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A multifunctional scanning force microscope for biological applications

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Wiegräbe, W., Knapp, H., Eberhart, H., Gatz, R., Hartmann, T., Heim, M., et al. (1995). A multifunctional scanning force microscope for biological applications. Review of Scientific Instruments, 66(N8), 4124-4129.

Many questions to be tackled by scanning force microscopy (SFM) require the comparison of several nontopographic signals, like electrical conductance, friction, and elasticity. Especially in biology, which is our main field of interest, most of these signals are superimposed. To disentangle them, it is advantageous to measure them simultaneously. Because all known SFMs; home-built or commercial, allow either no or only very few such signals to be measured simultaneously, we developed the new multimode SFM. Moreover, we have applied new modes which measure breakdown voltages of thin insulators and static friction. The presented SFM is designed to investigate such properties of biological material, simultaneously. In addition, the instrument uses some new features, not used elsewhere: The elasticity signal is utilized for a reverse feedback during contact loss which makes imaging with very small forces practicable. The elasticity signal is further used to perform a very smooth approach, to prevent damage to tip and sample. Features like a movable sample stage, light microscopic access, and enhanced computer control using a Macintosh IIfx are described. The liquid cell is designed such that no seal is necessary which would disturb the scanner movement. As an application requiring these features, results obtained on a DPPC Langmuir–Blodgett film in the two phase coexistence region on a partly conductive support are shown. One can distinguish areas in the liquid expanded phase from areas in the liquid condensed phase using the information contained in the topographic, elastic, frictional, and conductivity signals. Correct interpretation was only possible using the simultaneously collected different signals. ©1995 American Institute of Physics.