Laser-promoted nanostructure evolution and nanoparticle alignment

A cone microstructure has been used as a template to generate nanotips and to promote nanoparticle alignment. A quasi-periodic array of nanotips is produced when the laser-induced cone microstructure is subject to chemical etching due to tapering of the cone tips. Nanoparticles can be produced on the surface of a silicon specimen by irradiating it in the presence of an inert gas atmosphere. The backscattered material that is re-deposited on the substrate, upon irradiation at fluences close to the melting threshold, is composed of a thin film intermixed with extremely small nanoparticles. Further irradiation promotes film clustering and nanoparticle formation. In the presence of cones, the nanoparticles become aligned into straight and long (∼1 mm) lines whose spacing is close to the laser wavelength. This result suggested an ordering mechanism similar to that occurring for laser-induced periodic surface structures. The relation between nanoparticle line spacing and angle of incidence of the radiation supported this similarity. Nanoparticle ordering also was promoted by laser-enhanced chemical vapor deposition (LCVD) using polarized light, when a laser-induced periodic surface nanostructure was present in the substrate.