Atomic structure of grain boundaries in iron modeled using the atomic density function

A model based on the continuous atomic density function (ADF) approach is applied to predict the atomic structure of grain boundaries (GBs) in iron. Symmetrical [100] and [110] tilt GBs in bcc iron are modeled with the ADF method and relaxed afterwards in molecular dynamics (MD) simulations. The shape of the GB energy curve obtained in the ADF model reproduces well the peculiarities of the angles of 70.53 deg. [$\Sigma$ 3(112)] and 129.52 deg. [$\Sigma$ 11(332)] for [110] tilt GBs. The results of MD relaxation with an embedded-atom method potential for iron confirm that the atomic GB configurations obtained in ADF modeling are very close to equilibrium ones. The developed model provides well-localized atomic positions for GBs of various geometries.Comment: 8 pages, 8 figures, revised versio

Mechanical alloying of Cu and Fe induced by severe plastic deformation of a Cu-Fe composite

A filamentary composite elaborated by cold drawing was processed by High Pressure Torsion (HPT). The nanostructure resulting from this severe plastic deformation (SPD) was investigated thanks to scanning electron microscopy, transmission electron microscopy, X-ray diffraction and 3D atom probe. Although the mutual solubility of Cu and Fe is extremely low at room temperature in equilibrium conditions, it is shown that nanoscaled Fe clusters dissolve in the Cu matrix. The non-equilibrium copper supersaturated solid solutions contain up to 20at.% Fe. The driving force of the dissolution is attributed to capillary pressures and mechanisms which could enhanced the atomic mobility during HPT are discussed. We conclude that the interdiffusion is the result of a dramatic increase of the vacancy concentration during SPD.Comment: 20 page

Dynamic effective properties of a random configuration of cylinders in a fluid

International audienceThe dynamic effective properties of a random medium consisting in a uniform concentration of cylindrical scatterers in an ideal fluid are looked for, with special focus on low frequencies. The effective medium is described as an isotropic viscous fluid whose mass density and dilation viscosity depend on frequency, and whose shear viscosity is nil. An explicit expression of the reflection coefficient of a harmonic plane wave incident upon the interface between the ideal fluid and the random medium may be obtained at low frequency, using the Fikioris and Waterman's approach, in two ways. In the first one, the low frequency assumption is introduced from the very beginning, while in the second one, the same hypotheses than those used by Linton et al. [J. Acoust. Soc. Am. 117 6, 2005] to calculate the effective wavenumber are used first, and, then, the low frequency assumption. In both cases, comparison of this reflection coefficient with that at the interface between the ideal fluid and the effective viscous fluid provides the effective density, which, coupled to the effective wavenumber, provides the effective dilatation viscosity. In the first case, the effective parameters found are identical to those found by Mei et al. [Phys. Rev. B 76, 2007] in a different way, while in the second case they are expressed in terms of form functions of the cylinders that reduce at low frequency to those found by Martin et al. [J. Acous. Soc. Am. 128, 2010]. PACS no. 43.20.Fn, 43.35.B

Relation between the Ultrasonic Attenuation and the Porosity of a RTM Composite Plate

AbstractWe propose a comparative study of X-ray tomography and ultrasonic reflection methods, for determining the porosity of a composite plate realized in LOMC with an industrial process. We measure the attenuation of ultrasound propagating in the thickness by using 10MHz plane transducer in pulse-echo mode. Comparing these results to the 2D porosity tomographic map allows establishing a relation between attenuation and porosity. A C-scan picture of the plate given by the echoes reflected by the rear surface also provides a local information on the attenuation. Furthermore, we propose a method for the mapping of the reflecting sources as the included bubbles and the interfaces resin/fibers

Influence of the supersaturation on Si diffusion and growth of Si nanoparticles in silcion-rich silica

International audienceComb-drive micro-electro-mechanical systems oscillators for low temperature experiments Rev. Sci. Instrum. 84, 025003 (2013) Influence of the embedding matrix on optical properties of Ge nanocrystals-based nanocomposite J. Appl. Phys. 113, 053512 (2013) Fabrication of Bi2Te3 nanowire arrays and thermal conductivity measurement by 3ω-scanning thermal microscopy J. Appl. Phys. 113, 054308 (2013) Controlled route to the fabrication of carbon and boron nitride nanoscrolls: A molecular dynamics investigation J. Appl. Phys. 113, 054306 (2013) Electrodynamic control of the nanofiber alignment during electrospinning Appl. Phys. Lett. 102, 053111 (2013) Additional information on J. Appl. Phys. SiO X /SiO 2 multilayers have been prepared using magnetron sputtering and annealed in order to induce the growth of Si nanoparticles in Si-rich sublayers. This sample has undergone several successive annealing treatments and has been analyzed using a laser-assisted tomographic atom probe. This allows the phase separation between Si and SiO 2 and the growth process to be studied at the atomic scale as a function of annealing temperature. Si diffusion coefficient is estimated from the accurate measurement of matrix composition and Si particle size. We demonstrate that the diffusion coefficient in SiO X is supersaturation dependent, leading to a decrease in silicon particle growth kinetics during annealing. In addition, we use our measurements to predict the critical thickness for efficient SiO 2 diffusion barriers

