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Publications
Publications (106)
Edges fractal approach in graphene e Defects density gain a b s t r a c t To optimize the technological development together with energy gain, the crucial materials needs to be tailored in a smart way to benefit a maximum from the property-structure relation. Herein we propose the way to increase a defect density in graphene moving from 1D linear e...
The metal-insulator transition and the original magnetic phase that appear in vanadium oxide nanoclusters epitaxially embedded in an MgO matrix are studied via electron transport, magneto-resistance, and X-ray circular dichroism measurements. The metal-insulator transition temperature is observed to be in the range of 1.5–27 K. We observe, from 0.3...
An alkaline membrane fuel cell (AMFC) is considered as a promising technology allowing to convert chemical energy of a fuel, for example hydrogen, into electricity. The use of alkaline electrolytes opens up possibility of utilizing low-cost transition metal catalysts, which are unstable in acidic electrolytes. Herein, we developed a facile and effi...
Metastable Ti1−xAlxN films have the more outstanding functional properties in the range of composition around x = 0.6 for their use as protective coatings. They exhibit complex texture because of the phase transition between TiN-like rocksalt and AlN-like wurtzite structures. The competitive growth between cubic and wurtzite domains is studied in m...
Manganese oxides are known as active catalysts for the oxygen reduction reaction (ORR) in alkaline media. Being poor electronic conductors, for electrochemical applications, most of Mn oxides are either mixed with or supported on carbon materials, which impart electronic conductivity to the composite electrodes. A number of recent publications repo...
To optimize the technological development together with energy gain, the crucial materials needs to be tailored in a smart way to benefit a maximum from the property-structure relation. Herein we propose the way to increase a defect density in graphene moving from 1D linear edges to fractal edges, also highlight the fractal nature of graphene struc...
We report on the growth and magnetic properties of La2/3Sr1/3MnO3/SrTiO3/CoFe2 hard-soft magnetic systems prepared by pulsed laser deposition on SrTiO3(001) substrates. In situ reflection high-energy electron diffraction along the [100]SrTiO3 substrate azimuth and atomic force microscopy measurements reveal that La2/3Sr1/3MnO3 and SrTiO3 grow both...
Physical vapour deposition technology is well suited to the deposition of advanced TiAlN-based coatings. Among these thin films, multilayer systems consisting of stacked layers of metallic Ti1 − xAlx and nitride Ti1 − xAlxN with x around 0.5 are expected to have improved mechanical properties with respect to single nitride layers of the same compos...
Pr0.8Na0.05K0.15MnO3 sample was prepared by solid-state reaction method. Refinement of the X-ray diffraction patterns shows that the sample is single phase and crystallizes in the orthorhombic structure with Pbnm space group. This result was confirmed by using the electron diffraction pattern for the sample using the [001] orientation. Analyzing te...
In this study, the authors synthesized perovskite-carbon composites by the In Situ AutoCombustion (ISAC) method. By physical-chemical characterization it was observed that nanoparticles of the LaMnO3±δ perovskite phase are well dispersed in the carbon matrix and are primarily located in the mesopores and small macropores of the Vulcan carbon. By el...
Proton exchange membrane (PEM) electrolyzers are attracting an increasing attention as a promising technology for the renewable electricity storage. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is applied for in situ monitoring of the surface state of membrane electrode assemblies with RuO2 and bimetallic Ir0.7Ru0....
Dopant impurities, such as gallium (Ga), indium (In), and phosphorus (P), were incorporated into silicon-rich silicon oxynitride (SRSON) thin films by the ion implantation technique. To form siliconnanoparticles, the implanted layers were thermally annealed at temperatures up to 1100 °C for 60 min. This thermal treatment generates a phase separatio...
Oxides on the surface of Pt electrodes are largely responsible for the loss of their electrocatalytic activity in the oxygen reduction and oxygen evolution reactions. In this work we apply near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study in operando the electrooxidation of a nanoparticulated Pt electrode integrated in a mem...
Nanostructures with controlled size, morphology, and composition represent a main challenge in materials science because controlling these parameters is fundamental to optimizing the subsequent functional properties. Aggregated nanostructures, combining both individual and collective properties of nanocrystals, offer interesting perspectives to des...
The structural and chemical order are the most important parameters governing the physical properties of the Heusler compounds. Here, we give a comprehensive overview of the correlations between structural and chemical order, electronic transport (longitudinal and transverse) and magnetic (static and dynamic) properties of Co2FeAl0.5Si0.5 Heusler a...
