Relation between Surface Relaxation and Surface Force Constants in Clean and Oxygen-Covered Ni(001)

Abstract

Ion shadowing and blocking measurements show that the first interlayer spacing of Ni(001) is contracted if the surface is clean, but expanded if it is covered by half a monolayer of oxygen. The thermal vibration amplitude of surface atoms is strongly enhanced. A simple tight-binding model relates the change in first interlayer spacing to a change in surface force constants, and explains the recently measured surface phonon dispersion curves.