Direct observation of subsurface oxygen on the defects of Pd(100)

Oxygen adsorption and desorption on a Pd(100) surface with a mesoscopic def ect were studied by photoemission electron microscopy (PEEM). The defect su rface, with an area of approximately 200 x 60 mu m(2), behaved differently from the perfect Pd(100) surface towards the adsorption of oxygen. When sat urated, both surface oxygen and subsurface oxygen coexisted on the defect s urface, whereas only surface oxygen was present on the Pd(100) surface. Upo n heating, subsurface oxygen diffused back to the surface and desorbed with surface oxygen at the same time. The difference in oxygen adsorption abili ty between the defect surface and the perfect Pd(100) surface can be attrib uted to different structures of these two surfaces. (C) 1999 Elsevier Scien ce B.V. All rights reserved.