Molecular Studies on Laser Ablation Processes of Polymeric Materials by Time-Resolved Luminescence Spectroscopy

Abstract

By fluorescence analyses just upon laser ablation and of ablated surface, molecular aspects of ablation mechanism were elucidated and a characterization of ablated materials was performed. Laser fluence dependence of poly(N-vinylcarbazole) fluorescence indicates the inportance of mutual interactions between excited singlet states. As the fluence was increased, a plasma-like emission was also observed, and then fluorescence due to diatomic radicals was superimposed. While the polymer fluorescence disappeared mostly during the pulse width, the radicals attained the maxi mum intensity at 100 ns after irradiation. Fluorescence spectra and their rise as well as decay curves of ablated surface and its nearby area were affected to a great extent by ablation. This phenomenon was clarified by probing fluorescence under a microscope.There are a number of reports concerning laser ablation of polymeric materials in relation to microelectronics technology (1-8).Most of the polymers studied were polyimide, poly(methyl methacrylate), poly(ethylene terephthalate) and some photoresists. They have carbonyl as well as amino groups and hetero-atoms. In view of photophysics and photochemistry, this means that fluorescence lifetime is very short, intersystem crossing occurs with high quantum yield, and they are photochemically reactive (9).On the other hand, there are other series of polymers having π-electronic chromophore such as N-carbazolyl and 1-pyrenyl groups, whose photophysical properties are quite different from the above polymers and whose laser chemistry is studied in detail. A relation among interchromophoric interaction, spectral shape and geometrical structure in the excited singlet, triplet, cationic and anionic 1 Current address: ERATO, JRDC (1988-1993), 15 Morimoto-cho, Shimogamo, Sakyo-ku,