Ordered growth of substituted phthalocyanine thin films: Hexadecafluorophthalocyaninatozinc on alkali halide (100) and microstructured Si surfaces

Physical vapor deposition of hexadecafluorophthalocyaninatozinc (F16PcZn) i s performed under UHV conditions from monolayer coverages to an average thi ckness of about 20 nm on the (100) surfaces of NaCl, KCl, and KBr and on qu artz glass as well as on microstructured interdigitated electrode arrays on amorphous SiO2. UV-vis absorption spectroscopy indicates stacks of cofacia l parallel molecules for thin films on SiO2 and NaCl, whereas a component t ypical for a head-to-tail arrangement of molecules is detected on KCl and K Br. Atomic force microscopy shows well-defined crystals oriented in a defin ed azimuth angle relative to the substrate lattice on KCI. and KBr, indicat ing a growth in molecular square lattices parallel to the substrate surface which is confirmed by molecular mechanics and periodic surface potential c alculations. Plateaus of molecules predominantly standing upright on the su rface are seen for the films on NaCl and SiO2 which is confirmed by the rel ative intensity of optical absorptions and by the electrical conductivity c hanges observed during growth on SiO2. The temperature dependence of the el ectrical conductivity of films on SiO2 yields an increase of the thermal ac tivation energy around 200 degrees C corresponding to a loss in spectral fi ne structure as reported earlier [J. Phys. Chem. B 1999, 103, 3078]. A clea r correlation is seen between film structure and electrical as well as opti cal properties of molecular semiconductor thin films.