AFM image based pattern detection for adaptive drift compensation and positioning at the nanometer scale

The key function of AFM is to control the position of the probe according to imaging operation modes. These imaging modes yield multiple channels of data representing various probe responses to the same sample pattern. An algorithm based on the spatial and temporal correlation of the multiple channel data, corresponding to the same surface patterns, was developed to derive the pattern position with sub-pixel resolution in real time. This precise measurement of the pattern location serves as an input to an estimator of the drift velocity. An auxiliary position control was applied to compensate the drift between the probe tip and the sample. This pattern location measurement has higher noise rejection than any individual channel of the image, providing a reference location for drift compensation. Experimental data with sub nanometer drift control and nanoasperity measurements based on the auxiliary positioning are presented.