Abstract
When a target is ablated in an atmosphere of an inert buffer gas by low-intensity
laser radiation (no greater than 10<sup>5</sup>W/cm<sup>2</sup>), nanoparticles
self-assemble into low-dimensional fractal structures. The dependences of the efficiency
of the self-assembly process on the composition of the silicon-silica target and the
pressure of the buffer gas manifest a distinct correlation with percolation in the
plasma of the laser flare. A structure with a fractal dimension of
d<sub>f</sub>>2 is formed most efficiently close to the three-dimensional
percolation threshold p<sub>c</sub>≈0.3, where p<sub>c</sub> is the ratio of the number
density of silicon atoms to the number of all the atoms in the laser flare. Close to the
two-dimensional percolation threshold (p<sub>c</sub>≈0.5), fractal structures are
observed with d<sub>f</sub><2, assembled on a plane. The main structural elements
of the observed objects are one-dimensional structures--chains of tens of nanoparticles,
with a characteristic size of about 80nm. Results of a study of fractal nanostructures
by scanning electron microscope are presented, an x-ray structural analysis is carried
out, and the photoluminescence is studied.
© 2008 Optical Society of America
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