ORGANIC MOLECULAR-BEAM DEPOSITION COMBINED WITH A LASER-INDUCED CHEMICAL-REACTION

In order to control both molecular structures and molecular orientatio n simultaneously, we investigated organic molecular beam deposition co mbined with a laser-induced photochemical reaction. Bis(ethynylstyryl) benzene (BESB) films of trans,trans-isomer were deposited by this new method. The cis,cis-molecules were sublimed and cis-to-trans photoiso merization was conducted upon KrF excimer laser irradiation (lambda = 248 nm) in this process. The laser irradiation after and during the de position at the substrate temperature of 25 degrees C yielded amorphou s films. In contrast, the growth of well-oriented crystalline films wa s achieved upon the laser irradiation during the deposition at the sub strate temperature of 60 degrees C. At this substrate temperature only the trans,trans-molecules were deposited on the substrate surface, wh ich indicated that unreacted cis,cis-isomer was re-evaporated from the substrates. It can be explained that the crystal growth proceeds favo rably due to the surface migration of the trans,trans-isomer and the a bsence of the cis,cis-isomer. It was thus found that simultaneous prog ress of the laser-induced isomerization and the deposition caused the growth of the well-oriented crystalline films of trans,trans-BESB.