Unraveling Atomic and Electronic Surface Structure and Dynamics from Angular Photoelectron Distributions.

Angle-resolved photoelectron spectroscopy (ARPES) is a powerful tool in solid state sciences. Beside the direct measurement of the energy-momentum dispersion relation, the angular distribution of the photoelectron current reveals the structural environment of the emitting atoms via photoelectron diffraction effects. Moreover, in the case of molecular layers, the angular distribution of emission from molecular orbitals can be directly related to their charge density distribution via so-called orbital tomography.

Influence of surface defect density on the ultrafast hot carrier relaxation and transport in [Formula: see text] photoelectrodes.

Cuprous oxide ([Formula: see text]) is a promising material for photoelectrochemical energy conversion due to its small direct band gap, high absorbance, and its Earth-abundant constituents. High conversion efficiencies require transport of photoexcited charges to the interface without energy loss. We studied the electron dynamics in [Formula: see text](111) by time-resolved two-photon photoemission for different surface defect densities in order to elucidate the influence on charge carrier transport.

Combined orbital tomography study of multi-configurational molecular adsorbate systems.

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.

Polarization-sensitive pulse reconstruction by momentum-resolved photoelectron streaking.

The precise knowledge of the electric field in close proximity to metallic and dielectric surfaces is a prerequisite for pump-probe experiments aiming at the control of dynamic surface processes. We describe a model to reconstruct this electric field in immediate surface proximity from data taken in photoelectron THz-streaking experiments with an angle-resolved electron analyzer. Using Monte-Carlo simulations we are able to simulate streaking experiments on arbitrary surfaces with a variety of initial electron momentum distributions and to reconstruct the effective electric field at the surface.

Delayed electron emission in strong-field driven tunnelling from a metallic nanotip in the multi-electron regime.

Illuminating a nano-sized metallic tip with ultrashort laser pulses leads to the emission of electrons due to multiphoton excitations. As optical fields become stronger, tunnelling emission directly from the Fermi level becomes prevalent. This can generate coherent electron waves in vacuum leading to a variety of attosecond phenomena.

Erratum: "Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations" [Struct. Dyn. 2, 035102 (2015)].

[This corrects the article DOI: 10.1063/1.4922611.

Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations.

A THz-pump and x-ray-probe experiment is simulated where x-ray photoelectron diffraction (XPD) patterns record the coherent vibrational motion of carbon monoxide molecules adsorbed on a Pt(111) surface. Using molecular dynamics simulations, the excitation of frustrated wagging-type motion of the CO molecules by a few-cycle pulse of 2 THz radiation is calculated. From the atomic coordinates, the time-resolved XPD patterns of the C 1s core level photoelectrons are generated.

Energy distribution curves of ultrafast laser-induced field emission and their implications for electron dynamics.

Energy distribution curves of laser-induced electron pulses from a tungsten tip have been measured as a function of tip voltage and laser power. Electron emission via tunneling through and/or excitation over the surface barrier from photoexcited nonequilibrium electron distributions are clearly observed. The spectral shapes largely vary with the emission processes and are strongly affected by electron dynamics.

Time-resolved photoelectron spectroscopy to probe ultrafast charge transfer and electron dynamics in solid surface systems and at metal-molecule interfaces.

Photoelectron spectroscopy (PES) is a versatile tool, which provides insight into electronic structure and dynamics in condensed matter, surfaces, interfaces and molecules. The history of PES is briefly outlined and illustrated by current developments in the field of time-resolved PES. Our group's research is mostly aimed at studying ultrafast processes and associated lifetimes related to electronic excitation at solid surfaces.

Robust spin polarization and spin textures on stepped Au(111) surfaces.

The influence of structural defects, in the form of step lattices, on the spin polarization of the spin-orbit split Shockley surface state of Au(111) has been investigated. Spin- and angle-resolved photoemission data from three vicinal surfaces with different step densities are presented. The spin splitting is preserved in all three cases, and there is no reduction of the spin polarization of individual subbands, including the umklapp bands induced by the step lattice.

Optical control of field-emission sites by femtosecond laser pulses.

We have investigated field-emission patterns from a clean tungsten tip apex induced by femtosecond laser pulses. Strongly asymmetric modulations of the field-emission intensity distributions are observed depending on the polarization of the light and the laser incidence direction relative to the azimuthal orientation of tip apex. In effect, we have realized an ultrafast pulsed field-emission source with site selectivity.