Atomic force microscopy (AFM) evolved from the observation of the effects of mechanical contact during scanning tunnelling microscopy imaging. Thus, even from its first inception, tribology and atomic force microscopy have been inextricably linked. Whilst not all tribological phenomena have been intentional or welcomed in AFM measurements there has also been a concerted effort to apply AFM to the field of nanotribology. Due to its highly localised measurement ability, the microscope can be applied to a variety of tribological processes which are too laterally specific to be investigated by Surface Forces Apparatus or nano-indentation devices.

At the core of this lies the microscope's ability to form single asperity contacts a few nanometres across due to the very sharp probe tip, shown in the figure below. However, in order to be usefully applied, AFM measurements must be quantified and the identity of the tip and sample material must be known. These features are not trivial due to the design and environment of most microscopes and the scale of the measurements where even minute traces of contamination can have noticeable impact on quantitative measurements.

Figure (a) SEM micrograph of a typical microfabricated silicon cantilever showing the basic measurement technique employed in AFM. (b) SEM micrograph of the sharp tip of a silicon sensor with ultrasharp carbon nanotube tip attached.

In most standard instruments forces are not applied directly. Instead displacements are usually applied to the sample and forces are often calculated from the multiplication of roughly calibrated displacements and the arbitrarily known spring constant of the force sensor. The use of such measurements has lead to widespread scepticism of the application of AFM to tribological problems. However, various calibration methods with both a theoretical and experimental basis can be employed and new experimental techniques and modifications have been implemented which greatly improve the credibility of the instrument as a measurement device for tribological processes.


Our linked publications:

S. P. Jarvis, H. Yamada, K. Kobayashi, A. Toda and H. Tokumoto, "Normal and Lateral Force Investigation using Magnetically Activated Force Sensors", Appl. Surf. Sci., 157, 314 (2000).
S. P. Jarvis and H. Tokumoto "Measurement and interpretation of forces in the atomic force microscope", Invited Review, Probe Microscopy 1, 65 (1997).
S-.I. Yamamoto, H. Yamada, S. P. Jarvis, M. Motomatsu and H. Tokumoto "Detection of similar elastic properties using a magnetic force controlled AFM", Thin Films - Stresses and Mechanical Properties VI, Mater. Res. Soc. Proc. 436, 385 (1997).
S. P. Jarvis, H. Yamada, S.-I. Yamamoto and H. Tokumoto "A new force controlled atomic force microscope for use in ultrahigh vacuum", Rev. Sci. Instrum. 67, 2281 (1996).
S. P. Jarvis, T. P. Weihs, A. Oral and J. B. Pethica, "Mechanics of contacts at less than 100·scale: indentation and AFM", Thin Films - Stresses and mechanical Properties IV, Mater. Res. Soc. Proc. 308 (1993) 127.
T. P. Weihs, Z. Nawaz, S. P. Jarvis and J. B. Pethica, "Limits of imaging resolution for atomic force microscopy of molecules" Appl. Phys. Lett., 59 (1991) 3536.