STM-INDUCED LUMINESCENCE STUDY OF POLY(P-PHENYLENEVINYLENE) BY CONVERSION UNDER ULTRACLEAN CONDITIONS

Curing-temperature-dependent spectroscopic studies of the conversion p rocess of the sulfonium chloride prepolymer to the conjugated polymer poly(p-phenylenevinylene) reveal an enhancement of the luminescence ef ficiency when the films are converted under ultrahigh-vacuum condition s. In these experiments, luminescence is excited by electron injection from the tip of a scanning tunneling microscope and the maximum lumin escence efficiency is found between 225 degrees and 260 degrees C. The optimum conversion temperature, the total luminescence yield, and the spectral features of the luminescence depend on the substrate materia l, heating gradient, and composition and purity of the prepolymer. The curing-temperature dependence of the Franck-Condon intensity distribu tion has a complex behavior. Maximum luminescence efficiency is charac terized by a spectrum where the upsilon = 0,1 vibronic transition has maximum relative intensity. Images of scanning-tunneling-microscopy-ex cited luminescence show intensity fluctuations within surface domains as small as a few nanometers in diameter, regions that correlate with the topographic features of the poly(p-phenylenevinylene) surface.