Schottky barrier height at an organic/metal junction: A first-principles study of PTCDA/X(X=Al,Ag)

Abstract

First-principles calculations within the density-functional theory have been performed for a 3,4,9,10 perylenetetracarboxylic dianhydride ͑PTCDA͒ molecule deposited on Al͑111͒ and Ag͑111͒ substrates, focusing on the structural and electronic properties. The relatively large interplanar distance between the PTCDA plane and the Al surface, along with the small adsorption energy, suggest the interaction to be pretty weak. Moreover, the analysis of Mulliken population combined with the density of states shows that the main interactions occur in the molecular anhydride end groups, whereas the perylene core is basically unaffected by the Al substrate. Very similar results are obtained for PTCDA deposited on the Ag͑111͒ surface, the interaction being even weaker than with Al, as expected for the less reactive noble metal. As for the technologically important issue of the potential lineup, our results show that the PTCDA/Al contact has a rectifying character, with a p-type Schottky barrier height of about 1.5 eV. This same value is obtained for the PTCDA/Ag contact, irrespective of the interface geometry. This suggests that, irrespective of the underlying metal, the Fermi level is pinned at the same energy position with respect to the PTCDA highest occupied molecular orbital, in excellent qualitative agreement with experimental findings.

First-principles study of the dipole layer formation at metal-organic interfaces

“…The widths increase with decreasing molecule-metal distances (to ∼ 0.3 eV at d = 3.0Å, for instance). These results agree with the widths found in previous DFT calculations of adsorbed PTCDA, 106 as well as with those typically found for other adsorbed molecules such as pentacene.…”

“…a moderate binding of ∼ 0.5 eV/molecule, 100 or a very weak binding of 0.1 eV/molecule, or even a purely repulsive binding curve. 51,54,106,108,109 In the calculations where binding was obtained, the equilibrium distance (∼ 3.4Å) is significantly larger than the experimental equilibrium distance (2.9Å). 49,53 In contrast, LDA calculations on PTCDA on Ag(111) give equilibrium distances of 2.8Å 106 and 2.7Å, 51 which are in better agreement with experiment.…”

“…To study the effect of the packing density of PTCDA molecules, we also perform calculations on the structure used by Picozzi et al, 106 see Fig. 1(a).…”

Role of van der Waals interaction in forming molecule-metal junctions: flat organic molecules on the Au(111) surface

“…However, in many cases, e.g. for DNA bases 8,11,12,14,16 and melamine molecules on the Au(111) surface, 15,28 perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) molecules on the Ag(111) surface, 19,22,23 benzene 26 and PTCDA 30 molecules on the Au(111), Cu(111) and Ag(111) surfaces the calculated adsorption energies are too small (of the order of 0.1-0.2 eV) which is inconsistent with experimental observations of the desorption temperatures for these molecules (around 100-300 1C). This failure of standard generalized gradient approximation (GGA) functionals, such as e.g.…”

Adsorption structure and scanning tunneling data of a prototype organic-inorganic interface: PTCDA on Ag(111)

“…The purpose of the present paper is to discuss the theoretical aspects of this work in detail and to explore their relation to the experimental results more systematically. Although a lot of work has already been devoted to the theoretical understanding of the PTCDA:Ag͑111͒ system, 10,15,17,18,20,23 it still constitutes a big challenge to theory for two reasons. On the one hand, this is due to the high numerical demand of carrying out calculations for systems of this size and complexity.…”