Nanostructure of a cold drawn tempered martensitic steel

The carbon atom distribution in a tempered martensitic steel processed by cold drawing was investigated with a three-dimensional atom probe. Data clearly show that cementite starts to decompose at the early stage of deformation. This indicates that the driving force of cementite decomposition during plastic deformation is not related to a strong increase of the interfacial energy. Carbon atmospheres were also analysed. They probably result from pipe diffusion of carbon atoms along dislocations pined by Fe3C carbides.Comment: 12 page

Nanoscale evidence of erbium clustering in Er-doped silicon-rich silica

International audiencePhotoluminescence spectroscopy and atom probe tomography were used to explore the optical activity and microstructure of Er 3+-doped Si-rich SiO 2 thin films fabricated by radio-frequency magnetron sputtering. The effect of post-fabrication annealing treatment on the properties of the films was investigated. The evolution of the nanoscale structure upon an annealing treatment was found to control the interrelation between the radiative recombination of the carriers via Si clusters and via 4f shell transitions in Er 3+ ions. The most efficient 1.53-μm Er 3+ photoluminescence was observed from the films submitted to low-temperature treatment ranging from 600°C to 900°C. An annealing treatment at 1,100°C, used often to form Si nanocrystallites, favors an intense emission in visible spectral range with the maximum peak at about 740 nm. Along with this, a drastic decrease of 1.53-μm Er 3+ photoluminescence emission was detected. The atom probe results demonstrated that the clustering of Er 3+ ions upon such high-temperature annealing treatment was the main reason. The diffusion parameters of Si and Er 3+ ions as well as a chemical composition of different clusters were also obtained. The films annealed at 1,100°C contain pure spherical Si nanocrystallites, ErSi 3 O 6 clusters, and free Er 3+ ions embedded in SiO 2 host. The mean size and the density of Si nanocrystallites were found to be 1.3 ± 0.3 nm and (3.1 ± 0.2) × 10 18 Si nanocrystallites·cm −3 , respectively. The density of ErSi 3 O 6 clusters was estimated to be (2.0 ± 0.2) × 10 18 clusters·cm −3 , keeping about 30% of the total Er 3+ amount. These Er-rich clusters had a mean radius of about 1.5 nm and demonstrated preferable formation in the vicinity of Si nanocrystallites

Atomic scale observation of phase separation and formation of silicon clusters in Hf higk-κ silicates

International audienceHafnium silicate films were fabricated by RF reactive magnetron sputtering technique. Fine microstructural analyses of the films were performed by means of high-resolution transmission electron microscopy and atom probe tomography. A thermal treatment of as-grown homogeneous films leads to a phase separation process. The formation of SiO2 and HfO2 phases as well as pure Si one was revealed. This latter was found to be amorphous Si nanoclusters, distributed uniformly in the film volume. Their mean diameter and density were estimated to be about 2.8 nm and (2.960.4) 1017 Si-ncs/cm3, respectively. The mechanism of the decomposition process was proposed. The obtained results pave the way for future microelectronic and photonic applications of Hf-based high-j dielectrics with embedded Si nanocluster

Growth-in-place deployment of in-plane silicon nanowires

International audienceUp-scaling silicon nanowire (SiNW)-based functionalities requires a reliable strategy to precisely position and integrate individual nanowires. We here propose an all-in-situ approach to fabricate self-positioned/aligned SiNW, via an in-plane solid-liquid-solid growth mode. Prototype field effect transistors, fabricated out of in-plane SiNWs using a simple bottom-gate configuration, demonstrate a hole mobility of 228 cm2/V s and on/off ratio >103. Further insight into the intrinsic doping and structural properties of these structures was obtained by laser-assisted 3 dimensional atom probe tomography and high resolution transmission electron microscopy characterizations. The results could provide a solid basis to deploy the SiNW functionalities in a cost-effective way

Atomic scale investigation of Cr precipitation in copper

The early stage of the chromium precipitation in copper was analyzed at the atomic scale by Atom Probe Tomography (APT). Quantitative data about the precipitate size, 3D shape, density, composition and volume fraction were obtained in a Cu-1Cr-0.1Zr (wt.%) commercial alloy aged at 713K. Surprisingly, nanoscaled precipitates exhibit various shapes (spherical, plates and ellipsoid) and contain a large amount of Cu (up to 50%), in contradiction with the equilibrium Cu-Cr phase diagram. APT data also show that some impurities (Fe) may segregate along Cu/Cr interfaces. The concomitant evolution of the precipitate shape and composition as a function of the aging time is discussed. A special emphasis is given on the competition between interfacial and elastic energy and on the role of Fe segregation