Paper EW-TuL3
Momentum Microscope for Angular and Time Resolved Imaging of Valence Band Electron States

Tuesday, October 21, 2008, 1:00 pm, Room Exhibit Hall

We demonstrate the application of a novel design of a photoelectron microscope in combination with an imaging energy filter for momentum resolved photoelectron detection. We image the complete momentum distribution of photoexcited electron states in an energy plane through the Brillouin zone. The basic concept of the microscope is to project the momentum image from the back focal plane of the objective lens of a Photoelectron Emission Microscope (PEEM) through an energy filter onto an image detector. Our design is based on a PEEM with an imaging energy filter. The spherical (α²) aberrations of the imaging energy filter are strongly reduced by a novel analyzer design. Together with a time resolved imaging detector it is possible to combine spatial, momentum, energy and time resolution of photoelectrons within the same instrument. The time resolution of this type of energy analyzer can be reduced to below 100 ps. The complete ARUPS pattern of a Cu(111) sample excited with He I, is imaged in parallel and energy resolved up to the photoelectron emission horizon (at ±90°). Excited with a Mercury light source (hν = 4.9 eV) the Shockley surface state at the energy threshold is imaged clearly in k-space. With the high transmission and time resolution of this instrument, possible new measurements are discussed: Time and polarization resolved ARUPS measurements, probing changes of bandstructure due to chemical reactions, in-situ thin film growth and investigation of phase transitions e.g. melting or martensitic transformations.