Nanoscale phase transitions under extreme conditions within an ion track
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Ram Devanathan and William J. Weberb) Pacific Northwest National Laboratory, Richland, Washington 99352
Marcel Toulemonde Centre Interdisciplinaire de Recherche sur les Ions, les Mate´riaux et la Photonique (CIMAP), Commissariat a l’e´nergie atomique et aux e´nergies alternatives, Centre national de la recherche scientifique, Ecole national superieure d’Ingenieurs de Caen (CEA-CNRS-ENSICAEN) and University of Caen, 14070 Caen, France (Received 8 February 2010; accepted 26 April 2010)
The dynamics of track development due to the passage of relativistic heavy ions through solids is a long-standing issue relevant to nuclear materials, age dating of minerals, space exploration, and nanoscale fabrication of novel devices. We have integrated experimental and simulation approaches to investigate nanoscale phase transitions under the extreme conditions created within single tracks of relativistic ions in Gd2O3(TiO2)x and Gd2Zr2–x TixO7. Track size and internal structure depend on energy density deposition, irradiation temperature, and material composition. Based on the inelastic thermal spike model, molecular dynamics simulations follow the time evolution of individual tracks and reveal the phase transition pathways to the concentric track structures observed experimentally. Individual ion tracks have nanoscale core-shell structures that provide a unique record of the phase transition pathways under extreme conditions. I. INTRODUCTION
Heavy ions traveling at relativistic velocities are created by nuclear fission, high-energy particle accelerators, and cosmic events. Fission-fragment tracks are the primary source of radiation damage in nuclear fuels,1 and fission tracks in minerals are used extensively for agedating and thermochronology to reconstruct the timetemperature history of the Earth’s crust.2,3 Cosmic rays in space can disrupt or damage electronic devices used in space exploration,3,4 and ion irradiation is used to create complex nanostructures, such as cylindrical nanopores, nanoscale surface structures, and templates for nanofabrication.3,5 The highly localized extreme conditions induced by ions with MeV to GeV energies have been used to manipulate the properties of materials at the nanoscale.3,5,6 The resulting nano-sized track is the atomic-scale record of the extreme energy deposition over exceedingly short time periods. Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] Present address: University of Tennessee, Knoxville, TN 37996. This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy DOI: 10.1557/JMR.2010.0180 1344
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 7, Jul 2010 Downloaded: 17 Jul 2014
Relativistic heavy ions, often referred to as swift heavy ions, lose their energy predominantly through inelastic interactions with electrons, so-called electronic energy loss, on femtosecond tim
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