A new endstation to perform operando chemical analysis at solid–liquid interfaces by means of ambient pressure x-ray photoelectron spectroscopy (APXPS) is presented. The endstation is located at the Swiss Light Source and can be attached to the soft x-ray in situ spectroscopy beamline (X07DB) for solid–gas type experiments and to a tender x-ray beamline (PHOENIX I) for solid–liquid interface experiments. The setup consists of three interconnected ultrahigh vacuum chambers: one for sample preparation using surface science techniques, the analysis chamber for APXPS experiments, and an entry-lock chamber for sample transfer across the two pressure regimes. The APXPS chamber is designed to study solid–liquid interfaces stabilized by the dip and pull method. Using a three-electrode setup, the potential difference across the solid-electrolyte interface can be controlled, as is demonstrated here using an Ir(001) electrode dipped and pulled from a 0.1M KOH electrolyte. The new endstation is successfully commissioned and will offer unique opportunities for fundamental studies of phenomena that take place at solid–liquid interfaces and that are relevant for fields such as electrochemistry, photochemistry, or biochemistry, to name a few.

The electronic band structure governs the electron dynamics in solids. It defines a group velocity and an effective mass of the electronic wave packet. Recent experimental and theoretical studies suggest that an electron acquires the effective mass of its excited state over distances much larger than the lattice period of the solid. Therefore, electron propagation on atomic length scales was typically considered to be free-electron-like. Here, we test this hypothesis by probing attosecond photoemission from a Cu(111) surface. We use attosecond pulse trains in the extreme-ultraviolet (21–33 eV) to excite electrons from two initial bands within the 3d-valence band of copper. We timed their arrival at the crystal surface with a probing femtosecond infrared pulse, and found an upper limit of $350\pm 40$ as ($1\mathrm{as}={10}^{-18}\mathrm{s}$) for the propagation time an electron requires to assume the effective mass of its excited state. This observation implies that a final-state Bloch wave packet forms within a travel distance of 5–7 Å, which is at most two atomic layers. Using well-established theory, our measurements demonstrate the importance of the band structure even for atomic-scale electron transport.

Molecular reactivity is determined by the energy levels and spatial extent of the frontier orbitals. Orbital tomography based on angle-resolved photoelectron spectroscopy is an elegant method to study the electronic structure of organic adsorbates, however, it is conventionally restricted to systems with one single rotational domain. In this work, we extend orbital tomography to systems with multiple rotational domains. We characterise the hydrogen evolution catalyst Co-pyrphyrin on an Ag(110) substrate and compare it with the empty pyrphyrin ligand. In combination with low-energy electron diffraction and DFT simulations, we fully determine adsorption geometry and both energetics and spatial distributions of the valence electronic states. We find two states close to the Fermi level in Co-pyrphyrin with Co $$3d$$3 d character that are not present in the empty ligand. In addition, we identify several energetically nearly equivalent adsorption geometries that are important for the understanding of the electronic structure. The ability to disentangle and fully elucidate multi-configurational systems renders orbital tomography much more useful to study realistic catalytic systems.