Formation of conic microstructures in the pulsed laser evaporation of solids

摘要

A study was made of the origination and the development of large-scale self-organising microstructures on the surface of monocrystalline Si and several other materials (Ge, Ti) in their vaporisation by pulsed laser radiation (copper vapour laser, λ = 510.6 nm, τ = 20 ns). The structurL formation occurs under repeated pulsed laser irradiation (～10{sup}4 pulses with an energy density of 1 - 2 J cm{sup}(-2)) in the absence of optical breakdown of the medium above the target surface in the 1-10{sup}5 Pa pressure range in a wide range of angles of laser radiation incidence on the surface. The structures are cones with an apex angle of ～20 - 25°, which grow towards the laser beam. It is shown that the spatial period of the structures developing during laser evaporation is determined by the period of the waves arising on the melt surface and is equal to 10-20 μm. It was determined employing x-ray diffraction analysis that the modified substrate region has a polycrystalline structure and consists of crystallites with dimensions ranging from 40 to 70 nm, depending on the pressure of the ambient atmosphere.