Using photoemission spectroscopy, we determine the relationship between electronic energy level alignment at a metal-molecule interface and single-molecule junction transport data. We measure the position of the highest occupied molecular orbital (HOMO) relative to the Au metal Fermi level for three 1,4-benzenediamine derivatives on Au(111) and Au(110) with ultraviolet and resonant X-ray photoemission spectroscopy. We compare these results to scanning tunnelling microscope-based break-junction measurements of single molecule conductance and to first-principles calculations. We find that the energy difference between the HOMO and Fermi level for the three molecules adsorbed on Au(111) correlate well with changes in conductance and agree well with quasiparticle energies computed from first-principles calculations incorporating self-energy corrections. On the Au(110) that presents Au atoms with lower-coordination, critical in break-junction conductance measurements, we see that the HOMO level shifts further from the Fermi level. These results provide the first direct comparison of spectroscopic energy level alignment measurements with single molecule junction transport data.

The geometry and bonding of N-heterocyclic carbenes to metal surfaces depends on the substituents on the N-atoms.

We studied the formation of graphene nanoribbons (GNRs) via the self-assembly of 10,10'-dibromo-9,9'-bianthryl precursor molecules on gold surfaces with different synchrotron spectroscopies. Through X-ray photoemission spectroscopy core-level shifts, we followed each step of the synthetic process, and could show that the Br-C bonds of the precursors cleave at temperatures as low as 100 degrees C on both Au(111) and Au(110). We established that the resulting radicals bind to Au, forming Au-C and Au-Br bonds. We show that the polymerization of the precursors follows Br desorption from Au, suggesting that the presence of halogens is the limiting factor in this step. Finally, with angle-resolved ultraviolet photoemission spectroscopy and density functional theory we show that the GNR/Au interaction results in an upshift of the Shockley surface state of Au(111) by similar to 0.14 eV, together with an increased electron effective mass