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

Highlights: • The α-FeSi₂ nanowires epitaxially grown on Si(110) can be stable up to 750 °C. • The stable temperature of the nanowires is much lower than that of the bulk α-FeSi₂ due to their small size and high relative surface area. • With increasing annealing temperature, the α-FeSi₂ nanowires undergo an Ostwald ripening process and transform into large β-FeSi₂ nanorods or three-dimensional nanocrystals. • The reduction in surface energy drives the transformation from metallic α-FeSi₂ phase to semiconducting β-FeSi₂ phase. - 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 0.2 eV with respect to the α-FeSi₂ NWs.