Quantitative determination of atomic buckling of silicene by atomic force microscopy

Most 2D materials possess a prominent atomic buckling, in contrast to their flat graphene counterpart. Upon epitaxial growth, complex restructuring, defects, and grain boundaries coexist on the surface with variable corrugations complicating an accurate determination using conventional diffraction techniques. To address this, we use atomic force microscopy with CO-terminated tips and numerical calculations to unveil the structure, local symmetry, and defects of a prototypical buckled 2D system, e.g., silicene on Ag(111). Based on site-dependent force spectroscopy, we provide a quantitative determination of the buckling magnitude of these phases with subangstrom precision. This method offers opportunities to study the interplay between structural and electronic properties in other emerging buckled systems with unprecedented resolution.The atomic buckling in 2D textquotedblleftXenestextquotedblright (such as silicene) fosters a plethora of exotic electronic properties such as a quantum spin Hall effect and could be engineered by external strain. Quantifying the buckling magnitude with subangstrom precision is, however, challenging, since epitaxially grown 2D layers exhibit complex restructurings coexisting on the surface. Here, we characterize using low-temperature (5 K) atomic force microscopy (AFM) with CO-terminated tips assisted by density functional theory (DFT) the structure and local symmetry of each prototypical silicene phase on Ag(111) as well as extended defects. Using force spectroscopy, we directly quantify the atomic buckling of these phases within 0.1-r A precision, obtaining corrugations in the 0.8- to 1.1-r A range. The derived band structures further confirm the absence of Dirac cones in any of the silicene phases due to the strong Ag-Si hybridization. Our method paves the way for future atomic-scale analysis of the interplay between structural and electronic properties in other emerging 2D Xenes.