Pascal Andreazza

Pascal Andreazza
Université d'Orléans | UO · Interface, Confinement, Materiaux et Nanostructures ICMN

Professor in Physics

About

93
Publications
10,312
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Introduction
Structure and kinetics of nanoalloys and metal-based nanoparticles (1-5nm). size reduction and interface effects on their structure: order-disorder, phase transition, equilibrium and metastable structure and organization on a substrate : wetting, diffusion, coalescence, ripening. laboratory and synchrotron radiation X-ray scattering GISAXS-GIWAXS, GIXD, SAXS-XRD. growth and aeging in ultrahigh vacuum and under temperature and gas-liquid effects. simulations of cluster structure and X-ray spectra
Additional affiliations
October 1992 - present
Université d'Orléans
Position
  • Professor (Full)

Publications

Publications (93)
Article
The chemical stability of supported CoPt nanoparticles in out-of-equilibrium core-shell configurations was investigated mainly by anomalous grazing incidence small angle x-ray scattering (AGISAXS) in association with combined transmission electron microscopy and x-ray absorption spectroscopy. CoPt nanoparticles were prepared at room temperature by...
Article
The Ag/Co nanoalloy system is a model system situated energetically at the limit of stability of the core-shell chemical ordering with respect to a simple phase separation behavior. This makes the system highly susceptible to effects of the environment, such as interaction with a substrate. However, kinetic effects may also be exploited by careful...
Article
Full-text available
Understanding of cobalt nanorods' (Co NRs) formation still remains challenging when it comes to enhancing their anisotropic properties applicable in magnetic or catalytic areas. Herein, we propose a mechanism for the morphological transition from spherical cobalt nanoparticles (NPs) to Co NRs over time (9 h) in a mixture of [CoCl(PPh3)3] and oleyla...
Article
Atomic motions and morphological evolution of growing Co-Ag nanoparticles are followed in situ and in real time, by wide and small angle X-ray scattering obtained simultaneously in grazing incidence geometry (GISAXS and GIWAXS), in single or multi-wavelength anomalous modes. The structural analysis of the experimental data is performed with the aid...
Article
Full-text available
Palladium clusters are grown using a gas aggregation source coupled to magnetron sputtering with oxygen as reactive gas. Clusters with a mean size between 2.6 and 3.3 nm are obtained. Oxygen enhances the deposition rate by a factor 3 (from 4 to 11 mg/h cm ⁻²) at the expense of the formation of larger clusters and the modification of the cluster com...
Article
Full-text available
The size increase of a nanoscale material is commonly associated with the increased stability of its ordered phases. Here we give a counterexample to this trend by considering the formation of the defect-free L11 ordered phase in AgPt nanoparticles, and showing that it is better stabilized in small nanoparticles (up to 2.5 nm) than in larger ones,...
Article
The magnetoelectric coupling mechanism in Ni/BiFe 0.95 Mn 0.05 O 3 heterostructures is investigated through a detailed microstructural study of the BiFe 0.95 Mn 0.05 O 3 film and a chemical analysis of the Ni/BiFe 0.95 Mn 0.05 O 3 interface. The four structural variants expected in BiFe0.95Mn0.05O3 are detected by high resolution X-ray diffraction...
Poster
Morphologie d'îlots nanométriques de Pt et Ag en température par diffusion des rayons X Objectifs :-Etude in situ de la morphologie des nanoparticules (NPs) de platine (Pt) et d'argent (Ag) en température. Méthodes: Elaboration des nanoparticules Méthode pour les sonder : Diffusion des rayons X aux petits angles en incidence rasante (GISAXS)[1] Sim...
Article
Full-text available
A binary blend of poly(isoprene-block-styrene-block-(2-vinylpyridine)) (ISP) triblock terpolymers, having the same chain length but different compositions, was used to achieve an ordered lattice with 4-fold symmetry of rectangular-shaped rods of poly(isoprene) (I) and poly(2-vinylpyridine) (P). In given conditions, the I and P domains were oriented...
Article
Room temperature manipulation of the ferromagnetic state via an electric field is investigated in Ni/ BiFe0.95Mn0.05O3 thin film heterostructures. A 600% increase in the magnetic coercive field of the Ni layer is observed at the initial DC electrical poling of the ferroelectric BiFe0.95Mn0.05O3 layer. The magnetoelectric effect is remanent, and the...
