The description of TappingMode AFM

TappingMode AFM, the most commonly used of all AFM modes, is a patented technique (Veeco Instruments) that maps topography by lightly tapping the surface with an oscillating probe tip. The cantilever's oscillation amplitude changes with sample surface topography, and the topography image is obtained by monitoring these changes and closing the z feedback loop to minimize them. TappingMode has become an important AFM technique, as it overcomes some of the limitations of both contact and non-contact AFM. By eliminating lateral forces that can damage soft samples and reduce image resolution, TappingMode allows routine imaging of samples once considered impossible to image with AFM, especially in contact mode.

Another major advantage of TappingMode is related to limitations that can arise due to the thin layer of liquid that forms on most sample surfaces in an ambient imaging environment, i.e., in air or some other gas. The amplitude of the cantilever oscillation in TappingMode is typically on the order of a few 10's of nanometers, which ensures that the tip does not get stuck in this liquid layer. The amplitude used in non-contact AFM is much smaller, as different forces are being measured. As a result, the non-contact tip often gets stuck in the liquid layer unless the scan is performed at a very slow speed. In general, TappingMode is much more effective than non-contact AFM for imaging larger scan sizes that may include large variations in sample topography. TappingMode can be performed in gases, liquids, and some vacuum environments.


Examples (click to enlarge)

Surface of the integrated circuit. Scan field 70x70um.

Erytrocyte (red blood cell). Scan field 9x9um.

Human hair. Scan field 52x80um.

Wing of the moth. Scan field 5x5um.

TGT1 test surface which is used to measure the scanning tip. Scan field 10x10um.

Surface of the bottom side of a DVD with visible imprinted pits and lands coming from another DVD (without technological cover). Scan field 20x20um.

Surface of memory cells in EPROM chip. Scan field 30x30um.

Edible salt (NaCl) crystals. Scan field 60x60um.

Liquid crystal surface. Scan field 1x1um.

Surface of the polytetrafluoroethylene covering. Scan field 50x50um.

Test structures in integrated circuit. Scan field 80x80um.

Edge of unused lancet. Scan field 7,3x8,7um.


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