Low-Energy Ion Scattering Measurements from an Al-Pd-Mn Quasicrystal

Abstract

Energy-angle distributions of low-energy inert-gas ions scattered from surfaces provide information about surface composition and structure. We have measured energy spectra of He + scattered from an Al 71 Pd 20 Mn 9 quasicrystal, which was oriented perpendicular to the 5-fold axis, along various azimuthal directions. Strong scattering signals are seen from Al and Pd, but only a weak Mn signal is observed. From measurements made of He + at an oblique angle of incidence scattered in the forward direction, we observe a 72° periodicity in the azimuthal dependence of the scattering signal intensity from Al surface atoms. The effect arises from shadowing effects involving neighboring surface atoms and provides direct evidence that Al surface atoms exist in a local environment with 5-fold symmetry. In addition, measuring the variation of the signal intensity with incidence angle provides information about neighboring atom distances, which compare favorably with a model of the quasicrystal surface derived from the bulk structure. ABSTRACTEnergy-angle distributions of low-energy inert-gas ions scattered from surfaces provide information about surface composition and structure. We have measured energy spectra of He + scattered from an Al 71 Pd 20 Mn 9 quasicrystal, which was oriented perpendicular to the 5-fold axis, along various azimuthal directions. Strong scattering signals are seen from Al and Pd, but only a weak Mn signal is observed. From measurements made of He + at an oblique angle of incidence scattered in the forward direction, we observe a 72• periodicity in the azimuthal dependence of the scattering signal intensity from Al surface atoms. The effect arises from shadowing effects involving neighboring surface atoms and provides direct evidence that Al surface atoms exist in a local environment with 5-fold symmetry. In addition, measuring the variation of the signal intensity with incidence angle provides information about neighboring atom distances, which compare favorably with a model of the quasicrystal surface derived from the bulk structure.

Tiling of the fivefold surface of Al70Pd21Mn9

“…This is in agreement with the results of LEED [11,12]. Recent LEIS measurements of the surface [19] have identified a characteristic distance of 7.5±0.1Å; our results suggest that this corresponds to the Al-Al distance along the edges of the pentagons.…”

STM study of the atomic structure of the icosahedral Al-Cu-Fe fivefold surface

“…2, 3͒ and i-Al-Cu-Fe ͑Ref. 4͒ fivefold (5 f ) surfaces-and the result has been supported in the former case by data from x-ray scattering, 5 low-energy ion scattering, 6 and temperatureprogrammed desorption. 7 However, these techniques provide only averaged information on surface structure.…”