Radiation aging of nonmetallic materials: specific aspects

Under irradiation, all materials experience various forms of structural evolution, from the simplest, associated with point defect creation and accumulation, to complex phase changes, either towards equilibrium or nonequilibrium structures. In nonmetallic ceramics the same processes are known or probable; however, the nature of bonding, partly ionic and partly covalent, as well as the complexity associated with the long range character of the Coulomb interaction, have long posed great difficulties in defect and aging studies under irradiation. Our aim here is to review the current state of knowledge, stressing the specific characteristics of nonmetallic materials, from primary defect creation to collective behavior, with respect to both experimental facts as well as to modeling perspectives. Given the broad field covered, we will illustrate the problem by choosing a few model materials, mostly oxides, in which the whole spectrum of phenomena has been handled. We will begin with threshold energy studies, then go to microstructure formation and evolution, radiation enhanced diffusion results, and lastly to phase changes. To cite this article: Y. Limoge, C. R. Physique 9 (2008).     

Radiation effects in concentrated alloys and compounds: equilibrium and kinetics of driven systems

What organization of condensed matter does resist irradiation, as a function of irradiation conditions? How to characterize the latter? We survey the advances in the field during the past three decades, when irradiation effects reduce to nuclear collisions. While in simple cases (structure defined by a scalar order parameter) one may define a stochastic potential, which yields the stationary states of the compounds under irradiation and their respective stability, in more general cases, we are left with brute force atomistic simulations to explore materials' behaviour as a function of irradiation conditions. Special attention is given to the kinetics of concentration fields under irradiation, a question with several practical implications. We conclude that irradiation conditions are best defined by three parameters: the cascade features (number of displacements and replacements, length of replacement sequences, …), the frequency of cascade occurrence, and the cumulated dose. We suggest cascade features be named ‘(elementary) dose’ and the cascade occurrence frequency ‘dose rate’. To cite this article: G. Martin, P. Bellon, C. R. Physique 9 (2008).     

Helium and point defect accumulation: (i) microstructure and mechanical behaviour

Ferritic/martensitic (F/M) steels are good candidate structural materials for the future fusion reactors and spallation sources. However, irradiation of steels is known to produce hardening, loss of ductility, shift in ductile to brittle transition temperature (DBTT) and reduction of fracture toughness and creep resistance starting at low doses. Helium (He), produced by transmutation during the irradiation, also impacts mechanical properties. Numerous experimental and theoretical studies on the evolution of the microstructure of steels under irradiation have been conducted until now. We review the effect of irradiation-induced point defects and in particular of He on the mechanical properties of F/M steels. To cite this article: R. Schäublin et al., C. R. Physique 9 (2008).     

AC transport in carbon-based devices: challenges and perspectives

Time-dependent fields are a valuable tool to control fundamental quantum phenomena in highly coherent low dimensional electron systems. Carbon nanotubes and graphene are a promising ground for these studies. Here we offer a brief overview of driven electronic transport in carbon-based materials with the main focus on carbon nanotubes. Recent results predicting control of the current and noise in nanotube based Fabry–Pérot devices are highlighted. To cite this article: L.E.F. Foa Torres, G. Cuniberti, C. R. Physique 10 (2009).     

Nucleation of magnetisation reversal, from nanoparticles to bulk materials

We review models for the nucleation of magnetisation reversal, i.e. the formation of a region of reversed magnetisation in an initially magnetically saturated system. For small particles, models for collective reversal, either uniform (Stoner–Wohlfarth model) or non-uniform like curling, provide good agreement between theory and experiment. For microscopic objects and thin films, we consider two models, uniform (Stoner–Wohlfarth) reversal inside a nucleation volume and a droplet model, where the free energy of an inverse bubble is calculated, taking into account volume energy (Zeeman energy) and surface tension (domain wall energy). In macroscopic systems, inhomogeneities in magnetic properties cause a distribution of energy barriers for nucleation, which strongly influences effects of temperature and applied field on magnetisation reversal. For these systems, macroscopic material parameters like exchange interaction, spontaneous magnetisation and magnetic anisotropy can give an indication of the magnetic coercivity, but exact values for nucleation fields are, in general, hard to predict. To cite this article: J. Vogel et al., C. R. Physique 7 (2006).     

Fresnel phase matching: a universal phase matching scheme

We present new theoretical concepts for Fresnel phase matching. A guided wave approach is described, which allows us to intrinsically take into account all the physical processes involved. To cite this article: M. Raybaut et al., C. R. Physique 8 (2007).     

Charge transport in carbon nanotubes based materials: a Kubo–Greenwood computational approach

In this contribution, we present a numerical study of quantum transport in carbon nanotubes based materials. After a brief presentation of the computational approach used to investigate the transport coefficient (Kubo method), the scaling properties of quantum conductance in ballistic regime as well as in the diffusive regimes are illustrated. The impact of elastic (impurities) and dynamical disorders (phonon vibrations) are analyzed separately, with the extraction of main transport length scales (mean free path and localization length), as well as the temperature dependence of the nanotube resistance. The results are found in very good agreement with both analytical results and experimental data, demonstrating the predictability efficiency of our computational strategy. To cite this article: H. Ishii et al., C. R. Physique 10 (2009).     

