Photoacid Generation in Polymer Solids Induced and Observed with Near-Field Scanning Optical Microscopy.

Abstract

Near-field scanning optical microscopy (NSOM) has been used both to induce and to observe acid generation from a photoacid generator (PAG) doped in poly(methylmethacrylate) (PMMA) films. As a PAG, p-nitrobenzyl 9,10-dimethoxyanthracene-2-sulfonate (NAS) is used. Acid from PAG is monitored by fluorescence from a pH sensitive dye, Nile blue A (NBA). Our NSOM has a spatial resolution of 100 nm which is evaluated from the measurements of a chromium test pattern. A 442 nm radiation from an NSOM probe is used for inducing photoacid generation, and a 660 nm fluorescence from NBA cations which is excited with a 620 nm light passing through the NSOM probe is used for imaging the spatial distribution of the photoacid. The photoacid-generated area is successfully observed using fluorescence from NBA cations. Comparison between the topographic and NSOM image reveals that NSOM fluorescence image is not affected by the topographic features which are not formed by photochemical reactions.