Molecular Assemblies on Insulating Ultrathin Films Analyzed by NC-AFM and KPFM

Recently porphyrin-based molecules have proven to be promising candidates to form self-assembled structures oil insulating Surfaces. Their close similarity to hemoglobin and chlorophyll-based molecules makes them promising candidates for functional building parts in molecular electronics. To analyze their opto-electronic activity, new measurement methods have to be applied. We investigated the formation of such Molecular assemblies On Ultrathin insulating films by means of a room temperature non-contact atomic force microscope (NC-AFM) in combination with a Kelvin probe force microscope (KPFM). As a substrate we used a Cu(111) Surface, where either ultrathin KBr or NaCl films are deposited. Oil those surfaces the evaporated cyano-porphyrins ire forming one- and two-dimensional structures that are comparable to file ones observed oil bulk alkali halides. The simultaneously measured surface potential clearly shows a material contrast between the molecules and the insulating films. Finally, we succeeded in obtaining variations of the surface potential induced by the molecular assemblies at the molecular level.