AVS 51st International Symposium
    Nanometer-scale Science and Technology Tuesday Sessions
       Session NS-TuP

Paper NS-TuP22
Nanoscale Patterning by Pulsed Laser Irradiation and Nanoparticle Alignment

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: Y.F. Guan, The University of Tennessee, Knoxville
Authors: Y.F. Guan, The University of Tennessee, Knoxville
A.J. Pedraza, The University of Tennessee, Knoxville
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One- and two-dimensional nanostructure arrays have been generated in silicon by pulsed-laser irradiation, using a Lloyd's mirror configuration. The nanostructures consisted of periodic ripples and protrusions that could reach an amplitude of 20 nm and a height of 80 nm, respectively. The ripple nanostructure was used as a template for the alignment of gold nanoparticles. The gold was first sputter-deposited on the rippled surface at a grazing angle, and subsequently annealed at 700 °C. Atomic force and high resolution scanning electron microscopy studies revealed that the nanoprotrusions are preceded by the formation of extended ripples. The present experiments show that the Lloyd's mirror configuration strongly enhances the formation of ripples and that nanoprotrusions form at the intersection of two mutually orthogonal sets of ripples. On the other hand, when a Lloyd's mirror is not added only 1-D ripple formation was observed, with no protrusions. Interference of the incoming or refracted laser beam and the laser light scattered by the surface undulations has been long recognized as the cause of periodic ripple formation. It is concluded that the gradient of surface tension arising from a temperature gradient is responsible for the formation of the nanoripple structure, and the breakdown of the ripples into aligned nanoprotrusions is due to a second temperature modulation along the ripple lines. The intersection of two mutually perpendicular ripple structures and the very high reflectivity of the nanoprotrusion tips are the causes that promote this secondary laser light modulation.