MBE growth of para-hexaphenyl on GaAs(001)-2x4

The morphology of para-hexaphenyl (PHP) grown on GaAs(001) by molecular beam epitaxy has been studied using atomic force microscopy (AFM). For elevated substrate temperatures between 90 and 170 degrees C and a deposition rate of 0.7 Angstrom s(-1), it was found that hexaphenyl on GaAs(001)-2 x 4 forms well-defined, three-dimensional islands of a rectangular shape oriented in [100]. Their constant width indicates that PHP is epitaxially grown as a coherently strained organic material. The island density shows the Arrhenius behavior resulting in activation barrier of (0.90+/-0.04) eV. The normalized island size distributions closely resemble that of a critical island size of one. On the basis of the AFM measurements, X-ray diffraction data, and geometrical considerations, we developed a structural model for PHP grown on GaAs(001). (C) 1998 Elsevier Science B.V. All rights reserved.