The surface properties of a model membrane electrode assembly of a high-temperature proton-exchange-membrane fuel cell with a nanostructured PtAu working electrode were studied under operando conditions (polarization, humidified H2 atmosphere, 150 °C) using near-ambient-pressure photoelectron spectroscopy (NAP–XPS). NAP–XPS proved to be a powerful...
The current challenge in the field of nano-medicine is the design of multifunctional nano-objects effective both for the diagnosis and treatment of diseases. Here, dendronized FeO1-x@Fe3-xO4 nanoparticles with spherical, cubic, and octopode shapes and oxidized Fe3-xO4 nanocubes have been synthesized and structurally and magnetically characterized....
Spherical core−shell Co x Fe 1−x O@Co y Fe 3‑y O 4 nanoparticles (NPs) as well as spherical and cubic shaped CoFe 2 O 4 NPs were synthesized through a thermal decomposition method by adjusting parameters such as the nature of precursors and ligands. The use of metal (iron and/or cobalt) oleates and stearates as precursors in the presence of oleic a...
We report on the changes on the microstructural, hardness, and corrosion properties induced by carbo-chromization of 316L stainless steel prepared by Spark Plasma Sintering technique. The thermo-chemical treatments have been performed using pack cementation. The carburizing and chromization were carried out between 1153 K (880 °C)/4 h to 1253 K (98...
Nanometric size Zn-doped SnO2 particles with Zn concentration varying from 1 to 6 % were prepared using the co-precipitation method. X-ray diffraction patterns show for all samples a typical rutile-type tetragonal structure of SnO2 without any additional peaks from spurious phases. These results together with transmission electron microscopy analys...
Sub-10 nm CoPt nanoparticles were slowly grown at 400 °C in epitaxy on a NaCl substrate. Their faceted shape was analyzed using state-of-the-art TEM techniques: aberration-corrected imaging, electron tomography, and probe-aberration-corrected scanning transmission electron microscopy. These nanoparticles consist in truncated octahedrons with a chem...
The control of the magnetization of a material with an electric field would make the design and the integration of novel electronic devices possible. This explains the renewed interest in multiferroic materials. Progress in this field is currently hampered by the scarcity of the materials available and the smallness of the magnetoelectric effects....
In this study, silicon rich silicon oxynitride layers containing more than 15% nitrogen were deposited by electron cyclotron resonance assisted plasma enhanced vapor deposition in order to form silicon nanoparticles after a high temperature thermal annealing. The effect of the flows of the precursor gases on the composition and the structural prope...
We report on the epitaxial growth of 100 nm thick triclinic γ-CoV2O6 thin films deposited by pulsed laser deposition on TiO2(100) substrate. The layers were grown in narrow experimental conditions, at 600 °C and 0.1 millibar oxygen pressure. X-ray diffraction and transmission electron microscopy evidenced the presence of two variants and the follow...
Core–shell nanoparticles (NPs), which consist in a ferrimagnetic (FIM)/antiferromagnetic (AFM) interface and result in exchange bias coupling, became recently of primary importance in the field of magnetic nanoparticles. The enhancement of some applications such as hyperthermia or magnetic storage media based on the miniaturization of devices is co...
The L10-MPt alloys (M = Co, Fe, FeNi) are interesting due to their high magnetic anisotropy as arrays of nanoparticles or nanostructures may be used in high density storage media devices. CoPt, FePt and NiPt alloy layers have been prepared by molecular beam epitaxy or cathodic sputtering, epitaxied on MgO(100) substrates. The layers have the L10 te...
The aim of the present study is to check the influence of annealing under vacuum and a mixture of N(2)-H(2) atmosphere on the magnetic properties of polycrystalline Co-doped CeO(2) diluted magnetic oxides (DMOs) with Co concentrations of 5 at% synthesized using the coprecipitation technique. X-Ray diffraction (XRD) patterns and transmission electro...
We report on the effect of the film thickness on the magnetic properties of Ca₃Co₂O₆films with an emphasis on the magnetization steps usually observed in the M-H curves below 10 K. Films with thicknesses between 35 and 200 nm all present two magnetic transitions at about T(C₁) = 22 K and T(C₂) = 10 K, corresponding to a 3D long range ferrimagnetic...
We have studied the Si initial growth mechanisms on LaAlO3(001), a crystalline oxide with a high dielectric constant (high-κ material). The clean LaAlO3(001) substrate exhibits a c(2×2) reconstruction that can be attributed to surface O vacancies.Si deposit by molecular beam epitaxy was studied as a function of both deposition temperature and thick...
