Symmetry Changes At The Surface Of Al₇₀Pd₂₀Mn₁₀

Abstract

Sputtering with Ar+ ions induces structural phase transitions at the pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10. Sputtering at different temperatures changes the surface composition, thereby stabilizing different structures. At room temperature, the structure changes to body-centered cubic but, at elevated temperatures, it displays decagonal symmetry. In both cases, annealing the sample restores both the bulk composition and the icosahedral symmetry of the original surface.

Quasicrystal surfaces: structure and potential as templates

“…This structure does not extend to the bulk, however, because reflection Laue x-ray diffraction indicates that the icosahedral structure is still intact beneath the surface. If the sample temperature is held between 500 and 700 K while sputtering, a thick (2 nm) decagonal epilayer can be observed by SEI having a composition equal to Al 22 Pd 56 Mn 22 [54].…”

Epitactic textures of fcc Al on icosahedral Al-Pd-Mn quasicrystal

“…[3][4][5] In this case a twofold-symmetry axis of the cube is aligned along a fivefold-symmetry axis of the QC, and one threefold axis of the approximant nearly coincides with one threefold axis of the icosahedron. 3,6 However, this surface layer was found to be unstable; it reverts to its original chemical composition and to the icosahedral structure as a result either of annealing-induced surface segregation of Al at 400°C or as a result of a mild annealing up to 150°C after vacuum deposition of Al onto the sample surface. On the other hand, if the Al concentration in the near-surface region is too high, the QC is not in the stable region of the phase diagram any more.…”

“…This different relative arrangement of the symmetry axes of the (m3 m) and the (5 3 m) point group is found to be different from the orientation of a surface layer in the bcc structure obtained through sputtering the i-QC. 3,6 In this arrangement there are common symmetry elements belonging to the point group (m3 ), which is therefore the subgroup common to both structures. 14 The Monte Carlo simulations allow the assumption that the concave depletions are suitable places for initial seeds of fcc Al crystals that are coherently oriented relative to the quasicrystal matrix.…”

The surface science of quasicrystals

“…Here, the apparent tenfold pattern recorded using low energy electron diffraction (LEED) derives from five cubic domains rotated from each other by 72 • . Similarly, a decagonal epilayer of composition equal to Al 22 Pd 56 Mn 22 can be formed while ion bombarding the sample held between 500 and 700 K [14]. In all cases, annealing the sample above 700 K for several hours restores the nominal bulk composition and a quasiperiodic order at the surface.…”

“…Similarly, a decagonal epilayer of composition equal to Al 22 Pd 56 Mn 22 can be formed while ion bombarding the sample held between 500 and 700 K [14]. In all cases, annealing the sample above 700 K for several hours restores the nominal bulk composition and a quasiperiodic order at the surface.…”