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We have utilized scanning tunneling microscopy (STM) and low energy electron diffraction to determine the structural properties of two types of metal-phthalocyanines (MPcs), i.e., cobalt-phthalocyanine (CoPc) and hexadecafluorinated copper-phthalocyanine (F16CuPc) on the Ag(100) surface. For coverage close to one monolayer, both systems form long-range ordered structures with square unit cells. The size and rotation of the unit cell with respect to the silver lattice depend on the chemical composition of MPc. Both types of molecules prefer adsorption with around a 30° angle between the molecular axis and the [011] silver direction. The CoPcs mainly arrange in a (5 × 5)R0 phase; however, two additional local arrangements, a 26×26R11○ and a (7 × 7)R0, were detected by STM. The F16CuPcs form a 29×29R22○ structure. The co-adsorption of CoPc and F16CuPc on the Ag(100) surface in a 1:1 ratio leads to the formation of a compositionally ordered chessboard-like 52×52R45○ structure. During filled states imaging, the different appearance of the central part of each MPc allows us to distinguish CoPcs from F16CuPcs. Regardless of the applied voltage polarity, the ligands of F16CuPcs appear brighter than the ligands of CoPcs.

Using the retarding field diode method for detection of the work function changes, we explore the low-energy electron (0 to 3 eV) reflectivity of Ag(100) covered with a layer of CoPc molecules. The molecular layer significantly reduces the electron reflectivity from the sample surface. The maximum of the sample current, which is associated with minimum of electron reflectivity is observed for 1 ML of CoPc. The reflectivity is diminished from above 50% for the clean sample to almost 20% for the coverage of 1 ML. Additionally, we show that the large change in reflectivity greatly influences the determination of changes in work function (Δϕ) when the retarding field diode method is used without normalization to the saturation currents of each I–V diode curve.

We propose the modification to the Anderson method of work function change (Δϕ) measurements. In this technique, the kinetic energy of the probing electrons is already low enough for non-destructive investigation of delicate molecular systems. However, in our implementation, all electrodes including filament of the electron gun are polarized positively. As a consequence, electron bombardment of any elements of experimental system is eliminated. Our modification improves cleanliness of the ultra-high vacuum system. As an illustration of the solution capabilities, we present Δϕ of the Ag(100) surface induced by cobalt phthalocyanine layers.

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