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International audience; Transparent conductive oxide films are suitable sensitive layers for gas sensors and biosensors, provided that their intrinsic properties are controlled, notably considering their thickness dependence. The present paper reports on a study of the variation of some physical properties of polycrystalline Sb doped SnO2 films according to the film thickness. Films were deposited onto Si and glass substrates by aerosol pyrolysis. Their thickness was varied in a range of 20-280 nm. The electrical resistivity, the roughness, the optical constant, the microstructure and the texture were investigated. Correlated evolutions of the resistivity and the surface roughness are found in relation with the evolutions of both the microstructure and the texture. Two main successive growth steps were evidenced which are delimited by a critical film thickness. Below this thickness of approximately 100-120 nm, a strong dependence of physical properties with the thickness is evidenced whereas for thicker films no significant change is evidenced. A two-step growth model is proposed to explain this behaviour. This mechanism growth is to be considered in view of the integration of SnO2 films as sensitive layers in biosensors. Notably, in the case of biosensors based on the label-free electrochemical detection of biomolecules, it is recommended to use films with thicknesses ranging above the critical thickness value of 100-120 nm in order to obtain optimized, reproducible and comparable responses of biosensors. (c) 2012 Elsevier B.V. All rights reserved.

La 2 Zr 2 O 7 (LZO) thin films are used as buffer layers in second generation high Tc superconductor tapes. The microstructure of LZO films grown by metalorganic decomposition is characterized by the presence of nanovoids throughout the whole thickness of the films. We introduced an out-gassing plateau under vacuum during the pyrolysis process to decrease the size of voids. The temperature of this plateau was determined by Fourier transformed infrared spectroscopy, electron back scattering diffraction and X-Ray diffraction characterizations. The dwelling time was also varied. Transmission Electron Microscopy (TEM) studies revealed that a high heating ramp in combination with a less than an hour pyrolysis plateau decreased pore size. The deposition rate during dip-coating was also decreased to enhance out-gassing at the plateau. Successive LZO layers were deposited and energy filtered TEM images at C K-edge were performed to identify the role of carbon in the nucleation mechanisms.

International audience; Erbium-doped yttrium oxide films are prepared from yttrium acetylacetonate (Y(C(5)H(7)O2)(3)) and erbium (III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate) (Er(TMHD)(3)) under standard conditions by UV-aerosol-assisted metal-organic (AA-MOCVD), using air with controlled humidity as the carrier gas. The structure and deposition rate are optimized by studying three experimental parameters; substrate temperature, relative humidity (RH) of the carrier gas, and UV-assistance. Taking all these parameter effects under consideration, the maximum deposition rates are reached under low humidity air and with UV-assistance. Nevertheless, as-deposited Er:Y(2)O(3) films crystallize in the Y(2)O(3) cubic structure and present a very low organic contamination when depositions take place under high air humidity and with UV-assistance. The refractive index of yttrium oxide films under these conditions are relatively high, reaching 1.86 when deposited at 410 degrees C.

International audience; In this study, we investigate the growth and internal properties of polyelectrolyte multilayer films made of poly(l-lysine) and hyaluronan (PLL/HA) under pH-amplified conditions, that is, by alternate deposition of PLL at high pH and HA at low pH. We focus especially on the influence of the molecular weight of HA in this process as well as on its concentration in solution. Film growth was followed by quartz crystal microbalance and by infrared spectroscopy to quantify the deposited mass and to characterize the internal properties of the films, including the presence of hydrogen bonds and the ionization degree of HA in the films. Film growth was significantly faster for HA of high molecular weight (1300 kDa) as compared with 400 and 200 kDa. PLL was found to exhibit a random structure once deposited in the films. Furthermore, we found that PLL-ending films are more stable when they are placed in PBS than their HA counterparts. This was explained on the basis of more cohesive interactions in the films for PLL-ending films. Finally, we quantified PLLFITC diffusion into the films and observed that PLL diffusion is enhanced when PLL is paired with the HA of high MW. All together, these results suggest that besides purely physicochemical parameters such as variation in pH, the molecular weight of HA, its concentration in solution, and the possibility to form intermolecular HA association play important roles in film growth, internal cohesion, and stability.

International audience; We report on a comparative investigation of the incorporation of group III, IV and V impurities in 3C–SiC heteroepitaxial layers grown by the vapour–liquid–solid (VLS) mechanism on on-axis a-SiC substrates. To this end, various Si-based melts have been used with addition of Al, Ga, Ge and Sn species. Homoepitaxial a-SiC layers grown using Al-based melts were used for comparison purposed for Al incorporation. Nitrogen incorporation depth profile systematically displays an overshoot at the substrate/epilayer interface for all the layers. Ga and Al incorporations follow the same distribution shape as N whereas this is not the case for the isoelectronic impurities Ge and Sn. This suggests some interaction between Ga/Al and N coming from the high bonding energy between the group III and V elements, which does not exist with Ge and Sn. This is why both incorporate as a cluster. A model of incorporation is proposed taking into account metal-N and metal-C bonding energies together with the solid solubility of the corresponding nitrides.

