Electron Spectroscopy Using Metastable Atoms as Probes for Solid Surfaces.

Absorption spectra of tetracene and pentacene layers prepared by vapor deposition onto cooled substrates were measured as a function of sample formation temperature Tf, evaporation rate and recording temperature. Profile-analysis indicates that the main absorption peak is of gaussian shape. The width varies between 300 cm−1 and 650 cm−1, higher values referring to lower formation temperatures and/or higher evaporation rates and reflecting larger fluctuation of the site-energies. Appearance of a second electronic band equivalent to the upper Davydov component in the crystal spectrum indicates presence of short-range order. The low-energy behavior is dominated by a structural defect. No Urbacht-tail is observed. It is concluded that tetracene and pentacene layers represent examples for intermediate structural disorder.

H. Müller

Papers

Emission spectra of non-crystalline tetracene films