Publications

2014

• Epitaxial growth of Si(Ge) materials on Si and GaAs by low temperature PECVD: towards tandem devices
  
  • Cariou Romain
  , 2014. This thesis focuses on epitaxial growth of Si and SiGe at low temperature (200°C) by Plasma Enhanced Chemical Vapor Deposition (PECVD), and its application in thin film crystalline solar cells. Our goal is to gain insight into this unusual growth process, as well as to investigate the potential of such low temperaturedeposited material for single and multi-junction solar cells. First, we have proposed a one pump-down plasma process to clean out-of-the-box c-Si wafer surface and grow epitaxial layers of up to 8µm thick, without ultra-high vacuum, in a standard RF-PECVD reactor. By exploring the experimental parameters space, the link between layer quality and important physical variables, such as silane dilution, ion energy, or deposition pressure, has been confirmed. Both material and electrical properties were analyzed, and we found that epitaxial quality improves with film thickness. Furthermore, we could bring evidence of SiGe and Ge epitaxial growth under similar conditions. Then, with the whole process steps <200°C, we have achieved PIN heterojunction solar cells on highly doped substrates with 1-4µm epitaxial absorber, reaching 8.8% efficiency (without light trapping) and 80.5% FF. Replacing Si absorber by epitaxial Si0:73Ge0:27 resulted in 11% boost in Jsc. The use of an engineered wafer/epitaxial layer interface and stress enables easy lift-off: e.g. we successfully bonded 1.5µm thick 10cm^2 epi-Si to glass. Additionally, we have considered the impact of photonic nanostructures on device properties. Together, the control of growth, transfer and advanced light trapping are paving the way toward highly efficient, ultrathin (<10µm) and low cost c-Si cells. Finally, in contrast with general trend of growing III-V semiconductors on Si, we have studied the hetero-epitaxial growth of Si on III-V. Good crystal quality was achieved by direct Si deposition on GaAs, thanks to reduced thermal load and suppressed polarity issues in this approach. Using MOCVD, we could build GaAs cells with 20% efficiency and III-V tunnel junctions reaching 55A/cm^2. Tunneling improvement upon H-plasma exposure was shown. Those results, combined with III-V layer lift-off, validate milestones toward high efficiency tandem AlGaAs(MOVD)/SiGe(PECVD) metamorphic solar cells.
• Fabrication, characterization and modeling of microcrystalline silicon-carbon alloys thin films
  
  • Gaiaschi Sofia
  , 2014. Despite continuous effort, thin-film silicon multi-junction solar cells are still limited by the light-induced degradation of amorphous materials that they employ − hydrogenated amorphous silicon layers (a-Si:H) or amorphous silicon-germanium (a-SiGe:H) layers. To survive, this technology must fully benefit from the ease with which it allows multi-band gap photovoltaic (PV) devices to be assembled. To this end, materials that are stable under light soaking and have an electronic band gap between that of hydrogenated microcrystalline silicon (µc-Si:H, 1.1 eV) and that of a-Si:H (1.7 eV) are needed. The goal of this PhD thesis was to develop a new class of materials satisfying all these requirements by alloying carbon and silicon. Indeed, hydrogenated microcrystalline silicon-carbon alloys (µc-Si1−xCx:H) are a promising candidate for expanding the toolbox of useful materials for thin-film photovoltaics. The interest in these alloys lies in the possibility of easily varying their effective band gap by changing the amount of carbon in their composition. In this thesis, the usefulness of such materials in thin-film PV devices was probed using a broad range of deposition and characterization techniques. Using thin-film growth techniques at low temperatures (175−300° C), the range in which such electronically useful materials can be grown has been explored. It was confirmed that even in the condition of small crystallites, no stable sub-stoichiometric Si-C crystalline phase exists (i.e. no parallel for silicon-rich c-SiGe has been observed). Under all deposition techniques utilized, these materials were composed of submicron-size silicon crystallites embedded in an amorphous silicon-carbon (a-Si1−xCx:H) matrix. However, while the presence of the crystallites assures a higher conductivity compared to a-Si1−xCx:H, the carbon incorporation leads to an effective energy gap larger than that of microcrystalline silicon, supporting our investigation of these materials as promising optoelectronic layers. In the first part of this work, different Plasma Enhanced Chemical Vapor Deposition strategies have been investigated to achieve the widest range of processing conditions and to learn the most about the growth conditions required to produce a high quality µc-Si1−xCx:H material. Material properties were extensively characterized both on the structural side and also from an electrical point of view, in order to establish a correlation between the deposition parameters and the microstructural, transport and defect-related properties. The extensive set of results has allowed the proposal of a coherent growth model for such µc-Si1−xCx:H thin films. Exploiting these results, PV devices using these alloys as active layers were made. Although the absolute levels of efficiency (around 3.5 %) are not as high as state-of-the-art microcrystalline silicon, this work showed that it is possible to obtain variations in the open circuit voltage by varying the amount of carbon incorporated in such µc-Si1−xCx:H alloys. This important result shows that a process parameter other than silane dilution can be used to control this aspect of device performance. PV performances are modest so far, which is expected as these are the first ever results concerning the application of such a new class of materials as the active layer in thin-film solar cells. However, with further advancements in such materials, their replacement of the less stable a-SiGe:H is not unforeseeable.
• Study and optimization of the growth of a-Si:H on wet-chemically textured c-Si substrates for the enhancement of a-Si:H/c-Si heterojunction solar cells
  
