• Hofmann, T.; Kojda, D.; Haseeb, H.; Wallacher, D.; Sobolev, O.; Habicht, K.: Phonons in highly-crystalline mesoporous silicon: The absence of phonon-softening upon structuring silicon on sub-10 nanometer length scales. Microporous and Mesoporous Materials 312 (2021), p. 110814/1-7

Open Access Version

This article presents inelastic thermal neutron scattering experiments probing the phonon dispersion in mesoporous silicon with pores 8 nm across. Scattering studies reveal the energy–momentum relation for transverse and longitudinal phonons along the high symmetry directions 𝛤𝐿, 𝛤𝐾 and 𝛤𝑋 in the Brillouin zone. The dispersion up to phonon energies of 35 meV unambiguously proves that the phonon group velocities in highly-crystalline silicon are not modified by nanostructuring down to sub-10 nanometer length scales. On these length scales, there is apparently no effect of structuring on the elastic moduli of mesoporous silicon. No evidence can be found for phonon-softening in topologically complex, geometrically disordered mesoporous silicon putting it in contrast to silicon nanotubes and nanoribbons.