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

Physical vapor deposition of hexadecafluorophthalocyaninatozinc (F16PcZn) is performed under UHV conditions from monolayer coverages to an average thickness of about 20 nm on the (100) surfaces of NaCl, KCl, and KBr and on quartz glass as well as on microstructured interdigitated electrode arrays on amorphous SiO2. UV-vis absorption spectroscopy indicates stacks of cofacial parallel molecules for thin films on SiO2 and NaCl, whereas a component typical for a head-to-tail arrangement of molecules is detected on KCl and KBr. Atomic force microscopy shows well-defined crystals oriented in a defined azimuth angle relative to the substrate lattice on KCI. and KBr, indicating a growth in molecular square lattices parallel to the substrate surface which is confirmed by molecular mechanics and periodic surface potential calculations. Plateaus of molecules predominantly standing upright on the surface are seen for the films on NaCl and SiO2 which is confirmed by the relative intensity of optical absorptions and by the electrical conductivity changes observed during growth on SiO2. The temperature dependence of the electrical conductivity of films on SiO2 yields an increase of the thermal activation energy around 200 degrees C corresponding to a loss in spectral fine structure as reported earlier [J. Phys. Chem. B 1999, 103, 3078]. A clear correlation is seen between film structure and electrical as well as optical properties of molecular semiconductor thin films.