Vanadium oxides, alloys and silicides exhibit a broad variety of electronic, magnetic and structural properties, including high melting point, high hardness and corrosion resistance which made it compounds important for the material engineering field. In order to understand the properties of nanostructured vanadium and vanadium oxides, surface science research has been devoted to investigate the growth of vanadium deposited on different substrates, such as, SiO2, TiO2, Cu and Cu3Au-O. Studies concerning self-organized vanadium oxide nanostructures and vanadium surface reconstructions show the potential applications of vanadium on nanostructured materials as model catalysts and nanodimensional standards. In this work, we investigate the size distribution and shape transition of self-assembled vanadium silicide nano-needles and nanoclusters growth on Si(111) 7x7 surface by scanning tunneling microscopy (STM). The nanostructures were formed by submonolayer vanadium deposition at room temperature up to 1100K (called as reactive deposition epitaxy). As a function of temperature, both, flat (2D) hexagonal shaped clusters and needle-clusters have been obtained. Substrate temperature and also deposition rate can be adjusted in order to tuning the nanostructures features. The nano-needles grow following a severe surface energy minimization, as a step-by-step growth at single half unit 7x7 cell as a detailed image analysis suggest. The nano-needles growth direction follow a corner-hole alignment which grows at certain 60° with respect each other at the substrate isotropic directions. The nanostructures have typical aspect ratio range of 4-8 and height range of 1-2nm. Based on high resolution STM images an on-top structure model for the nano-needles exposing atomically flat surfaces was proposed.

Acknowledgements

This work has been supported by CNPq-PROMETRO and in part by CAPES.

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