Thermal stability of iron silicide nanowires epitaxially grown on Si(110) substrates

Abstract

Metallic α-FeSi2 nanowires (NWs) are epitaxially grown on Si(110) at 650°C. Their evolution as a function of annealing temperature has been studied in situ by scanning tunneling microscopy. The NWs are stable up to 750°C, which is much lower than that of the bulk α-FeSi2. With further increasing the annealing temperature, some NWs begin to shrink in length and transform into wider and higher semiconducting β-FeSi2 nanorods or three-dimensional (3D) islands at 925°C. The phase transformation is driven by the reduction in surface energy. On the other hand, some α-FeSi2 NWs begin to dissolve and become thinner until disappearing. The growth of the β-FeSi2 nanorods or 3D nanocrystals follows the Ostwald ripening mechanism, i.e., the large islands grow in size at the expense of the small ones. X-ray photoelectron spectroscopy study shows that the Fe 2p peaks of β-FeSi2 nanocrystals exhibit a negative shift of 0.2eV with respect to the α-FeSi2 NWs.