Self-limited growth of triangular PtO2 nanoclusters on the Pt(111) surface.

The high temperature oxidation of the Pt(111) surface with molecular oxygen has been studied using scanning tunnelling microscopy and low energy electron diffraction (LEED). Results indicate a self-limited growth of well-ordered PtO2 nanoclusters which have an O-Pt-O trilayer structure. Each nanocluster has a triangular shape and nucleates at the Pt(111) surface step edge due to the mobility of Pt atoms. The triangular PtO2 nanoislands on the upper and lower Pt(111) terraces represent two mirror domains with the mirror plane perpendicular to the substrate and aligned along the [Formula: see text] direction of the latter. LEED data obtained from the nanostructured PtO2/Pt(111) surface show a characteristic (2 x 2) pattern. Different oxidation conditions lead to the formation of chemisorbed oxygen on the Pt(111) surface alongside PtO2 nanoclusters. Oxygen adsorbs on the surface forming a variety of structures which result in (3 x 3), (5 x 5) and (7 x 7) LEED patterns.

Atomic scale spin-dependent STM on magnetite using antiferromagnetic STM tips.

STM tips made from antiferromagnetic MnNi have been used to investigate the atomic structure of the (001) and (111) surfaces of Fe3O4. The clean (001) surface displays a ( radical2 x radical2)R45 degrees superlattice, which is attributed to charge-ordering on the surface, where Fe(2+)-Fe2+ and Fe(3+)-Fe3+ dimers can be discriminated. The oxygen-terminated (111) surface is characterized by a hexagonal superlattice with a periodicity of 42 A. Oxygen vacancies are observed in atomically resolved images of this superlattice. In the presence of an external magnetic field of 60 mT, a significant change in the atomic corrugation in the topmost oxygen layer around each of these defects is observed. The results on both (001) and (111) surfaces are discussed in terms of possible spin-polarized effects.

Atomically resolved spin-dependent tunneling on the oxygen-terminated Fe3O4(111).

We employ spin-polarized STM to study the spin-dependent tunneling between a magnetite (111) sample and an antiferromagnetic tip through a vacuum barrier at room temperature. Atomic scale STM images show significant magnetic contrast corresponding to variations in the local surface states induced by oxygen vacancies. The estimated variations in tunneling magnetoresistance of 250% suggest that the spin-transport properties are significantly altered locally by the presence of surface defects.