Metallic silicides constitute an important part of current microelectronics, serving as Schottky barriers and ohmic contacts, gate electrodes, local interconnects, and diffusion barriers [1–3]. Silicide nanowires, self-organized on the Si(110) surface, are considered as building blocks of future nanoelectronics and have been intensively investigated . However, the reports about their crystal structure remain contradictory, spanning cubic (s or γ) [5–7] and tetragonal (α)  phases. Furthermore, in nanostructures the lattice vibrational waves (phonons) deviate drastically from those in bulk crystals, giving rise to anomalies in thermodynamic, elastic, electronic, and magnetic properties. Hence, a thorough understanding of the physical properties of these materials requires a comprehensive investigation of the crystal structure and lattice dynamics as a function of the nanowire size.
Using extended x-ray absorption fine structure (EXAFS) spectroscopy and nuclear inelastic scattering (NIS) we performed a systematic study of the crystal structure and the lattice dynamics of endotaxial FeSi$_2$ nanowires, which are in-plane embedded into the Si(110) surface. The EXAFS results unveiled the formation of the metastable, surface-stabilized α phase. The Fe-partial phonon density of states, obtained by the NIS experiment, exhibits a broadening of the spectral features with decreasing nanowire width and a pronounced vibrational anisotropy that originates from the specific orientation of the tetragonal α−FeSi$_2$ unit cell on the Si(110) surface. The results from first-principles calculations are fully consistent with the experimental observations .
 S.P. Murarka, Intermetallics 3, 173 (1995).
 L. J. Chen, Silicide Technology for Integrated Circuits (Institution of Electrical Engineers, London, 2004).
 L.J. Chen, JOM 57, 24 (2005).
 P.A. Bennett et al., Thin Solid Films 519, 8434 (2011).
 S. Liang et al., Appl. Phys. Lett. 88, 113111 (2006).
 S. Liang et al., J. Cryst. Growth 295, 166 (2006).
 D. Das et al., Appl. Phys. Lett. 105, 191606 (2014).
 Z.-Q. Zou et al., Appl. Surf. Sci. 399, 200 (2017).
 J. Kalt et al., Phys. Rev. B 102, 195414 (2020).