ENERGY-LOSS IMAGE-FORMATION IN SCANNING-TRANSMISSION ION MICROSCOPY

One contrast parameter which can be used to form images in scanning transmission ion microscopy (STIM) is the energy loss of individual transmitted ions. This paper explores three techniques which can be used if energies of several ions are measured at each incident beam location. The techniques are energy averaging, summing of events within a preset energy window, and median filtering of energy values. Median filtering is the method of choice to reduce noise and to sharpen certain features. Examples of line scans of a sharp edge and of a ramp-like knife edge are presented. With median filtering localization of features to within 10% of beam size is demonstrated. A mechanism for identifying and mapping unresolved spatial structure is proposed. The other techniques are shown to be better tools for beam-profile diagnostics.