β Scribed by Gauthier-Manuel, B.; Garnier, L.
No coin nor oath required. For personal study only.
Classical atomic force microscopes use a soft cantilever spring to convert the interaction between a tip and a surface into a displacement. This leads to indirect force measurement and instability in the case of attractive forces. We have developed a new kind of force sensor to overcome these limitations. The principle is to place a tip glued on a small magnet in levitation in a magnetic Γeld. A servo-loop ensures the stability of the equilibrium in the vertical direction and allows the measurement of forces. It is monitored by an optical sensor that measures continuously the actual position of the tip with a sensitivity of 10 pm. With such a device it is possible to obtain the van der Waals attraction up to the molecular contact without jump. A digital signal processing board stops the approach of the tip just before contact to prevent any deterioration of the surface during the measurement. This allows images of soft and brittle surfaces, such as a microΓltration membrane.
π SIMILAR VOLUMES
We use the Meissner effect of su~rconductors to calculate the levitation forces acting on a magnet placed above a superconducting ring. We discuss the applications of our model caiculation to estimates of the interaction forces in macro engineering designs, and of the micro surface roughness effect