  A nanorod structure has been observed on the Ho/Ge(111) surface using
scanning tunneling microscopy (STM). The rods do not require patterning of the
surface or defects such as step edges in order to grow as is the case for
nanorods on Si(111). At low holmium coverage the nanorods exist as isolated
nanostructures while at high coverage they form a periodic 5x1 structure. We
propose a structural model for the 5x1 unit cell and show using an ab initio
calculation that the STM profile of our model structure compares favorably to
that obtained experimentally for both filled and empty states sampling. The
calculated local density of states shows that the nanorod is metallic in
character.
