(0 0 1) V surface structures analysed by RHEED and STM

In this paper, the single-crystalline (0 0 1) V surface is studied by electron diffraction, Auger spectroscopy, and scanning tunnelling microscopy (STM). (1×1), (5×5) (and sometimes 6×6) surface atomic arrangement are observed in correlation with the oxygen surface concentration. For less than 0.15 ml of oxygen, no reconstruction is detected. The (5×5) surface structure is observed for an oxygen coverage in the range 0.15–1.2 ml. However, a pseudo-(1×1) surface structure can also be observed near 1 ml of oxygen. The STM analysis demonstrates that the (5×5) reconstruction results in fact from a mixing of (5×1) and (1×5) domains. At the atomic scale, the images show that the electronic density is modified over two parallel atomic lines every five but also six atomic distances. For the pseudo-(1×1) reconstructed surface, these lines are still present, but, depending on the density of vacancies, (6×1) up to (12×1) periodicities can be observed locally. We find that the periodicity linearly increases with the number of vacancies. The extension of this linear dependence up to the lack of vacancies leads to the (5×1) periodicity. These surface reconstructions lead to unusual reflection high-energy electron diffraction (RHEED) patterns, that are perfectly explained by the surface morphology. Finally, RHEED measurement of the in-plane lattice parameter allows us to demonstrate that the (5×5) reconstructed surface is compressed. This behaviour allows us to propose a model for the (0 0 1) V surface reconstructions induced by oxygen.