MORPHOLOGICAL RESTORATION OF ATOMIC-FORCE MICROSCOPY IMAGES

Atomic force microscopy (AFM) images of biomolecules, and other struct ures similar in size, are enlarged because of the finite size of the p robe tip. We present a method based on morphological image processing that allows one to analyze and correct the enlargement. Morphological restoration is ideal in some regions, giving the exact sample surface. In other regions, it gives a surface with improved resolution. The me thod uses measured, realistic tip shapes, not idealized functions. Tip surfaces are generated by restoring images of known gold spheres havi ng diameters of about 10 nm. We generate tip images of carbon and Si3N 4 probes and find good correlation with scanning electron microscopy. Generated tip surfaces are used to restore images of unknown objects t o produce images at enhanced resolution. Diameters of contours at cons tant elevation are changed by as much as 25%. In addition to improving resolution, morphological restoration also corrects distortions due t o imaging with asymmetrical tips. The approach uses methods. and softw are readily available to the atomic force microscopist.