Radiation Damage
1) Radiation damage in nanofoams
The key to perfect radiation endurance is perfect recovery. Since surfaces are perfect sinks for defects, a porous material with a high surface to volume ratio has the potential to be extremely radiation tolerant, provided it is morphologically stable in a radiation environment. Experiments and computer simulations on nanoscale gold foams reported here show the existence of a window in the parameter space where foams are radiation tolerant. We analyze these results in terms of a model for the irradiation response that quantitatively locates such window that appears to be the consequence of the combined effect of two length scales dependent on the irradiation conditions: (i) foams with ligament diameters below a minimum value display ligament melting and breaking, together with compaction increasing with dose (this value is typically
5 nm for primary knock on atoms (PKA) of
15 keV in Au), while (ii) foams with ligament diameters above a maximum value show bulk behavior, that is, damage accumulation (few hundred nanometers for the PKA's energy and dose rate used in this study). In between these dimensions, (i.e.,
100 nm in Au), defect migration to the ligament surface happens faster than the time between cascades, ensuring radiation resistance for a given dose-rate. We conclude that foams can be tailored to become radiation tolerant.
2) Sputtering from nanofoams
Porous materials are ubiquitous in the universe and weathering of porous surfaces plays an important role in the evolution of planetary and interstellar materials. Sputtering of porous solids in particular can influence atmosphere formation, surface reflectivity and the production of the ambient gas around materials in space. Several previous studies and models have shown a large reduction in the sputtering of a porous solid compared to the sputtering of the non-porous solid. Using molecular dynamics simulations we study the sputtering of a nanoporous solid with 55% of the solid density. We calculate the electronic sputtering induced by a fast, penetrating ion, using a thermal spike representation of the deposited energy. We find that sputtering for this porous solid is, surprisingly, the same as that for a full density solid, even though the sticking coefficient is high.
Publicaciones:
1- Are Nanoporous Materials Radiation Resistant? E. M. Bringa, J. D. Monk, A. Caro, A. Misra, L. Zepeda-Ruiz, M. Duchaineau, F. Abraham, M. Nastasi, S. T. Picraux, Y. Q. Wang, and D. Farkas, NanoLetters, accepted for publication (2012). Online version available. DOI: 10.1021/nl201383u
2- Sputtering from a porous material by penetrating ions, J.F. Rodriguez-Nieva, E.M. Bringa, T.A. Cassidy, R.E. Johnson, A. Caro, M. Fama, M.J. Loeffler, R.A. Baragiola, and D. Farkas, Astrophys. J. Lett. (2011).
Integrantes:
Colaboradores:
Alfredo Caro (LANL, USA)
Diana Farkas (Va Tech, USA)
Robert.E. Johnson (UVa, USA)
Raul Baragiola (UVa, USA)
J. Rodriguez-Nieva (MIT, USA)