Decagonal Epilayers on the Icosahedral Quasicrystal Al₇₀Pd₂₀Mn₁₀

The pentagonal surface of the icosahedral quasicrystal Al₇₀Pd₂₀Mn₁₀ becomes decagonal upon sputtering with Ar⁺ ions at elevated temperatures. This decagonal surface has a vastly different chemical composition ( Al₂₂Pd₅₆Mn₂₂) than bulk decagonal quasicrystals ( Al₇₀Pd₁₀Mn₂₀) and is coherent with the icosahedral substrate across the entire macroscopic sample. The transformation of this surface back to the original icosahedral structure and composition during annealing is followed in real space and in real time with secondary-electron imaging. The structural changes during this transformation are discussed in light of current models of decagonal and icosahedral quasicrystals.