101 research outputs found
Superconductivity in TTF[Ni(dmit)2]2 films
We report on the observation of a superconducting transition in a fiber-like film of the TTF[Ni(dmit)2]2 phase electrodeposited on silicon substrates. Superconductivity is evidenced by a broad drop of the resistance below 0.8K under the application of a hydrostatic pressure of 7.7 kbar. Zero resistance is not reached due to the contribution of inter-fiber resistance. Superconductivity is confirmed by the application of a magnetic field perpendicular to the plane of the film. The critical field determined on the film is in agreement with that obtained in bulk single crystals
An efficient protection of stainless steel against corrosion: Combination of a conversion layer and titanium dioxide deposit
In the present work, a novel process has been developed to improve the corrosion properties of ferritic stainless steels. Titanium oxide coatings have been deposited onto stainless steel by solâgel process after a pre-functionalization of the substrate in a conversion bath. Gel titania was prepared by hydrolysis of a titanium butoxide through a solâgel process. Duplex systems "conversion layer/uniform TiO2 coating" have been prepared on stainless steels using a dipping technique and thermal post-treatments at 450 °C. The preparation of solâgel coatings with specific chemical functions offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. The morphology and structure of the coatings were analysed using scanning electron microscopy with field effect gun (SEM-FEG), Mass spectroscopy of secondary ions (SIMS) and X-ray diffraction (XRD). The anticorrosion performances and the ageing effects of the coatings have been evaluated in neutral and aggressive media by using several normalized tests. The results show that the conversion layer was not sufficient to protect steel but solâgel TiO2 coatings, anchored on the metal substrate via the conversion layer, show good adhesion with the substrate and act as a very efficient protective barrier against corrosion. So, duplex layers with TiO2 nanoparticle coatings on steels exhibit an excellent corrosion resistance due to a ceramic protective barrier on metal surface. Analysis of the data indicates that the films act as geometric blocking layers against exposure to the corrosive media and increase drastically the lifetime of the substrate
Chemical vapor deposition of iron, iron carbides, and iron nitride films from amidinate precursors
Iron bis(N,N-diisopropylacetamidinate) [Fe2(”-iPr-MeAMD)2(2-iPr-MeAMD)2] and iron bis(N,N-di-tert-butylacetamidinate) [Fe(tBu-MeAMD)2] were used as precursors for the metallorganic chemical vapor deposition (MOCVD) of iron-containing compounds including pure iron, iron carbides, Fe3C and Fe4C, and iron nitrides Fe4C. Their decomposition mechanism involves hydrogen migration followed by dissociation of the FeâN bond and the release of free hydrogenated ligand (HL) and radicals. Surface intermediates are either released or decomposed on the surface providing FeâN or FeâC bonds. MOCVD experiments were run at 10 Torr, in the temperature ranges of 350â450°C with Fe2(”âiPr-MeAMD)2(2-iPr-MeAMD)2 and 280â350°C with Fe(tBu-MeAMD)2. Films prepared from Fe2(”âiPr-MeAMD)2(2-iPr-MeAMD)2 contain Fe, Fe3C, and Fe4C. Those prepared from Fe(tBu-MeAMD)2 contain Fe, Fe3C, and also Fe4C or Fe4N, depending on the temperature and hydrogen to precursor ratio (H/P) in the input gas. The room-temperature coercive field of films processed from Fe(tBu-MeAMD)2 is 3 times higher than that of the high temperature processed Fe4N films
Spin density wave and superconducting properties of nanoparticle organic conductor assemblies
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.The magnetic susceptibilities of nanoparticle assemblies of two Bechgaard salts (TMTSF)2PF6 and (TMTSF)2ClO4, have been studied vs temperature and magnetic field. In the bulk these materials exhibit a spin density wave formation (TSDW=12K) and superconductivity (Tc=1.2K), respectively. We show from inductive (susceptibility) measurements that the nanoparticle assemblies exhibit ground-state phase transitions similar to those of randomly oriented polycrystalline samples of the parent materials. Resistivity and diamagnetic shielding measurements yield additional information on the functional nanoparticle structure in terms of stoichiometric and nonstoichiometric composition.This work was supported by NSF-DMR Grants No. 1005293 and No. 1309146, and the NHMFL is supported by NSF Cooperative Agreement No. DMR-1157490, the State of Florida, and the U.S. Department of Energy. I.C. thanks the French MinistĂ©re de lâEnseignement SupĂ©rieur et de la Recherche (MESR) for a Ph.D. grant.Peer Reviewe
Facile synthesis of nanoparticles of the molecule-based superconductor Îș-(BEDT-TTF)2Cu(NCS)2
Well-dispersed roughly spherical nano-objects of the molecule-based superconductor Îș-(BEDT-TTF)2Cu(NCS)2 have been prepared in an organic solution by using an easy synthetic route. Long alkyl-chain aconitate esters have been used as growth controlling agents. Nano-objects exhibiting sizes in the 35â120Â nm range are made of aggregated individual smaller nanoparticles ranging from 3 to 10Â nm. Nanoparticle powders have been studied by X-ray diffraction, high resolution electron microscopy and atomic force microscopy in the conductivity mode.
