Regensburg 2019 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 19: Thermoelectricity

HL 19.3: Talk

Tuesday, April 2, 2019, 12:00–12:15, H33

Phonons in mesoporous silicon: the influence of nanostructuring on the dispersion in the Debye regime — •Tommy Hofmann and Klaus Habicht — Helmholtz Zentrum Berlin für Materialien und Energie, Berlin, Deutschland

This contribution presents a comprehensive scattering study of nanostructured silicon [1]. Neutron and x-ray scattering experiments elucidate structural and dynamical properties of electrochemically etched, porous silicon membranes with pores roughly 8 nm across. In particular, inelastic cold neutron scattering techniques reveal the phonon dispersion of the nanostructured, single crystalline samples in the linear Debye regime for energy transfers up to 4 meV whereas inelastic thermal neutron scattering experiments provide access to the dispersion closer to the zone boundary. A modified dispersion relation characterized by systematically reduced sound velocities manifests itself in altered elastic properties of porous silicon when compared to bulk silicon. Its relevance for nanostructured silicon as thermoelectric material of interest is discussed. In this context, we give an outlook on phonon lifetime measurements to ascertain directly phonon scattering rates in nanostructured silicon by means of neutron spin-echo studies.

[1] T. Hofmann, D. Wallacher, R. Toft-Petersen, B. Ryll, M. Reehuis, and K. Habicht. Phonons in mesoporous silicon: the influence of nanostructuring on the dispersion in the Debye regime. Microporous and Mesoporous Materials, 243:263*270, 5 2017.