COMPACT STAND-ALONE ATOMIC-FORCE MICROSCOPE

A stand-alone atomic force microscope (AFM) featuring large scan, friction measurement, atomic resolution, and liquid operation, has been developed. Cantilever displacements are measured using the optical beam deflection method. The laser diode and focusing lens are positioned inside the piezo tube and the cantilever at the end of the piezo tube. Because the laser beam stays on the cantilever during scanning, the scan range is solely determined by the characteristics of the piezo tube. In our case 30 x 30 x 9.5 mum3 (xyz). The optical beam deflection detection method allows simultaneous measurement of height displacements and torsion (induced by lateral forces) of the cantilever. AFM images of dried lymphocytes reveal features in the torsion images, which are only faintly visible in the normal height images. A new way of detecting the nonlinear behavior of the piezo tube is described. With this information the piezo scan is linearized. The nonlinearity in a 30-mum scan is reduced from 40% to about 1%, as is illustrated with images of a compact disk. The stand-alone AFM can be combined with a (confocal) inverted microscope, yielding a versatile setup for biological applications.