Design, fabrication, and characterization of polymer-based cantilever probes for atomic force microscopes

Micromachined polymer-based cantilever probes have been proposed for atomic force microscopes (AFMs) in order to enable noninvasive, rapid high-resolution topography imaging and mechanical measurements of live biological samples. Polymer-based probes developed to date still consist of a rather stiff cantilever with a relatively high spring constant prone to causing deformation and/or distortion of biological sample surfaces during scanning and a rather blunt tip that limits high-resolution topography imaging. This paper reports the design, fabrication, and characterization of soft polymer-based AFM probes. The proposed probe design and fabrication process utilize an acrylic polymer as the structural material, sequential depositions of low and high viscosity acrylic polymers, and a properly patterned optical reflection coating in order to achieve low effective spring constants (less than 0.01 N/m), relatively small tip radii (as small as 40 nm), and relatively low strain gradient (around 10^-4/μm). The fabricated polymer AFM probes are calibrated and characterized through experiments and used to obtain AFM height and deflection images of a live mammalian cell in liquid. Experimental results show that the above design specifications have been successfully achieved.