Direct observation of atomic structures in the surface reconstruction of Ir and Pt (001), (110), and (131) surfaces

Abstract

Atomic structures and atomic steps in the reconstruction of Ir and Pt (001), (110), and (131) surfaces, induced by nanosecond-pulsed-laser heating, have been observed in the field-ion microscope. The quasihexagonal arrangement of atoms in a (1×5)-reconstructed Ir (001) plane is revealed for the first time by mapping the position of surface atoms in a reconstructed layer while it is gradually field evaporated. The Pt (001) surface reconstructs during annealing via a disordered phase. The final ordered phase has a structure similar to the (1×5) structure of Ir(001). However, the closely packed atomic rows of the top layer are now rotated by a small angle from the [110] direction, and there is no quasihexagonal arrangement of atoms. Thus even though field-ion images of these surfaces are consistent with models proposed from studies using low-energy electron diffraction and other macroscopic techniques, there are a few significant differences in the detailed atomic arrangements. Pt and Ir (110) surfaces reconstruct from the (1×1) to the (1×2) structure by breaking of [110] atomic rows into fragments of two to several atoms and by lateral and cross-channel jumps of these fragments. The simultaneous jump of small rows of atoms is probably induced by surface soliton waves. The (131) surface of Pt and Ir also tends to reconstruct from the (1×1) to the (1×2) structure. The (1×2) structure we have observed for Pt and Ir (110) and (131) surfaces is consistent with the ‘‘simple’’ missing-row model.