Radiation effects in nanoparticles

Ion irradiation is turning out as a very useful tool for producing nanoparticles in phases that are hard or impossible to obtain otherwise. In addition to promoting chemical ordering in, for instance, FePt particles [1], irradiation has recently been shown to provide a means to remove grain boundaries from alloyed (CuAu, FePt) multiply twinned particles, turning them single-crystalline [2,3]. Irradiation can also be used to densify porous cluster-assembled films without dramatically increasing the grain size [4]. Thus, irradiation provides a versatile tool for controlled engineering of nanoscale systems. We will give an overview of our recent work on radiation effects in nanoparticles. Specifically, the multiply-twinned to single-crystalline transformation, which has been shown to occur via transient amorphization of the alloyed particles, is discussed [3]. The transformation is surprising, as it occurs in alloys, which are known not to amorphize in bulk. In addition to phase transitions, we will review defect production by, on one hand, cascade-producing irradiation [5] (e.g., 25 keV Ga on Au) and, on the other, irradiation in the single knock-on regime [6,7] (e.g., 3 keV He on Pt). The defect production mechanisms and the differences between irradiation response of nanosized and bulk systems are discussed.

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[2] O. Dmitrieva et al., J. Appl. Phys. 97, 10N112 (2005).
[3] T. T. Järvi et al., EPL 85, 26001 (2009).
[4] K. Meinander and K. Nordlund, Phys. Rev. B 79, 045411 (2009).
[5] T. T. Järvi et al., EPL 82, 26002 (2008).
[6] T. T. Järvi et al., Phys. Rev. B 80, 132101 (2009).
[7] T. T. Järvi et al., J. Appl. Phys. 102, 124304 (2007).