A pi-bonded-chain-stacking-fault (pi-SF) model is proposed for the Si(
lll)4x1-In surface structure. The model incorporates 4x1 Si(111) subst
rate reconstruction consisting of the sixfold Si rings in the faulted-
unfaulted sequence connected through fivefold and sevenfold Si rings.
Indium atoms (0.75 ML) reside above sixfold and fivefold Si rings whil
e sevenfold Si rings form pi-bonded chains between In ridges.