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Dive into the research topics where V. Potin is active.

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Featured researches published by V. Potin.


Angewandte Chemie | 2014

Maximum noble-metal efficiency in catalytic materials: atomically dispersed surface platinum.

Albert Bruix; Yaroslava Lykhach; Iva Matolínová; Armin Neitzel; Tomáš Skála; Nataliya Tsud; Mykhailo Vorokhta; Vitalii Stetsovych; Klára Ševčíková; Josef Mysliveček; Roman Fiala; Michal Václavů; Kevin C. Prince; Stéphanie Bruyère; V. Potin; Francesc Illas; Vladimír Matolín; Jörg Libuda; Konstantin M. Neyman

Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalysts surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria nanopocket, which binds Pt(2+) so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt-CeO2 nanocomposites showing high Pt efficiency in fuel-cell catalysis we also identify these anchoring sites.


Computational Materials Science | 2000

An empirical potential for the calculation of the atomic structure of extended defects in wurtzite GaN

N Aı̈choune; V. Potin; P. Ruterana; A. Hairie; G. Nouet; E. Paumier

Abstract The Stillinger–Weber potential has been parametrized for GaN with bond-type dependent parameters to allow efficient atomic simulations of large systems containing wrong, dangling and extra bonds. The input data for the fit are the experimental elastic constants of wurtzite structure and wrong bond energies deduced from ab initio calculation. The potential in then applied to zincblende structure and to planar defects. The predicted values are compared to experimental observation and previous computations.


Langmuir | 2010

Platinum-Doped CeO2 Thin Film Catalysts Prepared by Magnetron Sputtering

Vladimír Matolín; Iva Matolínová; Michal Václavů; Ivan Khalakhan; Mykhailo Vorokhta; Roman Fiala; Igor Píš; Z. Sofer; Jana Poltierova-Vejpravova; Toshiyuki Mori; V. Potin; Hideki Yoshikawa; S. Ueda; Kazuyo Kobayashi

The interaction of Pt with CeO(2) layers was investigated by using photoelectron spectroscopy. The 30 nm thick Pt doped CeO(2) layers were deposited simultaneously by rf-magnetron sputtering on a Si(001) substrate, multiwall carbon nanotubes (CNTs) supported by a carbon diffusion layer of a polymer membrane fuel cell and on CNTs grown on the silicon wafer by the CVD technique. The synchrotron radiation X-ray photoelectron spectra showed the formation of cerium oxide with completely ionized Pt(2+,4+) species, and with the Pt(2+)/Pt(4+) ratio strongly dependent on the substrate. The TEM and XRD study showed the Pt(2+)/Pt(4+) ratio is dependent on the film structure.


Journal of Applied Physics | 1997

The atomic structure of {101̄0} inversion domain boundaries in GaN/sapphire layers

V. Potin; P. Ruterana; G. Nouet

Using high resolution electron microscopy and extensive image simulation, the atomic structure of the inversion boundaries has been determined in GaN layers grown on sapphire by electron cyclotron resonance assisted molecular beam epitaxy. They form nanometric domains (5–20 nm) limited by {1010} planes crossing the whole epitaxial layer. These small dimensions excluded the use of more conventional microscopy methods such as convergent beam diffraction for their characterization. For image simulations, up to 10 models including the well known Austerman–Gehman and Holt ones were considered for the boundary atomic structure. The overall agreement with the observed contrast was reached for a Holt type model of structure in which the boundary plane contains two wrong bonds per atom. Although the overall atomic configuration is neutral in {1010} boundary planes, it is expected to be highly energetic in ionic materials like GaN due to the difference in Ga–Ga and N–N bond length and local charge difference. Thi...


Applied Physics Letters | 1999

Evidence for multiple atomic structure for the {101̄0} inversion domain boundaries in GaN layers

V. Potin; G. Nouet; P. Ruterana

Atomic structure investigation has been carried out on {1010} inversion domain boundaries in GaN layers grown by molecular beam epitaxy. A method based on the comparison of the stacking sequences of GaN on both sides of the boundary is proposed in order to distinguish between different models. Experimental evidence is shown for two atomic configurations of the boundary plane. Depending probably on the growth conditions, the Holt model, which has been theoretically characterized as highly energetic, can also exist for the {1010} inversion domain boundaries in GaN epitaxial layers.


