Molecular Beam Deposition of Organic Nonlinear Optical Materials

ABSTRACTThin films of the organic nonlinear optical materials 4‘-nitrobenzylidene-3-acetamino-4- methoxy-aniline (MNBA), and 2-cyclooctylamino-5-nitropyridine (COANP) have been deposited by organic molecular beam epitaxy. Homoepitaxial growth has been demonstrated for both materials. MNBA thin films were grown heteroepitaxially on lattice-matched ethylenediammonium terephthalate (EDT) substrates. Under optimum growth conditions, similar to those valid for homoepitaxial growth of the same material, i.e. at substrate temperatures of 80°C, and growth rates of 0.1 Å/s, highly oriented films were deposited in an island growth mode. Nonlinear optical second-harmonic generation experiments confirmed the macroscopic orientation of the deposited MNBA thin films. Growth experiments with MNBA and COANP on inorganic substrates lead to amorphous or polycrystalline films, depending primarily on the substrate temperature. A spontaneous recrystallization process, occurring in COANP thin films under ambiant conditions, led to the formation of macroscopic nonlinear optically active domain structures.