Silicene monolayers grown on Ag(111) surfaces demonstrate a band gap that istunable by oxygen adatoms from semimetallic to semiconducting type. By usinglow-temperature scanning tunneling microscopy, it is found that the adsorptionconfigurations and amounts of oxygen adatoms on the silicene surface arecritical for band-gap engineering, which is dominated by different buckledstructures in R13xR13, 4x4, and 2R3x2R3 silicene layers. The Si-O-Si bonds arethe most energy-favored species formed on R13xR13, 4x4, and 2R3x2R3 structuresunder oxidation, which is verified by in-situ Raman spectroscopy as well asfirst-principles calculations. The silicene monolayers retain their structureswhen fully covered by oxygen adatoms. Our work demonstrates the feasibility oftuning the band gap of silicene with oxygen adatoms, which, in turn, expandsthe base of available two-dimensional electronic materials for devices withproperties that is hardly achieved with graphene oxide.
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