Understanding imaging modes in the helium ion microscope

Recent investigations are gaining us a better understanding of the nature of the beam-sample interactions in the helium ion microscope and what they mean for the image information provided. In secondary electron (SE) imaging, for example, the surface sensitivity is attributed to the low SE-II fraction. Voltage contrast imaging shows the ability to see both buried structures and to probe the conductance to ground of surface contacts. It is found, however, that the prominence of these two types of contrast varies oppositely with beam energy, yielding information about the nature of the interactions that gives rise to them. Transmission ion imaging can yield information about material density, atomic number, grain structure, and electronic structure. It is possible to capture the top-side SE signal, bright field signal, and dark field signal from a given sample simultaneously. The detection of diffraction contrast is under investigation.