  • Sobkowicz Igor Paul
  , 2014. This thesis is the result of the work carried out on the passivation of anisotropically wet-etched crystalline silicon by hydrogenated amorphous silicon deposited by low-temperature RF PECVD. Firstly, the (100) and (111) crystalline orientations were studied to understand the impact thereof on a-Si:H growth. Wet-chemical etching of crystalline silicon was then addressed in order to choose the best recipe to texture silicon wafers and thereby increase their light-trapping properties. Surprisingly, the deposition of a-Si:H on textured wafers was tested and passivation under our standard conditions was not evident at all. Indeed, we experienced huge losses in effective lifetime and implied Voc. We could at first explain this difference by the larger surface and thus larger number of dangling bonds exhibited by textured wafers. However, we imagined that randomly distributed pyramid landscapes could be imperfectly defined in their natural {111} crystallographic orientation and that they rather contained a particular set of specific surface orientations. Such being the case, this would in turn foster particular growth modes locally. Consequently, we decided to use a method that is counter-intuitive for textured c-Si wafers in order to obtain a perfectly abrupt a- Si:H/c-Si interface. The improvements were striking and showed great reproducibility while HR-TEM/STEM analyses clearly indicated that the interface was made more abrupt indeed. This allowed us to procede towards our main goal: improving a-Si:H/c- Si heterojunction (SHJ) solar cell efficiencies on textured c-Si n-type wafers. A proper cleaning routine was defined, the cleanliness of the whole fabrication chain processes (no clean-room conditions) was optimized and adequate layer stacks were developed to enhance SHJ solar cells. As a consequence, a 2x2 cm2 (n)c-Si HJ solar cell was fabricated with a conversion efficiency as high as 20.1% with a Voc of 701 mV, a Jsc of 37.5 mA/cm2 and a FF of 76.3%. This cell contains the two major improvements we have introduced in the conventional HJ solar cell architecture. Implementation of these improvements required a study of their impact on the SHJ solar cell resilience to TCO deposition and on their final J(V) characteristics. A new semi-industrial PECVD cluster tool was installed and new PECVD processes were defined to assess its potential for passivation studies and to check its reproducibility features. As a result, we obtained a 11.3 ms effective lifetime with a 734 mV implied Voc on a symmetrical i/i stack.
• Flexible organic–inorganic hybrid layer encapsulation for organic opto-electronic devices
  
