Formation of conic microstructures upon pulsed laser evaporation of solids

The appearance and development of large-scale self-organising microstructur es on the surface of monocrystalline Si and several other materials (Ge, Ti ) are studied upon their evaporation by 20-ns pulses from a copper vapour l aser at 510.6 nm. The structures were formed upon repeated pulsed laser irr adiation (similar to 10(4) pulses with an energy density of 1-2 J cm(-2)) i n the absence of optical breakdown of the medium above the target surface i n the 1 - 10(5) Pa pressure range in a wide range of angles of laser radiat ion incidence on the surface. The structures are cones with an apex angle o f similar to 20 - 25 degrees, which grow towards the laser beam. It is show n that the spatial period of the structures developing during laser evapora tion is determined by the period of the waves arising on the melt surface a nd is equal to 10-20 mum. The x-ray diffraction analysis showed that the mo dified substrate region has a polycrystalline structure and consists of cry stallites with dimensions ranging from 40 to 70 nm, depending on the pressu re of the ambient atmosphere.