Magnetic Activation

By placing a magnetic particle directly behind the AFM tip  we are able to apply forces to the probe via a magnetic field. It is then possible to vibrate the probe well below resonance in an oscillating magnetic field in order to directly measure the force gradient of the tip-sample interaction. We have extended this method of activation to make the resonance method of FM detection possible. This is better suited for high-resolution imaging in the liquid environment compared to the off resonance method because faster imaging is possible and this reduces problems associated with thermal drift. Although previously only used in ultra-high vacuum, by implementing the magnetically activated dynamic (MAD) mode for driving the oscillation we have been able to remove unwanted resonances in the rest of our liquid cell, which can occur with alternative driving methods. This is illustrated in Figures (1) and (2).
Magnetic ActivationFigure 1: Schematic illustrating that activation of a cantilever via MAD mode.
Magnet on TipFigure 2: Scanning electron microscope (SEM) image of a magentic particle attached to the back of an AFM cantilever.

  1. A novel force microscope and point contact probe, Jarvis, S. P., Oral, A., Weihs, T. P., and Pethica, J. B., Review of Scientific Instruments, 64, 3515-3520, (1993). [PDF]