Structural stability in materials under electronic excitation is different from that at the ground state. It is expected that electronic excitation effects on the structural stability will be enhanced in nanoparticles which have high surface to volume ratio and high atomic mobility. Recently, it was found by that when GaSb particles were excited by 75 keV electrons, the compound transforms to a two-phase consisting of an antimony core and a gallium shell or an amorphous phase, or remains the original crystalline phase, depending on particle size and/or temperature [1,2]. In the present paper, we studied by situ transmission electron microscopy the influence of defects induced by lower energy electronic excitation on the phase separation in GaSb particles. When GaSb particles kept at 430 K were excited by 25 keV electrons, primary defects such as gallium vacancies and interstitials which are mobile at this temperature are formed in the particles. In the first stage, the gallium vacancies form a void in the individual particles and interstitials segregate near the surface. In the second stage, when the deviation from stoichiometric composition by a compositional fluctuation in the interior of GaSb particles is increased, the increase of the resultant lattice strain energy brings about the breakdown of zincblende structure and the consequent phase separation proceeds. The high production yield of the primary defects by 25 keV electron excitation remarkably enhances the phase separation in GaSb compound nanoparticles.
[1] H. Yasuda et al., Phys. Rev. Lett. 92, 135501 (2004).
[2] H. Yasuda et al., Euro. Phys. J. D 37, 231 (2006).
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