11:00-12:00
Scanning Tunneling Spectroscopy of Molecules on Thin Insulating Films
Prof. Jascha Repp(Institute of Experimental and Applied Physics, University of Regensburg, Germany)
-
Ultrathin insulating films on metal substrates facilitate the use of the scanning
tunneling microscope to study the electronic properties of single atoms and
molecules, which are electronically decoupled from the metallic substrate.
In the case of molecules on ultrathin NaCl films the electronic decoupling allows
the direct imaging of the unperturbed molecular orbitals, as will be shown in the
cases of individual pentacene and oligothiophene molecules.
The bistability in the position of the two hydrogen atoms in the inner cavity of single
free-base naphthalocyanine molecules constitutes a two-level system that was
manipulated and probed by scanning tunneling microscopy. The molecules can
be switched in a controlled fashion between the two states by excitation induced
by the inelastic tunneling current. The tautomerization reaction can be probed by
resonant tunneling through the molecule and is expressed as considerable changes
in the conductance through the molecule. We also demonstrated a coupling of the
switching process so that the charge injection in one molecule induced tautomerization
in an adjacent molecule.