Decagonal Epilayers on the Icosahedral Quasicrystal ${\mathrm{Al}}_{70}{\mathrm{Pd}}_{20}{\mathrm{Mn}}_{10}$

The pentagonal surface of the icosahedral quasicrystal ${\mathrm{Al}}_{70}{\mathrm{Pd}}_{20}{\mathrm{Mn}}_{10}$ becomes decagonal upon sputtering with ${\mathrm{Ar}}^{+}$ ions at elevated temperatures. This decagonal surface has a vastly different chemical composition ( ${\mathrm{Al}}_{22}{\mathrm{Pd}}_{56}{\mathrm{Mn}}_{22}$) than bulk decagonal quasicrystals ( ${\mathrm{Al}}_{70}{\mathrm{Pd}}_{10}{\mathrm{Mn}}_{20}$) 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.