Electronic structure of self‐assembled Sm nanostructure on HOPG studied by in‐situ photoemission spectroscopy and scanning probe microscopy

Abstract

In-situ photoemission spectroscopy of Sm over-layer on HOPG in the coverage regime of 0.3∼10.0 Å has been performed at room temperature in the 4d-4f resonance energy region by using monochromatic synchrotron radiation light. Based on analysis of the spectra taken at hν =134 eV (close to divalent samarium resonance), it is indicated that the divalent feature predominates the valence band spectra for the coverage below than 1.0 Å, while the trivalent structures are enhanced for Sm over-layer coverage higher than the 1.0 Å. However, in the case of valence band spectra are excited with the photon of energy of 141 eV at trivalent samarium resonance, the trivalent feature dominates the spectra across over the 0.6∼10.0 Å coverage of Sm over-layer. The mixed valence in the present Sm over-layer system might be heterogeneous in nature. Our first result indicates that the VUV irradiation of Sm makes an important role for stimulating the degeneration of divalent multi-configuration during the vacuum ultraviolet photoemission spectroscopy.

High-resolution photoelectron spectroscopy study of Kondo metals: SmSn3and Sm0.9La0.1<

“…It is known that in the incident photon energy range of the Sm 4d-4f resonance, the Sm 2+ component mainly originates from the surface layer. Consequently, the Sm 2+ surface state is probed at these photon energies, 36,37 whereas the Sm 3+ component is considered to be from the bulk even at these incident energies. At the surface the Sm atoms are less coordinated; their cohesive energy is therefore lower than that of the bulk Sm atoms, which results in the surface Sm atoms tending to be in the divalent state.…”