Tip-induced spectral dynamics of single molecules

Manipulation of spectral dynamics of single molecules (SM) by a metallized scanning probe tip is demonstrated. The Stark effect of the zero-phonon lin es of single pentacene molecules in a p-terphenyl host at 1.8 K is investig ated by applying a voltage to the tip in contact with the sample. The measu red Stark shifts exhibit a plateau and the line widths depend on the electr ic field. These anomalies are explained by a model based on two-level syste ms with field-dependent double-well potentials. The experimental data show that the two-level systems are induced by the tip. (C) 2001 Elsevier Scienc e B.V. All rights reserved.