  • Majee Subimal
  • Cerqueira Maria Fátima
  • Tondelier Denis
  • Geffroy Bernard
  • Bonnassieux Yvan
  • Alpuim Pedro
  • Bouree Jean Eric
  Progress in Organic Coatings, Elsevier, 2014, 80, pp.27 - 32. In this work we produce and study the flexible organic–inorganic hybrid moisture barrier layers for the protection of air sensitive organic opto-electronic devices. The inorganic amorphous silicon nitride layer (SiN$_x$:H) and the organic PMMA [poly (methyl methacrylate)] layer are deposited alternatingly by using hot wire chemical vapor deposition (HW-CVD) and spin-coating techniques, respectively. The effect of organic–inorganic hybrid interfaces is analyzed for increasing number of interfaces. We produce highly transparent (∼80% in the visible region) hybrid structures. The morphological properties are analyzed providing a good basis for understanding the variation of the water vapor transmission rate (WVTR) values. A minimum WVTR of 4.5×10$^{−5}$ g/m$^2$ day is reported at the ambient atmospheric conditions for 7 organic/inorganic interfaces. The hybrid barriers show superb mechanical flexibility which confirms their high potential for flexible applications. (10.1016/j.porgcoat.2014.11.015)
  DOI : 10.1016/j.porgcoat.2014.11.015
• Méthode différentielle pour la mesure de matrices de Mueller 4X4 déportée par fibre optique
  
  • Vizet Jérémy
  • Manhas Sandeep
  • Deby Stanislas
  • Vanel Jean-Charles
  • Boito Paola
  • Verdier Mireille
  • de Martino Antonello
  • Pagnoux Dominique
  , 2014.
• Familial occurrence and heritable connective tissue disorders in cervical artery dissection.
  
  • Debette Stéphanie
  • Goeggel Simonetti Barbara
  • Schilling Sabrina
  • Martin Juan José
  • Kloss Manja
  • Sarikaya Hakan
  • Hausser Ingrid
  • Engelter Stefan
  • Metso Tiina M
  • Pezzini Alessandro
  • Thijs Vincent
  • Touzé Emmanuel
  • Paolucci Stefano
  • Costa Paolo
  • Sessa Maria
  • Samson Yves
  • Béjot Yannick
  • Altintas Ayse
  • Metso Antti J
  • Hervé Dominique
  • Lichy Christoph
  • Jung Simon
  • Fischer Urs
  • Lamy Chantal
  • Grau Armin
  • Chabriat Hugues
  • Caso Valeria
  • Lyrer Philippe A
  • Stapf Christian
  • Tatlisumak Turgut
  • Brandt Tobias
  • Tournier-Lasserve Elisabeth
  • Germain Dominique P
  • Frank Michael
  • Baumgartner Ralf W
  • Grond-Ginsbach Caspar
  • Bousser Marie-Germaine
  • Leys Didier
  • Dallongeville Jean
  • Bersano Anna
  • Arnold Marcel
  Neurology, American Academy of Neurology, 2014, 83 (22), pp.2023-2031. In a large series of patients with cervical artery dissection (CeAD), a major cause of ischemic stroke in young and middle-aged adults, we aimed to examine frequencies and correlates of family history of CeAD and of inherited connective tissue disorders. We combined data from 2 large international multicenter cohorts of consecutive patients with CeAD in 23 neurologic departments participating in the CADISP-plus consortium, following a standardized protocol. Frequency of reported family history of CeAD and of inherited connective tissue disorders was assessed. Putative risk factors, baseline features, and 3-month outcome were compared between groups. Among 1,934 consecutive patients with CeAD, 20 patients (1.0%, 95% confidence interval: 0.6%-1.5%) from 17 families (0.9%, 0.5%-1.3%) had a family history of CeAD. Family history of CeAD was significantly more frequent in patients with carotid location of the dissection and elevated cholesterol levels. Two patients without a family history of CeAD had vascular Ehlers-Danlos syndrome with a mutation in COL3A1. This diagnosis was suspected in 2 additional patients, but COL3A1 sequencing was negative. Two patients were diagnosed with classic and hypermobile Ehlers-Danlos syndrome, one patient with Marfan syndrome, and one with osteogenesis imperfecta, based on clinical criteria only. In this largest series of patients with CeAD to date, family history of symptomatic CeAD was rare and inherited connective tissue disorders seemed exceptional. This finding supports the notion that CeAD is a multifactorial disease in the vast majority of cases. (10.1212/WNL.0000000000001027)
  DOI : 10.1212/WNL.0000000000001027
• Microcrystalline silicon deposited from SiF4/H2/Ar plasmas and its application to photovoltaics
  
