Electric field influence on the observation of molecules with a scanning tunneling microscope

With a specially developed double‐tip scanning tunneling microscope the influence of a lateral electric field on the ordering of the liquid‐crystal molecules (10CB) was observed. In this setup two independent scanning units could work on a common substrate with different tunneling voltages and currents. No interference between the two tunneling currents was observed down to tip distances of 2 μm. This result means that it is unlikely that surface currents are a major contribution to the imaging mechanism on nonconducting molecules. The additional electric field was observed to alter the alignment of the molecules on the substrate. Modified scanning tunneling spectroscopy by tip voltage modulation was used to characterize the conductivity of the phenyl and alkyl parts of the molecules at tip potentials between 0 and 1.2 V.