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Jabakhanji B.,CNRS Charles Coulomb Laboratory | Jabakhanji B.,Middle East College | Kazazis D.,CNRS Laboratory for Photonics and Nanostructures | Desrat W.,CNRS Charles Coulomb Laboratory | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We present the magnetoresistance (MR) of highly doped monolayer graphene layers grown by chemical vapor deposition on 6H-SiC. The magnetotransport studies are performed on a large temperature range, from T=1.7 K up to room temperature. The MR exhibits a maximum in the temperature range 120-240 K. The maximum is observed at intermediate magnetic fields (B=2-6 T), in between the weak localization and the Shubnikov-de Haas regimes. It results from the competition of two mechanisms. First, the low-field magnetoresistance increases continuously with T and has a purely classical origin. This positive MR is induced by thermal averaging and finds its physical origin in the energy dependence of the mobility around the Fermi energy. Second, the high-field negative MR originates from the electron-electron interaction (EEI). The transition from the diffusive to the ballistic regime is observed. The amplitude of the EEI correction points towards the coexistence of both long- and short-range disorder in these samples. © 2014 American Physical Society.


Charpagne M.-A.,MINES ParisTech | Charpagne M.-A.,Safran Group | vennEguEs P.,CNRS Heteroepitaxy Applied Research Center | Billot T.,Safran Group | And 2 more authors.
Journal of Microscopy | Year: 2016

This paper demonstrates the existence of large γ’ precipitates (several micrometres in diameter) that are coherent with their surrounding matrix grain in a commercial γ–γ’ nickel-based superalloy. The use of combined energy dispersive X-ray spectrometry and electron backscattered diffraction (EBSD) analyses allowed for revealing that surprising feature, which was then confirmed by transmission electron microscopy (TEM). Coherency for such large second-phase particles is supported by a very low crystal lattice misfit between the two phases, which was confirmed thanks to X-ray diffractograms and TEM selected area electron diffraction patterns. Dynamic recrystallization of polycrystalline γ–γ’ nickel-based superalloys has been extensively studied in terms of mechanisms and kinetics. As in many materials with low stacking fault energy, under forging conditions, the main softening mechanism is discontinuous dynamic recrystallization. This mechanism occurs with preferential nucleation on the grain boundaries of the deformed matrix. The latter is then being consumed by the growth of the newly formed grains of low energy and by nucleation that keeps generating new grains. In the case of sub-solvus forging, large γ’ particles usually pin the migrating boundaries and thus limit grain growth to a size which is determined by the distribution of second-phase particles, in good agreement with the Smith–Zener model. Under particular circumstances, the driving force associated with the difference in stored energy between the growing grains and the matrix can be large enough that the pinning forces can be overcome, and some grains can then reach much larger grain sizes. In the latter exceptional case, some intragranular primary γ’ particles can be observed, although they are almost exclusively located on grain boundaries and triple junctions otherwise. In both cases, primary precipitates have no special orientation relationship with the surrounding matrix grain(s). This paper demonstrates the existence of high fractions of large γ’ precipitate (several micrometres in diameter) that are coherent with their surrounding matrix grain, in a commercial γ–γ’ nickel-based superalloy. Such a configuration is very surprising, because there is apparently no reason for the coherency of such particles. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society


PubMed | Safran Group, MINES ParisTech, Safran and CNRS Heteroepitaxy Applied Research Center
Type: Journal Article | Journal: Journal of microscopy | Year: 2016

This paper demonstrates the existence of large precipitates (several micrometres in diameter) that are coherent with their surrounding matrix grain in a commercial - nickel-based superalloy. The use of combined energy dispersive X-ray spectrometry and electron backscattered diffraction (EBSD) analyses allowed for revealing that surprising feature, which was then confirmed by transmission electron microscopy (TEM). Coherency for such large second-phase particles is supported by a very low crystal lattice misfit between the two phases, which was confirmed thanks to X-ray diffractograms and TEM selected area electron diffraction patterns. Dynamic recrystallization of polycrystalline - nickel-based superalloys has been extensively studied in terms of mechanisms and kinetics. As in many materials with low stacking fault energy, under forging conditions, the main softening mechanism is discontinuous dynamic recrystallization. This mechanism occurs with preferential nucleation on the grain boundaries of the deformed matrix. The latter is then being consumed by the growth of the newly formed grains of low energy and by nucleation that keeps generating new grains. In the case of sub-solvus forging, large particles usually pin the migrating boundaries and thus limit grain growth to a size which is determined by the distribution of second-phase particles, in good agreement with the Smith-Zener model. Under particular circumstances, the driving force associated with the difference in stored energy between the growing grains and the matrix can be large enough that the pinning forces can be overcome, and some grains can then reach much larger grain sizes. In the latter exceptional case, some intragranular primary particles can be observed, although they are almost exclusively located on grain boundaries and triple junctions otherwise. In both cases, primary precipitates have no special orientation relationship with the surrounding matrix grain(s). This paper demonstrates the existence of high fractions of large precipitate (several micrometres in diameter) that are coherent with their surrounding matrix grain, in a commercial - nickel-based superalloy. Such a configuration is very surprising, because there is apparently no reason for the coherency of such particles.


Lacroix B.,CNRS Center for Research on Ions, Materials and Photonics | Chauvat M.P.,CNRS Center for Research on Ions, Materials and Photonics | Ruterana P.,CNRS Center for Research on Ions, Materials and Photonics | Nataf G.,CNRS Heteroepitaxy Applied Research Center | De Mierry P.,CNRS Heteroepitaxy Applied Research Center
Applied Physics Letters | Year: 2011

For the next-generation solid state lighting, the production of high quality semipolar (11 2- 2) GaN layers on sapphire obtained using asymmetric epitaxial lateral overgrowth (ELO) method has been investigated. This type of ELO leads to efficient blocking of the basal stacking faults (BSFs) in the bulk, and enables the formation of nondefective layers at the surface. The BSFs terminate due to generation of prismatic stacking faults along a well defined boundary. The corresponding intensity of GaN band edge photoluminescence emission is increased by more than four orders of magnitude in comparison to that from semipolar templates. © 2011 American Institute of Physics.


