  The structure of the Al_{70}Pd_{21}Mn_{9} surface has been investigated using
high resolution scanning tunnelling microscopy (STM).
  From two large five-fold terraces on the surface in a short decorated
Fibonacci sequence, atomically resolved surface images have been obtained. One
of these terraces carries a rare local configuration in a form of a ring.
  The location of the corresponding sequence of terminations in the bulk model
M of icosahedral i-AlPdMn based on the three-dimensional tiling T*(2F) of an
F-phase has been estimated using this ring configuration and the requirement
from the LEED work of Gierer et al. that the average atomic density of the
terminations is 0.136 atoms per A^2.
  A termination contains two atomic plane layers separated by a vertical
distance of 0.48 A. The position of the bulk terminations is fixed within the
layers of Bergman polytopes in the model M: they are 4.08 A in the direction of
the bulk from a surface of the most dense Bergman layers.
  From the coding windows of the top planes in terminations in M we conclude
that a Penrose (P1) tiling is possible on almost all five-fold terraces. The
shortest edge of the tiling P1, is either 4.8 A or 7.8 A.
  The experimentally derived tiling of the surface with the ring configuration
has an edge-length of 8.0 +- 0.3 A and hence matches the minimal edge-length
expected from the model.