Article
Full-text available
We investigated the dissolution of a natural Fe-containing dolomite [Ca1.003Mg0.972Fe0.024Mn0.002(CO3)2] under acidic conditions (pH 3-5.5) with atomic force microscopy (AFM) at 20 °C, and with batch dissolution experiments at 80 °C. Dolomite dissolution proceeded by two identified mechanisms: removal of dolomite layers through spreading and coales...
Chapter
Full-text available
Metallic nanoparticles made of more than one element (i.e. nanoalloys) are developed because they can present synergetic effects which enhance a wide range of properties in many fields of science such as reactivity, magnetic storage or medical imaging. Taking advantage of both alloying and size effects, the so-called nanoalloys have considerably wi...
Conference Paper
Over the past few decades, the use of nanostructures for the miniaturization of electrical components, creating new tools for medical diagnosis or even in the fields of pharmacology and cosmetics has become quite indispensable and industrially backed. Nanoparticles (NPs), in particular, are situated between the molecular level and bulk matter size....
Article
Full-text available
Solvo-thermal vapor annealing (STVA) was employed to induce microphase separation in a lamellar forming block copolymer (BCP) thin film containing a readily degradable block. Directed self-assembly of poly(styrene)-block-poly(D,L-lactide) (PS-b-PLA) BCP films using topographically patterned silicon nitride was demonstrated with alignment over macro...
Article
Full-text available
+33 (0)2 3849 4352 KEYWORDS. gas aggregation source, magnetron sputtering, platinum, nanoclusters, catalyst. Abstract. PdPt catalysts with different morphologies and atomic ratios have been synthesized on native SiO2/Si and on proton exchange membrane. The combination of the gas-aggregation source and of the magnetron sputtering techniques allows t...
Article
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Among nanoalloys, Co–Pt type (CoPt or FePt) supported nanostructures are very interesting systems due to the direct link between atom arrangement and magnetic behavior. In addition, these alloys become model systems in the field of nanoalloys, due to the diversity of atom arrangements either present in the bulk state or specific to the nanoscale (c...
Article
Full-text available
Platinum nanocrystals and its derivative with palladium and cobalt have a fundamental interest due to their large field of application in chemistry and physics. Their properties are strongly dependent on the shape and composition. However the chemical route is far to allow control both shape and composition. In this paper, we show both experimental...
Article
Full-text available
This paper reports the preparation and properties of color-switchable fluorescent carbon nanodots (C-dots). C-dots that emit dark turquoise and green-yellow fluorescence under 365 nm UV illumination were obtained from the hydrothermal decomposition of citric acid. Dark green fluorescent C-dots were obtained by conjugating prepared C-dots to form C-...
Conference Paper
Full-text available
The gas-aggregation source technique with a planar magnetron is used for the production of PtX (X = Pd or Au) catalyst nanoclusters on polymeric substrate used in low temperature fuel cell. The target material is sputtered by employing either a DC power supply or a high-power impulse magnetron sputtering power device known to enhance the degree of...
Chapter
Because the nanoalloy properties are directly connected to their structural and chemical arrangements, the experimental investigations of these features by dedicated techniques is of primary importance, especially in order to understand and to control the nanoalloy formation or evolution mechanisms. In this chapter, we focus on the X-ray scattering...
Article
Full-text available
As atomic structure and morphology of particles are directly correlated to their functional properties, experimental methods prob-ing local and average features of particles at the nanoscale elicit a growing interest. Anomalous small-angle X-ray scattering (ASAXS) is a very attractive technique to investigate the size, shape and spatial distributio...
Article
Full-text available
Nanostructured platinum-carbon thin films were prepared by magnetron co-sputtering method for designing efficient catalytic thin films, like fuel cells electrodes. The in-depth morphology of composite films was studied using surface sensitive X-ray techniques (grazing incidence small-angle scattering and reflectivity), consolidated by electron micr...
Article
ZnO nanowires (NWs) with different diameters were obtained by controlling the particles of ZnO sub-layer (SL) exploring hydrothermal method; the diameter of the epitaxial NWs could be tuned from 60 to 146 nm when using SL with a thickness of 70 nm. The thickness of the SL would influence the orientation of the NWs. The top agglomerate NWs could be...
Article
Full-text available
Aligned ZnO nanowires (NWs) were obtained by hydrothermal method using annealed ZnO film as seed layer.Besides Si(400), only ZnO(002) diffraction peak was observed in X-ray diffraction(XRD) pattern. The lasing emissions were observed in optically pumped aligned ZnO NWs. Multi-mode emission peaks emerged when the excitation power density exceed the...
