We have studied a Si(111)2 x 2-Fe surface exposed to nitric oxide at room temperature with Auger electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM). The surface local structure of Si(111)2 X 2-Fe has been modeled to be similar to that of Si(111)7 X 7; both structures have Si adatom and Si first-layer restatom, but the restatom in the former surface bonds to Fe atoms. It is known that NO molecules dissociatively adsorb on Si(111)7 x 7 surface, especially atop adatoms. Before the exposure to the Si(111)2 x 2-Fe surface, STM images showed 2 X 2 islands on the 2 X 2 terrace. After the exposure, the 2 X 2 islands were eroded at the island edge while the 2 x 2 terrace was stable against nitric oxide. We ascribed the inert property of the 2 x 2 terrace, and the reactive property of the 2 x 2 island edges and the 7 x 7 terrace, primarily to the Si restatom with different neighbor atoms. (C) 2004 Elsevier B.V. All rights reserved.