Sub-100-nm pattern formation through selective chemical transformation of self-assembled monolayers by soft X-ray irradiation

A new nanopatterning system based on a soft X-ray induced chemical transformation of a nitro-substituted aromatic imine monolayer has been developed. The molecular layer was exposed to soft X-rays, and the involved chemical transformation on the molecular layer was analyzed by using Fourier transform infrared reflection-absorption spectroscopy. As a result, we could confirm that the nitro group on the imine monolayer was cleaved upon the soft X-ray irradiation, leaving the hydrophobic phenyl unit intact on the monolayer surface, while the imine functionality was transformed into a new nonhydrolyzable one. However, the source of the hydrogen atom for the reduction and the final functionality at the para position of the aromatic group are unknown yet. Whereas, we could restore the hydrophilic amine functionality from the unexposed imine monolayer through hydrolysis, These phenomena were applied to the patterning of self-assembled monolayers featuring alternating height, chemical reactivity, and wettability. Alternating surface wettability is evident when water is sprayed on a macroscopically patterned substrate and the plate is tilted to drip the water. Also, atomic force microscope images revealed patterns as small as less than or equal to 100 nm with regular height and phase variations. The patterned monolayer was further modified with a linker and Cy3-tagged oligonucleotide, sequentially. Fluorescence images showed that the above molecules were selectively immobilized onto the amine-terminated region of the patterned surface.