A -bonded-chain-stacking-fault (-SF͒ model is proposed for the Si͑111͒4ϫ1-In surface structure. The model incorporates 4ϫ1 Si͑111͒ substrate reconstruction consisting of the sixfold Si rings in the faultedunfaulted sequence connected through fivefold and sevenfold Si rings. Indium atoms ͑0.75 ML͒ reside above sixfold and fivefold Si rings while sevenfold Si rings form -bonded chains between In ridges.

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Atomic hydrogen interaction with the Si͑111͒4ϫ1-In surface phase was studied using low-energy electron diffraction, Auger electron spectroscopy, and scanning tunneling microscopy. Upon hydrogen action mostly Si-In outer bonds are broken and are replaced by Si-H, and In is freed to form islands without Si movement. It was found that the underlying atomic layer of a substrate of the Si͑111͒4ϫ1-In surface phase has a reconstruction with the same periodicity as the In layer. A structural model of this substrate reconstruction is proposed based on the recently proposed extended Pandey chain model for the Si͑111͒3ϫ1 Ag-and alkalimetals-induced substrate reconstruction.