Effect of surface thermal vibrations on the azimuthal-angle distribution ofNi+ejected from Ni(111) byAr+bombardment

The azimuthal-angle distribution of ${\mathrm{Ni}}^{+}$ ions ejected from Ni(111) by bombardment with 2.0-keV ${\mathrm{Ar}}^{+}$ has been measured as a function of temperature in the range 263–500 K. The results show that the anisotropy of the ${\mathrm{Ni}}^{+}$ azimuthal-angle distribution is nearly independent of temperature up to 300 K, but decreases rapidly as the temperature increases from 320 to 380 K. The ${\mathrm{Ni}}^{+}$ azimuthal anisotropy appears to be nearly independent of temperature above ∼390 K. The experimental results are well described by molecular-dynamics simulations that account for thermal vibrations in the top atomic Ni layer. Comparison of the experimental results with the results of molecular-dynamics simulations is used in combination with the Debye model, to reveal information about the magnitude of vibrational displacements in the top atomic layer.