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The scanning tip, depending upon the operation mode, is usually a pulled or stretched optical fiber coated with metal except at the tip or just a standard AFM cantilever with a hole in the center of the pyramidal tip. Standard optical detectors, such as avalanche photodiode, photomultiplier tube (PMT) or CCD, can be used.
The AFM tips are fabricated using silicon micro machining and the precise positioning of the microSQUID loop is achieved using electron beam lithography. [33] The additional attachment of a quantum dot to the tip apex of a conductive probe enables surface potential imaging with high lateral resolution, scanning quantum dot microscopy. [34]
The latter geometry further requires a lateral centering of the two particles, which can be either achieved with an optical microscope or an AFM scan. The results obtained in these two different geometries can be related with the Derjaguin approximation. The force measurements rely on an accurate value of the spring constant of the cantilever.
Figure 1: Photograph of an AFM system which can be used for chemical force microscopy. In materials science, chemical force microscopy (CFM) is a variation of atomic force microscopy (AFM) which has become a versatile tool for characterization of materials surfaces.
In Pin Point PFM, the AFM tip does not contact the surface. The tip is halted at a height at which a predefined force threshold (a threshold at which piezoelectric response is optimal) is reached. At this height, the piezoelectric response is recorded before moving to the next point. In Pin Point mode, tip wear off is reduced significantly.
For example, carbon nanotube tips in conjunction with AFM provides an excellent tool for surface characterization in the nanometer realm. CNT tips are also used in tapping-mode Scanning Force Microscopy (SFM), which is a technique where a tip taps a surface by a cantilever driven near resonant frequency of the cantilever.
Excitation and detection scheme in bimodal AFM. The cantilever is excited at its first two eigenmodes with frequencies and . Upon interaction with the sample, the components of the tip's response are processed. The topography is obtained by keeping = constant. In a bimodal AM-FM configuration, two feedback loops act on the 2nd mode.
Chemical compositional mapping AFM-IR can also be used to perform chemical imaging or compositional mapping with spatial resolution down to ~10-20 nm, [18] limited only by the radius of the AFM tip. In this case, the tuneable infrared source emits a single wavelength, corresponding to a specific molecular resonance, i.e. a specific infrared ...