Positive submicron lithography using uncoated or far-field apertured SNOM tips on organic crystals

Previously, the mechanism of face-specific, crystal-packing determined feature formations in organic solid-state photolysis were elucidated in detail by AFM [G. Kaupp et al., Mol. Cryst. Liq. Cryst. 276 (1996) 315; G. Kaupp, Comprehensive Supramolecular Chemistry; G. Kaupp et al., J. Vac. Sci. B 15 (1997) 1521.; G. Kaupp, Adv. Photochem. 19 (1994) 119]. As a result the photodimerizations of 9-chloroanthracene [G. Kaupp et al., Mol. Cryst. Liq. Cryst. 276 (1996) 315; G. Kaupp, Comprehensive Supramolecular Chemistry; G. Kaupp et al., J. Vac. Sci., B 15 (1997) 1521.] and 2,5-dibenzylidenecyclopentanone [G. Kaupp et al., J. Vac. Sci., B 15 (1997) 1521.; G. Kaupp, J. Microscopy 174 (1994) 15] were used to judge the sizes of the illuminated spots with good and sometimes less perfect uncoated scanning near-field optical microscope (SNOM) tips. Lithography on photostable absorbing organic crystals at 488 nm occurred now by radiationless decay of thermally insulated molecules of the indigoid dye 2-(p-dimethylaminobenzylidene)-3-oxo-2,3-dihydrothionaphthene (1): positive cones formed by local surface melting of the crystal that were not chemically transformed and thus gave no SNOM contrast. When choosing a 400 nm far-field apertured tip [G. Kaupp et al., 4th Near-Field Optics Conf., Jerusalem, 1997] at 1 μW for 10 s the cones were 60 nm high with half-widths of 300 nm and peak to peak distances of 600 nm. Such submicron lithography is of importance for the characterization of SNOM tips and might be improved further for high density data storage.