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Methods

Ultrafast surface dynamics

We study a variety of electronic processes on the femtosecond time scale. Our main experimental tool is two-photon photoemission (2PPE) . We use femtosecond laser pulses for the optical excitation of the surfaces and subsequent photoemission. Photoelectrons are detected in ultrahigh vacuum via hemispherical and ellipsoidal display analyzers. Complementary information on the valence and core electronic structure is gained from UPS and XPS.

Scanning tunneling microscopy and spectroscopy

Our main experimental tool is the STM. Besides instruments that operate in ultra-high vacuum at room temperature we also have two instruments that work at liquid helium temperatures. These are dedicated to the investigation of electronic properties of surface and adsorbates by STS.

Low-energy electron diffraction

Whereas STM can at best help to identify surface structures a true analysis of the positions of the atoms at and near a surface needs to be done by a diffraction method. We use LEED combined with structural analysis of LEED intensity spectra to resolve the surface structure.

Density functional theory

We use density functional theory (DFT) as a tool to verify our structural analyses and to gain insight into the energetics and electronic properties of the systems.