Publications

2018

• Diameter controlled growth of SWCNTs using Ru as catalyst precursors coupled with atomic hydrogen treatment
  
  • Bouanis Fatima Zahra
  • Florea Ileana
  • Bouanis M
  • Muller D
  • Nyassi A
  • Le Normand François
  • Pribat Didier
  Chemical Engineering Journal, Elsevier, 2018, 332, pp.pp 92-101. In this work, we present a practical approach for controlling single walled carbon nanotubes (SWCNTs) diameter distribution through thin film Ru catalyst, coupled with hydrogen pre-treatment. Uniform and stable Ru nanoclusters were obtained after dewetting the Ru thin films under atomic hydrogen pre-treatment. SWCNTs were synthetized by double hot filament chemical vapor deposition (d-HFCVD) on SiO2/Si substrates at different temperatures. We found that the temperature is an important synthesis parameter that in fluences the diameter distribution of the final SWCNTs. Statistical analysis of the Raman radial breathing modes evidences the growth of highly enriched semi-conducting SWCNTs (about 90%) with narrow diameter distribution that correlates directly with the catalyst particle size distribution. Electrical measurement results on as-grown SWCNTs show good thin-film transistor characteristics. (10.1016/j.cej.2017.09.073)
  DOI : 10.1016/j.cej.2017.09.073
• Investigation of a plasma--target interaction through electric field characterization examining surface and volume charge contributions: modeling and experiment
  
  • Viegas Pedro
  • Slikboer Elmar
  • Obrusník Adam
  • Bonaventura Zdenek
  • Sobota Ana
  • Garcia-Caurel Enric
  • Guaitella Olivier
  • Bourdon Anne
  Plasma Sources Science and Technology, IOP Publishing, 2018, 27. Numerical simulations and experiments are performed to better understand the interaction between a pulsed helium plasma jet and a dielectric target. The focus of this work lies on the volume and surface charge influence on the electric field distribution. Experimentally, the electric field due to surface charges is measured inside an electro-optic target under exposure of a plasma jet, using the optical technique called Mueller polarimetry. For the first time, the time-resolved spatial distributions of both the axial and radial components of electric field inside the target are obtained simultaneously. A 2D fluid model is used in a complementary way to the experiments in order to study separately the contribution of volume charges and surface charges to the spatio-temporal evolutions of the electric field during the plasma--surface interaction. The experimental investigation shows that the average axial and radial components of electric field inside the dielectric target, only due to surface charges, are lower than generally reported for electric field values in the plasma plume. Thanks to the phenomenological comparison with experiments, simulations show that during the plasma--surface interaction two effects sequentially determine the electric field inside the target: firstly, a relatively high electric field is observed due to the proximity of the ionization front; afterwards, in longer timescales, lower electric fields are induced due to the contribution of both leftover volume charges close to the target and surface charges deposited on its surface. The experimental technique provides a unique way to examine this second phase of the plasma--surface interaction. (10.1088/1361-6595/aadcc0)
  DOI : 10.1088/1361-6595/aadcc0
• La quête des températures ultrabasses
  
  • Suchet Daniel
  , 2018. Des vendeurs de glace à l'industrie cryogénique, le froid est souvent perçu comme un produit. Pour le physicien, le froid, réduction de l'agitation aléatoire des particules, apparaît plutôt comme une force productrice, capable de faire émerger des structures complexes et de métamorphoser les propriétés des objets. Les basses températures ont été l'enjeu d'une course effrénée dont la première phase a pris fin en 1908 avec la liquéfaction de l'ensemble des gaz connus. Loin de clore l'aventure, cette étape a fait surgir des nouveaux états de la matière qui ne peuvent être interprétés que par la mécanique quantique. Pour étudier la supraconductivité, la superfluidité ou la condensation de Bose-Einstein, les expériences actuelles visent des températures dites ultrabasses, à quelques milliardièmes de degré au-dessus du zéro absolu. Cette présentation propose une mise en perspective historique de la recherche des très basses températures et une introduction aux expériences actuelles d'atomes froids.
• A comment on ‘‘The interaction of X 2 (X = F, Cl, and Br) with active sites of graphite” [Xu et al., Chem. Phys. Lett., 418, 413 (2006)]
  
