Momentum-dependent excitations in highly ordered films ofpara-hexaphenyl

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Abstract
Highly textured para-hexaphenyl films have been investigated using electron energy-loss spectroscopy in transmission. The alignment of the crystallites in the free standing para-hexaphenyl films is determined by electron diffraction. Energy-loss functions for momentum transfers parallel and perpendicular to the molecular axis have been recorded. It is shown directly that a bandlike model—the so-called quasi-band-structure—is an appropriate tool to describe the momentum-dependent electronic excitations in such finite size systems, even if the molecules under consideration consist of only six repeat units as in hexaphenyl.