Lattice dynamics of epitaxial strain-free interfaces

Abstract

We report a systematic lattice dynamics study of the technologically important Fe 3 Si/GaAs heterostructure for Fe 3 Si layer thicknesses of 3, 6, 8, and 36 monolayers. The Fe-partial phonon density of states obtained by nuclear inelastic scattering exhibits up to a twofold enhancement of the low-energy phonon states compared to the bulk material for layer thicknesses of 8 monolayers and below. First-principles calculations explain the observed effect by interface-specific phonon states originating from the significantly reduced atomic force constants and allow for achieving a comprehensive understanding of the lattice dynamics of epitaxial strain-free interfaces.

Phonon confinement and spin-phonon coupling in tensile-strained ultrathin EuO films

“…Combined experimental and theoretical studies of strainfree metal/semiconductor heterostructures 42 and metallic multilayers 43 demonstrated that the force constants of the atoms located at the interface are drastically reduced compared to the bulk values. This gives rise to an entirely different PDOS of the interface layers from that of a bulk material.…”

“…In particular, up to a two-fold enhancement of the number of low-energy states along the interface was measured and theoretically confirmed for the strain-free Fe 3 Si/GaAs interface. 42 Due to the grazing-incidence scattering geometry used in our experiment we determine the in-plane projected PDOS. Therefore, the observed discrepancy between experiment and theory up to 5 meV and between 12 and 15 meV most likely originates from the EuO/YAlO 3 interface-specific PDOS.…”

Ab initio and nuclear inelastic scattering studies of Fe3Si/GaAs heterostructures

“…For variant C, the features entail a remarkable agreement between model and experiment. In general, variant C leads to the lowest residual sum squared (values in Table IV are normalized to variant C) and yields the best agreement with the expected A value of 0.14 [46]. The deviations between experiment and theory observed for all variants in the range 17-27 meV may arise from the additional phonon modes induced by the Ge/Fe 3 Si interface that is not accounted for by the model.…”

“…with g if (E, Q if ) and g bulk (E, Q bulk ) being the calculated [46]). Furthermore, due to the grazing incidence geometry of the experiment, only the in-plane PDOS is measured, which allows for a comparison with the calculated xy-projected PDOS.…”

“…1. In our previous work [46], we have presented solely the results obtained for variant C. In Fig. 7, the calculated phonon dispersion relations and phonon density of states (PDOS) are presented.…”