Contrast modes in a 3D ion transmission approach at keV energies

Scanning transmission imaging in the helium ion microscope using a microchannel plate with a delay line detector

A detection system based on a microchannel plate with a delay line readout structure has been developed to perform scanning transmission ion microscopy (STIM) in the helium ion microscope (HIM). This system is an improvement over other existing approaches since it combines the information of the scanning beam position on the sample with the position (scattering angle) and time of the transmission events. Various imaging modes, such as bright field and dark field or the direct image of the transmitted signal, can be created by post-processing the collected STIM data. Furthermore, the detector has high spatial and temporal resolution, is sensitive to both ions and neutral particles over a wide energy range, and shows robustness against ion beam-induced damage. A special in-vacuum movable support gives the possibility of moving the detector vertically, placing the detector closer to the sample for the detection of high-angle scattering events, or moving it down to increase the angular resolution and distance for time-of-flight measurements. With this new system, we show composition-dependent contrast for amorphous materials and the contrast difference between small-angle and high-angle scattering signals. We also detect channeling-related contrast on polycrystalline silicon, thallium chloride nanocrystals, and single-crystalline silicon by comparing the signal transmitted at different directions for the same data set.