MOMENTUM-DEPENDENT EXCITATIONS IN HIGHLY ORDERED FILMS OF PARA-HEXAPHENYL

Highly textured para-hexaphenyl films have been investigated using ele ctron energy-loss spectroscopy In transmission. The alignment of the c rystallites in the free standing para-hexaphenyl films is determined b y electron diffraction. Energy-loss functions for momentum transfers p arallel and perpendicular to the molecular axis have been recorded. It is shown directly that a bandlike model-the so-called quasi-band-stru cture-is an appropriate tool to describe the momentum-dependent electr onic excitations in such finite size systems, even if the molecules un der consideration consist of only six repeat units as in hexaphenyl. [ S0163-1829(97)06340-6].