Self-organized 3D structures under laser evaporation of solids: formation and properties

Abstract

The review of recent results is presented on laser-assisted formation of self-organized 3D structures under laser irradiation solids (Si, Ge, Ti, W, Nb, Mo, stainless steel, etc.) by sufficiently long sequence of laser pulses of order of 10⁴. At laser fluence close to the melting threshold this leads to appearance of an array of micro-cones on the solid surface that grow towards the laser beam axis. The spatial period of the micro-cones is determined by that of the capillary waves on the melt surface and is typically of 10-20 μm. The formation of 3D structures is interpreted as the non-linear stage of the instability of the melt on laser-exposed solid surface, where the feedback is due to the variation of surface reflectivity with the angle of incidence of laser radiation and concentration of incident radiation into the bottom of the sinusoidal relief. The formation of 3D structures is assigned to displacement of the melt under gradient of the surface tension (Marangoni effect). The reflectivity of the 3D array of micro-columns is studied in a wide range of wavelengths from 0.2 to 25 μm. The low-threshold field electron emission of 3D structures on Si is demonstrated.