surface science ELSEMER Applied Surface Science 96-98 (1996) 569-571 Laser implantation of fluorescent molecules into polymer films H. Fukumura * , Y. Kohji, H. Masuhara Department of Applied Physics, Osnkn Linirersity, Suita. Osaka 565, Japan Received 22 May I995 Abstract A new method to implant molecules into polymers by nanosecond pulse laser irradiation has been developed on the basis of studies of laser ablation. Fluorescent molecules were implanted into polymer films having different glass transition temperature. The distribution of fluorescent molecules in an implanted layer was obtained by using total internal reflection fluorescence spectroscopy. 1. Introduction Recently we have reported a novel method for doping polymer films with aromatic molecules by laser irradiation [l]. We have developed and pro- posed this method based on our recent mechanistic studies on laser ablation of polymer films doped with aromatic molecules. Time-resolved spectroscopy re- vealed that aromatic molecules embedded in a poly- mer matrix hardly decompose but generate hot do- mains in the matrix when irradiated with an intense laser pulse [2,3]. The hot domains lead to a transient expansion of the polymer surface even below the ablation threshold as has clearly been shown by highly sensitive nanosecond time-resolved interfer- ometry [4]. To explain efficient conversion of photon to thermal energy in aromatic molecules, we pro- posed ‘cyclic multiphotonic absorption’, namely, the repetition of internal conversion and photoexcitation in the excited states [5]. This is supported by the fact * Corresponding author. Tel.: + 81-6-879-7838; fax: +81-6. X76-8580; e-mail: fukumura@ap.eng.osaka-u.ac.jp. that the effective absorbance of doped polymer films at the laser wavelength varies depending on the excitation intensity [6]. This method of doping is spatially selective and may be applicable to various combinations of molecules and polymers having no common sol- vents, and could have a high potential for future application. One problem which is not revealed yet is how deep molecules can be implanted and what kinds of factors affect the implantation depth. To obtain the depth of implantation, we used fluorescent molecules as dopants and measured fluorescence in- tensity under total internal reflection conditions. Fur- thermore, we do not know what polymer property is important in this process. Here an effect of glass transition temperature CT,) of polymer films on the implantation depth was also studied. 2. Experimental Poly(methy1 methacrylate) (PMMA) films includ- ing 5.5 wt% diphenyl anthracene (DPA) or 3.5 wt% pyrene were prepared by spin-coating on quartz plates 0169.4332/96/$1.5.00 0 1996 Elscvicr Science B.V. All rights reserved SSDI 0169-4332(95)00532-3