Research at LSI
Laboratoire des Solides Irradiés
(UMR 7642 CEA - CNRS - Ecole polytechnique)
The name “Irradiated Solids” takes its origins in the history of the laboratory, which has been strongly marked by the study of the radiation effects in nuclear materials. The name still summarizes very well the present research of the LSI, which centers on three major axes: Excitations in solids, defects in materials and their consequences, and nanomaterials obtained by irradiation.
Study of excitations in solids
Obtaining a fundamental understanding of the behavior of solids under any type of excitation remains a real challenge in the field of condensed-matter physics. To illustrate some of the problems studied at the LSI we can mention the activities of the “Theoretical Spectroscopy” group, which is within the framework of the “European Theoretical Specroscopy Facility” network, develops the theories that are needed to perform ab initio calculations of experimental spectra (like those obtained e.g. by synchrotron radiation). The “Radiation-Matter Interactions”group studies the kinetic aspects of the electronic excitations in solids that are obtained during a femto-second intense laser pulse. The research subjects encompass: The understanding of the mechanisms that are underlying the creation of defects within insulators, the resilience to flux of high-power optics devices, and excitation-induced phase transitions in materials that present strong electronic correlations. (The latter subject is studied within the framework of the FemtoArpes project). Lower-energy excitations are related to electronic-transport phenomena. The “Physics and Chemistry of Nano-Objects" team focuses its interests specifically on one-dimensional nano-systems (nanowires, nanotubes) and more in particular on effects in connection with the electron spin (within the “nanospintronics” centre). The “Materials Science Theory” group performs theoretical studies of carrier lifetime problems, which are strongly dominated by the interaction of the excited electrons with the atomic-lattice vibrations of the material.
Defects in materials and consequences
In materials, defects can be produced as a direct consequence of irradiation. These defects modify the physicochemical properties of the materials. More in particular they are responsible for the so-called aging under irradiation, which limits the lifetime of devices and equipments that are being used in electronuclear and space technology applications. Such defects are studied by the “Radiation-Matter Interactions” group. Nevertheless, the irradiation-induced effects in solids are not different in nature from the native defects. Therefore irradiation may prove a choice tool for the study of such defects or of the relation between the structure of a material and its properties. Irradiation can then be used to monitor the properties of materials, as is done by the “Superconductivity and Sensors” group in its studies of high-critical temperature (Tc) superconductors (oxides, pnictides) or of “exotic” superconductors, where the irradiation reveals itself then as a method to study the fundamental properties of solids. Moreover, irradiation techniques allow one to obtain physicochemical states that are not accessible by classical methods of synthesis, rendering it this way possible to design new materials (“Radiation-Matter Interactions” group and “Physics and Chemistry of Nano-Objects” group). Finally, defects in solids are also studied theoretically by the “Materials Science Theory” group.
Nanomaterials obtained by irradiation
A specific example of the new properties that may be obtained by irradiation is the nanostructuration of materials, which can be caused by an intense localization of the energy deposition and the consequences thereof. E.g. the “Physics and Chemistry of Nano-Objects” group uses swift heavy-ion irradiation to obtain nanoporous polymeric membranes whereby the pore size and geometry are controlled at the nanoscale. Furthermore, both the radiografting techniques developed by this group and the technique of electrochemical growth within a matrix developed by the “Superconductivity and Sensors” group, allow to obtain complex and hybrid nanomaterials, that can be used in a wide field of applications, such as biomedical applications, anti-pollution devices, the manufacturing of magneto-restrictive nano-captors , and proton-mixing membranes for fuel cells. Finally, irradiation can be used to drive the precipitation-dissolution properties of solid solutions, with the aim of obtaining colloids with size distributions that cannot be reached by chemical methods.