Organic molecular beam deposition combined with laser-induced chemical reactions

In order to fabricate functional organic thin films, we investigated organic molecular beam deposition combined with laser-induced chemical reactions. Bis(ethynylstyryl) benzene (BESB) films of trans,trans-isomer were deposited by this new method. The cis,cis-BESB was sublimed and cis-to-trans photoisomerization was induced upon KrF excimer laser irradiation (lambda = 248 nm). The growth of the well-oriented crystalline films was achieved upon the laser irradiation during the deposition at the substrate temperature of 60 degrees C. At this substrate temperature only trans,trans-BESB was deposited on the substrate surface, which indicated that unreacted cis,cis-isomer was re-evaporated from the substrates. It can be explained that the crystal growth favorably proceeded due to the enhancement of the surface migration of the trans,trans-isomer and no hindrance of the cis,cis-isomer. We also fabricated thin films of a reaction product by inducing an intermolecular reaction of BESB with biphenyl-dithiol (BPDT) upon the laser irradiation during the deposition. It is thus found that the new process made it possible to produce the functional organic thin films, which were difficult to be evaporated by the conventional vacuum process. We discussed the chemical reactions and the deposition behavior in our process.