International audience; La2Zr2O7 (LZO) formation of bulk powders and of films by Chemical Solution Deposition (CSD) process have been studied using propionates. The treatment involved a one step cycle in the reducing forming gas (Ar-5%H2) to be compatible with Ni-5at%W RABITS. Large amount of residual carbon was found in LZO powders formed in these conditions (10 wt %). The volume fraction of the cube texture in LZO films on Ni-5at%w RABITS was found to be a function of the speed of the gas flown above sample. This phenomenon is discussed in considering the C deposited from the carbon-containing gases emitted during the pyrolysis of the precursor. Using proper conditions (950 °C and the speed of gas of 6.8×10-2 m/s), LZO films with good surface crystallinity could be obtained on Ni-5at%W RABITS as demonstrated by X-ray diffraction, electron backscattered diffraction and RHEED. The existence of residual carbon in oxide films is a common question to films deposited by CSD processes under reducing condition.

The NiRABiTS/La2Zr2O7MOD/YBa2Cu3 O7MOCVD structure is a promising architecture for (YBCO) coated conductors. We succeeded in growing highly textured superconducting YBCO films on LZO-buffered Ni-5 at%W (NiW) substrates by metalorganic chemical vapor deposition (MOCVD). A single LZO buffer layer grown by metalorganic decomposition (MOD) is sufficient to ensure structural compatibility between YBCO and Ni, and to protect the substrate from oxidation during YBCO deposition. Textured Ni substrates obtained by rolling technique have intrinsic defects such as grain boundaries and rolling scratches. It is not easy to highlight their effects on LZO and YBCO films by usual measurements like XRD or SEM. The combination of Electron Backscattered Diffraction (EBSD) and Magneto-Optics imaging (MO) is useful to image grain boundaries and flux distribution in coated conductors. It provides complementary information on superconducting film qualities. These two techniques allowed us to understand how the microstructure of the LZO buffer layer and thus of the YBCO film is linked to the current density in this simple heterostructure.

First and original results are reported regarding the surface evolution of two kinds of oxide film after covalent grafting and hybridization of hairpin oligonucleotide probes. These hairpin probes were monolabelled with a 1.4 nm gold nanoparticle. One kind of oxide film was rough Sb doped SnO 2 oxide film and the other kind was smooth SiO 2 film. Same process of covalent grafting, involving a silanization step, was performed on both oxide surfaces. Atomic force microscopy (AFM) was used to study the evolution of each oxide surface after different steps of the process: functionalization, probe grafting and hybridization. In the case of rough SnO 2 films, a slight decrease of the roughness was observed after each step whereas in the case of smooth SiO 2 films, a maximum of roughness was obtained after probe grafting. Step height measurements of grafted probes could be performed on SiO 2 leading to an apparent thickness of around 3.7 ± 1.0 nm. After hybridization, on the granular surface of SnO 2 , by coupling AFM with SEM FEG analyses, dispersed and well-resolved groups of gold nanoparticles linked to DNA duplexes could be observed. Their density varied from 6.6 ± 0.3 × 10 10 to 2.3 ± 0.3 × 10 11 dots cm −2 . On the contrary, on smooth SiO 2 surface, the DNA duplexes behave like a dense carpet of globular structures with a density of 2.9 ± 0.5 × 10 11 globular structures cm −2 .

We report on the heteroepitaxial growth of 3C-SiC layers by Vapor-Liquid-Solid (VLS) mechanism on various α-SiC substrates, namely on- and off-axis for both 4H and 6H-SiC(0001), Si and C faces. The Si-Ge melts, which Si content was varied from 25 to 50 at%, were fed by 3 sccm of propane. The growth temperature was varied from 1200 to 1600°C. It was found that singledomain 3C-SiC layers can be obtained on 6H-SiC off and on-axis and 4H-SiC on-axis, while the other types of substrate gave twinned 3C-SiC material. As a general rule, one has to increase temperature when decreasing the Si content of the melt in order to avoid DPB formation. It was also found that twinned 3C-SiC layers form at low temperature while homoepitaxy is achieved at high temperature.

Thin films of HfO 2 were deposited on (100)Si/SiO 2 by liquid-injection metal-organic (MO)CVD using [Hf(O t Bu) 2 (mmp) 2 ) dissolved in octane as the precursor. A precise thickness control on the nanometer scale was obtained by controlling the volume of injected precursor solution. Films of thickness below 10 nm were studied by means of X-ray reflectometry (XRR), attenuated total reflection infrared spectroscopy (ATR), and atomic force microscopy (AFM). Films are amorphous for deposition temperatures below 350 °C; they are polycrystalline at deposition temperature of 360 °C and above, except for ultrathin films. Under the deposition conditions used, the main crystalline phase is the monoclinic phase as shown by ATR. AFM reveals smooth surfaces for both amorphous and polycrystalline films. The equivalent oxide thickness measured in MOS structures depends linearly on the film's thickness, and a relative dielectric permittivity e r of 19 is obtained, which is consistent with that expected for the monoclinic phase of bulk HfO 2 . Leakage current densities of the order of 1×10 -4 A cm -2 for films with a physical thickness of 3.1 nm are obtained. Rapid thermal annealing under ammonia reduces the fixed charges in the oxide (Q ox < 1×10 11 cm -2 ) as well as the interfacial charge density (D it peak = 8×10 10 eV -1 cm -2 ).

