Abstract
We use helium spin-echo spectroscopy (HeSE) to investigate the dynamics of the diffusion of benzene adsorbed on Cu(111). The results of these measurements show that benzene moves on the surface through an activated jump-diffusion process between the adsorption sites on a Bravais lattice. Density Functional Theory (DFT) calculations with van der Waals (vdW) corrections help us understand that the molecule diffuses by jumping through non-degenerate hollow sites. The results of the calculations shed light on the nature of the binding interaction between this prototypical aromatic molecule and the metallic surface. The highly accurate HeSE experimental data provide a quantitatively stringent benchmark for the vdW correction schemes applied to the DFT calculations and we compare the performances of several dispersion interaction schemes.
Highlights
The self-assembly of aromatic molecules and polymers on the surface of semiconductors and metals is a key component in the design and production of organo-electronics and photovoltaic devices, as well as being central in corrosion protection and coating technologies
In previous works we have explored the dynamics of the cyclopentadienyl anion (Cp), pyrrole and thiophene adsorbed on the same Cu(111) surface.[6,7,8,9]
It is well-known that Density Functional Theory (DFT), in its classic local density approximation (LDA) or generalised gradient approximation (GGA), is local in nature; a major effort has been undertaken in the last decade or so to overcome this restriction, by applying correction schemes or ad hoc modi cations to popular functionals such as PBE or B88
Summary
The self-assembly of aromatic molecules and polymers on the surface of semiconductors and metals is a key component in the design and production of organo-electronics and photovoltaic devices, as well as being central in corrosion protection and coating technologies. The self-assembly process is characterised by three main factors: the surface-molecule binding, the intermolecular interactions between adsorbed precursors, and the dynamic behaviour (i.e., surface diffusion, rotational entropy and conformational mobility) of the adsorbate. Among these factors, the surface dynamics of the adsorbed precursor are by far. Benzene is the most fundamental building block in Polycyclic Aromatic Hydrocarbons (PAHs) and forms a part of several of the p-conjugated molecules and polymers employed in organic electronics, such as PTCDA, PTCDI, rubrene, polyphenylene and derivatives.[2,3,4,5] The ability to characterise and predict the self-assembly properties of this large class of molecules intrinsically depends on our understanding of the interactions and dynamic behaviour of this iconic six-membered aromatic ring when con ned on the surface of single crystals. In previous works we have explored the dynamics of the cyclopentadienyl anion (Cp), pyrrole and thiophene adsorbed on the same Cu(111) surface.[6,7,8,9] The combination of state of the art helium spin-echo spectroscopy (HeSE) and density functional theory calculations has provided insight into the role of charge transfer and ionic binding in aromatic adsorption,[8,9] and the contribution of rotational,[6] vibrational[7] and other external degrees of freedom[10] to molecular transport on surfaces
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