Optically-stimulated surface diffusion exploited for directed self-assembly on amorphous semiconductors

Nanoscale device fabrication technologies require toolsets for miniaturization and organization of materials at nanometer dimensions. A new surface self-assembly method at the 10-200 nm length scale was developed using amorphous semiconducting materials. Patterned optical or electron beam exposure yielded a spatially varying surface mass flux that, when performed at an annealing temperature just at the cusp of crystallization, provided the extra nudge to crystallize subcritical nuclei in regions dictated by the light flux. The full-fledged crystallites then grew by surface diffusion and Ostwald ripening until the desired fraction of the film have accreted onto the original nuclei. This technique used TiO₂ as the substrate material. This scheme is applicable in various semiconducting materials on nearly arbitrary substrates to form nanoarrays, nanowalls, and possibly three-dimensional structures. Possible applications include chalcogenide semiconductors for data storage media, nanoparticles arrays for direct use in sensors and solar cells, and semiconductor arrays for indirect use as seed layers for the subsequent deposition of sintered particle films in fabricating advanced ceramics and devices such as rechargeable batteries, solar cells, gas sensors, and photonic band gap materials in solar windowpanes. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).