Micrometer- and Nanometer-Scale Photopatterning Using 2-Nitrophenylpropyloxycarbonyl-Protected Aminosiloxane Monolayers

Abstract

An approach to nanopatterning is reported in which a scanning near-field optical microscope coupled to a near-UV laser is used to selectively deprotect 2-nitrophenylpropyloxycarbonyl (NPPOC)-protected aminosiloxane monolayers on glass. UV deprotection was studied for unpatterned samples using X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Highly efficient photodeprotection of the NPPOC moiety was observed upon irradiation at both 325 and 364 nm, and complete deprotection was found to occur within minutes. The resulting amine-terminated surfaces were then derivatized using trifluoroacetic anhydride (TFAA) and aldehyde-functionalized polymer nanoparticles. Contact angle and XPS measurements postderivatization indicated that surface functionalization was extensive, with the NPPOC-deprotected surfaces and aminopropylsiloxane control materials exhibiting essentially identical characteristics. Micrometer-scale patterns were fabricated using mask-based exposure, functionalized with polymer nanoparticles, and characterized by atomic force microscopy. Nanometer-scale patterns were fabricated using near-field exposure and characterized by friction force microscopy. The nanopatterns were derivatized with TFAA. The resulting images exhibited a clear contrast inversion that was due to an inversion of surface polarity in the patterned areas and confirmed that high spatial resolution (ca. 100 nm) was readily achievable.