Oxygen interaction with Mo(100) studied by XPS, AES and EELS

The adsorption, chemisorption and oxide formation of molecular oxygen was studied on the (100) surface of molybdenum single crystal by following the changes in Mo 3d photoelectron lines and the characteristic losses in EELS. For estimation of the oxygen content, both XPS and AES were applied. At the room temperature the oxygen content saturates rapidly resulting in a small broadening in the Mo 3d photoelectron lines. In EELS one loss line was detected sensitive to oxygen exposure. The estimated maximum coverage approaches two monolayers. When increasing the temperature and oxygen exposure the broadening of the Mo 3d lines stays quite constant but after certain temperature and exposure to oxygen the broadenings start to increase. At elevated temperatures the Mo 3d lines change to a broad band of overlapping Mo 3d lines which can be separated into individual components of Mo, MoO2 and MoO3. In EELS one bulk plasmon is split into two different structures and into an additional feature. At room temperature the chemisorbed oxygen determines the adsorption mechanism while at elevated temperatures a stepwise transition to Mo oxides seems established.