STRUCTURE AND DYNAMICS OF NIAL(110)

We have measured the surface phonon dispersion for the (110) face of the ordered alloy NiAl using high resolution electron energy loss spectroscopy (EELS) with ΔE = 20-45 cm-1. Our experimental results are compared with lattice dynamical calculations employing a Born-von Karman model up to third-nearest neighbour. Good agreement between the experimental and calculated dispersion curves is obtained when the force constant between first layer nickel atoms and second layer aluminum atoms is increased and the force constant between first layer aluminum atoms and second layer nickel atoms is decreased. These force constant changes indicate a surface rippling where first layer nickel atoms are displaced inwards and first layer aluminum atoms are displaced outwards. This is in qualitative agreement with a structural model based on low energy electron diffraction (LEED) I/V data and a medium energy ion scattering (MEIS) study. © 1990 Pergamon Press plc.