Observations of Individual Cu-Phthalocyanine Molecules Deposited on Nano-Tips in the Field Emission Microscope

Using a field emission microscope (FEM), the first image ever of isolated individual molecules was reported in the 1950s. At that time, the Cu-Phthalocyanine (Cu-Pc) molecule was imaged in different configurations, namely two- and four-leaf patterns. These various apparent shapes were linked to the location of the molecule on particular atomic planes of the relatively quite large FEM tip apex used at that time. We report here on how the fabrication of an extremely sharp FEM tip with an apex of the size of the molecule to be imaged provides a unique opportunity to study the behavior of one molecule at a time on the tip apex. Preliminary data are presented where two adsorption states have been observed according to the electronic cloud FEM images of the molecule. Since the atomic structure of the tip can be determined first from a field ion microscope image, the interaction of the molecule with tip apex surface atoms, and thus the molecule adsorption conformation can be readily determined.