AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1+EM-TuA

Paper SS1+EM-TuA4
Surface Reconstructions of Fe@sub 3@O@sub 4@(001)

Tuesday, October 26, 1999, 3:00 pm, Room 606

Session: Oxides: Growth and Structure
Presenter: U. Diebold, Tulane University
Authors: B. Stanka, Tulane University
W. Hebenstreit, Tulane University
U. Diebold, Tulane University
S.A. Chambers, Pacific Northwest National Laboratory
Correspondent: Click to Email
We have investigated the structural changes to the Fe@sub 3@O@sub 4@(001) surface which are induced by different sample treatments. The samples consisted of ~5000 Å thick films of Fe@sub 3@O@sub 4@(001) , grown with oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) on MgO(001) substrates. To study the surface termination, structure, morphology, and composition, scanning tunneling microscopy (STM), low energy electron diffraction (LEED), low energy He@sup +@ ion scattering (ISS), and x-ray photoelectron spectroscopy (XPS) were used. A (@sr@(2) x @sr@(2))R45° reconstruction relative to bulk-terminated Fe@sub 3@O@sub 4@ is induced by heating in oxygen (10@sup -6@ - 10@sup -7@ mbar) at temperatures between 250°C and 500°C after a through-air transfer from the MBE chamber. Our STM results show an appearance consistent with a B-layer termination, which consists of a layer of octrahedrally coordinated Fe and tetrahedrally coordinated O, along with one O vacancy per unit cell. This surface is autocompensated, or charge neutral, and is therefore expected to be stable. Further annealing in UHV causes a transformation to either a (1 x n) or a (2@sr@(2) x @sr@(2))R45 structure. In both cases, a (@sr@(2) x @sr@(2))R45 reconstructed surface can be regained reproducibly by annealing in oxygen. Interestingly, at no time do we observe the other autocompensated termination, which consists of one-half monolayer of tetrahedrally coordinated Fe(III), despite its observation in other laboratories. Thus, it appears that the surface termination is critically dependent on the method of surface preparation.