Atom Tracking AT 5

Dynamically track local maxima or minima and compensate for drift in 3D

Atom tracking module
Atom tracking module performing drift compensation
Image with atom tracking tip motion
Example image showing the circular path of the tip over an atom (stm simulator image)

The Atom tracking module adds atom tracking capability to the Nanonis Base Package. It is designed to track topographical features (not only atoms) dynamically and can therefore measure and compensate for thermal drift and sample tilt. A fully automated procedure automatically calculates drift velocity and sample tilt in both X and Y-directions as well as drift in Z-direction and compensates for these. This module is of particular interest when the tip position has to follow a local extremum (e.g. an atom or molecule, maximum or minimum) between point-spectroscopy or when scanning a small scan area where drift is highly noticeable.

Combined with custom spectroscopy scripts the atom tracking module is a powerful tool. It ensures that measurement sequences lasting several hours can be performed without losses in postitioning accuracy. Its tight integration with the Nanonis software simplifies this otherwise cumbersome operation significantly.

The atom tracking module works according to the following principle: by applying a sinusoidal modulation to the x and y-coordinate, the tip defines a rotational plane. The z-position of the tip is then demodulated with two lock-in detectors using this modulation as a reference, leading to the slope along x and y directions, that is ∂z/∂x and ∂z/∂y. These signals are then used as the input for the I-controller feedback loop, which adjust the tip x/y position in order to minimize the slopes, i.e. the tilt of the plane in which the tip rotates. In this way, the tip x/y position is locked on top of a local extremum which can be an atom, molecule, island, pit or any other local feature


  • lock onto a feature of any size and track it
  • measure drift and automatically compensate for it
  • measure the local sample tilt and compensate for it
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Atom tracking module with tip path display
Atom tracking module with display of the tip path during tracking
Atom tracking module with slope display
Atom tracking module with display of the rotational plane slope
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Atom Manipulation with Nanonis SPM Controller
Atom manipulation often attracts the interest of researchers, not only for observing artificial patterns on the surface, but also since it allows preparing ideal “samples” on surfaces, designed for a specific measurement. At the same time, however, it often requires a complete custom made scanning probe controller. Although the first systematic atom manipulation was demonstrated in 1990s, it is still challenging for mostresearchers. This application notes shows how the fully-digital Nanonis SPM controller with its LabVIEW Programming Interface can significantly reduce the technical challenges and simplify the manipulation process.
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Friction force microscopy (FFM) is a powerful tool which allows us to study the origin of friction in single asperity contacts. The observation of atomic stick-slip and its variation with load, during the sliding of tip against another solid surface provides detailed information about the dissipation mechanisms. Statistical averaging of repeated measurements with good control over experimental parameters is of crucial importance for reliable FFM measurements.
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Feenstra Type of Spectroscopy: Making use of the Programming Interface
Spectroscopic measurements in STM are an important tool for the investigation of the electronic states at surfaces. When combined with the variable tip-sample separation technique this type of spectroscopy leads to high dynamic range, 5 to 6 orders of magnitude, in the measured current and conductance even on the semiconductor surfaces with low surface state density.
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Improved Atomic Scale Contrast via Bimodal DFM: Dual OC4
Frequency-modulation atomic force microscopy (FM-AFM) is an efficient and already widely spread technique to obtain atomically resolved images of insulating or metallic surfaces. Typically, FM-AFM is based on scanning a sharp tip of a macroscopic cantilever over the surface, where the tip-surface distance is usually controlled by the frequency shit (f1) of the first normal resonant mode (f1) of the cantilever. The atomic-scale contrast arises from short range forces; e.g. covalent or ionic bonds, thus the detection sensitivity of the FM-AFMcan be improved by using small tip oscillation amplitudes comparable to the decay length of the short-range forces, ~ 0.1 nm. A lot of efforts are put in this direction in the FM-AFMfield, mainly based on the excitation of a tuning fork sensor or higher flexural modes of cantilevers characterized by largerstiffness.
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Mapping the Orbital Structure of Impurity Bound States in a Superconductor
Superconductivity is a low-temperature phenomenon caused by the pairing of electrons via interactions me-diated by the environment. A signature of supercon-ductivity is that no single electron can be injected at low energies because the only possible states are the ones corresponding to pairs of electrons. Hence, an absolute gap in the density of states (DOS) is a finger-print of conventional superconductors. In s-wave su-perconductors such as lead the paired electrons (i.e. the Cooper pairs) have opposite spin. An external magnetic field forces the electron spins to align, there-by breaking the pairing and destroying superconductivity.
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