I. Monnet

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Papers by I. Monnet

Unzipping graphene: Extendend defects by ion irradiation

arXiv (Cornell University), Sep 24, 2010

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Experimental approach and atomistic simulations to investigate the radiation tolerance of complex oxides: Application to the amorphization of pyrochlores

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014

Both experimental approach and atomistic simulations are performed in order to investigate the in... more Both experimental approach and atomistic simulations are performed in order to investigate the influence of the composition of pyrochlores on their radiation tolerance. Therefore, Gd 2 Ti 2 O 7 and Gd 2 Zr 2 O 7 were irradiated with 4 MeV Au and 92 MeV Xe ions in order to study the structural changes induced by low and high-energy irradiations. XRD results show that, for both irradiations, the structural modifications are strongly dependent on the sample composition: Gd 2 Ti 2 O 7 is readily amorphized, whereas Gd 2- Zr 2 O 7 is transformed into a radiation-resistant anion-deficient fluorite structure. Using atomistic simulations with new interatomic potentials derived from the SMTB-Q model, the lattice properties and the defect formation energies were calculated in Gd 2 Ti 2 O 7 and Gd 2 Zr 2 O 7 . Calculations show that titanates have a more covalent character than zirconates. Moreover, in Gd 2 Ti 2 O 7 the formation of cation antisite defects leads to strong local distortions around Ti-defects and to a decrease of the Ti coordination number, which are not observed in Gd 2 Zr 2 O 7 . Thus, the radiation resistance is related to the defect stability: the accumulation of structural distortions around Ti-defects could drive the Gd 2 Ti 2 O 7 amorphization induced by irradiation.

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Energy deposition by heavy ions: Additivity of kinetic and potential energy contributions in hillock formation on CaF2

Scientific Reports, 2014

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Damage creation in porous silicon irradiated by swift heavy ions

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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An improved gallium liquid metal ion source geometry for nanotechnology

Microelectronic Engineering, 2004

In this work we present a liquid metal ion source (LMIS) geometry we have developed specifically ... more In this work we present a liquid metal ion source (LMIS) geometry we have developed specifically for evaluating the potential of focused ion beams in nano-fabrication. The ion-emitter we present and detail hereafter was designed to use gallium and developed to improve both the directivity and on-axis current density of the emitted beam. In the case of a gallium beam, experimental test results are presented concerning emission stability, current voltage characteristics and in situ high voltage (1 MV) transmission electron microscope (HVTEM) observations of the emitting apex. We have developed a LMIS with unconventional operational characteristics: the threshold voltage is 17 kV (twice the normal voltage), and the on-axis angular intensity is 80 lA/sr (compared to 20 lA/sr normally). With this source we were able to demonstrate the possibility to realise nano-fabrication experiments close or below the 10 nm scale. The required ion probe properties would have been inaccessible without dedicated source development effort.

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A comparison between different oxide dispersion strengthened ferritic steel ongoing in situ oxide dissolution in High Voltage Electron Microscope

Journal of Nuclear Materials, 2012

Abstract ODS materials are considered for nuclear applications but previous experimental studies ... more Abstract ODS materials are considered for nuclear applications but previous experimental studies have shown a partial dissolution of some oxides under neutron irradiation. In this work, electron irradiations were used to evaluate the stability of the oxides depending on the chemical composition of the oxide dispersion. Four ferritic steels based on EM10 (Fe–9Cr–1Mo) and reinforced respectively by Al 2 O 3 , MgO, MgAl 2 O 4 and Y 2 O 3 , were studied. These materials were irradiated with 1 MeV or 1.2 MeV electrons in a High Voltage Electron Microscope. This technique allows to follow one single oxide and to determine the evolution of its size during the irradiation. In situ HVEM observations indicate that the dissolution rate depends on the chemical composition of the oxide, on the temperature and on the irradiation dose.

Amorphization of oxides in ODS steels/materials by electronic stopping power

Journal of Nuclear Materials, 2012

Abstract Oxide dispersion strengthened (ODS) ferritic/martensitic steels are being considered for... more Abstract Oxide dispersion strengthened (ODS) ferritic/martensitic steels are being considered for high temperature and high fluence nuclear applications, such as structural components in fusion reactors. In this work, Transmission Electron Microscopy is used to study the effect of swift heavy ion irradiation (74 MeV Kr ions up to 10 16 ions m −2 ) on the microstructure of the DT2203Y05 ODS material. The amorphous ion tracks induced by ion irradiation are clearly visible inside the oxides. This evidences that the mechanism responsible for the amorphization of oxides is linked to the high electronic energy loss along the ion trajectory.