  • Dornstetter Jean-Christophe
  , 2014. Silicon tetrafluoride is a good candidate to replace silane as silicon precursor in plasmas used to deposit thin films. It has been demonstrated by previous Ph.D. thesis at LPICM that microcrystalline silicon, grown from SiF4/H2/Ar gas mixtures, leads to excellent thin film transistors. This thesis is dedicated to another application: photovoltaic devices. A new challenge arises because several micron thick layers are required in microcrystalline silicon thin film PIN solar cells. Therefore a better and deeper understanding of SiF4/H2/Ar plasmas is necessary to optimize the deposition rate of microcrystalline silicon. SiF4/H2/Ar plasmas have been studied thanks to mass spectrometry and the specificity of such gas mixtures is demonstrated to be the formation HF molecules via the recombination of atomic F and molecular H2. We found that a H2-limited process is associated to amorphous growth and all H2 is used to form HF. On the contrary, an excess of H2 leads to microcrystalline growth. A simple yet accurate model, strongly based on experimental data, has been developed to explain the amorphous-to-microcrystalline transition and enables a controlled tuning of plasma parameters leading to an increase of deposition rate. Moreover, the contribution of plasma generated nanoparticles has been clarified, in particular their crystallization in the plasma phase. The microcrystalline silicon, fabricated from SiF4/H2/Ar, is a high quality material: a density of defects as low as 3x10-3cm-1 has been deduced from absorption below the bandgap (at 0.8eV). By using the fluorinated chemistry for the deposition of the intrinsic absorber layers in thin film PIN solar cells, open-circuit voltage as high as 536mV has been obtained for highly crystallized layers, leading to an efficiency of 9.2%.
• Control over the ion flux obtained by sawtooth-like waveforms in radiofrequency capacitively coupled plasmas
  
  • Bruneau Bastien
  • Novikova T.
  • Lafleur Trevor
  • Booth Jean-Paul
  • Johnson Erik
  , 2014.
• In-situ spectroscopic ellipsometry of microcrystalline silicon deposited by plasma-enhanced chemical vapor deposition on flexible Fe–Ni alloy substrate for photovoltaic applications
  
  • Mrázková Z.
  • Torres-Rios A.
  • Ruggeri R.
  • Foldyna M.
  • Postava K.
  • Pištora J.
  • Roca I Cabarrocas P.
  Thin Solid Films, Elsevier, 2014, 571. (10.1016/j.tsf.2014.06.009)
  DOI : 10.1016/j.tsf.2014.06.009
• In-Plane Epitaxial Growth of Silicon Nanowires and Junction Formation on Si(100) Substrates
  
  • Yu Lw
  • Xu Mk
  • Xu J
  • Xue Zg
  • Fan Z
  • Picardi G
  • Fortuna F
  • Wang Jz
  • Chen Kj
  • Cabarrocas Pri
  Nano Letters, American Chemical Society, 2014, 14 (issue : 11), pp.6469-6474. Growing self-assembled silicon nanowires (SiNWs) into precise locations represents a critical capability to scale up SiNW-based functionalities. We here report a novel epitaxy growth phenomenon and strategy to fabricate orderly arrays of self-aligned in-plane SiNWs on Si(100) substrates following exactly the underlying crystallographic orientations. We observe also a rich set of distinctive growth dynamics/modes that lead to remarkably different morphologies of epitaxially grown SiNWs/or grains under variant growth balance conditions. High-resolution transmission electron microscopy cross-section analysis confirms a coherent epitaxy (or partial epitaxy) interface between the in-plane SiNWs and the Si(100) substrate, while conductive atomic force microscopy characterization reveals that electrically rectifying p-n junctions are formed between the p-type doped in-plane SiNWs and the n-type c-Si(100) substrate. This in-plane epitaxy growth could provide an effective means to define nanoscale junction and doping profiles, providing a basis for exploring novel nanoelectronics. (10.1021/nl503001g)
  DOI : 10.1021/nl503001g
• Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth
  
  • Maurice J.-L.
  • Pribat Didier
  • He Z
  • Patriarche G
  • Cojocaru Costel Sorin
  Carbon, Elsevier, 2014, 79, pp.93. The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalystparticles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are "replaced" by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering themechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality. (10.1016/j.carbon.2014.07.047)
  DOI : 10.1016/j.carbon.2014.07.047
• Validation d'un système de déport de lumière à fibres optiques hautement birefringentes pour application à la polarimétrie de Mueller endoscopique
  