Article
Full-text available
Structural and order/disorder phase transitions in bimetallic Co50Pt50 nanoparticles induced by annealing have been investigated combining in situ small and wide angle x-ray scattering methods. The support of Monte Carlo simulations within a semiempirical tight-binding potential provides a realistic description of the CoPt cluster structure in the...
Article
Full-text available
Degradation of historical buildings is mainly due to the intrusion of water which is the main vector of pollutants. Different types of surface treatment have been proposed to avoid or limit this effect. One alternative to chemical treatments is the use of the carbonatogenesis property of some bacteria. This bacterial production has been evidenced o...
Article
Full-text available
Ultra-small CoPt nanoparticles (NPs) with a mean diameter of 1.3 nm (around 100 atoms) were deposited on a thin 5 nm self-supported amorphous carbon membrane. The effects of focused irradiation with a newly developed Ga(+) ion source were studied by transmission electron microscopy. While the overall coverage of the NPs remained constant, the mean...
Article
Full-text available
Nucleation and growth of supported CoPt nanoparticles were studied in situ and in real time by combined grazing incidence small-angle x-ray scattering (GISAXS) and grazing incidence x-ray diffraction (GIXD). GISAXS provides morphological features of nanoparticles as a function of size, shape and correlation distance between particles, while GIXD al...
Article
An almost linear relation between the Pt amount and the orbital to spin moment ratio (μl/μs) has been found in Cox Pt100–x nanoparticles prepared by vapour deposition and possessing a well defined chemically disordered crystallographic structure. X-ray magnetic circular dichroism (XMCD) measurements done at the L2,3Co edges show that a 4.0 nm, x =...
Article
Full-text available
The structure and morphology of 1 to 3 nm size CoPt nanoparticles have been investigated in situ and in real time under different conditions: growth at 500 degrees C or at room temperature (RT) followed by annealing at 500 degrees C. The small-angle x-ray scattering measurements show size and temperature dependent growth mode with particle motions...
Article
Full-text available
In the present work, we report a growth and structural study of Co50Pt50 nanoparticles prepared on amorphous carbon substrate by ultra high-vacuum evaporation and investigated by transmission electron microscopy. The size evolution with the amount of CoPt shows a Volmer Weber behavior. At room temperature the nanoparticle diameter follows a t0.41 p...
Article
Co-Pt and Co nanoparticles (similar to 2 nm diameter) of different composition and crystal structure have been studied by X-ray magnetic circular dichroism (XMCD) at the Co L-2,L-3 edges. The magnetic properties of the samples, covered with a thin protecting layer of Al2O3, depend upon the composition, order and presence of Co oxide contamination....
Article
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We investigate the growth of CoPt-based nanostructures on thermally oxidized Si(100) substrates by ultrahigh-vacuum coevaporation at 50, 400, and 650 °C substrate temperatures. The thermal evolution of the bimetallic deposits has been studied by x-ray photoelectron spectroscopy (XPS) as well as x-ray diffraction (XRD) in grazing incidence. This stu...
Article
Full-text available
ZrTiAlCuNi films are deposited by plasma sputtering from an alloyed target prepared by induction – cold crucible melting method. The films are found to be amorphous and exhibit a composition very similar to the target one. It is shown that the amorphous character of the deposits is rather due to the high glass forming ability (GFA) of the Zr-based...
Article
ZnO nanostructures are synthesized by a simple physical vapor phase transport technique using metallic clusters as the catalyst. Two kinds of catalyst are used: gold and platinum. The shape and growth direction were investigated by scanning electron microscopy, transmission electron microscopy and using X-ray diffraction. Depending on the metal use...
Article
The electroplating techniques for metal aggregates and films deposition commonly use an electric current to reduce metal ions in solution, but are restricted to conducting substrate. This new electrochemical technique permits coating of insulating or conducting substrates with metals having controlled aggregate size and growth speed. The basis of o...
Article
Full-text available
A mechanical and micro structural characterization has been done in diamond coating deposited on TA6V titanium alloys using X-ray diffraction. The CVD deposition process used allows elaborating layers at moderated temperature (600 °C). Varying the precursor gas composition, the purity level (sp3), the morphology (columnar or fine grains) and the ro...
Article
An original electrochemical process to prepare SnO2 gas sensors is detailed and correlated to electrical behaviour under gas environment. In particular conditions, Tin material was electrodeposited on insulating substrate to form a thin film principally composed of a single layer of individual nanoaggregates (5–10 nm in size). After tin electrodepo...
