  We demonstrate the structural sensitivity and accuracy of the standing wave
technique at a high repetition rate free-electron laser, FLASH at DESY in
Hamburg, by measuring the photoelectron yield from the surface SiO2 of Mo/Si
multilayers. These experiments open up the possibility to obtain unprecedented
structural information of adsorbate and surface atoms with picometer spatial
accuracy and femtosecond temporal resolution. This technique will substantially
contribute to a fundamental understanding of chemical reactions at catalytic
surfaces and the structural dynamics of superconductors.