  • Lechner Christoph
  • Baranek Philippe
  • Vach Holger
  Chemical Physics Letters, Elsevier, 2018, 698. A comment on "The interaction of X2 (X = F, Cl, and Br) with active sites of graphite" [Xu et al., Chem. Abstract In their article, Xu et al. [1] present the adsorption energies for the chemisorption of the three halogens F 2, Cl 2, and Br 2 on the active sites of graphite. The three investigated systems are the three most stable surfaces, (001), (100), and (110); the latter two are also called zigzag and armchair surface, respectively. Due to some inconsistencies in their article, we re-evaluated the results of Xu et al. in order to investigate the impact on the adsorption energies of the halogens. For the (001) surface, our results agree with Xu et al. However, for the other two surfaces, we find major differences. Contrary to Xu et al., we find that the halogens adsorb the strongest on the zigzag surface. The second strongest adsorption is found on the armchair surface for the symmetric configurations, the third strongest for the asymmetric configurations. Several reasons are given which explain this discrepancy. The most striking source of error in the work of Xu et al. is due to the fact that they did not choose the correct spin multiplicities for the model systems which means that they performed the calculations in excited states. This leads to errors between 50-600% for the zigzag surface and 3-42% for the armchair surface. (10.1016/j.cplett.2018.02.067)
  DOI : 10.1016/j.cplett.2018.02.067
• Mueller microscopy of anisotropic scattering media: theory and experiments
  
  • Novikova Tatiana
  • Lee Hee Ryung
  • Li Pengcheng
  • Garcia-Caurel Enric
  • Ossikovski Razvigor
  • Lotz Christian
  • Groeber-Becker Florian Kai
  • Dembski Sofia
  • Yoo Thomas Sang Hyuk
  • Fournier Corinne
  • Georges Marc
  • Popescu Gabriel
  , 2018, 10677, pp.1067718. (10.1117/12.2306943)
  DOI : 10.1117/12.2306943
• Experimental benchmark of kinetic simulations of capacitively coupled plasmas in molecular gases
  
  • Donkó Z.
  • Derzsi A.
  • Korolov Ihor
  • Hartmann P.
  • Brandt S.
  • Schulze J.
  • Berger B.
  • Koepke M.
  • Bruneau Bastien
  • Johnson Erik
  • Lafleur Trevor
  • Booth Jean-Paul
  • Gibson Andrew
  • O'Connell D.
  • Gans T.
  Plasma Physics and Controlled Fusion, IOP Publishing, 2018, 60 (1), pp.014010. We discuss the origin of uncertainties in the results of numerical simulations of low-temperature plasma sources, focusing on capacitively coupled plasmas. These sources can be operated in various gases/gas mixtures, over a wide domain of excitation frequency, voltage, and gas pressure. At low pressures, the non-equilibrium character of the charged particle transport prevails and particle-based simulations become the primary tools for their numerical description. The particle-in-cell method, complemented with Monte Carlo type description of collision processes, is a well-established approach for this purpose. Codes based on this technique have been developed by several authors/groups, and have been benchmarked with each other in some cases. Such benchmarking demonstrates the correctness of the codes, but the underlying physical model remains unvalidated. This is a key point, as this model should ideally account for all important plasma chemical reactions as well as for the plasma-surface interaction via including specific surface reaction coefficients (electron yields, sticking coefficients, etc). In order to test the models rigorously, comparison with experimental ?benchmark data? is necessary. Examples will be given regarding the studies of electron power absorption modes in O 2 , and CF 4 ?Ar discharges, as well as on the effect of modifications of the parameters of certain elementary processes on the computed discharge characteristics in O 2 capacitively coupled plasmas. (10.1088/1361-6587/aa8378)
  DOI : 10.1088/1361-6587/aa8378
• Electrical and morphological behavior of carbon nanotubes synthesized within porous anodic alumina templates
  
