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nanotimes News in Brief

12-03 :: March/April 2012

Atomic Force Microscopy // Researchers Validate Simplified Lateral Force Calibration Technique for AFM

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esearchers from the NIST Center for Nanoscale Science and Technology and the NIST Material

Measurement Laboratory (US) have demonstrated that a simpler technique for calibrating lateral sensiti- vity in an atomic force microscope (AFM) agrees with an earlier method developed at NIST to within 5%. The equivalence of these two independent methods represents an important step towards traceable accu- racy in lateral force microscopy and will allow scien- tists to better understand the atomic-scale origins of friction across a wide range of materials. The NIST “HammerHead” (HH) method relies on precise positioning of the arms of a specially-fabricated, tee- shaped cantilever over well-defined alignment marks in a surface; a torque is applied at different locations on the cantilever arm by pressing it against a small sphere attached to the edge of the surface. The ratio of the change in the normal (vertical) signal to the lateral signal can be used to calibrate sensitivity and extract friction forces corresponding to the lateral signals measured during an experiment. The new “Diamagnetic Lateral Force Calibrator” (D-LFC) method, developed at Brown University, requires fewer independent measurements. While the D- LFC method is preferable for most circumstances, because it uses fewer parameters and therefore has greater precision, the HH method can be advan- tageous if contact between the probe tip and the calibration surface must be avoided.

© Based on Material by NIST, USA

In the diamagnetic lateral force calibration method, an AFM cantilever (shown here is a NIST HammerHead can- tilever) presses against the surface of a piece of graphite that levitates in a magnetic field. When the magnetic field is moved horizontally in the AFM, friction between the AFM tip and graphite surface causes the cantilever to twi- st. This twist leads to a change in the lateral signal in the AFM that is used to calibrate friction directly, based on the spring constant of the graphite in the magnetic field. © NIST

Sarice S. Barkley, Zhao Deng, Richard S. Gates, Mark G. Reitsma, and Rachel J. Cannara: Quantitative comparison of two independent lateral force calibration techniques for the atomic force microscope, In: Review of Scientific In- struments, Vol. 83(2012), Issue 2, February 2012, Article 023707, DOI: 10.1063/1.3685243 [6 pages]: http://dx.doi.org/10.1063/1.3685243