Neutral-ionic phase transition : a thorough ab-initio study of TTF-CA

The prototype compound for the neutral-ionic phase transition, namely TTF-CA, is theoretically investigated by first-principles density functional theory calculations. The study is based on three neutron diffraction structures collected at 40, 90 and 300 K (Le Cointe et al., Phys. Rev. B 51, 3374 (1995)). By means of a topological analysis of the total charge densities, we provide a very precise picture of intra and inter-chain interactions. Moreover, our calculations reveal that the thermal lattice contraction reduces the indirect band gap of this organic semi-conductor in the neutral phase, and nearly closes it in the vicinity of the transition temperature. A possible mechanism of the neutral-ionic phase transition is discussed. The charge transfer from TTF to CA is also derived by using three different technics.Comment: 11 pages, 9 figures, 7 table

Tungsten diffusion in silicon

International audienc

Interface formation and growth of a thin film of ZnPcCl8/Ag(111) studied by photoelectron spectroscopy

International audienc

Substrate-mediated ordering and defect analysis of a surface covalent organic framework

We investigate the growth of a two-dimensional polymer obtained by dehydration of 1,4-benzenediboronic acid (BDBA). The molecules are vapor deposited under ultrahigh vacuum conditions on well-oriented noble metal—Ag(111), Ag(100), Au(111), and Cu(111)—surfaces.Molecular flux and substrate temperature are varied to obtain a polymer of optimum quality, whose structure best approaches that of an ideal honeycomb network. We find that a high molecular flux (~0.1 monolayer/minute) is necessary to initiate BDBA polymerization on all surfaces at room temperature. Once polymerization has extensively taken place, the robust surface network can resist a temperature of 450 ?C. However, various kinds of defects are present within this two-dimensional surfacepolymer. Statistical analyses, primarily based on the minimal spanning tree approach, are performed to quantify polymer order. They indicate that Ag(111) and Ag(100) surfaces are better templates than Au(111) surfaces for polymer formation, far more than Cu(111) ones. The influence of the metal nature on the polymer growth is discussed with respect to the surface diffusion of adsorbed molecules