In mapping the specimen surface by the STM, the surface topography is, in principle, convoluted with the profile of the tunneling tip. Only with a delta-shaped tip profile does the information measured by the STM agree with the true surface topography. To obtain a faithful mapping of the specimen surface by the STM, therefore, we must aim at manufacturing a tunneling tip that is as close to the delta shape as possible. This aim is almost always achieved at atomically smooth specimen surfaces for every tunneling tip, irrespective of its mode of manufacture. However, to examine specimen surfaces with large local height differences, of the kind occuring at grain boundaries of polycrystalline materials, for instance, special care must be devoted to the tip preparation. The objective is then the macroscopic generation of ultra-thin tunneling tips. Here, the question arises of the mechanical (in)stability of these ultra-thin tips and any consequent disturbances on the mapping, as the lowest resonant frequencies of such tip types may lie in a region where they can be exited by the scan motion of the STM. In the present paper, quantitative answers are given to these questions for the first time. We set up a 3D finite-element model of a real ultra-thin tunneling tip, performed a modal analysis to get information about possible modes of oscillation and their resonant frequencies, and calculated the harmonic response to estimate the effect of these oscillations on the mapping.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics