Surface Core Level Shifts of the Lanthanide Metals Ce⁵⁸-Lu⁷¹: A Comprehensive Experimental Study

Abstract

Synchrotron radiation excited photoelectron spectra of the 4f emission region for all lanthanide metals Cess to Lu" (except Pm6') have been recorded. Photon energies ranging from 30 eV to 200 eV have been used to excite the 4f electrons with maximum surface sensitivity. The 4f emission spectra of all metals studied, with the exception of Ce, show 4f emission from the surface layer atoms and the bulk atoms as clearly separated structures with different binding energies. For Ce no unambiguous separation of the 4f structure into bulk and surface emission could be made. We fitted the experimental spectra with calculated 4f emission spectra obtained by adding a bulk and a shifted surface multiplet for each metal. The intensity ratios within the multiplets were obtained from an atomic calculation utilizing the intermediate coupling scheme.The intensity ratio between bulk and surface emission (I$ls) and the magnitude of the surface core level shift (SCS) were used as fit parameters. The deduced SCSs are all positive (towards higher binding energy), 0.40 eV-0.77 eV, and in fair agreement with calculated SCSs using the Johansson-Mktensson-Rosengren model. For the trivalent lanthanides we found a systematic variation of the SCSs through the series, which can be attributed to differences in the actual electron distribution between s, p and d-like valence states. For the trivalent Sm we found the surface to be completely divalent and deduced a surface shift of > 0.46 eV, being the energy necessary to change the surface valency.

Исследование валентного перехода в системе О-=SUB=-2-=/SUB=--Yb-Si(111) с помощью метода фотоэлектронной спектроскопии с угловым разрешением

“…Таким образом, поверхностный сдвиг 4 f -уровня для нанопленки иттербия толщиной 16 ML, нанесенной на Si(111) подложку, составляет 0.58 eV. Эта величина хорошо согласуется с данными, полученными для трехмерных образцов иттербия (см., например, [9]). …”

Optical and magneto-optical properties of single crystals of RFe{sub 2} (R = Gd, Tb, Ho, and Lu) and GdCo{sub 2} intermetallic compounds

“…There are broad peaks in the theoretical conductivity around 3.0 eV in both GdFe2 Energy (eW unoccupied 4f levels of bulk Gd metal are -8.5 and 3.5 eV with respect to the Fermi level, respectively, from PES and'IPES data [123]. The LSDA calculations for GdFez by the LMTO method by Hiroshi [124] give the locations of the occupied and unoccupied…”

Photoemission study of some novel materials: rare earth/transition metal interface, Ba06K04BiO3 and AlPdMn

“…Photoemission experiments have shown that the surface atoms might have a different 4f configuration than the bulk atoms [Allen 1980, Wertheim 1978, Lang 1979. Figure 1.5 [Gerken 1985] shows the Sm valence spectrum obtained at three different photon energies. Multiple peaks observed in the spectrum can be grouped into two subsets, one from the bulk emission (4f5 to 4f4), and the other from the surface emission (4f6 to 4f5).…”

“…Comparison between an XPS-spectrum and two spectra recorded at 35 eV and 100 eV photon energy of the 4f emission region of Sm. Also shown are the multiplet intensities for the bulk emission (4f5 to 4f^), the surface emission (4f^ to 4f5) and the buUc BIS transition (4f5 to 4f6) (after [Gerken 1985]). …”

“…As the The photoemission data provide more evidence of the existence of an fcc(ll 1) like reconstruction of Eu on the Ta(llO) surface. Figure 4.4 shows the photoemission spectra of the 4f level in Eu, one XPS-spectrum (A1 Ka, 1486.6eV) and the other recorded at 100 eV photon energy [Gerken 1985]. Eu has the 4f^ configuration, the final states for the excited 4f^ configuration are ^Fj (J = 0,1,...6) i.e.…”