  • Manhas Sandeep
  • Vizet Jérémy
  • Boulogne Hervé
  • Guénard Romain
  • Dexet Alain
  • Brevier Julien
  • Deby Stanislas
  • Vanel Jean-Charles
  • de Martino Antonello
  • Pagnoux Dominique
  , 2014.
• Corrosion of titanium and zirconium under Ar irradiation in the low MeV range: an XPS and SE study
  
  • Gorse-Pomonti D.
  • Dragoe N.
  • Barthes-Labrousse M-G
  • Garcia-Caurel E
  • Bérerd N.
  , 2014.
• Permeation barrier performance of Hot Wire-CVD grown silicon-nitride films treated by argon plasma
  
  • Majee S
  • Fátima Cerqueira Maria
  • Tondelier D
  • Vanel J.C.
  • Geffroy B
  • Bonnassieux Y
  • Alpuim P
  • Bourée Jean Eric
  Thin Solid Films, Elsevier, 2014, 575, pp.72-75. In this work SiN x thin films have been deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) technique to be used as encapsulation barriers for flexible organic electronic devices fabricated on polyethylene terephthal-ate (PET) substrates. First results of SiN x multilayers stacked and stacks of SiN x single-layers (50 nm each) separated by an Ar-plasma surface treatment are reported. The encapsulation barrier properties of these different multilayers are assessed using the electrical calcium degradation test by monitoring changes in the electrical conductance of encapsulated Ca sensors with time. The water vapor transmission rate is found to be slightly minimized (7 × 10 −3 g/m 2 day) for stacked SiN x single-layers exposed to argon plasma treatment during a short time (2 min) as compared to that for stacked SiN x single-layers without Ar plasma treatment. (10.1016/j.tsf.2014.10.009)
  DOI : 10.1016/j.tsf.2014.10.009
• Strongly correlated alignment of fluorinated 5,11-bis(triethylgermylethynyl)anthradithiophene crystallites in solution-processed field-effect transistors
  
  • Kim Chang-Hyun
  • Hlaing Htay
  • Payne Marcia M.
  • Yager Kevin G.
  • Bonnassieux Yvan
  • Horowitz Gilles
  • Anthony John E.
  • Kymissis Ioannis
  ChemPhysChem, Wiley-VCH Verlag, 2014, 15 (14), pp.2913-2916. The crystallinity of an organic semiconductor film determines the efficiency of charge transport in electronic devices. This report presents a micro-to-nanoscale investigation on the crystal growth of fluorinated 5,11-bis(triethylgermylethynyl)anthradithiophene (diF-TEG-ADT) and its implication for the electrical behavior of organic field-effect transistors (OFETs). diF-TEG-ADT exhibits remarkable self-assembly through spin-cast preparation, with highly aligned edge-on stacking creating a fast hole-conducting channel for OFETs. (10.1002/cphc.201402360)
  DOI : 10.1002/cphc.201402360
• A review on plasma-assisted VLS synthesis of silicon nanowires and radial junction solar cells
  
  • Misra Soumyadeep
  • Yu Linwei
  • Chen Wanghua
  • Foldyna Martin
  • Cabarrocas Pere Roca I
  Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47 (39), pp.393001. (10.1088/0022-3727/47/39/393001)
  DOI : 10.1088/0022-3727/47/39/393001
• Optimization of blue and green phosphoresecent organic light-emitting diodes (pholeds)by optical simulation
  
  • Declairieux Céline
  • Jung S.
  • Gijun Seo
  • Derbal-Habak Hassina
  • Romain M.
  • Thiéry Sébastien
  • Tondelier Denis
  • Poriel Cyril
  • Rault-Berthelot Joelle
  • Geffroy Bernard
  , 2014.
• Determination of collagen fiber orientation in histological slides using Mueller microscopy and validation by second harmonic generation imaging.
  