We report on the structural and magnetic properties of 5 at. % Co-doped CeO2 films grown on LaAlO3(001) substrates by pulsed laser deposition. A series of epitaxially grown samples made under different oxygen partial pressures ranging from 10−4 to 10−1 mbar showed a ferromagnetic signal at room temperature. This signal is independent on the oxygen...
To test whether the interface between an Fe-alloy electrode and a SrTiO3 (STO) tunnel barrier constitutes or not a good spin injector, we have studied the transport and magnetic properties of CoFe2 (7.5nm)/SrTiO3 (3nm)/CoFe2 (1 nm)/NiFe (8 nm) stacks prepared by pulsed-laser deposition on STO(001) substrates and varied the STO barrier deposition te...
We investigated the structural and optical properties of Eu-doped ZnO thin films made by sol-gel technique and magnetron reactive sputtering on Si (100) substrate. The films elaborated by sol-gel process are polycrystalline while the films made by sputtering show a strongly textured growth along the c-axis. X-ray diffraction patterns and transmissi...
We report on the nature and origin of structural defects at a nanometric scale in incommensurate Ca3Co4O9 thin films deposited by pulsed laser ablation on Al2O3(001) substrates. X-ray diffraction suggests that the deposited films have a well defined texture and that are free of spurious phases. However, cross section scanning high resolution transm...
La2/3Sr1/3MnO3 (LSMO)/Ca3Co2O6 bilayers have been grown by pulsed laser deposition, and their structural and magnetic properties have been investigated with an emphasis on the interface exchange interaction. It is found that both Ca3Co2O6 and LSMO layers are textured and continuous, with a homogeneous thickness and with a sharp interface. The magne...
The design, synthesis, and some properties of magnetic nanocrystals of ferrite functionalized by luminescent prodendritic ligands are described. Multipotent hybrids resulting from the coupling of an inorganic nanocore (metallic, alloy, or oxide nanoparticle) embedded in an organic shell currently elicit sustained research activity in various areas...
The design, synthesis, and some properties of magnetic nanocrystals of ferrite functionalized by luminescent prodendritic ligands are described. Multipotent hybrids resulting from the coupling of an inorganic nanocore (metallic, alloy, or oxide nanoparticle) embedded in an organic shell currently elicit sustained research activity in various areas...
Al-doped ZnCoO films were grown by sol-gel process onto Si O <sub>2</sub> and Si(100) substrates. Structural analysis shows that all samples have the hexagonal würtzite structure with a slight preferential orientation along the c -axis. The insertion of Al and Co into the ZnO matrix has been experimentally evidenced by UV-visible spectroscopy and t...
We report here the growth of Pt electrodes presenting at the same time an ultraflat surface (rms=0.3 nm) and a perfect (111) monocrystalline orientation. These electrodes were grown by pulsed laser deposition on yttrium-stabilized zirconia (111), using a few nanometers thick titanium adhesion layer. Such high crystalline quality electrodes allow th...
Hard–soft systems with magnetic transition metal electrodes and ZnO barrier of variable thickness have been epitaxially grown by pulsed laser deposition on MgO(100) substrates. The structural reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) analysis have shown an epitaxial growth of the CoFe2 bottom electrode, the per...
The structure and the nature of magnetism of ZnO and Zn1−xCoxO (CZO) thin films (0⩽x⩽0.09) deposited on glass substrate at 450°C by spray pyrolysis technique is investigated. All the CZO thin films have the ZnO wurtzite structure with a preferential orientation along the c-axis and had no impurity phase. This was also confirmed by transmission elec...
The present study focused on ZnO thin films fabricated by sol–gel process and spin coated onto Si (1 0 0) and quartz substrates. ZnO thin films have a hexagonal würtzite structure with a grain diameter about 50 nm. Optical properties were determined by photoluminescence (PL) and absorption spectroscopy. The absorption spectrum is dominated by a sha...
The present study focuses on the structural and optical properties of ZnO thin films fabricated by sol-gel process and spin coated onto Si (100) and quartz substrates. The ZnO films have a hexagonal wurtzite structure with a grain size of about 50 nm. The x-ray photoelectron spectroscopy measurements reveal the presence of Zn <sup>2+</sup> and of z...
