Synthesis and ordering of nanostructures using laser light

This dissertation focuses on the formation of 1-D and 2-D nanoscale structures induced by the KrF excimer UV laser irradiation of silicon (lambda = 248 nm). Relatively low laser energy density (Ed <= 1 J/cm 2) is required to produce nanostructures. Alignment of 2-D nanoripple structures and nanoprotrusions has been realized by using Lloyd's mirror configuration.; Laser-generated silicon microcone arrays were used as templates for the growth of nanocolumns. The formation mechanism of the microstructure is reviewed, and the origin and growth of nanocolumns are discussed. The formation mechanism of nanocolumns requires highly localized melting, which explains why they fail to form on a flat surface but can grow atop the microcones.; Field emission properties from both microcones and nanocolumns have been measured. The high aspect ratio (height/tip radius) of nanocolumns makes them suitable for various field emission applications.; One- and two-dimensional (1-D and 2-D) nano-rippled structures produced in silicon by UV laser irradiation were investigated using atomic force and scanning electron microscopy. One and two beam illumination of the substrate was used to generate the nanostructures. Single beam irradiation was done using p-polarized laser light, while the two beam incidence was employed by using a Lloyd's mirror arrangement to reflect part of the beam onto the substrate. The structures were characterized by direct measurement of the ripple spacing or by measurements done on the fast Fourier transform of their AFM images. Under single beam illumination, only 1-D gratings were generated on the substrate surface. The grating lines were perpendicular to the projection of the electric field of the incident light on the substrate surface. For the two-beam illumination, it was very difficult to obtain the Lloyd's mirror characteristic interference pattern due to the poor coherency of the laser employed. Nonetheless, the use of a Lloyd's mirror not only strongly enhanced the production of rippled structures, but also produced 2-D gratings. The gratings generated with this arrangement are many millimeters long and cover the entire laser illuminated area. In contrast with one-beam illumination, linearly polarized light was not required to promote the rippled structures. Experimental evidence strongly suggests the following: (1) The p-component of the laser light is responsible for ripple formation; (2) Ripples can propagate with increasing number of pulses; (3) The ripple structure is produced while the silicon is melted. (Abstract shortened by UMI.)...