Research Area: Dynamics at Interfaces

Prof. Helmut Zacharias

We are concerned with physical and chemical processes upon, within and underneath surfaces and interfaces. A goal is to contribute in understanding catalytic surface reactions. In order to investigate the dynamic of such reactions, the systems under investigation are optically excited and the contributions of the internal states (rotation and vibration) of the different molecules as well as their spatial alignment are probed via the interaction with pulsed, tunable laser radiation. For resolving the dynamics of these very fast processes, laser pulses with extreme short duration are required. Newest laser technologies permit the generation of laser pulses with pulse durations within the range of few femtoseconds.

Numerous commonly used surface-science characterization and preparation techniques are utilized for experiments with clean and adsorbate-covered metal, metallic oxide and semiconductor surfaces under ultrahigh vacuum conditions (UHV). Photoelectron spectroscopy in the ultraviolet (UPS) and in the X-ray range (XPS), Auger electron spectroscopy (AES),  inverse photoemission (IPE), spin polarized photoelectron detection and low-energy electron diffraction (LEED) are some of them. Tunable pulsed laser radiation (f.e. OPCPA) is used to investigate the electronic structure and states of surfaces, interfaces and molecules before and after a chemical reaction or after the desorption from a surface. Light in the wavelength range from the mid infrared (MIR) to the extreme ultraviolet spectral region (XUV) is employed.

Our attention is especially focused on the development of sources for ultrashort light pulses in the extreme ultraviolet (XUV) and X-ray range by High Harmonics (HHG) from 20 to 300 eV (XUV, soft X-ray) and pulse duration is in the order of some 10 fs. Another short pulse X-ray source (hv ~ 1 .. 20 keV) with high brilliance will be developed by radiation from a hot laser-produced plasma. The high spot resolution in the sub-nanometer range and the ultra short pulse time of this source is optimal for X-ray photoelectron spectroscopy (XPS) and electron spectroscopy for chemical analysis (ESCA).The photoelectrons can be analyzed by a photoelectron emission microscope (PEEM) with an integrated electron spectrometer.  

For the "Free Electron LASer in Hamburg" (FEL), called FLASH  at DESY, we construct an autocorrelator for splitting the FEL pulse in two pulses with adjustable time delay for interference and pump-probe experiments, for example to simulate interstellar chemistry.

Our research objects are listed on the top of this page under "Forschung/Research".