Growth process of vacuum deposited copper phthalocyanine thin films on rubbing-treated substrates

Surface morphology, crystal lattice spacings and crystallite size of copper phthalocyanine (CuPc) thin films grown on rubbed surfaces were probed at different stages of growth, by means of atomic force microscopy (AFM) and X-ray diffraction (XRD). The films consisted of many slender crystallites extending along the rubbing direction, due to the alpha-type columnar structure along the same direction. AFM revealed that the aspect ratio of crystal domains increases as the films grow, implying a change in the ratio of crystal growth rates in the two different directions parallel to the substrates. XRD demonstrated marked differences in the two intercolumnar directions. The molecular spacing is expanded in the thickness direction at the initial stage of growth, while it remains constant throughout the growth in the lateral (c-axis) direction. The crystallite size in the thickness direction is always comparable to the film thickness, while the size in the c-axis direction shows no change.