Scanning tunneling microscopic images of the 5-fold surface of icosahedral Al-Pd-Mn quasicrystals were calculated by using ab initio density functional methods. The scanning tunneling microscopic signal was produced mainly by Al atoms in the surface plane. The Pd atoms were seen as dark spots. The reason for their small contribution to the scanning tunneling microscopic current was a small local density of states around the Fermi level and the localized d -character of the Pd states. The local paramagnetic density of states on Mn atoms was much higher than that on Pd atoms and therefore Mn atoms were seen in the scanning tunneling microscopic images as bright spots. A direct comparison of the experimental images obtained from the scanning tunneling microscopy with the ab initio calculated scanning tunneling microscopic images revealed that the characteristic features of the images, dark pentagonal holes, could also be created by surface vacancies and not only by truncated Bergman clusters as had been supposed before.

Surface Vacancies at the Fivefold Icosahedral Al-Pd-Mn Quasicrystal Surface – a Comparison of ab initio Calculated and Experimental STM Images. M.Krajčí, J.Hafner, J.Ledieu, R.McGrath: Physical Review B, 2006, 73[2], 024202 (8pp)