PtNi alloys are known to exhibit a tendency towards chemical ordering,
which also effects surface segregation. Scanning tunneling microscopy
results obtained in the strain field of dislocations on PtxNi1-x(110)
surfaces show a (2 x 1) superstructure of alternating Pt and Ni atoms
in some regions close to the dislocation core. In other regions, the
apparent height of all surface atoms is equal, in agreement with low e
nergy ion scattering results yielding a surface concentration of almos
t 100% Ni. This indicates that the strain present in the vicinity of d
islocations influences both the surface composition and chemical order
. The experimental results are compared to simulation calculations of
chemical ordering and segregation, using embedded atom method potentia
ls and linear elasticity theory. The simulations indicate that the (2
x 1) superstructure is due to an L1(0) ordered phase in regions where
the tetragonal distortion of the L1(0) phase with respect to the cubic
substrate can alleviate stress. It is argued that this dislocation-in
duced ordering can immobilize dislocations.