  • Bancelin Stéphane
  • Nazac André
  • Ibrahim Bicher Haj
  • Dokládal Petr
  • Decencière Etienne
  • Teig Benjamin
  • Haddad Huda
  • Fernandez Hervé
  • Schanne-Klein Marie-Claire
  • de Martino Antonello
  Optics Express, Optical Society of America - OSA Publishing, 2014, 22 (19), pp.22561-22574. We studied the azimuthal orientations of collagen fibers in histological slides of uterine cervical tissue by two different microscopy techniques, namely Mueller polarimetry (MP) and Second Harmonic Generation (SHG). SHG provides direct visualization of the fibers with high specificity, which orientations is then obtained by suitable image processing. MP provides images of retardation (among other polarimetric parameters) due to the optical anisotropy of the fibers, which is enhanced by Picrosirius Red staining. The fiber orientations are then assumed to be those of the retardation slow axes. The two methods, though fully different from each other, provide quite similar maps of average fiber orientations. Overall, our results confirm that MP microscopy provides reliable images of dominant fiber orientations at a much lower cost that SHG, which remains the "gold standard" for specific imaging of collagen fibers using optical microscopy. (10.1364/OE.22.022561)
  DOI : 10.1364/OE.22.022561
• Development of efficient permeation barriers based on hot-wire CVD grown silicon-nitride multilayers for organic devices deposited on flexible substrates
  
  • Majee Subimal
  , 2014. Efficient gas-diffusion (permeation) barriers are needed for organic optoelectronic devices because the presence of moisture or oxygen can cause strong degradation. In order for these devices to operate continuously during a long term, so to be commercialized, a reliable flexible thin film encapsulation is required, which is a major challenge. Very low water vapor transmission rates of the order of 10-5 g/m2.day are required. To reach this goal two ways have been adopted: on one hand fabricating SiNx:H / SiNx:H multilayer barriers separated by a specific Ar plasma treatment, on the other hand fabricating the conventional inorganic/organic hybrid multilayer moisture barriers. We have chosen hot-wire chemical vapor deposition (HW-CVD) as the main technique for depositing the inorganic layers and a large part of our efforts has been devoted to the complete study of the parameters controlling the plasma treatment: the energy of the ions impinging the inorganic surfaces was crucial. Several analytical (morphological, structural, optical, electrical) techniques have been necessary to assess qualitatively and quantitatively the different layers composing the moisture barriers. A physical interpretation of the plasma process treatment has been given, based on the interface atomic rearrangements induced by the low energy ions (< 40 eV). For each way of encapsulation, we have obtained very low water vapor transmission rates (4 to 7 × 10-5 g/m2.day). Combining above two encapsulation methods, we have achieved extremely low WVTR rate (6 × 10-6 g/m2.day), which seems sufficient for the utilization of organic electronic devices.
• Direct Synthesis and Integration of Individual, Diameter-Controlled Single-Walled Nanotubes (SWNTs)
  
  • Bouanis Fatima Zahra
  • Cojocaru Costel-Sorin
  • Huc Vincent
  • Norman Evgeny
  • Chaigneau Marc
  • Maurice Jean Luc
  • Mallah Talal
  • Pribat Didier
  Chemistry of Materials, American Chemical Society, 2014, 26 (17), pp.5074–5082. We present a robust and versatile approach for the reproducible and controllable growth of single-walled carbon nanotubes (SWNTs) through a self-assembled mono-layer (SAM) technique coupled with an atomic hydrogen (Hat) pretreatment to control the catalytic metallic nanoparticles size and density. The nanoparticles are obtained from a self-assembled monolayer of metal complexes or salts on a SiO2 substrate using a two-step strategy. The oxide is first functionalized by silanization with a coordinating ligand leading to the formation of an anchoring SAM on the substrate. Then, metallic complexes such as ruthenium porphyrin (RuTPP) or metallic salts (FeCl3, RuCl3) are assembled by coordination bonds on the preformed organic SAM. Pyrolysis under radical hydrogen atmosphere of the as-prepared SAM yields metallic nanoparticles whose size and density are controlled and tuned. Using the as-formed nanoparticles as catalysts, SWNTs are grown by double hot-filament-assisted chemical vapor deposition (d-HFCVD). They exhibit a remarkably good crystalline quality, with a diameter (and type) strongly dependent on the nature of the initial catalyst precursor and its preparation. Field-effect transistors (FETs) with excellent characteristics were obtained using such in-place grown SWNTs. The electronic properties of the SWNTs can be tuned: the transistors obtained from Ru(TPP) and FeCl3 exhibit ION/IOFF current ratio up to ∼109, indicative of the direct growth of a high proportion of semiconducting nanotubes over than 98%. Such elevated values have been reported essentially for CNT-FETs devices based on individual semiconducting SWNTs. By contrast, devices obtained from the RuCl3 salt display ION/IOFF current ratio well below 102, indicating the direct growth of SWNTs highly enriched in metallic specimens. (10.1021/cm502282x)
  DOI : 10.1021/cm502282x
• 2-Substituted vs 4-substituted-9,9′-spirobifluorene host materials for green and blue phosphorescent OLEDs: a structure-property relationship study
  
