Zinc(II) tetraphenylporphyrin on Au(111) investigated by scanning tunnelling microscopy and photoemission spectroscopy measurements

Porphyrins are a versatile class of molecules, which have attracted attention over the years due to their electronic, optical and biological properties. Self-assembled monolayers of porphyrins were widely studied on metal surfaces in order to understand the supramolecular organization of these molecules, which is a crucial step towards the development of devices starting from thebottom-upapproach. This perspective could lead to tailor the interfacial properties of the surface, depending on the specific interaction between the molecular assembly and the metal surface. In this study, we revisit the investigation of the assembly of zinc-tetraphenylporphyrins on Au(111) in order to explore the adsorption of the molecular network on the noble metal substrate. The combined analysis of scanning tunneling microscopy (STM) imaging and core levels photoemission spectroscopy measurements support a peculiar arrangement of the ZnTPP molecular network, with Zn atoms occupying the bridge sites of the Au surface atoms. Furthermore, we prove that, at few-layers coverage, the interaction between the deposited layers allows a relevant molecular mobility of the adlayer, as observed by STM and supported by core levels photoemission analysis

Orbital selective overlayer-substrate hybridization in a Pb monolayer on Ag(111)

The electronic structure of a Pb overlayer on Ag(111) has been studied by angle-resolved photoemission spectroscopy. We identify three p bands. While the p(xy) bands are sharp and closely resemble the corresponding bands of a free-standing Pb layer, the p(z) band is strongly spread in energy and momentum. Tight-binding calculations of the electronic structure combined with structural calculations using the embedded atom method indicate a symmetry dependent hybridization with the Ag(111) surface. We propose a symmetry selective, surface state mediated coupling to the bulk continuum which results in a broadened line shape for the p(z) band only

Massless Dirac cones in graphene: Experiments and theory

The opening of a gap in single-layer graphene is often ascribed to the breaking of the equivalence between the two carbon sublattices. It is shown by angle-resolved photoemission spectroscopy that Ir- and Na-modified graphene grown on the Ir(111) surface presents a very large unconventional gap that can be described in terms of a phenomenological massless Dirac model. The consequences and differences of this model are discussed in comparison of the standard massive gap model, and the conditions under which such anomalous gap can arise from a spontaneous symmetry breaking are investigated

Spin-orbit split two-dimensional electron gas with tunable Rashba and Fermi energy

We demonstrate that it is possible to tune the Rashba energy, introduced by a strong spin-orbit splitting, and the Fermi energy in a two-dimensional electron gas by a controlled change of stoichiometry in an artificial surface alloy. In the BixPb1-x/Ag(111) surface alloy, the spin-orbit interaction maintains a dramatic influence on the band dispersion for arbitrary Bi concentration x, as is shown by angle-resolved photoelectron spectroscopy. The Rashba energy E-R and the Fermi energy E-F can be tuned to achieve values larger than one for the ratio E-R/E-F, which opens up the possibility for observing phenomena, such as corrections to the Fermi liquid or a superconducting state. Relativistic first-principles calculations explain the experimental findings

Local detection of spin-orbit splitting by scanning tunneling spectroscopy

We demonstrate that the spin-orbit coupling of two-dimensional surface states can be detected locally by scanning-tunneling spectroscopy (STS). The spin splitting of the surface state induces a singularity in the local density of states which can be detected as a distinct peak in the differential conductance spectrum. From the STS spectrum we can determine the Rashba energy as a measure of the strength of the spin splitting. Its detection and imaging are demonstrated for the surface alloys Bi and Pb on Ag(111), which exhibit particularly large spin-split band structures. The influence of the spin splitting on the surface-state STS spectra of close-packed noble metal surfaces is also discussed.</p

Local detection of spin-orbit splitting by scanning tunneling spectroscopy

We demonstrate that the spin-orbit coupling of two-dimensional surface states can be detected locally by scanning-tunneling spectroscopy (STS). The spin splitting of the surface state induces a singularity in the local density of states which can be detected as a distinct peak in the differential conductance spectrum. From the STS spectrum we can determine the Rashba energy as a measure of the strength of the spin splitting. Its detection and imaging are demonstrated for the surface alloys Bi and Pb on Ag(111), which exhibit particularly large spin-split band structures. The influence of the spin splitting on the surface-state STS spectra of close-packed noble metal surfaces is also discussed