In view of developing DNA biochips based on electric detection, well controlled DNA functionalisation of conductive substrate electrode is a challenging process. In this study, the whole process of functionalisation onto home made conductive films with controlled properties has been performed. The latter were Sb doped SnO2 thin films with increasing thickness deposited on oxidized Si using aerosol pyrolysis technique. Their surface morphology shows a roughness increasing with the thickness in association with the polycrystalline microstructure. The silanization process of the as-deposited films was particularly controlled using a combination of different techniques such as wettability and spectroscopic techniques, i.e. X-ray-reflectometry and X-ray photoelectron spectroscopy. The different results confirmed the presence of the silane on the films. The DNA grafting and hybridization to complementary DNA target labelled with fluorescent markers were clearly demonstrated using fluorescence microscopy. The influence of the Sb doped SnO2 film thickness in close relation with the SiO2 thickness on the fluorescence intensity was emphasized. This study has proved the feasibility of a high quality DNA functionalisation of conductive SnO2 films with controlled properties. Moreover, this validates the use of such films as potential substrate electrode for biochips based on the electric detection of DNA hybridization. (c) 2005 Elsevier B.V. All rights reserved.

A reel-to-reel MOCVD system has been designed to synthesize high quality YBCO coated tapes on Ni RABiTS (Rolling Assisted Biaxially Textured Substrates). Special buffer layer stackings have been deposited to improve the quality of the superconductor. Several buffer layers architectures rose in dense YBCO films with a similar texture, but fluctuations in critical current densities (Jc) were measured. Therefore, a more accurate and detailed measurement method such as Electron Backscattered Kikuchi Diffraction (BKD) has been used to assess the crystalline quality of the stackings. The studied sequence here was NiW /NiO /YSZ /CeO2 /YBCO. The grain and the subgrain structure as well as their size and disorientation have been analysed for each layer. First on Ni tape, secondly on the protecting NiO (200) buffer layer, then on the following CeO2 (200) film. Finally, unpublished BKD diagrams of the subsequent YBCO (001) films have been reported here. The grain evolution has been successfully studied showing the buffer layer effect on the grain growth. In this work we highlight the correlation between the misorientation of the grains (inducing NiO (111) growth and cracks) and the grain boundary morphology (size, grooves). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

CeO2 films formation is studied on single crystals and (1 0 0) oriented nickel substrates (Ni RABiTs) via the metal organic deposition technique. Ce(III) 2-ethylhexanoate: Ce(EH)3, in solution in toluene is used as chemical precursor. Homogeneous films are easily deposited by spin coating and their crystallisation performed at 800–900 °C leads to bi-axial texturation on MgO, STO and Ni RABiTs with the (2 0 0) planes parallel to the surface. In the case of Ni RABiTs, the degree of disorientation is directly linked to that of the template substrate. For Ni substrates, the conditions implemented avoid the oxidation of the Ni but allow the formation of the cerium oxide. These films are good candidates to be buffer layers in the architecture of coated conductors for high Tc superconducting cables applications.

As the sharpness of the metal-oxide interface is of major importance to develop efficient structures, we have studied the thermal stability of interfaces in a series of thin film samples where the metallic component was either Pt, Al, Pd, Ni, Nb or Ti deposited on a thin HfO2 film. Thermodynamic considerations have been carried out to determine the possible products of metal-oxide reaction at a temperature of 500 °C. The evolution of the as-deposited thin film structures as a function of annealing temperature has been analysed by combining various techniques and specifically using X-ray reflectometry. This particular technique allows one to detect very thin embedded interfaces, distinguish small density variations and determine accurately the thickness, the normal roughness and the density of each layer. In addition, reflectometry results have been correlated with atomic force microscopy and transmission electron microscopy observations of selected samples. Our results indicate that platinum, palladium and nickel are stable up to 500 °C on hafnium oxide. Annealed aluminium, an interfacial layer forms, whereas niobium and titanium present a diffuse interface.

A reel-to reel MOCVD system has been developed for a fast and economic process to get high quality YBCO coated conductor tapes. Several oxides buffer layer sequences (based on YSZ, CeO/sub 2/, Y/sub 2/O/sub 3/...) were then grown epitaxially on two kinds of tape. Effective stacking for MOCVD reported here are YSZ/Y/sub 2/O/sub 3//YBCO and YSZ/CeO/sub 2//YBCO, respectively, on oxidized Ni RABiTS microalloys (0,1% W) and on SS/YSZ (IBAD) tapes. First, EBSD and AFM techniques have been used to characterize the substrates. Superconducting YBCO films were fully characterized by SEM, XRD and AC susceptibility measurements Epitaxial growth was depicted with a strong in-plane and out-of plane texture: FWHM of YBCO /spl phi/-scans were 8.5/spl deg/ on Ni tape and 9/spl deg/ on IBAD Hastelloy tapes. High performances were also measured by AC susceptibility, with J/sub c/ values of 0.6 MA/cm/sup 2/ at 77 K (0 T) on Ni tape and close to 1 MA/cm/sup 2/ on IBAD substrates, with a sharp transition (/spl Delta/T/sub c/ < 0.4 K) and a T/sub c/ onset at 90 K. Deposition of 2 meter buffered YSZ and CeO/sub 2//YBCO films have also been performed showing good in-plane alignment (/spl phi/-scan YSZ: FWHM = 11/spl deg/) with a tape velocity set at 4 m/h.

