(001) V surface structures analysed by RHEED and STM

In this paper, the single-crystalline (001)V surface is studied by electron diffraction, Auger spectroscopy, and scanning tunnelling microscopy (STM). (1 x 1), (5 x 5) (and sometimes 6 x 6) surface atomic arrangement are obse rved in correlation with the oxygen surface concentration. For less than 0. 15 mi of oxygen, no reconstruction is detected. The (5 x 5) surface structu re is observed for an oxygen coverage in the range 0.15-1.2 mi. However, a pseudo-(1 x 1) surface structure can also be observed near 1 mi of oxygen. The STM analysis demonstrates that the (5 x 5) reconstruction results in fa ct from a mixing of (5 x 1) and (1 x 5) domains. At the atomic scale, the i mages show that the electronic density is modified over two parallel atomic lines every five but also six atomic distances. For the pseudo(1 x 1) reco nstructed surface, these lines are still present, but, depending on the den sity of vacancies, (6 x 1) up to (12 x 1) periodicities can be observed loc ally. We find that the periodicity linearly increases with the number of va cancies. The extension of this linear dependence up to the lack of vacancie s leads to the (5 x 1) periodicity. These surface reconstructions lead to u nusual reflection high-energy electron diffraction (RHEED) patterns? that a re perfectly explained by the surface morphology. Finally, RHEED measuremen t of the in-plane lattice parameter allows us to demonstrate that the (5 x 5) reconstructed surface is compressed. This behaviour allows us to propose a model for the (0 0 1) V surface reconstructions induced by oxygen. (C) 2 001 Elsevier Science B.V. All rights reserved.