Fivefold surface of quasicrystalline AlPdMn: Structure determination using low-energy-electron diffraction

Abstract

The atomic structure of the fivefold symmetric quasicrystal surface of icosahedral AlPdMn has been investigated by means of a dynamical low-energy-electron diffraction (LEED) analysis. Approximations were developed to make the structure of an aperiodic, quasicrystalline surface region accessible to LEED theory. A mix of several closely similar, relaxed, bulklike lattice terminations is favored, all of which have a dense Al-rich layer on top followed by a layer with a composition of about 50% Al and 50% Pd. The interlayer spacing between these two topmost layers is contracted from the bulk value by 0.1 Å, to a final value of 0.38 Å, and the lateral density of the two topmost layers taken together is similar to that of an Al(111) surface. The LEED structural result is qualitatively consistent with data from ion scattering spectroscopy, which supports an Alrich termination. Keywords Ames Laboratory, Physics and Astronomy Disciplines Biological and Chemical Physics | Physical Chemistry CommentsThis article is from Physical Review B 57, no. 13 (1998) The atomic structure of the fivefold symmetric quasicrystal surface of icosahedral AlPdMn has been investigated by means of a dynamical low-energy-electron diffraction ͑LEED͒ analysis. Approximations were developed to make the structure of an aperiodic, quasicrystalline surface region accessible to LEED theory. A mix of several closely similar, relaxed, bulklike lattice terminations is favored, all of which have a dense Al-rich layer on top followed by a layer with a composition of about 50% Al and 50% Pd. The interlayer spacing between these two topmost layers is contracted from the bulk value by 0.1 Å, to a final value of 0.38 Å, and the lateral density of the two topmost layers taken together is similar to that of an Al͑111͒ surface. The LEED structural result is qualitatively consistent with data from ion scattering spectroscopy, which supports an Al-rich termination. ͓S0163-1829͑98͒03713-8͔

Study of preferential sputtering and segregation effects on the surface composition of AlPdMn quasi‐crystals

“…The decrease in Mn concentration with annealing agrees with LEIS results [1,5] but is in contrast to MEIS results [3] which show a constant Mn surface concentration of about 5% up to 920 K and a rapid Mn increase to 16% at 958 K. The MEIS surface peak however measures the concentration of the top 2-3 atomic layers, so the low temperature Mn transport measured by LEIS can be explained as a movement from the surface layer to the layers immediately below. On the basis of LEED study of [5] Gierer et al, the Al-Pd-Mn surface as a topmost atomic plane containing mainly Al with a second plane containing approximately equal concentrations of Al and Pd with about 10% Mn. They also allow that Mn could substitute for Al in the top layer -a process which we believe accounts for the movement of Mn to the surface during sputtering and away from the surface during annealing.…”

“…1) produced a surface with almost no Mn and an LEIS Al/Pd ratio of 4.28. The surface composition for the clean-annealed surface has been measured twice before using LEIS [1,5] with different analysis protocols. As they have a high level of agreement in surface composition, this value, Al 83 Pd 16 Mn 1 , was used as the starting composition for our study.…”

“…[5] All ratios are expressed as a ratio of integrated yield as such quantities have greater statistical significance than peak heights.…”

“…Even the composition of the clean-annealed surface is subject to dispute. For example, previous low-energy ion scattering LEIS measurements [1,5] indicate a clean surface which is depleted in Mn and Pd compared to the bulk composition whereas AES measurements [4] give near bulk compositions. These differences are reconciled by noting that different analysis techniques probe different depths into the surface.…”

Local configurations on surfaces of icosahedral quasicrystals

“…On atomically resolved STM images some typical local configurations of atoms can be recognised [6,7,8]. It has been shown [2,6], that the experimentally observed features are consistent with a bulk terminated structure [9]. Several typical local arrangements of atoms were found by various groups.…”