes

Disponible dans les fichiers attachés à ce documen

Fabrication of a Complex Two-Dimensional Adenine Perylene-3,4,9,10-tetracarboxylic Dianhydride Chiral Nanoarchitecture through Molecular Self-Assembly

International audienceThe two-dimensional self-assembly of a nonsymmetric adenine DNA base mixed with symmetric perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules is investigated using scanning tunneling microscopy (STM). We experimentally observe that these two building blocks form a complex close-packed chiral supramolecular network on Au(111). The unit cell of the adenine PTCDA nanoarchitecture is composed of 14 molecules. The high stability of this structure relies on PTCDA PTCDA and PTCDA adenine hydrogen bonding. Detailed theoretical analysis based on the density functional theory (DFT) calculations reveals that adenine molecules work as a "glue", providing additional strengthening to the PTCDA-based skeleton of this sophisticated multicomponent nanoarchitecture. At the same time, we find that orientation and chirality of adenine molecules across the monolayer is likely to vary, leading to a disorder in the atomistic structure of the entire assembly

Two-Dimensional 1,3,5-Tris(4-carboxyphenyl)benzene Self-Assembly at the 1-Phenyloctane/Graphite Interface Revisited

International audienceTwo-dimensional (2D) self-assembly of star-shaped 1,3,5-tris(4-carboxyphenyl)benzene molecules is investigated. Scanning tunneling microscopy reveals that this molecule can form three hydrogen-bonded networks at the 1-phenyloctane/graphite interface. One of these structures is close-packed and the two other ones are porous structures, with hexagonal and rectangular cavities. The network with rectangular cavities appears to be the most stable structure

Time-resolved PhotoEmission Spectroscopy on a Metal/Ferroelectric Heterostructure

In thin film ferroelectric capacitor the chemical and electronic structure of the electrode/FE interface can play a crucial role in determining the kinetics of polarization switching. We investigate the electronic structure of a Pt/BaTiO3/SrTiO3:Nb capacitor using time-resolved photoemission spectroscopy. The chemical, electronic and depth sensitivity of core level photoemission is used to probe the transient response of different parts of the upper electrode/ferroelectric interface to voltage pulse induced polarization reversal. The linear response of the electronic structure agrees quantitatively with a simple RC circuit model. The non-linear response due to the polarization switch is demonstrated by the time-resolved response of the characteristic core levels of the electrode and the ferroelectric. Adjustment of the RC circuit model allows a first estimation of the Pt/BTO interface capacitance. The experiment shows the interface capacitance is at least 100 times higher than the bulk capacitance of the BTO film, in qualitative agreement with theoretical predictions from the literature.Comment: 7 pages, 10 figures. Submitted to Phys. Rev.