Photo-generation of acids and its fluorescence detection in a small area: a near-field write-once memory

A polymer film containing the photo-acid generator, 1,2-naphthoquinone-2-di azido-5-sulfonic acid sodium salt (SNQD), and a fluorescence pH indicator, seminaphthofluorescein (SNAFL-1), has been used as a near-field write-once memory medium. Near-field 455 nm light from a optical fiber tip with a nano -size (similar to 100 nm) aperture produced acids in a small area and the a cids were detected as the fluorescence intensity increased with the near-fi eld 488 nm excitation light. The fluorescent spot-size was as small as 160 nm and could be read many times without destruction.