Spin-resolved photoemission study of the reaction of O 2 with fcc Co(100)
1992; American Physical Society; Volume: 46; Issue: 7 Linguagem: Inglês
10.1103/physrevb.46.4198
ISSN1095-3795
AutoresW. Clemens, E. Vescovo, T. Kachel, C. Carbone, Wolfgang Eberhardt,
Tópico(s)Advanced Chemical Physics Studies
ResumoThe effect of ${\mathrm{O}}_{2}$ chemisorption on the electronic structure and magnetism of fcc Co overlayers, grown epitaxially on Cu(100), has been studied by use of spin- and angle-resolved photoelectron spectroscopy. At room temperature, for exposures between 2 and 7 L of ${\mathrm{O}}_{2}$, oxygen adsorbs dissociatively in an ordered c(2\ifmmode\times\else\texttimes\fi{}2) structure. [1 langmuir (L) \ensuremath{\equiv}${10}^{\mathrm{\ensuremath{-}}6}$ Torr sec.] The chemical interaction between the adsorbate and the substrate manifests itself through a reduction of the 3d surface-state emission at \ensuremath{\Gamma} near ${\mathit{E}}_{\mathit{F}}$. The oxygen bands exhibit an induced exchange splitting of 0.2\ifmmode\pm\else\textpm\fi{}0.1 eV at the center of the surface Brillouin zone. With higher ${\mathrm{O}}_{2}$ exposure, corresponding to the formation of a CoO surface phase, the photoemission spectra show evidence for strong correlation effects in the electronic structure. A satellite appears about 10 eV below ${\mathit{E}}_{\mathit{F}}$ in the spectra. The formation of the CoO surface-oxide phase is accompanied by a decrease in the photoelectron spin polarization revealing the quenching of the surface ferromagnetic order. At low temperatures (150 K) and high exposures of ${\mathrm{O}}_{2}$ the formation of a ${\mathrm{Co}}_{3}$${\mathrm{O}}_{4}$ phase was observed, which again has a different electronic structure.
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