Biaxially textured buffer layers and YBa 2 Cu 3 O 7 (YBCO) films were grown on NiO/Ni based substrates by pulsed injection MOCVD. High quality biaxially textured NiO layers have been prepared following an optimised recrystallisation–oxidation process. The yttria stabilized zirconia (YSZ) and its combination with CeO 2 and/or Y 2 O 3 were investigated in the role of buffer layers for YBCO. Thin biaxially textured buffer layers were deposited in a temperature range from 600 to 800 °C. The best superconducting properties correspond to the Ni/NiO/YSZ/Y 2 O 3 /YBCO architecture: YBCO layers were grown epitaxially and exhibited a critical temperature T c ∼90 K ( ΔT c ⩽1 K) and critical current densities J c ⩾5×10 5 A/cm 2 at 77 K.

Biaxially textured YBa 2 Cu 3 O 7 (YBCO) thin films, yttria stabilized zirconia (YSZ) and yttria (Y 2 O 3 ), CeO 2 buffer layers were grown in situ on NiO/Ni based substrates by Pulsed Injection MOCVD (PICVD) using monoglyme solutions of β-diketonates (Cu(thd) 2 , Ba(thd) 2 , Y(thd) 3 , Ce (thd) 2 , Zr(thd) 4 ). High quality textured nickel oxide layers have been prepared by SOE (Surface Oxydation Epitaxy) following an optimized recrystallisation-oxidation process.Thin YSZ/Y 2 O 3 biaxially textured buffer layers (thickness 200nm/200 nm) were deposited in a wide range of temperature (from 600°C to 800°C). Subsequent YBCO layers (thickness 750nm) on Ni/NiO/YSZ/Y 2 O 3 were grown epitaxially (ω-scan of YBCO FWMH=5°) and exhibited critical current densities Jc ≥3.10 5 A/cm 2 with a critical temperature Tc=90K and ΔTc ≤ 1 K. The best results were obtained for deposition temperatures of 600°C for YSZ, 675°C for Y 2 O 3 and 800°C for YBCO.

New phospho-silicide CoSi 3 P 3 has been synthesized and its crystal structure determined by single crystal X-ray diffraction ( R = 0.035, R W = 0.042). CoSi 3 P 3 ( Z = 4) crystallizes with the pseudo-orthorhombic symmetry and meriedric twinning in the space group P 2 1 . Lattice parameters are a = 5.899(1) A, b = 5.703(1) A, c = 12.736(1) A, β = 90°. The crystal structure can be described by zigzag chains of octahedra occupied by Co atoms alternating with zigzag chains of tetrahedra occupied by P or Si atoms. Single crystals of this phase have been investigated at room temperature by polarized Raman spectroscopy in the 100–600 cm −1 range. The results confirm the monoclinic symmetry of CoSi 3 P 3 . Magnetic susceptibility and electronic conductivity have been measured between 300 and 10 K. CoSi 3 P 3 is diamagnetic at room temperature and paramagnetic below 65 K. CoSi 3 P 3 is semiconducting at room temperature with an energy gap of about 0.12 eV.

International audience; Optimum parameters for the growing of YMnO3 films by pulsed liquid injection metalorganic chemical vapor deposition have been studied. Si substrates were used for the optimization of the deposition process. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that polycrystalline single phase YMnO3 films can be obtained for an optimal ratio of Y and Mn on the injected solution and either amorphous, metastable orthorhombic, and/or hexagonal YMnO3 phases can be obtained depending on the deposition temperature and precursors ratio. In a second stage, YMnO3 films were grown on SrTiO3 substrates. Pure epitaxial orthorhombic YMnO3 phase was confirmed by XRD. The films microstructure, characterized by scanning electron microscopy and TEM, shows a columnar growth. Each columnar grain grows epitaxially with three possible orientations.

New phospho-silicides RhSi 3 P 3 and IrSi 3 P 3 were synthesized and their crystal structures were determined by single crystal X-ray diffraction techniques. Both compounds are isostructural at room temperatures and crystallize with the monoclinic symmetry in the space group C2. Lattice parameters are a = 6.626(1) A, b = 7.210(1) A, c = 5.522(l) A and β = 118.31(1) ° for RhSi3P3 and a = 6.577(2) A, b = 7.229(2) A, c = 5.484(2) A and β = 117.91(2) ° for IrSi 3 P 3 . The crystal structure can be described by separated octahedra of Si or P atoms surrounding metallic atoms Rh or Ir. The octahedra are connected to each other by chains of type M-Si/P-Si/P-M. The atoms of P and Si are fourfold coordinated.

