A characterizer for determining the shape of a probe tip for an atomic force microscope and methods of fabricating and using the characterizer. The characterizer includes a micromachined crystalline structure with opposed edges separated by a width suitable for characterizing a dimension of the probe tip. At least one of the opposed edges overhangs an undercut region of the micromachined crystalline structure by an overhang distance that is greater than one third of the width. The probe tip is scanned across the edges of the characterizer for shape determination. The characterizer is formed by serially deep reactive ion etching and anisotropic etching (100) single crystal silicon. The opposed edges may be oxidation sharpened for use in profiling a bottom surface of the probe tip.