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O: Fachverband Oberflächenphysik

O 4: New Methods: Experiments

O 4.5: Vortrag

Montag, 18. März 2024, 11:30–11:45, MA 005

Quantifying monolayer coverage of endofullerenes by x-ray absorption spectroscopy from equivalent implanted ion doses — •W.C Lee¹, L. Yu¹, J. Oscarsson², M. W. Ochapski³, R. Sagehashi¹, Y. Zhang⁴, A. A. Popov⁴, Z. M. Gebeyehu³, L. Martini³, S. Forti³, C. Coletti³, B. Delley⁵, M. Muntwiler⁵, D. Primetzhofer², and T. Greber¹ — ¹Physik-Institut, Universität Zürich, Switzerland — ²Tandem Laboratory, Uppsala University, Sweden — ³Istituto Italiano di Technologia, Pisa, Italy — ⁴Leibniz-Institute, Dresden, Germany — ⁵Paul Scherrer Institute, Switzerland

With x-ray absorption spectroscopy (XAS), the structure of magnetic atoms in molecules may be accessed directly [1]. For Ho₃N@C₈₀ endofullerenes on graphene/SiO₂, we calibrated the surface coverage by comparing the molecular XAS signal with implanted Ho ion doses of 3×10¹⁴ cm⁻² that are directed to SiO₂ with energies between 2 and 115 keV. The corresponding Ho M₄₅ intensity as a function of implantation depth d can be extrapolated to the zero-depth intensity of absorbed molecules. The Ho signal attenuation scales with exp(-d/Λ), with Λ=10.3±0.7 nm. The Si K-edge signal attenuation reveals an influence of the implantation process on the Si density. The XA spectra indicate trivalent Ho for both molecules and implants, while spectral differences and comparison to multiplet theory [2] suggest an isotropic J=8 Ho 4f electron distribution for implants and J_z=±8 ground states in the molecules due to the defined intramolecular ligand field.

[1] R. Westerström, et al., Phys. Rev. Lett., 087201 (2015)[2] A. Uldry, et al., Phys. Rev. B, 85, 125133 (2012)

Keywords: Endofullerenes; Coverage calibration; x-ray absorption spectroscopy; final state multiplet calculations; ion implantation