The self-assembly of organic molecules on metal surfaces is of great interest for their central role in the development of molecular-based electronic and optical devices. In this work, we have investigated the adsorption of 1,4-phenylenediisocyanide (PDI) and 4,4'-biphenyldiisocyanide (BPDI) on the Au(111) surface through a combination of density functional theory (DFT), two-photon photoemission (2PPE) spectroscopy and low temperature scanning tunneling microscopy (STM). Our calculations have confirmed the adsorption structure and energetic stability of the adatom-induced, self-assembled molecular chains of -[PDI-Au]- and -[BPDI-Au]- motifs observed by STM. The corresponding adsorption energies were computed to be more than half eV larger than those of the vertical adsorption motifs in which only one isocyanide is bound to the gold substrate. It was found that substantial charge exchange occurs at the molecular-chain/substrate interface, and the magnitude of the induced surface dipole moment depends on both the coverage and the packing pattern of the one-dimensional molecular chains. The computed surface potential shift of -1.5 eV for the interlocked, closely-packed -[PDI-Au]- chains on Au(111) was in in excellent agreement with the measured work function reduction from 2PPE measurements.

Adatom-induced self-assembly of aromatic isocyanides on Au(111): Energetics, structure, and work function

245th National Meeting (2013)

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