F+G+O

Atomic-scale buckling of a Si layer.—Proof for the presence of Si atoms at the surface comes from the surface-sensitive Si 2⁢𝑝 photoelectron spectrum obtained at normal emission, shown in Fig. 2(a). The sharpness of the features is a clear indication of Si atoms in well-defined chemical environments different from those at the Si⁡(111)-(7 ×7) surface. As quantified by a peak fitting, the Si 2⁢𝑝 doublet consists of three components labeled 𝛼, 𝛽, and 𝛾, which are related to three different chemical environments of the Si ad-atoms, denoted Si𝐴, Si𝐵, and Si𝐶. Relative to the main peaks which have major contributions from the 𝛽 chemical state, 𝛾 and 𝛼 are shifted 140 ±5  meV and 260 ±5  meV, respectively. The respective areal weights for peaks 𝛼, 𝛽, and 𝛾 are 0.32 ±0.05, 0.55 ±0.05 and 0.13 ±0.05. The single in-plane position of a Si honeycomb structure matching the ratio between atomic sites derived from the spectrum within the error bars is

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