FORMATION AND CHARACTERIZATION OF EPITAXIAL PHTHALOCYANINE AND PERYLENE MONOLAYERS AND BILAYERS ON CU(100) - LOW-ENERGY-ELECTRON DIFFRACTION AND THERMAL-DESORPTION MASS-SPECTROMETRY STUDIES

Ordered monolayer and multilayer thin films of copper phthalocyanine (CuPc) and perylene dicarboxylic dianhydride (PTCDA) have been grown on Cu(100) single crystals. CuPc grows in a commensurate square lattice configuration, with two equivalent domains consisting of closest packed, flat lying Pc rings, rotated at +/-21.8-degrees from the principle Cu(100) axes. The dimensions of these square lattices (b1 = b2 = 13.7 angstrom) are comparable to those observed using other substrates which interact weakly with the Pc overlayer (layered metal dichalocogenides, cleavage faces of single-crystal salts). PTCDA grows in a commensurate rectangular lattice (5 square-root 2x4 square-root 2)-R = 45-degrees, whose dimensions (b1 = 14.5 angstrom, b2 = 18.1 angstrom) are significantly different than those seen on weakly interacting substrates. Low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy, and thermal desorption mass spectroscopy (TDMS) data for the adsorption of this molecule strongly suggest that the first monolayer is dissociatively adsorbed to the Cu(100) surface. Growth of ordered layers of PTCDA has also been carried out on a Cu(100) surface modified with 1-2 ML (monolayers) of an ordered CuPc film. LEED and TDMS data indicate the formation of a new commensurate rectangular unit cell (b1 = 13.7 angstrom, b2 = 20.5 angstrom) for these PTCDA/CuPc/Cu(I 00) overlayers, which suggest that the CuPc layer controls the architecture of the subsequent PTCDA layers. The formation of a wide range of highly ordered organic heterojunctions appears to be possible, starting with a strongly adsorbed first layer, on surfaces such as single-crystal metals.