![Fig. 2. Three diffraction peaks [(113), (300) and (214)] of the Ca 3 Co...](profile/Silviu-Colis/publication/240497094/figure/fig1/AS:298611914100737@1448206036174/Three-diffraction-peaks-113-300-and-214-of-the-Ca-3-Co-2-O-6-rhombohedral-phase_Q320.jpg)
Continuous Ca3Co2O6 thin films were fabricated on Al2O3(001) substrate by pulsed laser deposition. X-ray diffraction and cross-section transmission electron microscopy show that the deposited films are polycrystalline without any secondary phases. The magnetic properties of the films are similar to those reported for bulk polycrystalline samples. A...
The effect of surface inorganic-organic interactions on magnetic and structural properties of iron oxide magnetic nanoparticles functionalized by lipophilic stilbene molecules has been investigated. The molecules have been grafted through either phosphonate or carboxylate coupling agents. Mössbauer spectra recorded at 300 and 77K suggest a global c...
Hysteretic resistance switching is observed in epitaxial Fe / Cr / Mg O / Fe magnetic tunnel junctions under bias voltage cycling between negative and positive values of about 1 V . The junctions switch back and forth between high- and low-resistance states, both of which depend on the device bias history. A linear dependence is found between the m...
Layered cobalt oxides Ca3Co4O9 thin films have been grown directly on c-cut sapphire substrates using pulsed laser deposition. X-ray diffraction and transmission
electron microscopy characterizations show that the deposited films present the expected monoclinic structure and a texture
along the direction perpendicular to the Al2O3(001) plane. The C...
We report on the growth and structural properties of Ca3Co2O6 thin films deposited by pulsed laser ablation on SrTiO3 substrates heated at 700 °C. In situ reflection high-energy electron diffraction and ex situ atomic force microscopy observations reveal that Ca3Co2O6 grows in a three-dimensional (3D) mode with a surface roughness of about 1.5 nm r...
The quality of a SrTiO3 tunnel barrier deposited by pulsed laser deposition on SrTiO3 (001)‖Sr2FeMoO6 is investigated. Epitaxy and two-dimensional growth are obtained and the root-mean-square roughness is 0.3 nm. The distribution of the local current measured by conductive atomic force microscopy indicates that hot spots are almost absent. The stan...
Sr <sub>2</sub> Fe Mo O <sub>6</sub>/ Sr Ti O <sub>3</sub>/ Co Fe <sub>2</sub> trilayers grown by pulsed laser deposition on Sr Ti O <sub>3</sub> (001) are investigated by transmission electron microscopy and electron energy loss spectroscopy. The stack is epitaxial, independent of whether the Co Fe <sub>2</sub> electrode is grown at 500 or at 50 °...
In this work we show, in a transition-metal-semiconductor system, that
both the interfacial quality and the crystallographic structure of the
samples play an important role to allow the observation of the predicted
properties of the system. To reduce the interfacial mixing, Co/Si
multilayers were grown at 90K and different crystallization qualities...
We present structural and magnetic properties of three sets of structures: as-deposited CoPt films cosputtered at 900 K on MgO(110) substrates with a Pt(110) buffer layer and CoPt films deposited by molecular beam epitaxy directly on MgO(110) substrates at 900 K, as prepared and annealed at 900 K. All layers have the L10 tetragonal structure. The c...
X-ray magnetic circular dichroism (XMCD) and X-ray photoemission spectroscopy (XPS) are performed on a Sr2FeMoO6 thin film to explain the absence of tunnel magnetoresistance in a fully epitaxial magnetic tunnel junction integrating a Sr2FeMoO6 electrode, despite the high quality of the deposition. Although superconducting quantum interference devic...
We have used the coprecipitation technique to synthesize polycrystalline Co-doped SnO2 diluted magnetic semiconductors with Co concentrations of 0, 0.5, and 2.0%. X-ray diffraction patterns showed for all samples the expected SnO2 tetragonal structure with no additional peaks corresponding to parasitic phases. Transmission electron microscopy (TEM)...
Cobalt ferrite thin films have been elaborated by pulsed laser ablation of a CoFe2 metallic target on Si (100) substrates. The films were deposited at low temperature (300 °C) in various pressures of two different reactive atmospheres (O2/N2, 20:80 and O2). We present the influence of the nature of the reactive gas and of the deposition pressure on...
It turned out from room temperature electrical resistivity and magnetoresistance studies of electrodeposited Co metal and Co(Ru) dilute alloys that the incorporation of a small amount of Ru into Co significantly reduces the anisotropic magnetoresistance (AMR). The influence of Ru on the AMR of Co is explained by a drastic change of the asymmetry of...
