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Journal Article

Metallic-to-nonmetallic transition of Na coadsorbed with CO2 and H2O on the Cr2O3(111)/Cr(110) surface

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Ventrice, Jr., C. A., Ehrlich, D., Garfunkel, E. L., Dillmann, B., Heskett, D., & Freund, H.-J. (1992). Metallic-to-nonmetallic transition of Na coadsorbed with CO2 and H2O on the Cr2O3(111)/Cr(110) surface. Physical Review B, 46(19), 12892-12895. doi:10.1103/PhysRevB.46.12892.

Cite as: https://hdl.handle.net/21.11116/0000-000E-712F-F
Coadsorption of Na with CO2 and H2O on a thin Cr2O3(111) single crystal epitaxially grown on a single-crystal Cr(110) substrate has been performed to study the effects of the coadsorbates on the electronic properties of the Na species. High-resolution electron-energy-loss spectroscopy spectra as a function of Na overlayer coverage reveal a continuous attenuation of the Fuchs-Kliewer surface-phonon loss modes with near total attenuation by ∼2 monolayers (ML). Coadsorption with either H2O or CO2 returns the substrate Fuchs-Kliewer modes to a relative intensity approximately equal to that observed on the clean Cr2O3(111) surface. Angle-resolved photoemission spectroscopy (ARPES) measurements from the Cr2O3(111) surface demonstrate almost total attenuation of the Cr2O3(111) valence-band emission by a Na coverage of ∼2 ML with no return of Cr2O3(111) valence-band emission features upon coadsorption. These observations provide strong evidence that the development of a metallic Na overlayer results in a damping of the coupling interaction between the electron and the Fuchs-Kliewer phonons and that upon reaction with the coadsorbed species, a uniform dielectric overlayer is formed which permits the return of the Fuchs-Kliewer losses. The metallic-to-nonmetallic transition of the overlayer is also supported by the ARPES data which reveal suppression of emission from the Fermi level, the disappearance of the LVV Auger transition, and a shifting to higher binding energy of the Na 2p emission upon compound formation during coadsorption.