MORPHOLOGICAL RESTORATION OF ATOMIC-FORCE MICROSCOPY IMAGES

Atomic force microscopy (AFM) images of biomolecules, and other structures similar in size, are enlarged because of the finite size of the probe 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 method uses measured, realistic tip shapes, not idealized functions. Tip surfaces are generated by restoring images of known gold spheres having diameters of about 10 nm. We generate tip images of carbon and Si3N4 probes and find good correlation with scanning electron microscopy. Generated tip surfaces are used to restore images of unknown objects to produce images at enhanced resolution. Diameters of contours at constant elevation are changed by as much as 25%. In addition to improving resolution, morphological restoration also corrects distortions due to imaging with asymmetrical tips. The approach uses methods. and software readily available to the atomic force microscopist.