In situ studies of heterogeneous reactions using surface electron microscopies LEEM, MEM, and PEEM

Abstract

The preferred imaging techniques for the observation of physical and chemical processes at solid surfaces with high temporal and spatial resolution are low-energy electron microscopy (LEEM), mirror electron microscopy (MEM) and photoemission electron microscopy (PEEM). In these techniques the energy transfer to the surface during the imaging process itself is small so that surface processes such as adsorption, diffusion, chemical reactions etc. remain largely undisturbed.LEEM, MEM and PEEM, which all can be performed in an ultra-high-vacuum surface microscope of the Bauer/Telieps type, have been applied to the study of CO/O reaction-diffusion fronts on a Pt(100) surface saturated with CO. These fronts develop after admission of oxygen to the surface (10-6 mbar) at surface defects which provide adsorption sites for oxygen and thus initiate the autocatalytic oxidation process. The formed CO2 is instantaneously desorbed, freeing adsorption sites which are then occupied by oxygen from the gas phase. The front propagates over the whole surface, leaving behind an oxygen-covered region.