Simultaneous observation of surface topography and elasticity at atomic scale by multifrequency frequency modulation atomic force microscopy

Abstract

The authors integrated the frequency modulation (FM) technique into multifrequency atomic force microscopy (AFM). Based on theoretical considerations, simultaneous excitation of the cantilever oscillation at the first and second flexural modes allows us to acquire the surface topography and surface elasticity simultaneously. The authors performed multifrequency FM-AFM observation using a tungsten-coated silicon cantilever on a Ge(001) surface exhibiting a dimer structure at room temperature. The topography and the elasticity of the surface were successfully obtained at the atomic scale. The authors found that the dimer atoms around a missing dimer defect have higher elasticity than the other dimer atoms. This suggests that stiffer atomic bonding of the dimer atoms occurred as a result of the additional tensile strain field from the defect. Therefore, the multifrequency FM-AFM described in the present study is expected to be useful for the investigation of the surface elasticity at the atomic scale.