DETERMINATION OF ANISOTROPIC VIBRATIONS BY TENSOR LEED

We present a new method for the determination of anisotropic (and anharmonic) vibrations by the analysis of temperature dependent LEED intensities using the tenser LEED formalism. The method is applied to the adsorbate system Ni(100) c(2 x 4)K for temperature dependent data varying between 90 and 200 K. The root mean square displacements parallel to the surface are found to be as large as 0.5 Angstrom. This is about 10 times larger than the value perpendicular to the surface. The inclusion of anisotropic vibrations remarkably improves the experiment-theory fit. So, for T = 90 K the Pendry R-factor is reduced from 0.26 to 0.19. Though the investigated temperature range of 90-200 K is not large enough to see a strong temperature dependence, the expected trend of increasing vibration amplitudes with increasing temperature is visible.