Reconstructive phase transitions and effective adsorbate-adsorbate interactions: H/Mo(100) and H/W(100)

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Abstract
Low-energy electron-diffraction and infrared-absorption measurements of H/Mo(100) and H/W(100) surfaces show that, at low hydrogen coverages, the effective H-H interactions are very different for the two substrates, leading to island formation on Mo(100) and to a uniform H layer on W(100). The results can be explained by a phonon-mediated interaction mechanism for the hydrogen adatoms, according to which the difference in behavior is due to the difference in the coupling between substrate distortions induced by the individual adatoms. It is concluded that a realistic treatment of the adatom interactions should go beyond the rigid-substrate model and include the crucial role of soft surface phonons.