Role of functional groups in surface bonding of planarπ-conjugated molecules

Abstract

The trends in the bonding mechanism of 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) to the Ag(111), Ag(100), and Ag(110) surfaces were analyzed on the basis of data obtained from x-ray standing waves and dispersion-corrected density functional theory. Of importance are the attractive local O-Ag bonds on the anhydride groups. They are the shorter, the more open the surface is, and lead even to partly repulsive interactions between the perylene core and the surface. In parallel, there is an increasing charge donation from the Ag surface into the π system of the PTCDA. This synergism explains the out-of-plane distortion of the adsorbed PTCDA and the surface buckling.

Unexpected interplay of bonding height and energy level alignment at heteromolecular hybrid interfaces

“…First, the work function of the metal controls both adsorption height and LUMO binding energy: if the work function is low, the spatial extent of the charge spill out is small. This favours both small adsorption heights 5,[12][13][14] andassuming vacuum level alignment-large LUMO binding energies. Note that the push-back effect, that is, the Pauli repulsion of the electronic charge spill out of the metal caused by the approaching molecule, even strengthens this correlation: a larger push-back tends to reduce adsorption height and work function further, yielding even larger orbital binding energies.…”

“…Hence, one would expect that a smaller adsorption height should correspond to stronger chemical interaction. Indeed, it was recurrently observed that on more reactive surfaces, where chemical interaction is stronger, the adsorption heights tend to be smaller [1][2][3][4][5][6][7][8][9][10][11][12] . This empirical correlation is often a result of both local and extended (that is, p-) bonds 12 and of the charge spill-out profile above the surface (see below).…”

Adsorption geometry and interface states: Relaxed and compressed phases of NTCDA/Ag(111)

“…Analysis of adsorbed PTCDA or NTCDA on Ag(111) [10,20] provided clear evidence of a non-negligible relaxation of Ag surface atoms which did comprise not only an overall contraction of the vertical bonding distance but also introduced an extra corrugation of surface atoms underneath of PTCDA or NTCDA. As shown below, our calculations confirm that this is the case also for the NTCDA c-ML and r-ML phases discussed here.…”

“…The experimental value for C-atoms corresponds to averaging over all C-atoms for r -ML. two major contributions, similar to the case of PTCDA monolayers on different Ag surfaces [10]: Specifically, the derived geometry is determined by the interplay between attraction of the functional groups with silver atoms, repulsion of the carbon backbone from the substrate and the ability of the molecule and the surface to accommodate such distortions. The surface and interface state energies (E SS and E IS ) for r-ML and c-ML phases are presented in Table II.…”

“…For the well studied PTCDA system d ⊥ decreases from 3.27Å for PTCDA/Au(111) [8] to 2.86Å for PTCDA/Ag(111) [9,10] and to 2.81Å for PTCDA/Ag(100) [10]. At the same time the upshift of the Shockley state ∆E IS increases from 0.16 eV [11] to 0.66 eV [2], and to 0.95 eV [12], respectively, resulting in an inverse scaling of tronic structure calculations by comparing the results of different approaches and approximations with accurate experimental data.…”