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

para-Hexaphenyl grows on GaAs (001) in well-defined, three-dimensional isla nds 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 orientat ions 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) pla ne of hexaphenyl parallel to GaAs (001). In both cases, the b-axis of hexap henyl is parallel to [100]. The epitaxial growth of the needle-like hexaphe nyl is explained in terms of micro and rotation twinning. (C) 1999 Elsevier Science B.V. All rights reserved.