Single crystals of new high phosphorus-silicon content compounds of transition metal FeSi4P4, RuSi4P4 and OsSi4P4 have been obtained from tin flux. Powders of the same composition have been prepared by reaction of the elemental components in evacuated silica tubes. These compounds are isomorphic. Crystal structure of FeSi4P4 and RuSi4P4 have been determined from four-circle diffractometer data of single crystals.

Efforts to fabricate superconducting wires made of YBa2Cu3O7 (YBCO) on La2Zr2O7 (LZO) buffered and biaxially textured Ni-5 at.%W (NiW) are described. Wires were manually shaped from LZO buffered NiW tapes. Different diameters were produced: 1.5, 2 and 3 mm. The wires were further covered with YBCO grown by metal organic chemical vapor deposition (MOCVD). We developed an original device in which the round substrate undergoes an alternated rotation of 180° around its axis in addition to a reel-to-reel translation. This new approach allows covering the whole circumference of the wire with a YBCO layer. This was confirmed by energy dispersive x-ray spectroscopy (EDX) analysis coupled to a scanning electron microscope (SEM). For all wire diameters, the YBCO layer thickness varied from 300 to 450 nm, and the cationic composition was respected. Electron backscattering diffraction (EBSD) measurements were performed directly on an as-deposited wire without surface preparation allowing the investigation of the crystalline quality of the film surface. Combining EBSD with XRD results we show that YBCO grows epitaxially on the LZO buffered NiW wires. For the first time, superconductive behaviors have been detected on round substrates in both the rolling and circular direction. Jc reached 0.3 MA cm−2 as measured at 77 K by transport and third-harmonic detection. Those preliminary results confirm the effectiveness of the MOCVD for complex geometries, especially for YBCO deposition on small diameter wires. This approach opens huge perspectives for the elaboration of a new generation of YBCO-based round conductors.

International audience; In situ synthesis of inorganic nanoparticles (NPs) in polyelectrolytes multilayers (PEMs) has recently gained much attention. Due to the versatility of their composition, PEMs offer a unique opportunity to synthesize a variety of NPs. So far, mostly cationic precursors have been used and only few studies have investigated the possibility of using amine groups to bind anionic precursors. Here, we use exponentially growing poly(L-lysine)/hyaluronan (PLL/HA) films as a nanoreservoir to bind and sequester aurochlorate (AuCl4-) anions thanks to the large number of free amine groups. The polypeptide-polysaccharide reactive template enabled the formation in a spatially-confined environment of gold NP at a very high yield. The synthesized gold NPs were homogenous and well-dispersed in the nanocomposite. Importantly, there was no particular effect of the film-ending layer (either PLL or HA). The largest particles of similar to 9 nm and the largest amount of gold were obtained at acidic pH of 3. When the pH was increased, smaller and more numerous NPs were synthesized but the total amount of gold was lower. Based on UV-visible spectrometry, FTIR and TEM data, we finally propose a scheme for the mechanism of gold NPs formation, in which several groups of PLL and HA contribute to the binding of gold ions, the nucleation and growth of NPs, and their stabilization in the "bulk" of the film. (C) 2012 Elsevier Inc. All rights reserved.

1. IntroductionErbium-doped silica materials have received much researchinterest, since they emit light at 1.5 m, which is crucial fortelecommunication applications [1,2]. But erbium-doped silicateglasses are strongly limited by cooperative upconversion effectswhich occur even at low rare earth concentration in this materialdue to the rare earth clustering [3]. In order to avoid this phe-nomenon, crystalline host materials such as alumina have beenproposed as amplifying media [3,4]. The deposition of erbium-doped aluminium oxide films has been investigated by usingAerosol AssistedMOCVD(AA-MOCVD)atlowtemperaturedeposi-tion [5].However,thequalityofthealuminiumoxidefilmsreportedto date has not been so impressive. These films usually containedlarge amounts of carbon resulting from incomplete decompositionof the organic source [6]. In addition, the film growth rate was low.In thispaper,wereporttheeffectofUV-assistanceandairhumidityon the growth of erbium-doped alumina by AA-CVD.

International audience; TiO2-SiO2 nanocomposite films of various thicknesses have been deposited via a multilayer sol-gel route. These films exhibit a natural and persistent superhydrophilicity, which allows considering new applications for easy to clean surfaces. Atomic force microscopy, scanning and transmission electron microscopy, as well as ellipsometry and UV/visible spectrometry measurements, were performed to study how the multilayer procedure influenced the morphology and composition of composite films in relation to their thickness. The natural and photo-induced wettability of these films was studied and discussed in relation to morphology, composition, and thickness features. It is concluded that, while such features did not significantly influence the natural wettability of nanocomposite films, their photo-induced wettability was considerably enhanced when increasing their thickness, which favored a faster superhydrophilicity photo-regeneration when this natural property started to disappear after a long aging period in ambient atmosphere.

