Formation of conical microstructures upon laser evaporation of solids

The formation and development of the large-scale periodic structures on a s ingle crystal Si surface are studied upon its evaporation by pulsed radiati on of a copper vapor laser (wavelength of 510.6 nm, pulse duration of 20 ns ). The development of structures occurs at a high number of laser shots (si milar to 10(4)) at laser fluence of 1-2 J/cm(2) below optical breakdown in a wide pressure range of surrounding atmosphere from 1 to 10(5) Pa. The str uctures are cones with angles of 20-25 degrees, which grow towards the lase r beam and protrude above the initial surface for 20-30 mum. It is suggeste d that the spatial period of the structures (10-20 mum) is determined by th e capillary waves period on the molten surface. The X-ray diffractometry re veals that the modified area of the Si substrate has a polycrystalline stru cture and consists of Si nanoparticles with a size of 40-70 nm, depending o n the pressure of surrounding gas. Similar structures are also observed on Ge and Ti.