With the use of field ion microscopy we have investigated an atomic structure of a 1 Â 2 reconstruction of a Pt(110) and a Pt (331) crystallographic planes. For the Pt(110), a transition from a (1 Â 1) phase into the (1 Â 2) missing-row structure is observed upon annealing treatment at 450 K which is interpreted in terms of jumping or descending atom motions. For the Pt (331), a similar transition takes place upon heating at 600 K, and the atomic arrangement in two top 1 Â 2 layers is compatible with the so called saw-tooth model. We propose a new structural model for the Pt (331)-(1 Â 2) reconstruction.

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Two kinds of new nano tips with potential to magnetic application are fabricated. One is a PtCo alloy pyramidal tip formed by surface faceting, the other is a Pt based Co tip formed by the epitaxy with a proper growth mode. Ultra high vacuum-field ion microscopy with atomic resolution is used to investigate the atomic structures of the tip apex after various sharpen treatments.

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