Thin films of thulium and ytterbium-doped titanium oxide were grown by metal-organic spray pyrolysis deposition from titanium(IV)oxide bis(acetylacetonate), thulium(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate) and ytterbium(III) tris(acetylacetonate). Deposition temperatures have been investigated from 300{\deg}C to 600{\deg}C. Films have been studied regarding their crystallity and doping quality. Structural and composition characterisations of TiO2:Tm,Yb were performed by electron microprobe, X-ray diffraction and Fourier transform infrared spectroscopy. The deposition rate can reach 0.8 \mum/h. The anatase phase of TiO2 was obtained after synthesis at 400{\deg}C or higher. Organic contamination at low deposition temperature is eliminated by annealing treatments., Comment: 6 pages, 6 figures

International audience; The promising potential of a new platform for the label-free DNA detection by Surface Enhanced Raman Spectroscopy (SERS) is reported. This platform is composed of silver nanoparticles distributed over the surface of a TiO2 (anatase) film. DNA molecules are immobilized on the platform using a simple grafting procedure. The elaboration and biomodification of the platform involve wet chemistry routes and benefit from specific properties of its components. First, the photocatalytic activity of TiO2 films is used for the photoreduction of Ag salts leading to the Ag degrees nanoparticle deposition. Second, the grafting and surface distribution of DNA benefit from both the photo-induced hydrophilicity of TiO2 films and the chemical affinity between metallic silver and amine ligands. Despite a broad size distribution of the Ag degrees nanoparticles which affects the reproducibility of DNA Raman spectra, specific changes of DNA Raman line intensities observed in single strand and hybridized DNA attest that hybridization can reliably be detected and that a spatially addressed DNA detection is possible. (C) 2011 Elsevier B.V. All rights reserved.

International audience; We recently achieved heteroepitaxial growth of high-quality 3C-SiC on a 6H-SiC 0001 plane using an Si-Sc solvent. The present study seeks to determine the polytype transition mechanism from 6H to 3C that occurs during growth. 3C-SiC grows by 2D nucleation, which gives rise to flat domains, whereas 6H-SiC grows by spiral growth originating from threading screw dislocations in the seed crystal. 3C-SiC expands laterally, covering the spiral growth of 6H-SiC. This preferential growth of 3C-SiC can be explained in terms of geometrical selection due to different growth rates of the two polytypes. We developed a simple model that considers the step height and the step density. It predicts that growth of 3C-SiC by 2D nucleation will have a higher growth rate than 6H-SiC spiral growth in a certain supersaturation range. (C) 2011 Elsevier B.V. All rights reserved.

Thin‐film growth and compositional effects of c‐axis oriented YBa2Cu3O7−x (YBCO) thin films synthesized by metalorganic chemical vapor deposition have been investigated. The formation of single cation films using tetramethylheptanedionate precursors was shown to be mass controlled, exhibiting a ratio of deposited to evaporated species in the increasing order Ba, Y, and Cu. The physical properties of off‐stoichiometric YBCO films deposited on MgO substrates were measured in the compositional range 1.1≤Ba/Y≤2.3 and 1.5≤Cu/Ba≤4.6. While structural properties such as c‐axis values and rocking curves appeared unaffected to variations in cation stoichiometry, morphology was observed to be extremely sensitive even to slight changes in composition. Off‐stoichiometric layers with Cu/Ba≳1.5 were observed to exhibit Cu‐rich precipitates embedded in a 1:2:3 YBCO film matrix. The zero‐resistivity temperatures were above 77 K for all cation film compositions measured. However, sharp ac‐susceptibility transitions were r...

International audience; The influence of nitrogen impurity on the stabilization of 3C-SiC polytype has been studied during vapour-liquid-solid (VLS) growth on 6H-SiC(0001) seed with Si-Ge melt. By changing the partial pressure of N2 during growth, it was found that the proportion of 3C-SiC inside the grown material increases with N2 partial pressure. 6H inclusions are only found for high purity (low N2 content) conditions. The possible interactions proposed to explain this effect are divided in two effects: i) lattice parameter modification and ii) surface induced lateral enlargement variation. A combination of both effects is suspected.

International audience; The contact between alpha-SiC crystals and Si-Ge based melts provokes the nucleation of 3C-SiC islands on the crystal surface. Evolution of these islands as a function of various parameters was studied. On both 4H and 6H substrates, it was found that, after nucleation, 3C-SiC islands first enlarge and may form a complete 3C layer under certain conditions. The 3C deposit can then be dissolved by the liquid phase at high temperature or for prolonged contact at relatively moderate temperature. The graphite crucible is proposed to play a central role in these enlargement and dissolution mechanisms by providing extra carbon atoms on the seed surface (enlargement) or provoking thermal induced carbon transport toward the sidewall (dissolution). Several differences between the use of 4H and 6H substrates were also observed. (C) 2009 Elsevier BM. All rights reserved.

A conductor wire consisting of Ag/YBCO/LZO/Ni?5?at.%W RABITS has been processed as a cylindrical tube of millimetre diameter. Textured layers of LZO and YBCO were grown by chemical methods. Electron backscattered diffraction was used to characterize the texture of the LZO surface which was good enough to be used as a template for YBCO deposition. The YBCO layer was textured and had a superconducting transition at 88?K. However, the quality of both LZO and YBCO must be improved to consider practical applications in electrical current transport. On the other hand, this work demonstrates that epitaxial growth of oxides on a curved surface by using chemical methods is possible.