  • Sacco Leandro
  • Florea Ileana
  • Châtelet Marc
  • Cojocaru Costel-Sorin
  Journal of Physics: Materials, IOP Science, 2018, 1 (1), pp.015004. The synthesis of carbon nanotubes (CNTs) within porous anodic alumina (PAA) templates requires better understanding regarding their dynamic growth evolution, and how this is influenced by the geometrical features of the PAA. The growth of nanostructures, such as CNTs, becomes more complex when an exponential voltage decrease process is applied to thin the dielectric layer of the PAA matrix, because this process leads to the formation of a branched structure at the bottom of the pores. Here, we present direct evidence of the impact of the branched structure at the bottom of the PAA at different time-stages of the CNT synthesis. These studies reveal that when numerous branches are created, competition between the growing nanotubes is established during their formation. Additionally, large pores lead to flattened catalyst electrodeposition, promoting tube entanglement since more than one tube can grow in each pore. Interestingly, two different electrical behaviors are measured when considering PAA/CNT devices: linear response in the case of CNTs connecting two parallel electrodes, and nonlinear when junctions between the tubes are being promoted. These results highlight the relevance of having an in-depth understanding of the CVD growth evolution of carbon nanostructures within PAA templates, and simultaneously serve as a guiding procedure towards the fabrication of devices based on parallel organized CNT arrays. (10.1088/2515-7639/aad57f)
  DOI : 10.1088/2515-7639/aad57f
• Structural study of NiOx thin films fabricated by radio frequency sputtering at low temperature
  
  • Song Zhang
  • Bourgeteau Tiphaine
  • Raifuku Itaru
  • Bonnassieux Yvan
  • Johnson Erik
  • Ishikawa Yasuaki
  • Foldyna Martin
  • I Cabarrocas Pere Roca
  • Uraoka Yukiharu
  Thin Solid Films, Elsevier, 2018, 646, pp.209 - 215. (10.1016/j.tsf.2017.12.003)
  DOI : 10.1016/j.tsf.2017.12.003
• Light scattering by coupled oriented dipoles: Decomposition of the scattering matrix
  
  • Kuntman M Ali
  • Kuntman Ertan
  • Sancho-Parramon Jordi
  • Arteaga Oriol
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2018, 98. We study the optical response of two coupled oriented dipoles with the dimer axis perpendicular to the wave vector of light by analyzing how their scattering matrix can be decomposed. The scattering matrix can be written as a linear combination of three terms with a clear physical meaning: one for each particle and another that is responsible for the coupling and that vanishes for noninteracting or distant particles. We show that the interaction term may generate optical activity for certain scattering directions and that this effect manifests itself mostly in the near field. This simple and intuitive theory based on matrix and vector states of oriented dipoles also describes hybridization processes and Fano resonances. The decomposition method can be also formulated in terms of a hybrid basis that allows us to quantitatively determine the individual contribution of the in-phase and out-of-phase coupling modes to the overall intensity. Our method can help to understand the optical response of more complex nanostructures that can be decomposed into dipole terms. The results are illustrated in gold nanoantenna dimers which exhibit a strong dipolar resonance. (10.1103/PhysRevB.98.045410)
  DOI : 10.1103/PhysRevB.98.045410
• Adsorption of Atomic Hydrogen on Defect Sites of Graphite: Influence of Surface Reconstruction and Irradiation Damage
  
  • Lechner Christoph
  • Baranek Philippe
  • Vach Holger
  Carbon, Elsevier, 2018. The influence of surface reconstruction and defects due to irradiation damage on the trapping of hydrogen in nuclear graphite has been investigated at the ab initio level. Several models of defects and surfaces have been studied and compared with previously proposed traps, i.e. the zig-zag edge of dislocation loops and reconstructed surfaces of graphite crystallites. The relative stabilities of hydrogen adsorption on the (100), (110), and (001) graphite basic planes have been evaluated for different amounts of hydrogen coverage and various types of reconstruction. The unreconstructed (100) surface adsorbs hydrogen the strongest. The (100) and (110) surface reconstructions result in decreased stability for H adsorption compared to unrelaxed surfaces. Point defects caused by irradiation, such as mono-and divacancies, also trap hydrogen. We find that extended defects are weaker traps than monovacancies. This is true for surface defects as well as for bulk defects. The obtained results show that the existing hypothesis for trapping at dislocation loops has to be refined. Finally, an agreement with experiments is obtained for trapping on the reconstructed surfaces. (10.1016/j.carbon.2017.09.095)
  DOI : 10.1016/j.carbon.2017.09.095
• Medical device equipped with sensors
  
  • Barakat Abdul I.
  • Bozsak Franz
  • Bonnassieux Yvan
  • Le Pioufle Bruno
  • Français Olivier
  • Carreel Bruno
  , 2018.