Faucher M.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Cordier Y.,CNRS Heteroepitaxy Applied Research Center | Werquin M.,MC2 technologies | Buchaillot L.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | And 2 more authors.
Journal of Microelectromechanical Systems | Year: 2012

We investigate the response of a GaN microelectromechanical resonator where the strain detection is performed by a resonant high-electron mobility transistor (R-HEMT). The R-HEMT gate located above the 2-DEG (two-dimensional electron gas) appears to enable a strong control of the electromechanical response with a gate voltage dependence close to a transconductance pattern. A quantitative approach based on the mobility of the carriers induced in the device by the piezoelectric response of the GaN buffer is proposed. These results show for the first time the electromechanical transconductance dependence versus external biasing and confirm that active piezoelectric transduction is governed by the AlGaN/GaN 2-DEG transport properties. © 2012 IEEE.


Michaud J.-F.,University Pierre and Marie Curie | Portail M.,CNRS Heteroepitaxy Applied Research Center | Chassagne T.,NOVASiC | Zielinski M.,NOVASiC | Alquier D.,University Pierre and Marie Curie
Materials Science Forum | Year: 2015

The aim of this paper is to review the recent developments conducted by our groups for the achievement of 3C-SiC based heterostructures compatible for MEMS applications. It deals with different aspects, from the influence of the defects generated at the 3C-SiC/Si interface on the mechanical properties to the elaboration of new multilayered structures, required for specific applications like, for example, Atomic Force Microscopy. © (2014) Trans Tech Publications, Switzerland.


Xu X.,Aix - Marseille University | Xu X.,University Pierre and Marie Curie | Aqua J.-N.,Aix - Marseille University | Aqua J.-N.,University Pierre and Marie Curie | And 2 more authors.
Journal of Physics Condensed Matter | Year: 2012

We study the combination of the AsaroTillerGrinfeld morphological instability of a strained film and the organizing effect of an underlying patterned substrate. We use a continuum description of surface diffusion accounting for elasticity, surface energy and wetting interactions. We solve both the mechanical equilibrium and the growth dynamics during annealing at linear order in the film modulation amplitude. We characterize the kinetic phase diagram as a function of time, the film thickness and the ratio between the substrate and the instability wavelengths. We find that the film surface can skip from a configuration in phase with the substrate to either an out-of-phase or a non-ordered configuration, depending on the pattern wavelength and annealing time. © 2012 IOP Publishing Ltd.


Dasilva Y.A.R.,CNRS Center for Research on Ions, Materials and Photonics | Ruterana P.,CNRS Center for Research on Ions, Materials and Photonics | Lahourcade L.,INAC SP2M PSC | Monroy E.,INAC SP2M PSC | Nataf G.,CNRS Heteroepitaxy Applied Research Center
Materials Science Forum | Year: 2010

In the fabrication GaN-based devices, several growth orientations are currently under investigation in order to exploit material properties which are inaccessible using layers grown along the c-axis. However, such procedures rely on foreign substrates with large misfits. Therefore, complex crystallographic defects form in the epitaxial layers and have been the subject of extensive studies. They include threading dislocations and stacking faults, which can be within basal or prismatic planes. Out of the c-axis, depending on the growth orientation, the glide planes of perfect dislocations may be no longer available, complicating the relaxation processes. © (2010) Trans Tech Publications. © (2010) Trans Tech Publications.


Arenas O.,Université de Sherbrooke | Al Alam E.,Université de Sherbrooke | Thevenot A.,Université de Sherbrooke | Cordier Y.,CNRS Heteroepitaxy Applied Research Center | And 5 more authors.
IEEE Journal of the Electron Devices Society | Year: 2014

Temperature measurements in AlGaN/GaN high electron mobility transistors are required for proper device design, modeling and achieving appropriate reliability. These measurements usually require sophisticated equipment and extensive calibration. This study evaluates the feasibility of temperature measurements by integration of a Pt resistance thermal detector (RTD) in an "un-gated" transistor and evaluating their electrical interactions. The integrated RTD presents the advantage of being independent of the device. Micro RTD showed a linear response in the calibration interval (0 to 206 °C). Measured temperature values using the micro RTD are in agreement with 3D finite element simulations at multiple bias conditions in the "un-gated" transistor. Measurements show no noticeable electrical perturbation between the device and RTD under simultaneous operation. © 2013 IEEE.


Ben Amar A.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Faucher M.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Brandli V.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Cordier Y.,CNRS Heteroepitaxy Applied Research Center | Theron D.,CNRS Institute of Electronics, Microelectronics and Nanotechnology
Physica Status Solidi (A) Applications and Materials Science | Year: 2014

This paper presents a Young's modulus extraction method for thin film group III-nitrides materials such as GaN, AlN, and its ternary AlGaN. The AlGaN/GaN heterostructures are grown by molecular beam epitaxy on Si (111) substrate and designed for MEMS applications. Various cantilevers with a width of 10μm and lengths going from 100 to 310μm were fabricated. The Young's moduli are determined using the resonance frequencies measured by laser Doppler vibrometry (LDV). Finite element modeling (FEM) is used to consider the under-etching of the cantilevers at the anchor. In this study, we find that the Young moduli of GaN and AlN layers are respectively 261±60GPa and 339±78GPa that compares well with the results found in the literature for bulk materials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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