Spin-polarized scanning tunneling microscopy on ultrathin iron films on Be(0001)
Final Report Abstract
The Be(0001) surface is considered to be an ideal model system to host a two-dimensional (2D) electron gas with pronounced electron-electron and electron-phonon interactions that are decoupled from the bulk. Consequently, growing magnetic adlayers on Be(0001) raises expectations for the emergence of novel electronic and magnetic phases that result from the interactions between the 2D electron gas and the magnetic atoms. Within this project, the expitaxial growth of Fe on a clean Be(0001) surface is investigated with scanning tunneling microscopy (STM) and spectroscopy (STS) at low temperature and under ultrahigh vacuum conditions. Very clean Be(0001) surfaces have been prepared and investigated by STM and STS prior to the dosing of Fe. A pronounced surface state is found on Be(0001) that manifests as bias-dependent standing-wave patterns. A Fourier analysis of the data reveals a parabolic dispersive behaviour, which is characteristic for a two-dimensional free-electron gas confined to the Be(0001) surface. Moreover, signatures of the opening of inelastic phonon-mediated tunnel channels for electrons near the Fermi level are observed by STS. When dosing Fe atoms onto the Be(0001) surface, they are found to replace individual Be atoms in the topmost Be(0001) surface layer, driven by an atomic exchange. In contrast to our expectations, Fe is not found to continue the Be(0001) atomic lattice in a pseudomorphic hcp stacking. Instead, the nucleation of nanoislands with an atomically rough surface is observed for the low coverage regime below one atomic layer. For coverages above one atomic layer of Fe, the nanoislands show atomically well-ordered surfaces with numerous patches exhibiting a p(2×2) superstructure. A further increase of the Fe coverage results in the self-terminated growth of ultrathin films consisting of atomically well-ordered patches with a p(2×2) superstructure. Based on the atomic structure of the FeBe2 bulk alloy we develop an atomistic growth model, where the dosing of Fe transforms the topmost Be layer into a Kagome lattice that supports the formation of a 2D buckled honeycomb lattice of Fe atoms. STS data reveal a metallic behaviour together with a dip around the Fermi level, thereby indicating the combined electronic properties of Fe and Be. The experimental study demonstrates the epitaxial growth of Fe-Be ultrathin films on a Be(0001) substrate. The arrangement of the Fe atoms in a buckled honeycomb lattice in connection with the 2D electron gas of the Be(0001) surface makes this system an interesting candidate for further studies in terms of its magnetic spin texture and potential topological non-trivial properties.
Publications
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2019-06-18 (Poster): 8th Internation Conference on Scanning Probe Spectroscopy, Hamburg (Germany): “Scanning Tunneling Spectroscopy of a clean Be(0001) surface”
H. Osterhage, J.-H. Schmidt, R. Dao, V. Prikryl, S. Krause & R. Wiesendanger
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2021-03-01 (Poster): DPG SurfaceScience 21 (virtual meeting): “Epitaxial Growth of Fe on Be(0001) Studied by STM”
K. Oetker, H. Osterhage, R. Wiesendanger & S. Krause
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2021-03-01 (Poster): DPG SurfaceScience 21 (virtual meeting): “Phonon Mediated Tunneling into a 2D Electron Gas on the Be(0001) Surface”
H. Osterhage, K. Oetker, R. Wiesendanger & S. Krause
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2021-07-12 (Contributed Talk): International Conference on Nanoscience and Technology, Vancouver (Canada) (virtual meeting): “Phonon-Mediated Tunneling into Be(0001) Surface States Probed by Scanning Tunneling Spectroscopy”
H. Osterhage, K. Oetker, R. Wiesendanger & S. Krause
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2021-09-27 (Contributed Talk): 84th Annual Conference, Deutsche Physikalische Gesellschaft (virtual meeting): “Iron growth on Be(0001) studied by STM”
H. Osterhage, K. Oetker, R. Wiesendanger & S. Krause
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Phonon-mediated tunneling into a two-dimensional electron gas on the Be(0001) surface. Physical Review B, 103(15).
Osterhage, Hermann; Wiesendanger, Roland & Krause, Stefan
