Observation of linear solid-solid phase transformation in silicon nanoparticles

Abstract

In bulk single crystal silicon, the semiconducting diamond to metallic ß-Sn phase transformation nucleates on defects, and is manifested by a sharp uptake in light absorption at a threshold of ~ 11 Gpa, accompanied with the creation of nanosized (20-50 nm) fragmentation domains. We report on the observation of linear uptakes in the absorption and in the luminescence, and with insignificant spectral change in ultrasmall 1 nm Si particles. We associate the gradual absorption uptake and luminescence yield with silicon-metal transformation on the surface. The insignificant change in the spectral content of the luminescence points to surface stability for particles, which are smaller than the bulk fragmentation domain. First-principle atomistic calculations yield absorption behavior that exhibits gradual uptake followed by sharp uptake at ~ 9-11 Gpa. The results point to the conclusion that two dimensional surface-like phase transformations are manifested by linear uptake in absorption and luminescence. a) m-nayfeh@illinois.edu 2

Optics in Nanotechnology

“…The excitation of the blue luminescence band indicates a two photon excitation process, while the second harmonic indicates the breaking of the centrosymmetry. Other theoretical simulations showed that the mechanical strain exerted is extremely high, corresponding to a pressure of several Gpa [40]. Because atoms on the surface are under high strain, they can undergo large-amplitude molecular-like vibrations to relieve the strain [41]; and hence can also couple efficiently to thermal and mechanical stimuli.…”