Publications

2018

• Te doping of GaAs and GaInP using diisopropyl telluride (DIPTe) for tunnel junction applications
  
  • Hamon G.
  • Paillet N.
  • Alvarez J
  • Larrue A.
  • Decobert J.
  Journal of Crystal Growth, Elsevier, 2018, 498, pp.301-306. In this work, we have investigated the growth of highly n-doped gallium arsenide (GaAs) and gallium indium phosphide (GaInP) with tellurium (Te) by metal organic vapor phase epitaxy (MOVPE) using diisopropyl telluride (DIPTe), aiming at fabricating high performances tunnel junctions. A parametric study is performed in order to optimize the n++-type doping. Concentrations above 2.7 × 1019 cm−3 were achieved in both GaAs and GaInP layers. Using these Te-doped layers, we fabricated both n on p (n/p) and p on n (p/n) tunnel junctions. The p/n tunnel junction required additional annealing steps during growth, due to memory effect and surfactant properties of Te. We characterized GaAs/GaAs, GaAs/AlGaAs and AlGaAs/GaInP tunnel junctions with peak tunneling current densities as high as 250, 3000 and 1500 A/cm2 respectively. These tunnel junction performances are suitable for multijunction solar cells operating under high concentration. © 2018 (10.1016/j.jcrysgro.2018.07.003)
  DOI : 10.1016/j.jcrysgro.2018.07.003
• 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
• Medical device equipped with sensors
  
  • Barakat Abdul I.
  • Bozsak Franz
  • Bonnassieux Yvan
  • Le Pioufle Bruno
  • Français Olivier
  • Carreel Bruno
  , 2018.
• 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
• 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
• 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
• Deposition of hydrogenated silicon clusters for efficient epitaxial growth
  
  • Le Ha-Linh Thi
  • Jardali Fatme
  • Vach Holger
  Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2018. Epitaxial silicon thin films grown from the deposition of plasma-born hydrogenated silicon nanoparticles using plasma enhanced chemical vapor deposition techniques have widely been investigated due to their potential applications in photovoltaic and nanoelectronic device technologies. However, the optimal experimental conditions and the underlying growth mechanisms leading to high-speed epitaxial growth of thin silicon films from hydrogenated silicon nanoparticles remain far from being understood. In the present work, extensive molecular dynamics simulations were performed to study the epitaxial growth of silicon thin films resulting from the deposition of plasma-born hydrogenated silicon clusters at low substrate temperatures under realistic reactor conditions. Strong evidence is presented that a temporary phase transition of the substrate area around the cluster impact site to the liquid state is necessary for the epitaxial growth to take place. We predict further that a non-normal incidence angle for the cluster impact significantly facilitates the epitaxial growth of thin crystalline silicon films. (10.1039/c8cp00764k)
  DOI : 10.1039/c8cp00764k
• Novel three-dimensional carbon nanotube networks as high performance thermal interface materials
  
  • Kong Qinyu
  • Bodelot Laurence
  • Lebental Bérengère
  • Lim Yu Dian
  • Shiau Li Lynn
  • Gusarov Boris
  • Tan Chong Wei
  • Liang Kun
  • Lu Congxiang
  • Tan Chuan Seng
  • Coquet Philippe
  • Tay Beng Kang
  Carbon, Elsevier, 2018, 132, pp.359-369. Vertically aligned carbon nanotube (VACNT) arrays are considered as promising thermal interface materials (TIMs) due to their superior out-of-plane thermal conductivities. However the air gaps between adjacent CNTs within the CNT array hinder the in-plane heat transfer, thus significantly degrading the thermal performance of VACNT-based TIMs. To improve the in-plane thermal conduction of VACNT arrays, we propose a novel three dimensional CNT (3D CNT) network structure, where VACNTs are cross-linked by randomly-oriented secondary CNTs. Three different catalyst preparation methods for the secondary CNT growth are compared in terms of their ability to produce a dense network of secondary CNTs. The 3D CNT network grown using the chemical impregnation method shows a denser network structure, and thus is chosen for further thermal characterization. The temperature fields of the corresponding 3D CNT network under different heating powers are recorded using a 15 Œm-resolution infrared thermal imaging system. The in-plane thermal conductivity is then derived from these fields using numerical fitting with a 3D heat diffusion model. We find that the in-plane thermal conductivity of the 3D CNT network is 5.40 ± 0.92 W/mK, at least 30 times higher than the thermal conductivity of the primary VACNT array used to grow the 3D CNT network. (10.1016/j.carbon.2018.02.052)
  DOI : 10.1016/j.carbon.2018.02.052
• First-Principles Investigation of the Coupling-Induced Dissociation of Methane and its Transformation to Ethane and Ethylene
  
  • Varghese Jithin John
  • Saravanan Bharathi
  • Vach Holger
  • Peslherbe Gilles H.
  • Mushrif Samir H
  Chemical Physics Letters, Elsevier, 2018. Quantum chemical computations predict that compression of the methane dimer to an inter-nuclear separation lower than 2 Å facilitates a concerted coupling and dissociation of C-H bonds of the molecules to form ethane/ethylene. In this bimolecular, concerted mechanism, ethane formation is accompanied by production of H radicals from each methane moiety that may further abstract hydrogen atoms to lead to ethylene formation. Alternatively, transformation to ethane and ethylene proceeds via stepwise molecular hydrogen elimination, with the first eliminated hydrogen molecule originating from one of the methane moieties, accompanied by an intermolecular hydrogen transfer, and the second originating from both methyl groups.
• Conservation of the piezoelectric response of PVDF films under irradiation
  
  • Melilli G.
  • Lairez D.
  • Gorse D.
  • Garcia-Caurel E.
  • Peinado A.
  • Cavani O.
  • Boizot B.
  • Clochard M.-C.
  Radiation Physics and Chemistry, Elsevier, 2018, 142, pp.54-59. (10.1016/j.radphyschem.2017.03.035)
  DOI : 10.1016/j.radphyschem.2017.03.035