L10 -ordered FeNiPt2(001) thin films were prepared by the interdiffusion of FePt(001) and NiPt(001) layers codeposited on MgO(001) substrates by molecular beam epitaxy (MBE). A large uniaxial magnetic anisotropy (Ku=9.105J/m3) and a reduced magnetic transition temperature (Tc=400K) were obtained. Growth at 700K and a first annealing at 800K result...
Magnetite particles with an average size of 39 nm and good monodispersity have been synthesized by coprecipitation at 70 °C from ferrous Fe 2+ and ferric Fe 3+ ions by a (N(CH 3) 4 OH) solution, followed by hydrothermal treatment at 250 °C. The magnetite nanoparticles before the hydrothermal step display an average size of 12 nm and are highly oxid...
CoFe2/CoFe2O4 bilayers were made by pulsed laser ablation of a CoFe2 target on Si(I 0 0) substrates. The metallic layer was deposited first, in vacuum. The oxide was then deposited in an oxidizing O-2:N-2 (20:80) atmosphere. Two different procedures were used for the introduction of the oxidizing atmosphere in the deposition chamber: the laser abla...
The Co Fe <sub>2</sub>/ Co Fe <sub>2</sub> O <sub>4</sub> system has been considered for use as hard electrodes in spin valve devices. In this letter, we focus on the nature and intensity of the magnetic exchange coupling between the two phases. Co Fe <sub>2</sub>/ Co Fe <sub>2</sub> O <sub>4</sub> and Co Fe <sub>2</sub> O <sub>4</sub>/ Co Fe <sub>...
Thin films of CoFe2O4 have been fabricated by pulsed laser ablation of a metallic CoFe2 target at two different temperatures (200 and 400 °C) and in various O2:N2, 20:80 pressures [from 0.7 Pa (5×10-3 Torr) up to 26.7 Pa (2×10-1 Torr)]. Too low pressures resulted in an insufficient oxidation of the deposited material and an antiferromagnetic (Fe,Co...
Double perovskite Sr2FeMoO6 with cation disorder was investigated by means of the X-ray diffractometry, atomic resolution transmission electron microscopy, AC susceptibility, and 57Fe Mössbauer spectroscopy. Atomic resolution TEM measurements revealed the existence of domains with modulated crystal structure inside regions of the ideal double perov...
We compare structural and magnetic properties of CoPt films sputtered at 900 K on MgO(1 1 0) (with a Pt(1 1 0) buffer layer) and MgO(0 0 1) (with a Pt(0 0 1) buffer layer) substrates. We obtain a layer with the L1 0 tetragonal structure. The equiatomic L1 0 phase is a "natural" multilayer, which consists in a stacking along the [0 0 1] direction of...
We report on the possibility to prepare CoFe2/CoFe2O4 bilayers and multilayers by deposition of a CoFe2 layer followed by a partial oxidation in an Ar–O2 plasma. The CoFe2 alloy was deposited by argon sputtering onto a glass substrate and the deposition/oxidation procedure was repeated to obtain multilayered stacks. The prepared films are polycryst...
We report on the structural properties of a [Co30/Ir10]10× (Å) superlattice, as well as on the magnetic and transport properties of a Co15/Ir5/Co30 (Å) artificial ferrimagnetic system. The samples were grown by molecular beam epitaxy (MBE) on MgO(001) substrates covered with a Ir130 (Å) buffer layer. High resolution cross section and plan view tran...
The study of the CoFe2/CoFe2O4 system is of great interest due to its potential integration in magneto-resistive devices. CoFe2/CoFe2O4 multilayers were elaborated by plasma oxidation of sputtered CoFe2 layers. Exclusive attention is paid, in this paper, to the study by high resolution transmission electron microscopy of the crystallographic relati...
CoPt films grown on MgO001 substrates by molecular-beam epitaxy are expected to develop a very large uniaxial magnetocrystalline anisotropy and a high coercivity when the 001 single variant L1 0 structure develops along the growth direction. The present study investigates the growth conditions that provide the best structural quality of the films a...
We are interested in studying thin layers of CoPt alloy prepared by co-deposition sputtering. The CoPt layers are deposited on a MgO(001) substrate with a Pt(001) buffer layer. We obtain a layer with the L1 0 tetragonal structure, ordered in the growth direction. This equiatomic L1 0 phase is a ''natural'' multilayer which consists in a stacking al...
