COMPACT STAND-ALONE ATOMIC-FORCE MICROSCOPE

A stand-alone atomic force microscope (AFM) featuring large scan, fric tion measurement, atomic resolution, and liquid operation, has been de veloped. Cantilever displacements are measured using the optical beam deflection method. The laser diode and focusing lens are positioned in side the piezo tube and the cantilever at the end of the piezo tube. B ecause the laser beam stays on the cantilever during scanning, the sca n 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 det ection 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 detecti ng the nonlinear behavior of the piezo tube is described. With this in formation the piezo scan is linearized. The nonlinearity in a 30-mum s can 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 applica tions.