Molecular Images with the Projection Microscope. The Ionization Potential of Zinc Phthalocyanine

Abstract

The current emerging from single molecules of zinc phthalocyanine in field emission has been measured as a function of voltage. The data permit estimation of the ionization potential at ca 7 volts. Comparison of the experiments with a simple theory based on the emission of electrons from the molecule itself supports this view of image formation. It is shown that the images found are not diffraction patterns, but the result of electron optical effects. Emission measurements on molecules adsorbed on clean tungsten substrates show that irregularities of 5–10A exist on the best and cleanest of these surfaces.