Determination of shear stiffness based on thermal noise analysis in atomic force microscopy: Passive overtone microscopy

In torsional overtone microscopy, a dynamic atomic force microscopy technique, antisymmetric vibration modes of a v-shaped cantilever are used to investigate the elastic properties of the tip-sample contact. In order to minimize the vibration amplitude, no external excitation is added in the passive overtone mode. In this mode, the thermomechanical noise of the surface coupled cantilever at room temperature is analyzed. This allows the shear stiffness of the tip-sample contact to be extracted from the analysis of the power spectrum of the photodiode signal. The load dependence of the first torsional vibration on silicon, aluminum, and cadmium telluride surfaces is compared with a theoretical mechanical model.