A statistical TEM investigation of dislocation channeling mechanism in neutron irradiated zirconium alloys

Journal of Nuclear Materials, 2004

Plastic deformation in irradiated zirconium alloys occurs in a very heterogeneous manner at the g... more Plastic deformation in irradiated zirconium alloys occurs in a very heterogeneous manner at the grain scale by the clearing up of radiation-induced prismatic loops by gliding dislocations and the channeling of these dislocations inside narrow bands of the grain. A statistical TEM investigation of this mechanism has been performed on neutron irradiated recrystallized Zr alloys tested at 350°C. Due to the strong anisotropy of plastic deformation, different loading conditions have been investigated. It is shown that for transverse tensile tests and closed end burst tests, only basal channels are observed, whereas for axial tensile tests, prismatic and pyramidal channels are observed. This phenomenon can be understood in terms of texture and interactions between dislocations and irradiation induced loops. From Schmid factor calculations, we have also been able to prove that irradiation leads to a higher increase of critical resolved shear stresses for prismatic and pyramidal slip systems than for basal slip system.

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Stability of nano-oxides upon heavy ion irradiation of an ODS material

Journal of Nuclear Materials, 2011

Owing to their low swelling under irradiation and excellent creep properties, oxide dispersion st... more Owing to their low swelling under irradiation and excellent creep properties, oxide dispersion strengthened (ODS) materials are expected to play an important role as structural components for fusion reactors. These materials are reinforced by a nano-oxide dispersion. Hence, to ensure their good in-reactor mechanical properties, ODS materials have to keep their nano-size precipitates stable under neutron irradiation. The structural stability under irradiation of the oxides is analyzed in a Fe-18Cr-1W-0.3Ti alloy reinforced by 0.5Y 2 O 3 upon high-energy ion irradiations (92-MeV Xe) at room temperature (300 K) and at 780 K up to a fluence of 3 Â 10 14 cm À2 . The use of high-energy heavy ions allows a specific study of the effect of electronic interactions and low ballistic damages on oxides. Results provided by transmission electron microscopy show that the precipitates could exhibit an amorphization after irradiation at room temperature whereas the particles remain crystalline after irritation at 780 K.

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Nanoindentation investigation of heavy ion irradiated Ti3(Si,Al)C2

Journal of Nuclear Materials, 2010

Because of good damage tolerance, thermal stability and interesting mechanical properties, Ti3SiC... more Because of good damage tolerance, thermal stability and interesting mechanical properties, Ti3SiC2, belonging to Mn+1AXn phases, has been considered as a potential candidate material for applications in the future Gas Fast nuclear Reactors (GFR) such as components of fuel cladding working between 500°C and 800°C. However, the outstanding mechanical properties of Ti3SiC2 related to a layered microstructure could be impacted

Effect of combined local variations in elastic and inelastic energy losses on the morphology of tracks in ion-irradiated materials

Acta Materialia, 2013

Detailed analysis of the morphology of latent tracks created by swift heavy ions from the surface... more Detailed analysis of the morphology of latent tracks created by swift heavy ions from the surface entry point on a pyrochlore crystal to the end of the ion trajectory reveals continuous changes in the track diameter as a function of ion deceleration, loss of track parallelism beyond a certain depth and the evolution from continuous to discontinuous tracks. The tracks exhibit a layered structure composed of a non-crystalline core surrounded by a strained crystalline envelope. Furthermore, surprising local increases in the diameter of the latent tracks are readily observed. This feature can be interpreted using a model based on the concept of effective local energy deposition, defined as the sum of the inelastic energy deposited by the swift track-forming ion and the elastic energy deposited by a primary knock-on atom inside the ion track.

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Irradiation resistance of a nanostructured 316 austenitic stainless steel

IOP Conf. Ser.: Mater. Sci. Eng., 2014

Measurements and 3D Monte Carlo simulation of MeV ion transmission through conical glass capillaries

Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 2014

To investigate possible beam guiding and current density enhancement properties for conical glass... more To investigate possible beam guiding and current density enhancement properties for conical glass capillaries for MeV ions, transmission measurements with well collimated ion beams of 1 MeV He + and 71 MeV Xe 19+ were done. No guiding effect was observed and only decent enhancement factors e between 1 and 2 were measured and attributed to scattered particles. A 3D Monte Carlo simulation which is based on SRIM code was developed. The simulation reproduces the experimental results very well. This shows that the transmission properties of capillaries for MeV ion beams are governed by simple elastic scattering of the ions in the glass of the capillary.

