Speaker
Description
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 [4]. However, the reports about their crystal structure remain contradictory, spanning cubic (s or γ) [5–7] and tetragonal (α) [8] 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 [9].
References
[1] S.P. Murarka, Intermetallics 3, 173 (1995).
[2] L. J. Chen, Silicide Technology for Integrated Circuits (Institution of Electrical Engineers, London, 2004).
[3] L.J. Chen, JOM 57, 24 (2005).
[4] P.A. Bennett et al., Thin Solid Films 519, 8434 (2011).
[5] S. Liang et al., Appl. Phys. Lett. 88, 113111 (2006).
[6] S. Liang et al., J. Cryst. Growth 295, 166 (2006).
[7] D. Das et al., Appl. Phys. Lett. 105, 191606 (2014).
[8] Z.-Q. Zou et al., Appl. Surf. Sci. 399, 200 (2017).
[9] J. Kalt et al., Phys. Rev. B 102, 195414 (2020).