First principles calculations in iron: structure and mobility of defect clusters and defect complexes for kinetic modelling

Predictive simulations of the defect population evolution in materials under or after irradiation can be performed in a multi-scale approach, where the atomistic properties of defects are determined by electronic structure calculations based on the Density Functional Theory and used as input for kinetic simulations covering macroscopic time and length scales. Recent advances obtained in iron are presented. The determination of the 3D migration of self-interstitial atoms instead of a fast one-dimensional glide induced an overall revision of the widely accepted picture of radiation damage predicted by previously existing empirical potentials. A coupled ab initio and mesoscopic kinetic Monte Carlo simulation provided strong evidence to clarify controversial interpretations of electrical resistivity recovery experiments concerning the mobility of vacancies, self-interstitial atoms, and their clusters. The results on the dissolution and migration properties of helium in α-Fe were used to parameterize Rate Theory models and new inter-atomic potentials, which improved the understanding of fusion reactor materials behavior. Finally, the effects of carbon, present in all steels as the principal hardening element, are also shown. To cite this article: C.C. Fu, F. Willaime, C. R. Physique 9 (2008).     

Semiclassical relativistic strings in and long scalar operators in SYM theory

We review recent progress in quantitative checking of AdS/CFT duality in the sector of ‘semiclassical’ string states dual to ‘long’ scalar N=4 super Yang–Mills operators. In particular, we describe the effective action approach, in which the same sigma model type action describing coherent states is shown to emerge from the AdS₅×S⁵ string action and from an integrable spin chain Hamiltonian representing the SYM dilatation operator. To cite this article: A.A. Tseytlin, C. R. Physique 5 (2004).

Résumé

Nous passons en revue les progrès récents sur les vérifications quantitatives de la dualité AdS/CFT dans le régime où les états « semiclassiques » de cordes sont du aux « longs » opérateurs scalaires de la théorie de super Yang–Mills N=4. En particulier, nous décrivons l'approche effective, dans laquelle le modèle sigma décrivant les états cohérents est montré émerger de l'action de la corde sur AdS₅×S⁵ et de l'Hamiltonien d'une chaîne de spin intégrable représentant l'opérateur de dilatation en SYM. Pour citer cet article : A.A. Tseytlin, C. R. Physique 5 (2004).     

The Fe–Cr system: atomistic modelling of thermodynamics and kinetics of phase transformations

To understand the behaviour of irradiated defects and kinetic pathways of micro-structural evolution in Fe–Cr alloys, we use a combination of density functional theory with statistical approaches involving cluster expansions and Monte Carlo simulations. A lowest negative mixing enthalpy is found at 6.25% Cr that is consistent with our DFT prediction of an ordered Fe₁₅Cr structure. At 50% Cr, it is found that the predicted enthalpy of formation is 4 times smaller than that calculated by the CPA approach. Thermodynamic and precipitation properties are then discussed in term of segregation between the Fe₁₅Cr and α^′-Cr phases and of vacancy-mediated kMC simulation. To cite this article: D. Nguyen-Manh et al., C. R. Physique 9 (2008).     

Helium and point defect accumulation: (ii) kinetic modelling

The main outstanding issues regarding modeling He diffusion and defect accumulation in α-iron are reviewed. During recent years, first principles calculations have provided a better understanding of defect stability and migration properties in pure α-iron, and accurate values of energetics of He migration and He-vacancy interactions. Such information has been used by several authors to study damage evolution under different irradiation conditions using both kinetic Monte Carlo and rate theory models. In this article a review of the main results is provided, in particular for He desorption. The influence of impurities such as carbon is discussed as well as the main challenges ahead for modeling. To cite this article: M.J. Caturla et al., C. R. Physique 9 (2008).     

Organisation of carbon nanotubes and semiconductor nanowires using lateral alumina templates

Carbon nanotubes and semiconductor nanowires have been thoroughly studied for the future replacement of silicon-based complementary metal oxide semiconductor (CMOS) devices and circuits. However, the organisation of these nanomaterials in dense transistor arrays, where each device is capable of delivering drive currents comparable with those of their silicon counterparts is still a big challenge. Here, we present a novel approach to the organisation of carbon nanotubes and semiconductor nanowires, based on the use of porous lateral alumina templates obtained by the controlled anodic oxidation of aluminium thin films. We discuss the growth of nanomaterials inside the pores of such templates and show the feasibility of our approach. Our first results point to further work on controlling the synthesis of catalyst nanoparticles at the bottom of the pores, these particles being necessary to nucleate and sustain the growth of carbon nanotubes or semiconductor nanowires. To cite this article: D. Pribat et al., C. R. Physique 10 (2009).