SummaryQuartz tuning forks are being increasingly employed as sensors in non-contact atomic force microscopy especially in the “qPlus” design. In this study a new and easily applicable setup has been used to determine the static spring constant at several positions along the prong of the tuning fork. The results show a significant deviation from values calculated with the beam formula. In order to understand this discrepancy the complete sensor set-up has been digitally rebuilt and analyzed by using finite element method simulations. These simulations provide a detailed view of the strain/stress distribution inside the tuning fork. The simulations show quantitative agreement with the beam formula if the beam origin is shifted to the position of zero stress onset inside the tuning fork base and torsional effects are also included. We further found significant discrepancies between experimental calibration values and predictions from the shifted beam formula, which are related to a large variance in tip misalignment during the tuning fork assembling process.

In the ongoing effort to miniaturize the functional elements in electronic devices, molecular dimensions are currently approached. Scanning probe microscopy has demonstrated fascinating capabilities for bottom-up fabrication of atomically defined prototype structures. However, little is known about the underlying interactions during the manipulation of functional organic molecules with a scanning probe tip. Here, we demonstrate the use of noncontact atomic force microscopy at cryogenic temperatures for the lateral displacement of the organic prototype molecule 3,4,9,10-perylene-tetracarboxylicacid-dianhydride on the Ag(111) surface. During repeated manipulation cycles, we measure the precise lateral and vertical tip-molecule force profiles as well as the energy dissipation before and during the manipulation process. The jump of the molecule to an adjacent equivalent substrate lattice site occurs in the regime of repulsive lateral forces, thus constituting a "pushing" mechanism.

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