March 16, 2011 Wednesday 15:30
Ömer İlday, Bilkent University
Nonlinear Laser Lithography: Femtosecond Laser-Controlled Highly Ordered “Self-Assembly” of Self-Similar Titania Nanostructures

Abstract: We demonstrate ultrafast-laser-controlled self-assembly of titania (TiO2) nanostructures on Ti. The formation process is governed by a nonlinear feedback mechanism, involving interplay between the laser beam and scattering of light from existing nanostructures. The spatial profile of these structures, created by a self-similar fiber laser, is also self-similar. The governing dynamics and material properties completely determine all key features of the nanostructures, resulting in an unprecedented level of uniformity, approaching that of established laser lithographic techniques. By scanning the laser beam over the sample, various structures are obtained with orientations controlled by the laser polarization. New structures can be self-stitched to existing structures without discontinuities or irregularities, allowing coverage of arbitrarily large areas fast and with low-cost equipment. We also demonstrate that Ti thin films can be used as an intermediary to imprint titania nanostructures onto, e.g., silicon substrates. This flexible process is immune to large variations in laser power, spot size or scanning speed, thus allowing, for example, creation of structures on non-planar surfaces.