Adsorption Behavior of Nonplanar Phthalocyanines: Competition of Different Adsorption Conformations.

Elisabeth Wruss,Frank Schreiber,David A Egger,Alexander Gerlach,Egbert Zojer,Oliver T Hofmann,Elisabeth Verwüster

doi:10.1021/acs.jpcc.6b00312

Elisabeth Wruss, Frank Schreiber + Show 5 more

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https://doi.org/10.1021/acs.jpcc.6b00312

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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.

Highlights

Combining experiments and simulations has become a crucial approach in modern surface science for gaining in-depth atomistic insight into processes at interfaces
It helps to eliminate certain ambiguities that prevail when interpreting experimental data.[1−3] This is true for X-ray standing wave (XSW) experiments, which allow for the determination of adsorption distances with picometer resolution[4] and are, of crucial importance for rationalizing interface properties.[5−8] At the same time, such experiments allow for the determination of adsorption geometries only modulo the distance between crystallographic planes parallel to the surface.[9−11] they can provide two or more possible interpretations for the geometry of the adsorbate
density functional theory (DFT) calculations of the adsorbed molecules placed at the experimental adsorption distances supported the dominance of the Cl-down phase; full geometry optimization including van der Waals corrections could not be performed because, at that time, reliable van der Waals corrections were not yet widely available

Summary

INTRODUCTION

Combining experiments and simulations has become a crucial approach in modern surface science for gaining in-depth atomistic insight into processes at interfaces. For nonplanar, phtalocyanines (Pcs) the considered adsorption configurations comprise situations in which an intact molecule adsorbs with the molecular backbone parallel to the surface and the central metal atom (or metal−halogen bond) protruding perpendicular to it.[7,20,22−24] Deviating from this common view, we find here that, upon annealing or deposition onto sufficiently heated substrates, a situation with Cl dissociated from the molecule becomes a likely scenario This process might be more common in Cl-bearing Pcs than hitherto discussed

COMPUTATIONAL DETAILS

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES