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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.
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 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 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.
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Overall, the aforementioned characterization methods of tips can be categorized into three major classes. [76] They are as follows: Imaging tip using microscopy is used to take image of tip with microscopy, except scanning probe microscopy (SPM) e.g. scanning tunnelling microscopy (STM), atomic force microscopy (AFM) are reported. [70] [71] [72]
Kelvin probe force microscopy (KPFM), also known as surface potential microscopy, is a noncontact variant of atomic force microscopy (AFM). [ 1 ] [ 2 ] [ 3 ] By raster scanning in the x,y plane the work function of the sample can be locally mapped for correlation with sample features.
nc-AFM was the first form of AFM to achieve true atomic resolution images, rather than averaging over multiple contacts, both on non-reactive and reactive surfaces. [32] nc-AFM was the first form of microscopy to achieve subatomic resolution images, initially on tip atoms [42] and later on single iron adatoms on copper.