International audience; The early stage of 3C-SiC nucleation and islands enlargement on on-axis 6H-SiC(000 (1) over bar) (C face) were studied by changing the conditions of interaction of a Si(0.25)Ge(0.75) melt with the SiC substrate. After changing the temperature or the plateau duration at a fixed temperature, evolution in terms of shapes and sizes of the 3C-SiC islands was found. The observed islands enlargement in the early stage of interaction was explained by taking into account a carbon transport from the graphite crucible to the seed. Once the crucible reached its thermal and thermodynamical equilibrium with the liquid, the islands started to be dissolved inside the melt due to a possible but small thermal gradient from the seed (hotter) to the sidewalls of the crucible (colder). By adding propane in the gas phase before reaching this equilibrium, SiC growth by vapour-liquid-solid (VLS) mechanism was achieved and the 3C-SiC layers thus obtained were always found to contain a high density of twins. This is probably due to the fact that the density of 3C nuclei, after interaction between the SiGe melt and the SiC seed, was always very high which should prevent orientation selection, unlike the case of Si face. (c) 2009 Elsevier B.V. All rights reserved.

International audience; Vertically aligned MgO nanowires were epitaxially grown at 600 degrees C on Au-coated MgO (001) substrates by metal organic chemical vapor deposition using Mg(tmhd)(2) precursor. Discrete Au particles were embedded in the wires and distributed along the central axis. Scanning and transmission electron microscopy show that the orientation, diameter, and length of the wires strongly depend on the processing conditions such as oxygen partial pressure and reactive species flow rate as well as the starting Au thickness. Diameters down to 15-20 nm were obtained. The growth can be switched from vertical to horizontal wires by decreasing the period at which reactants are supplied.

Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh2Si2, U(Rh0.35Ru0.65)2Si2, NdRh2Si2 and CeRh2Si2. In order to obtain information on the localisation and diffusion properties of the muon, some measurements have been performed also on isostructural diamagnetic compounds. From our measurements. information on the magneto-crystalline anisotropy of the samples has been obtained. Depending on the compound, we found a static field distribution below the Neel temperature. We discuss the implications of this result on the magnetic properties of the various materials.

8 pages; International audience; Chemical deposition methods like MOD and MOCVD are promising approaches for coated conductors (CCs) due to their reduced cost and easy scaling. High quality La2Zr2O7 (LZO) buffer layers were prepared by MOD on Ni-5%at.W (NiW) RABiTS and subsequent YBCO layers (450 to 800 nm thick) were deposited by pulsed injection MOCVD, leading to a simple low cost architecture NiWRABiTS/LZOMOD/YBCOMOCVD. In this novel combination of MOD and MOCVD approach, a single LZOMOD buffer layer is sufficient to ensure structural compatibility between YBCO and NiW, and protect the substrate from oxidation during YBCO MOCVD. YBCO films were epitaxially grown on LZO and exhibited critical current densities Jc close to 1 MA/cm2 at 77 K with a critical temperature Tc =91 K and DTc < 1 K.

Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh2Si2 and CeRh2Si2. As the magnetic structure of these compounds is well known, these measurements can help to characterise their magnetic properties probed by μSR and to understand the μSR results of the heavy fermion compounds of the same crystallographic family. Our measurements show that the muons occupy two different crystallographic sites. The spectra of URh2Si2 and CeRh2Si2 in the magnetically ordered states are very different, probably reflecting their different magnetic structures. The spectra obtained on CeRh2Si2 are similar to the published spectra of the heavy fermion compound CeCu2.1 Si2. Muon spin rotation measurements on LaNi2As2 indicate that the muon is diffusing at 150 K.

We have performed 57Fe Mossbauer measurements on aligned iron-doped crystallites of La2-xSrxCuO4-y. From the intensity ratio of the two quadrupole lines we deduce that the main axis of the elctric-field gradient does not coincide with the c-axis of the lattice. This surprising result indicates that at the iron ion the local symmetry around the c-axis is not fourfold. The implications of this result are briefly discussed.

TiO2 thin films have been deposited at low temperature using a new atmospheric pressure deposition process, which combines remote Atmospheric Pressure (AP) Plasma with Pulsed Injection Metallorganic Chemical Vapour Deposition (PIMOCVD). The effects of post-discharge plasma and deposition parameters have been studied with respect to the deposition kinetics, morphology, and microstructure of TiO2 films. It is shown that well-crystallised TiO2 anatase films can be obtained at a temperature of only 275 °C. © 2007 Elsevier B.V. All rights reserved., This work has been financially support by the French project “Diademe”, funded by the MINEFI.

This article explores the possibilities of using Sb doped SnO2 thin films as potential electrode substrates for biosensors. Two series of electrodes were modified with electrogenerated functionalised polymeric films. The polymers investigated were biotinylated poly(ruthenium pyrrole) and poly(pyrrole benzophenone). AFM studies show polymer morphologies depending on the nature and roughness of the substrates.

