Surface projected electronic band structure and adsorbate charge transfer dynamics: Ar adsorbed on Cu(111) and Cu(100)

Ultrafast charge transfer at monolayer graphene surfaces with varied substrate coupling

The charge transfer rates of a localized excited electron to graphene monolayers with variable substrate coupling have been investigated by the core hole clock method with adsorbed argon. Expressed as charge transfer times, we find strong variations between ~3 fs (on graphene "valleys" on Ru(0001)) to ~16 fs (quasi-free graphene on SiC, O/Ru(0001), or SiO2/Ru). The values for the "hills" on Gr/Ru and on Gr/Pt(111) are in between, with the ratio 1.7 between the charge transfer times measured on "hills" and "valleys" of Gr/Ru. We discuss the results for Gr on metals in terms of hybridized Ru-C orbitals, which change with the relative Gr-Ru alignment and distance. The charge transfer on the decoupled graphene layers must represent the intrinsic coupling to the graphene empty π* states. Its low rate may be influenced by processes retarding the spreading of charge after transfer.

Pi resonance of chemisorbed alkali atoms on noble metals

We have performed a joint experimental and theoretical study of the unoccupied electronic structure of alkali adsorbates on the (111) surfaces of Cu and Ag. Combining angle- and time-resolved two-photon photoemission spectroscopy with wave packet propagation calculations we show that, along with the well known sigma resonance oriented along the surface normal, there exist long-lived alkali-localized resonances oriented parallel to the surface (pi symmetry). These new resonances are stabilized by the projected band gap of the substrate and emerge primarily from the mixing of the p and d Rydberg orbitals of the free alkali atom modified by the interaction with the surface.