A varying set-point AFM scanning method for simultaneous measurement of sample topography and elasticity

Atomic force microscopy (AFM) is a powerful tool for measuring the topography and mechanical properties in nano-scale. The topography of the sample can be achieved by contact mode scanning, while the mechanical properties can be investigated with the help of force curve. However the force curve characterizes the mechanical properties of the sample at a certain point. In many cases, it is important to get the elasticity distribution of the entire surface, which means a huge amount of points need to be selected for measuring force curves. It is obvious that this operation is very time-consuming. As generally known, AFM force curve represents the relationship between the piezo scanner displacement in z-axis and the deflection of the cantilever. Thus the topography images consisted of the vertical displacements of the scanner and the deflection images can be combined to investigate some features of the force curve. The deflection set-point is set to be a time-varying value for increasing the range of scanning data. It is assumed that the elasticity is continuous in a small neighborhood of a scanning point, then a Kalman filter is utilized for conducting data fusion in the neighborhood and estimating the elasticity of the sample.