A CONSTANT COMPLIANCE FORCE MODULATION TECHNIQUE FOR SCANNING FORCE MICROSCOPY (SFM) IMAGING OF POLYMER SURFACE ELASTICITY

A new method of force modulation scanning force microscopy (SFM) imagi ng based on a constant compliance feedback loop is presented, The feed back adjusts the loading force applied by the SFM tip to the surface i n order to maintain a constant compliance beneath the tip. The new met hod, constant compliance force modulation (CCFM), has the advantage of being able to quantify the loading force exerted by the tip onto the sample surface and thus to estimate the elastic modulus of the materia l probed by the SFM tip. Once the elastic modulus of one region is kno wn, the elastic moduli of other surface regions can be estimated from the spatial map of loading forces using the Hertz model of deformation . Force vs. displacement measurements made on one surface locality cou ld also be used to estimate the local modulus. Several model surfaces, including a rubber-toughened epoxy polymer blend which showed clearly resolved compliant rubber phases within the harder epoxy matrix, were analyzed with the CCFM technique to illustrate the method's applicati on.