International audience; The transfer by wafer-bonding of single-crystalline SiC thin films to a polycrystalline SiC support to obtain a “quasi-wafer” is an attractive way for lowering the cost of silicon carbide wafers. Such a process needs high quality polycrystalline substrates, with controlled and high-level bulk properties (thermal conductivity, electrical resistivity) and with very low surface roughness and surface bowing. Currently, polycrystalline SiC wafers which are available are siliconized SiC or CVD processed SiC wafers. Siliconized ceramic wafers are very heterogeneous (mixture of 3C, 6H, 15R and silicon), while CVD ones are of better quality (homogeneous and textured 3C). However neither the siliconized SiC nor the CVD SiC can be CMP polished with low roughness over large dimension. In this paper, wafers with large and textured grains (&gt ;1cm) are processed and characterized. The polishing of such structures is studied and optimized to obtain low surface roughness. To meet these requirements high temperature processes used for single crystal growth were selected. Structural investigations performed on the grown ingots showed an important influence of the used seed since no preferential crystallographic orientation was observed during the growth. The final polishing quality was of high level but step heights were observed between grains.

International audience; 3C-SiC nucleation on (0 0 0 1) 6H-SiC nominal surfaces was investigated during the heating-up step of the continuous feed-physical vapour transport (CF-PVT) growth technique. We focused on the heteropolytypic 6H-3C transition under silicon-rich gas phase for temperatures from 1800 to 2000 °C. Seed polarity effects were studied. The 3C proportion reached a maximum for a well-defined temperature which was higher on the C face than on the Si face. The 2D nucleation threshold for the 3C polytype was around 1825 °C on the Si face. 3C formation was closely connected to the surface morphology, i.e. to the development of facets (on-axis regions) on the Si face.

Nd/sub 2/Fe/sub 14/BH/sub x/ micron-size loose particles are synthesized by the oxide reduction-diffusion technique. When excess Ca is used as a reducing agent, an exothermic reaction is observed by washing under water, with production of native hydrogen that diffuses in the interstitial sites of the alloy. Depending on the experimental conditions, different contents of hydrogen intercalation are observed, with x ranging from x approximately 0 to x approximately 4-5. Cell parameters are observed to quickly increase with hydrogen uptake, resulting in a drastic and regular decrease of the coercivity. In order to understand the relation between the coercivity and the content of hydrogen uptake, 2 to 4 mu m size powders of a highly coercive Nd/sub 2/Fe/sub 14/B industrial alloy are submitted to a native hydrogen environment obtained through different chemical conditions. A very reliable relationship is established between the cell parameters (and thus the content of interstitial hydrogen) and the coercivity of the alloy particles. >

M-hexaferrite single crystals of chemical formulae BaFe12-2xIrxO19 with Me = Zn, Co and 0.3 < x < 0.9, were grown from a Bi2O3 flux. Crystal structure refinement studies showed that Ir and Zn cations are exclusively located on octahedral sites in R structural blocks. Saturation magnetizations of these ferrites are consistent with Gorter's spin arrangement, considering there to be a magnetic moment of 5μB on the Ir4+ cations.

International audience; Thick polycrystalline AlN layers were grown at low pressure using high temperature chemical vapor deposition (HTCVD). The experimental setup consists of a graphite susceptor heated by an induction coil surrounding a vertical cold wall reactor. The reactants used were ammonia (NH(3)) and aluminum chloride (AlCl(x)) species formed in situ via chlorine (Cl(2)) reaction with high purity aluminum wire. AlN films were deposited on a 55 mm diameter graphite susceptor between 1200 and 1600 degrees C. AlN layers have been characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and electron backscattered diffraction. The influence of temperature on growth rate, surface morphology, grain size, and crystalline structure is presented. Growth rates of up to 230 mu m/h have been reached. A nonpolar preferred orientation of AlN films is stabilized at a higher temperature. The potential of investigation in this new range of experimental conditions, i.e., high temperature and high growth rate, as well as deposition of nonpolar AlN crystals, is very promising for epitaxial growth and extends the field of applications. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3536477] All rights reserved

Y 2 Fe 17 and other REFebased compounds have been successfully nitrogenated by heating mixtures of powdered alloy with sodium azide at temperatures between 300 and 450°C. The high nitrogenation power of NaN 3 seems to come from its low decomposition temperature and an improved nitrogen diffusion rate through the particle surfaces cleaned by sodium.

The magnetoresistance of step-edge junctions based on La0.7Sr0.3MnO3 films was investigated using a Wheatstone bridge geometry. Two types of step-edge structures were prepared: The step was either fabricated by ion-beam etching of SrTiO3 (001) substrates or by wet-chemical etching of an insulating NdMnO3 layer deposited on SrTiO3 (001). Both the magnetoresistive and insulating layers were deposited by injection-metalorganic chemical vapor deposition. The temperature dependence of the magnetoresistance was explored for both types of junctions in different field orientations. The largest low-field magnetoresistance was obtained when the step was formed directly in the substrate; it was observed up to room temperature (∼1% for an applied field of ∼0.05 T) and at 40 K, it increased ∼12% under an applied field of ∼0.1 T. The hysteretic behavior for the two types of junctions appeared to be very different.