Résumé :
Des nano-objets sphĂ©riques et bien dispersĂ©s du supraconducteur molĂ©culaire Îș-(BEDT-TTF)2Cu(NCS)2 ont Ă©tĂ© prĂ©parĂ©s en solution organique Ă l'aide d'une mĂ©thode de synthĂšse relativement aisĂ©e. Des aconitates Ă longue chaĂźne alkyle ont Ă©tĂ© utilisĂ©s comme rĂ©gulateurs de croissance. Ces nano-objets de taille comprise entre 35 et 120 nm sont constituĂ©s de petites particules dont le diamĂštre individuel est de l'ordre de 3 Ă 10 nm. Les poudres nanoparticulaires ont Ă©tĂ© Ă©tudiĂ©es par diffraction des rayons X, par microscopie Ă©lectronique Ă haute rĂ©solution et enfin par microscopie Ă force atomique en mode conducteur
Nanoparticles of tetrathiafulvalene chloride derivatives grown in the presence of amphiphilic molecules
The work described in this paper is directed towards the electrosynthesis of TTFCl0,77 as spherical nanoparticles by using amphiphilic molecules, behaving as growth-controlling agents. The morphology and the size distribution of the particles were analyzed using transmission electron microscopy and the resulting powders were characterized by infrared and Raman spectroscopy along with X-ray diffraction. In the presence of dodecylamine, electron micrographs evidenced spherical and relatively well-dispersed nanoparticles exhibiting a mean diameter of about 10ânm. However, in the presence of N-octylfurfurylimine, a mixture of nanoparticles and sticks were formed. The best results in terms of smallness of particles size and narrowness size distribution were obtained in the presence of 1-octanamine, N-(2-thienylmethylene). Spherical nanoparticles exhibiting sizes in the 4â12ânm range with an average size of about 8ânm were observed. The nanoparticles powder exhibited a room temperature conductivity of about 0.01 S.cmâ1
Molecular conductors as nanoparticles in the presence of long-chain alkyl imidazolium salts or amphiphilic molecules
Nanoparticles of two molecule-based conductors, namely TTF·TCNQ and TTF[Ni(dmit)2]2, have been prepared in organic solution in the presence of ionic or nonionic species bearing a long-chain alkyl group, acting as growth-controlling agents. The size, morphology, and state of dispersion of the nanoparticles depended on the nature of the growth-controlling agent and the reaction temperature. In the presence of a long-chain alkyl-based ionic liquid at â50 °C, electron micrographs evidence that TTF·TCNQ nano-objects are frequently elongated, whereas TTF[Ni(dmit)2]2 nanoparticles are aggregated. In the presence of a neutral long-chain alkyl-based imine at room temperature, nanoparticles are spherical (mean diameter <20 nm) and well dispersed. Vibration spectra evidence that the amounts of charge transfer for TTF·TCNQ and TTF[Ni(dmit)2]2 as nano-objects are very similar to those for the same phases as bulk materials. According to the thermoanalytical investigations, the prepared nanoparticles are stable thermally up to approximately 200 °C, and their decomposition is generally a multi-step process. Their heat treatment results in various sulfur-containing volatiles (CS2, SO2, H2S); moreover, HCN is also detected in the case of nitrogen-containing molecules (TCNQ)
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