Formation of silicon nanostructures when a target is ablated by a quasi-continuous laser pulse

Abstract

When a target is ablated in an atmosphere of an inert buffer gas by low-intensity laser radiation (no greater than 105W∕cm2), 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 df>2 is formed most efficiently close to the three-dimensional percolation threshold pc≈0.3, where pc 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 (pc≈0.5), fractal structures are observed with df<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.