  • Thiery Sebastien
  • Declairieux Céline
  • Tondelier Denis
  • Seo Gijun
  • Geffroy Bernard
  • Jeannin Olivier
  • Métivier Rémi
  • Rault-Berthelot Joëlle
  • Poriel Cyril
  Tetrahedron, Elsevier, 2014, 70 (36), pp.6337 - 6351. We report a structure-property relationship study of four 9,9′-spirobifluorene (SBF) derivatives (4-5Pm-SBF, 2-5Pm-SBF, 4-Ph-SBF and 2-Ph-SBF), substituted with either phenyl or pyrimidine at the \C2\ or \C4\ position of the \SBF\ core. Structural, thermal, electrochemical and photophysical properties have been examined and correlated to theoretical calculations in order to study the influence of the nature and the position of the substituent. The emission properties of 4- versus 2-substituted \SBFs\ are noticeably different highlighting, in the excited state, the remarkable effect of substitution in ortho position of SBF. All compounds have been used as host material for green dopant in PhOLEDs with very high performances (2-5Pm-SBF: CE>58 cd/A, PE>35 lm/W, EQE>14%). More importantly, the two 4-substituted \SBFs\ have been used as host materials in blue PhOLEDs, displaying high performance and a decrease of \VTH\ for 4-5Pm-SBF due to the incorporation of the electron-withdrawing pyrimidine. (10.1016/j.tet.2014.05.081)
  DOI : 10.1016/j.tet.2014.05.081
• Application of the arbitrary decomposition to finite spot size Mueller matrix measurements
  
  • Ossikovski Razvigor
  • Garcia-Caurel Enric
  • Foldyna Martin
  • Gil José Jorge
  Applied optics, Optical Society of America, 2014, 53, pp.6030. Finite spot size Mueller matrix polarimetric measurements whereby the light spot impinges on two different areas of the sample, e.g., a grating and a substrate, are relatively frequently met in practice. It has been shown that if the Mueller matrix of one of the areas (the substrate) is known from an additional measurement then the Mueller matrix of the remaining medium (the grating) can be obtained from the (substrate-grating) overall response by the polarimetric subtraction method. We show that, provided a specific condition is fulfilled, the individual polarimetric responses of the two areas can be retrieved from the finite spot size measurement by using a special form of the arbitrary decomposition even if none of the individual responses is known a priori. The decomposition method is illustrated on a microelectronics grating structure and its accuracy, as well as limits of applicability, is discussed
• A 3D insight on the catalytic nanostructuration of few-layer graphene
  
  • Melinte G.
  • Florea I.
  • Moldovan S.
  • Janowska I.
  • Baaziz W.
  • Arenal R.
  • Wisnet A.
  • Scheu C.
  • Bégin-Colin S.
  • Bégin D.
  • Pham-Huu C.
  • Ersen O.
  Nature Communications, Nature Publishing Group, 2014, 5 (1). (10.1038/ncomms5109)
  DOI : 10.1038/ncomms5109
• Effect of Wettability on the Agglomeration of Silicon Nanowire Arrays Fabricated by Metal-Assisted Chemical Etching
  
  • Togonal A. S.
  • He Lining
  • Roca I Cabarrocas Pere
  Langmuir, American Chemical Society, 2014, 30 (34). (10.1021/la501768f)
  DOI : 10.1021/la501768f
• Hybrid photocathodes for solar hydrogen production : organic photovoltaics as a sensitizer of catalysts for water reduction
  
  • Bourgeteau Tiphaine
  • Cabaret Théo
  • Geffroy Bernard
  • Derycke Vincent
  • Jousselme Bruno
  , 2014.