title: Atom resolved evidence for a defective chemisorbed oxygen state at a Mg(0001) surface.
abstract: A chemisorbed oxygen state has been revealed for the first time by scanning tunnelling microscopy to be present at the interface between a (1 x 1)-O structure and overlying magnesium atoms; the step-height at the interface is between 0.14 and 0.15 nm and compatible with the presence of O delta- like states.