Streak contrast in field-ion micrographs

Abstract

Asymmetric field-ion microscope specimens have stable end-forms which are themselves asymmetric and cannot be field-evaporated to give an undistorted field-ion image. On such specimens surface steps may persist during field evaporation and give rise to image streaking through field-focusing of the ion beams from the step region. Persistent steps on asymmetric tips arise from prior cold work or deformation during the tip preparation process. Faulty electropolishing, which is responsible for the tip asymmetry, is thus the primary cause of streak contrast.