Direct fabrication of high aspect-ratio metal oxide nanopatterns via sequential infiltration synthesis in lithographically defined SU-8 templates.

Nanopatterning high aspect-ratio metal oxide structures remains challenging for conventional nanofabrication methods based on reactive ion etching due to marginal etch selectivity between target oxides and typical mask materials. Here, the authors report the application of sequential infiltration synthesis (SIS) on lithographically defined SU-8 polymer templates for patterning arbitrarily designed, high aspect-ratio metal oxide nanostructures with sub-50 nm linewidths, smooth vertical profiles, and three-dimensional (3D) morphologies difficult to achieve by the conventional fabrication methods. As examples, various AlO_x nanostructures with ∼40 nm linewidths and up to 16 aspect ratios were demonstrated, along with TiO_x in-plane nanowire arrays of controlled positional registrations. Detailed scanning and transmission electron microscopy studies revealed nanocrystalline and amorphous internal structures of respective AlO_x and TiO_x, as well as the swelling and contraction behaviors of polymer templates during the SIS process, which allowed the facile fabrication of high aspect-ratio, sub-50 nm-featured oxide nanopatterns with 3D morphologies. These results confirm the potential of vapor-phase material infiltration in directly nanopatterning complexly structured metal oxides. [ABSTRACT FROM AUTHOR]