Elsevier

Surface Science

Volume 215, Issue 3, 3 May 1989, Pages 363-377
Surface Science

The adsorption of atomic hydrogen on Cu(111) investigated by reflection-absorption infrared spectroscopy, electron energy loss spectroscopy and low energy electron diffraction

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Abstract

Hydrogen atoms were adsorbed on Cu(111) at 150 K. The vibrational spectrum of the adsorbed hydrogen was measured by both reflection-absorption infrared spectroscopy (RAIRS) and electron energy loss spectroscopy (EELS) in the temperature range 90–280 K. The saturated surface displayed a (3 × 3) LEED pattern which was converted to a (2 × 2) pattern on heating to 186 K. The vibrational spectrum observed by EELS was little affected by this structural transformation. The major energy loss peak at 1040 cm−1 was assigned to the symmetric stretching mode of hydrogen in a two-fold bridge site. The infrared spectrum revealed more detail, including a second sharp absorption band at 1150–1170 cm−1 which was assigned to the first overtone of the deformation mode of hydrogen in a two-fold bridge site.

The intensity of the electron energy loss peak, excited by dipole scattering, and of the infrared absorption bands provided an estimate for the effective charge, e, of the hydrogen adatom of 0.05–0.06e which is similar to values previously estimated for the hydrogen adatom on W(100).

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      The interactions of incident H atoms with Cu(111) has been extensively studied using LEED, HREELS, IRAS, helium atom scattering (HAS), and TPD [6,41,186–193]. Although there is general agreement in the literature that upon increasing exposure of H atoms, the (1 × 1) LEED pattern of clean Cu(111) transitions to a (2 × 2) pattern below θH = 0.5 ML and to a (3 × 3) pattern above θH = 0.5 ML [186,188,193], there is much debate regarding the assignment of the H atom adsorption sites responsible for peaks in vibrational spectra and the H2 desorption peaks in TPD data. Table 3 summarizes data for vibrational energies of adsorbed hydrogen from exposures of H atoms incident on Cu(111).

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    Present address: Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.

    ∗∗

    Present address: Analytical Support and Research Division, BP Research Centre, Chertsey Road, Sunbury on Thames, Middlesex, TW16 7LN, UK.

    ∗∗∗

    Permanent address: Department of Chemistry, Queen Mary College, Mile End Road, London E1 4NS, UK.

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