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Structural evolution of SiC nanostructured and conventional ceramics under irradiation

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008

Nanostructured ceramics are envisaged for next generation nuclear reactors. In this study, we per... more Nanostructured ceramics are envisaged for next generation nuclear reactors. In this study, we performed irradiation experiments on nanostructured and microstructured 3C-SiC samples, with 95 MeV Xe ions at room temperature. This energy permits the observation of the combined electronic and nuclear interaction with matter. The structural evolution of the sample under irradiation was followed by grazing incidence X-ray diffraction and transmission electron microscopy. The results do not reveal a complete amorphization, despite value of displacement per atom overcoming the total amorphization threshold determined for the monocrystalline 6H-SiC at room temperature with low energy ions. This may be attributed to competing effects between nuclear and electronic energy loss in this material.

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Role of electronic excitations and nuclear collisions for color center creation in AlxGa1−xN semiconductors

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2016

In this work, Al x Ga 1Àx N (x = 0; 0.1; 0.3; 0.5; 0.65; 0.7; 0.8; 1) wurtzite epilayers, grown o... more In this work, Al x Ga 1Àx N (x = 0; 0.1; 0.3; 0.5; 0.65; 0.7; 0.8; 1) wurtzite epilayers, grown on c-plane sapphire substrates, have been irradiated with Swift Heavy Ions at GANIL facility. Modifications induced by irradiation are characterized with in-situ optical absorption spectroscopy at 15 K. Spectra of these irradiated alloys exhibit optical absorption band formation, related to new energy levels in their bandgaps, whose positions only depend on the composition of the layer. However, these absorption bands are not observed in the Al x Ga 1Àx N with Al molar fraction less than 0.3, likely because the energy level of the corresponding defect is located above the conduction band. Moreover, using different irradiation conditions, a coupled effect between nuclear collisions and electronic excitations for these color center creation have been investigated. A synergy between these two phenomena has been shown and appears to be independent of the composition of the alloy.

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3D atom probe tomography of swift heavy ion irradiated multilayers

Nanometer scale layered systems are well suited to investigate atomic transport processes induced... more Nanometer scale layered systems are well suited to investigate atomic transport processes induced by high-energy electronic excitations in materials, through the characterization of the interface transformation. In this study, we used the atom probe technique to determine the distribution of the different elements in a (amorphous-Fe 2 Tb 5 nm/hcp-Co 3 nm) 20 multilayer before and after irradiation with Pb ions in the electronic stopping power regime. Atom probe tomography is based on reconstruction of a small volume of a sharp tip evaporated by field effect. It has unique capabilities to characterize internal interfaces and layer chemistry with sub-nanometer scale resolution in three dimensions. Depth composition profiles and 3D element mapping have been determined, evidencing for asymmetric interfaces in the as-deposited sample, and very efficient Fe-Co intermixing after irradiation at the fluence 7 × 10 12 ion cm −2. Estimation of effective atomic diffusion coefficients

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Radiation effects in nuclear materials: Role of nuclear and electronic energy losses and their synergy

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Irradiation damage in Gd2Ti2O7single crystals: Ballistic versus ionization processes

Physical Review B, 2011

The structural transformations induced in Gd 2 Ti 2 O 7 single crystals irradiated at high energi... more The structural transformations induced in Gd 2 Ti 2 O 7 single crystals irradiated at high energies (870-MeV Xe), where ionization processes (electronic stopping) dominate, and at low energies (4-MeV Au), where ballistic processes (nuclear stopping) dominate, have been studied via the combination of Rutherford backscattering spectrometry and channeling (RBS/C), Raman spectroscopy, and transmission electron microscopy (TEM) experiments. At high energy, amorphization occurs directly in individual ion tracks from the extreme electronic-energy deposition, and full amorphization results from the overlapping of these tracks as described by a direct impact model. The track diameters lie in the range 6-9 nm. At low energy, amorphization occurs via indirect processes, driven by ballistic nuclear energy deposition from the ions, that is accounted for in the framework of both direct-impact/defect-stimulated and multi-step damage accumulation models. The ion fluence for total amorphization of the irradiated layer is much higher at low energy (0.5 ion nm −2) than at high energy (0.05 ion nm −2), consistent with the nuclear stopping at low energy (5.2 keV/nm) compared to the electronic stopping at high energy (29 keV/nm).

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Damage in crystalline silicon by swift heavy ion irradiation

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012

We have studied damage of crystalline Si surfaces induced by electronic energy loss of swift heav... more We have studied damage of crystalline Si surfaces induced by electronic energy loss of swift heavy ions with an electronic stopping power of up to Se=12keV/nm. Scanning tunneling microscope images of the surface after irradiation under perpendicular as well as glancing angles of incidence showed no surface damage. We have performed theoretical calculations for the damage threshold within the two

SPORT: A new sub-nanosecond time-resolved instrument to study swift heavy ion-beam induced luminescence – Application to luminescence degradation of a fast plastic scintillator

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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