Article
Vertical aligned ZnO nanorods array was fabricated on Si with introducing a ZnO thin film as a buffer layer. Two different nucleation mechanisms were found in growth process. With using Au catalyst, Zn vapor could diffuse into Au nanoclusters with forming a solid solution. Then the ZnO nucleation site is mainly on the catalyst by oxidation of Au/Zn...
Article
The tin (Sn) electrochemical deposition on insulating substrates has been performed to elaborate a distribution of supported nanoaggregates for gas sensors applications. Depending on current density, the deposit has either the shape of dendrites or of a homogeneous, continuous layer, thinner than 20nm. In this study, fine current densities variatio...
Article
One dimensional ZnO nanorods were successfully fabricated on Si substrates via a simple physical vapor-phase transport method at 950 °C. A ZnO shell covered Au/Zn alloy is assumed as the nucleation site, then ZnO nanorods grow following a vapor-solid (VS) process. In order to guide the nanorod growth a c-axis oriented ZnO thin film and Au catalyst...
Article
ZnO nanostructures have been synthesized using a catalyst-assisted carbothermal reduction approach on Si substrate. By analyzing SEM images, two different growth mechanisms were found to grow ZnO nanostructures. At low growth temperature (900 and 950 °C), vapor–solid mode is dominant in the growth process. With increasing the growth temperature to...
Article
We study the steel surface modifications induced by irradiation of several lasers in air. The surface modifications are found to depend on the laser properties (Krf, 248 nm, 26 ns; XeCl, 308 nm, 25 ns; Nd:YAG, 1064 or 532 nm, 5 or 10 ns). The treated surface features (morphology, chemical composition and crystalline structure) are analysed by compl...
Article
Full-text available
Smooth fine-grained diamond (SFGD) coatings have been deposited by a two-step microwave PACVD process on titanium alloys at 600 °C. The first step consists in depositing, from a methane-rich CH4–H2 mixture, a sacrificial sp2-carbon containing layer that can diffuse partly or completely during the diamond growth which is carried out in a second step...
Article
Full-text available
Plasma sputter deposition experiments and simple molecular dynamics calculations are performed for highlighting the effects of plasma ions and kinetic energy of palladium atoms on the morphology of thin films. A transition between cluster and continuous film growth is observed. It is attributed to the kinetic energy of the depositing sputtered pall...
Article
Full-text available
The nucleation and islands growth of platinum have been followed from an early stage through to complete substrate coverage. Thus, this study of initial stages of thin film growth has allowed to improve the understanding of growth mechanisms and to control the final nanomaterials structure. In the presented deposition method, the metal atom source...
Article
Full-text available
316LVM, an austenitic stainless steel, was implanted at 49 keV with molybdenum ions. Implantation doses varied between 1×1015 and 3.5×1016 ions cm−2. The structure of the implanted layer was examined by grazing incidence X-ray diffraction. As a function of ion dose, expanded fcc austenite was first observed, then a tetragonal distortion of the fcc...
Article
Full-text available
Currently, while light alloys are useful for automotive industries, their weak wear behavior is a limiting factor. The excimer laser carburizing process reported here has been developed to enhance the mechanical and chemical properties of aluminum alloys. An excimer laser beam is focused onto the alloy surface in a cell containing 1bar methane or/a...
Article
Full-text available
The excimer laser cementation process reported is developed to enhance the mechanical and chemical properties of aluminum alloys. It would be interesting to use aluminum alloys in the automotive industry widely because of their low density, corrosion resistance and good workability. The motor weight can be reduced by replacing usual materials such...
Article
Plasma technologies are introduced in the field of hydrogen production related to fuel cells. Two ways are described: Plasma synthesis of catalysts and membranes for the production and purification of hydrogen and, direct production of hydrogen based on atmospheric plasma-assisted methane steam reforming.
Article
An experimental and numerical analysis has been undertaken to investigate the bending strength of transversely stitched T-joints using a fiber insertion process. Finite element analysis (FEA) was performed on the structural joint to predict failure loads and experiments were conducted to determine the modes of failure and ultimate failure strength....
Article
In this work, we study the deposition of palladium by a non-conventional plasma sputtering technique. The metal atom source is a biased wire which is sputtered by argon ions present in an HF-excited plasma. Two energetic plasma species (ions and metastable atoms) impinge onto the substrate surface during deposition and thus, may influence the growt...
Article
Pd on SiC catalysts have been prepared using two different physical processes: atomic beam deposition (ABD) and plasma sputtering deposition (PSD). Whatever the method, Pd deposition (ranging between 0.3 and about 12 monolayer equivalent) yields thin metal adlayers. However, the catalysts prepared by ABD exhibit a 2D-like growth, with a strong meta...