INPLANE ORDERING OF A DIBENZO[B,T]PHTHALOCYANINATO-ZN(II) THIN-FILM DUE TO THE ATOMIC STEP ARRAYS ON A SAPPHIRE ((1)OVER-BAR-012) SURFACE

Thin films of dibenzo[b,t]phthalocyaninato-Zn(II) (ZnDBPc) grown by UHV molecular-beam deposition on polished sapphire ((1) over bar 012) surfaces show in-plane ordering over the entire surface. To determine the mechanism of this ordering, the surface morphology of a sapphire substrate and the early stages of ZnDBPc film growth were examined by atomic force microscopy, X-ray diffraction, and polarization spectroscopy. Equally spaced parallel atomic step arrays were found on the sapphire ((1) over bar 012) surface. Their direction and spacing were directly related to the misorientation direction and angle of the polished surface from the exact ((1) over bar 012) surface and had no relation to the crystallographic axes of the sapphire. The ZnDBPc molecules stack themselves to form columnar crystal grains; the average direction of these columns is parallel to the atomic step direction. These findings suggest that the in-plane ordering of ZnDBPc on sapphire is governed by the misorientation direction of the polished surface, not by the crystallographic orientation or lattice matching, unlike ordinary epitaxial growth.