A molecular dynamics study of swift heavy ion irradiation of amorphous silica: the role of thermal effects

Rivera de Mena, Antonio; Prada, A.; Peña Rodríguez, Ovidio Y.; Crespillo Almenara, Miguel; Olivares, J.; Agullo Lopez, Fernando y Caturla Terol, Maria Jose (2012). A molecular dynamics study of swift heavy ion irradiation of amorphous silica: the role of thermal effects. En: "11th Computer Simulation of Radiation Effects in Solids (COSIRES)", 24/06/2012 - 29/06/2012, Santa Fe, USA. pp. 1-29.

Descripción

Título: A molecular dynamics study of swift heavy ion irradiation of amorphous silica: the role of thermal effects
Autor/es:
  • Rivera de Mena, Antonio
  • Prada, A.
  • Peña Rodríguez, Ovidio Y.
  • Crespillo Almenara, Miguel
  • Olivares, J.
  • Agullo Lopez, Fernando
  • Caturla Terol, Maria Jose
Tipo de Documento: Ponencia en Congreso o Jornada (Artículo)
Título del Evento: 11th Computer Simulation of Radiation Effects in Solids (COSIRES)
Fechas del Evento: 24/06/2012 - 29/06/2012
Lugar del Evento: Santa Fe, USA
Título del Libro: 11th Computer Simulation of Radiation Effects in Solids (COSIRES)
Fecha: Junio 2012
Materias:
Escuela: Instituto de Fusión Nuclear (UPM)
Departamento: Otro
Licencias Creative Commons: Reconocimiento - Sin obra derivada - No comercial

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Resumen

Irradiation with swift heavy ions (SHI), roughly defined as those having atomic masses larger than 15 and energies exceeding 1 MeV/amu, may lead to significant modification of the irradiated material in a nanometric region around the (straight) ion trajectory (latent tracks). In the case of amorphous silica, SHI irradiation originates nano-tracks of higher density than the virgin material (densification). As a result, the refractive index is increased with respect to that of the surroundings. Moreover, track overlapping leads to continuous amorphous layers that present a significant contrast with respect to the pristine substrate. We have recently demonstrated that SHI irradiation produces a large number of point defects, easily detectable by a number of experimental techniques (work presented in the parallel conference ICDIM). The mechanisms of energy transfer from SHI to the target material have their origin in the high electronic excitation induced in the solid. A number of phenomenological approaches have been employed to describe these mechanisms: coulomb explosion, thermal spike, non-radiative exciton decay, bond weakening. However, a detailed microscopic description is missing due to the difficulty of modeling the time evolution of the electronic excitation. In this work we have employed molecular dynamics (MD) calculations to determine whether the irradiation effects are related to the thermal phenomena described by MD (in the ps domain) or to electronic phenomena (sub-ps domain), e.g., exciton localization. We have carried out simulations of up to 100 ps with large boxes (30x30x8 nm3) using a home-modified version of MDCASK that allows us to define a central hot cylinder (ion track) from which heat flows to the surrounding cold bath (unirradiated sample). We observed that once the cylinder has cooled down, the Si and O coordination numbers are 4 and 2, respectively, as in virgin silica. On the other hand, the density of the (cold) cylinder increases with respect to that of silica and, furthermore, the silica network ring size decreases. Both effects are in agreement with the observed densification. In conclusion, purely thermal effects do not explain the generation of point defects upon irradiation, but they do account for the silica densification.

Más información

ID de Registro: 19792
Identificador DC: http://oa.upm.es/19792/
Identificador OAI: oai:oa.upm.es:19792
URL Oficial: http://cosires.newmexicoconsortium.org/
Depositado por: Memoria Investigacion
Depositado el: 06 Nov 2013 19:20
Ultima Modificación: 30 May 2017 16:08
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