Imaging biological macromolecules by STM: quantitative interpretation of topographs

Methods are discussed which permit the calibration of x-, y-, z-sensitivities, non-linearities and frequency responses of the scanning device of a scanning tunneling microscope (STM) either by interferometry or directly from STM topographs. A technique is presented to measure the frequency response of the complete STM feedback unit and to derive a maximum speed in z direction which allows one to estimate the maximum scanning speed still permitting one to track surface corrugations. The signal transfer characteristics of a STM are evaluated in a direct comparison with high resolution transmission electron microscopy on an identical specimen area. The various effects of contaminants between tip and specimen and the finite tip radius receive special attention.