INVESTIGATION OF MESOSCOPIC DOMAINS IN THIN ORGANIC FILMS USING NEAR-FIELD OPTICAL-ABSORPTION MAPPING

We have used a near-field scanning optical microscope (NSOM) to conduc t optical absorption mapping of a thin organic film of poly(phenylene vinylene) (PPV) and tris(8-hydroxy)quinoline aluminum (Alq). Using 488 nm light, NSOM transmission images revealed 100-300 nm 'dark' feature s scattered randomly across the film. However, these 'dark' features w ere not observed using 633 nm light. Simultaneously acquired topograph ic images revealed no significant changes in surface morphology over t he 'dark' features and indicated that the optical variation was not re lated simply to variations in film thickness or optical scattering. Th e origin of these 'dark' features is believed to be related to ordered domains in the thin organic film which has a different absorption spe ctrum as compared to a disordered film. The change in contrast observe d using 488 and 633 nm light was related to the optical absorption dif ference between the ordered and disordered regions at the two waveleng ths. (C) 1998 Elsevier Science B.V. All rights reserved.