Epitaxial growth of para-hexaphenyl on GaAs (001)-2 x 4

para-Hexaphenyl grows on GaAs (001) in well-defined, three-dimensional islands of a needle-like shape. The needles are oriented in [100] with respect to GaAs. The orientation of the hexaphenyl molecules within the needles has been studied using electron diffraction techniques. Two different orientations of the epitaxially grown hexaphenyl molecules on GaAs are identified. One with the (1001) plane and the other one with the (110 (2) over bar) plane of hexaphenyl parallel to GaAs (001). In both cases, the b-axis of hexaphenyl is parallel to [100]. The epitaxial growth of the needle-like hexaphenyl is explained in terms of micro and rotation twinning. (C) 1999 Elsevier Science B.V. All rights reserved.