Adsorption Behavior of Nonplanar Phthalocyanines: Competition of Different Adsorption Conformations

Abstract

Using density functional theory augmented with state-of-the-art van der Waals corrections, we studied the geometric and electronic properties of nonplanar chlorogallium-phthalocyanine GaClPc molecules adsorbed on Cu(111). Comparing these results with published experimental data for adsorption heights, we found indications for breaking of the metal–halogen bond when the molecule is heated during or after the deposition process. Interestingly, the work-function change induced by this dissociated geometry is the same as that computed for an intact adsorbate layer in the “Cl-down” configuration, with both agreeing well with the experimental photoemission data. This is unexpected, as the chemical natures of the adsorbates and the adsorption distances are markedly different in the two cases. The observation is explained as a consequence of Fermi-level pinning due to fractional charge transfer at the interface. Our results show that rationalizing the adsorption configurations on the basis of electronic interface properties alone can be ambiguous and that additional insight from dispersion-corrected DFT simulations is desirable.

The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces

“…Conversely, a significant impact of the GaCl dipole was obtained for intact molecules with upward-pointing Cl atoms. [208] Consequently, the measured work function allowed ruling out the latter configuration, but could not distinguish between the two former ones. This was possible only by an in-depth comparison between calculated [208] and measured [270] adsorption distances (which supported the existence of dechlorinated molecules).…”

“…Due to the larger average distance between the atoms in the substrate and those constituting the adsorbate it also causes a significantly reduced interaction energy. [208] In spite of the small van der Waals energy per atom, this effect is significant due to the resulting large van der Waals contact areas comprising a sizable number of atoms per molecule. In passing we note that for a priori less planar sub-phthalocyanines bearing polar ClB groups, the van der Waals attraction to the surface is even strong enough to essentially planarize the molecules with profound consequences also for the electronic properties of the adsorbate.…”

“…This also modifies the adsorption-induced work-function change (albeit in a more complex way than expected based solely on the molecular dipoles, as will be discussed in Section 5.4). [208] Dechlorination processes have also been observed for chloro-boron-subphthalocyanine (ClB-subPc) on Cu(111), although there it has been argued that only the molecules landing in Cl-down orientation undergo the dechlorination. [213]…”

“…Reproduced under the terms of the Creative Commons CC-BY license. [208] Copyright 2015, American Chemical Society. As the energy scale is aligned to the Fermi level, the latter also represents the work function of the system.…”

The Structure of VOPc on Cu(111): Does V═O Point Up, or Down, or Both?

“…The NIXSW data were reinterpreted as consistent with this dissociation model. 11 Finally, a scanned-energy mode photoelectron diffraction (PhD) investigation of VOPc on Au(111) led to the conclusion that in this system, the V–O bond points out of the surface. 12…”