The Crystalline Structure of Copper Phthalocyanine Films on ZnO(11̅00)

The structure of copper phthalocyanine (CuPc) thin films
(5–100
nm) deposited on single-crystal ZnO(11̅00) substrates by organic
molecular beam deposition was determined from grazing-incidence X-ray
diffraction reciprocal space maps. The crystal structure was identified
as the metastable polymorph α-CuPc, but the molecular stacking
was found to vary depending on the film thickness: for thin films,
a herringbone arrangement was observed, whereas for films thicker
than 10 nm, coexistence of both the herringbone and brickstone arrangements
was found. We propose a modified structure for the herringbone phase
with a larger monoclinic β angle, which leads to intrastack
Cu–Cu distances closer to those in the brickstone phase. This
structural basis enables an understanding of the functional properties
(e.g., light absorption and charge transport) of (opto)­electronic
devices fabricated from CuPc/ZnO hybrid systems.