• Koenraad, Pm Paul
• Salemink, Hwm
• Alvarado, Sf
• Janssen, René A. J.
• Müller, P.
• Kemerink, Martijn
• Wolter, Jh Joachim

Abstract

Scanning-tunneling spectroscopy expts. performed on conjugated polymer films are compared with three-dimensional numerical model calcns. for charge injection and transport. It is found that if a sufficiently sharp tip is used, the field enhancement near the tip apex leads to a significant increase in the injected current, which can amt. to more than an order of magnitude and can even change the polarity of the predominant charge carrier. We show that when charge injection from the tip into the org. material predominates, it is possible to probe the electronic properties of the interface between the org. material and a metallic electrode directly by means of tip height vs. bias voltage measurements. Thus, one can det. the alignment of the MO energy levels at the buried interface, as well as the single-particle band gap of the org. material. By comparing the single-particle energy gap and the optical absorption threshold, it is possible to obtain an est. of the exciton binding energy. In addn., our calcns. show that by using a one-dimensional model, reasonable parameters can only be extd. from z-V and I-V curves if the tip apex radius is much larger than the tip height. In all other cases, the full three-dimensional problem needs to be considered.

Topics

• impedance spectroscopy
• polymer
• experiment
• semiconductor
• one-dimensional