Philosophical Magazine | 2000

Growth defects in GaN layers on top of (0001) sapphire: A geometrical investigation of the misfit effect

P. Ruterana; V. Potin; B. Barbaray; G. Nouet

Abstract For GaN layers grown on (0001) Al2O3 a geometrical approach is proposed in order to explain the formation of {1010} inversion domain boundaries. As the epitaxial relationship is due to the continuation of anion stacking along the growth direction, the gallium atoms of the first layers have choices of sites to occupy. Therefore, islands related either by displacement vectors corresponding to the usual stacking fault of the hcp structure or inversion domains can form naturally on the (0001) sapphire surface. The inversion domains were found to be generated mostly at surface steps, where they are shown to minimize the large misfit along the c axis (20%).


Philosophical Magazine | 1999

The {1010} inversion domains in GaN/sapphire layers: An electron microscopy analysis of the atomic structure of the boundaries

V. Potin; G. Nouet; P. Ruterana

Abstract The {1010} inversion domains in GaN layers grown on sapphire substrate have been investigated by transmission electron microscopy. They are easily identified in multiple-beam dark-field images and by convergent-beam electron diffraction. Using dark field imaging, it was shown that the domain boundaries do not exhibit any translation in the basal plane. The atomic structure of the boundaries has been determined by comparison with geometrical models. In fact, three types of model can be used to interpret the observations; they correspond to the Holt, Austerman-Gehman and V or IDB∗ models. For each type of model, the boundary plane can be located in two positions, dependent on the cutting plane. Using the AB stacking sequences as seen in high-resolution electron microscopy images, two models were identified. The atomic structure of the boundaries was then determined in comparison with simulated images. In the investigated samples, Holt and V models are shown to exist in the two positions of the boun...


Applied Physics Letters | 2012

In-situ small-angle x-ray scattering study of nanoparticles in the plasma plume induced by pulsed laser irradiation of metallic targets

L. Lavisse; J.L. Le Garrec; L. Hallo; J.M. Jouvard; Sophie Carles; Juan Diego Sánchez Pérez; J. B. A. Mitchell; J. Decloux; M. Girault; V. Potin; H. Andrzejewski; M.C. Marco de Lucas; S. Bourgeois

Small angle x-ray scattering was used to probe in-situ the formation of nanoparticles in the plasma plume generated by pulsed laser irradiation of a titanium metal surface under atmospheric conditions. The size and morphology of the nanoparticles were characterized as function of laser irradiance. Two families of nanoparticles were identified with sizes on the order of 10 and 70 nm, respectively. These results were confirmed by ex-situ transmission electron microscopy experiments.


Materials Science and Engineering B-advanced Functional Solid-state Materials | 1999

TEM study of inversion domains in GaN layers grown on (0001) sapphire substrate

V. Potin; P. Ruterana; G. Nouet

Abstract The atomic structure of nanometric inversion domains in GaN layers has been investigated using high resolution electron microscopy and image simulation. These domains are limited by 10 1 0 planes; they cross the whole epitaxial layers until the surface in the center of small pyramids. For image simulation, six models were considered and a good agreement with the observations was obtained for a model characterized by an inversion and a c/2 translation.


ACS Applied Materials & Interfaces | 2014

Preparation of Magnetron Sputtered Thin Cerium Oxide Films with a Large Surface on Silicon Substrates Using Carbonaceous Interlayers

Martin Dubau; Jaroslava Lavková; Ivan Khalakhan; Stanislav Haviar; V. Potin; Vladimír Matolín; Iva Matolínová

The study focuses on preparation of thin cerium oxide films with a porous structure prepared by rf magnetron sputtering on a silicon wafer substrate using amorphous carbon (a-C) and nitrogenated amorphous carbon films (CNx) as an interlayer. We show that the structure and morphology of the deposited layers depend on the oxygen concentration in working gas used for cerium oxide deposition. Considerable erosion of the carbonaceous interlayer accompanied by the formation of highly porous carbon/cerium oxide bilayer systems is reported. Etching of the carbon interlayer with oxygen species occurring simultaneously with cerium oxide film growth is considered to be the driving force for this effect resulting in the formation of nanostructured cerium oxide films with large surface. In this regard, results of oxygen plasma treatment of a-C and CNx films are presented. Gradual material erosion with increasing duration of plasma impact accompanied by modification of the surface roughness is reported for both types of films. The CNx films were found to be much less resistant to oxygen etching than the a-C film.

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G. Nouet

Centre national de la recherche scientifique

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P. Ruterana

Centre national de la recherche scientifique

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Iva Matolínová

Charles University in Prague

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Vladimír Matolín

Charles University in Prague

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L. Imhoff

University of Burgundy

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Mykhailo Vorokhta

Charles University in Prague

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Ivan Khalakhan

Charles University in Prague

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