Homogeneous and inhomogeneous line shape of the electronic excitation of a single molecule on a surface

Abstract

Here, the authors perform a single-molecule spectroscopy experiment on an organic molecule (PTCDA) adsorbed on a KCl surface. The homogeneous line profile is approximately of Lorentzian shape. Although the molecule is slightly out-of-plane distorted due to the adsorption, the dephasing time is 0.70 ns, yielding sharp zero phonon lines. The inhomogeneous line profile of the ensemble is broader by a factor of about 200 and also of Lorentzian shape. This is due to the stochastic interaction with surface defects.