Structure evolution of mesoporous silica under heavy ion irradiations of intermediate energies Yu Lou a , Sandrine Dourdain a , Cyrielle Rey a , Yves Serruys b , David Simeone c , Nicolas Mollard d , Xavier Deschanels a, * a Institut de Chimie S eparative de Marcoule, UMR 5257 CEA/CNRS/ENSCM/Universit e de Montpellier, F-30207, Bagnols-sur-C eze, France b CEA Saclay, DEN-Service de Recherches de M etallurgie Physique, CEA, Universit e Paris-Saclay, F-91191, Gif-sur-Yvette, France c DEN/Service de Recherches M etallurgiques Appliqu ees, CEA, Universit e Paris-Saclay, F-91191, Centralesupelec/SPS/UMR-8085/LRC CARMEN, 92292, Chatenay Malabry, France d Universit e Grenoble Alpes, INAC/MEM, CEA, 38054 Grenoble, France article info Article history: Received 3 March 2017 Received in revised form 21 April 2017 Accepted 30 May 2017 Available online 1 June 2017 Keywords: Ion irradiation Mesoporous silica Thin film Radiation damage Pore collapse abstract Mesoporous sol-gel silica thin films were irradiated with gold ions of medium energies from 0.5 MeV to 12 MeV. In all cases these porous materials are compacted as a result of mesopore collapse and defor- mation. X-ray reflectivity and SEM measurement show that the total compaction (densification) is achieved for a fluence of about 2  10 14 cm 2 (~5  10 21 keV cm 3 ). The process of mesoporosity collapse seems different according to the irradiation regime (nuclear versus electronic). This effect results in a U- shaped evolution of the curve of the damage cross section as a function of the energy of ions Au. Infrared measurement of Au 0.5 MeV irradiated samples show a shift of TO 3 band towards lower wavenumber, related to Si-O-Si bond angle and Si-O bond length change. The sol-gel mesoporous and nonporous samples exhibit a delayed shift compared to thermal nonporous ones, which indicates that sol-gel materials are more radiation tolerant from this point of view. The sensitivity of these mesoporous structures to the damage caused by irradiation opens interesting prospects for obtaining self- conditioning materials. © 2017 Elsevier Inc. All rights reserved. 1. Introduction Ordered mesoporous material has been intensively studied since the elaboration of milestone M41S family mesoporous silica two decades ago [1]. According to the IUPAC definition, mesopore diameter is between 2 and 50 nm [2] which is larger than classic molecular sieves in the order of several Å. Its huge accessible sur- face, able to be functionalized, leads to potential applications such as adsorption [3,4], catalysis [5], sensoring [6] and gas storage [7]. In the nuclear field, especially for radioactive waste conditioning, ordered mesoporous silica materials present some advantages [8]. The huge specific surface up to 1500 m 2 g 1 along with function- alization can adsorb radionuclides efficiently and selectively. After the adsorption process, the mesopores could be closed under relatively soft conditions like mild thermal treatment, suited chemical stresses, in order to ensure a durable confinement. Such a combined process is called separation-conditioning. Additionally, the temperature of the mesoporous silica material preparation could be quite low (sol-gel route) compared to the traditional bo- rosilicate nuclear glass (~1200  C) which facilitates the capture of volatile radionuclides. This ability of mesoporous structure to collapse under given stresses is thus of great advantage regarding the foreseen applications, but it also raises the question of the behavior of such materials under self-irradiation. The aim of this paper is thus to study the effect of radiation damages onto meso- porous structures and a possible radiation induced collapse thereof. External irradiations by ions were used for that. Only few studies on the irradiation effect of mesoporous structure have been proposed. In the electronic energy deposition regime, Klaumünzer irradi- ated amorphous nanoporous silica (Vycor glasses) by swift heavy ions above ion track threshold and proposed a model of pressure and stress relaxation near hot fluidic tracks, which explains the beam induced shrinkage [9,10]. Dourdain et al. irradiated ordered mesoporous silica thin films with track-inducing Xe 92 MeV ions * Corresponding author. ICSM, Site de Marcoule, B^ at. 426 e BP17171, F-30207, Bagnols-sur-C eze, France. E-mail address: xavier.deschanels@cea.fr (X. Deschanels). Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso http://dx.doi.org/10.1016/j.micromeso.2017.05.057 1387-1811/© 2017 Elsevier Inc. All rights reserved. Microporous and Mesoporous Materials 251 (2017) 146e154