Dark-Field Scanning Transmission Ion Microscopy via Detection of Forward-Scattered Helium Ions with a Microchannel Plate

A microchannel plate was used as an ion sensitive detector in a commercial helium ion microscope (HIM) for dark-field transmission imaging of nanomaterials, i.e. scanning transmission ion microscopy (STIM). In contrast to previous transmission HIM approaches that used secondary electron conversion holders, our new approach detects forward-scattered helium ions on a dedicated annular shaped ion sensitive detector. Minimum collection angles between 125 mrad and 325 mrad were obtained by varying the distance of the sample from the microchannel plate detector during imaging. Monte Carlo simulations were used to predict detector angular ranges at which dark-field images with atomic number contrast could be obtained. We demonstrate atomic number contrast imagingviascanning transmission ion imaging of silica-coated gold nanoparticles and magnetite nanoparticles. Although the resolution of STIM is known to be degraded by beam broadening in the substrate, we imaged magnetite nanoparticles with high contrast on a relatively thick silicon nitride substrate. We expect this new approach to annular dark-field STIM will open avenues for more quantitative ion imaging techniques and advance fundamental understanding of underlying ion scattering mechanisms leading to image formation.

Another Way to Implement Diffraction Contrast in SEM

SEM users are familiar with two forms of contrast in SEM images: topographic contrast and atomic number contrast. We can now add a third form of contrast. Contrast can arise due to the different orientation of grains in the sample. However, in normal operation this con trast is very weak, since in the SEM the beam includes a range of incident angles. This has the effect of averaging out diffraction contrast from the different orientations of the grains. This contrast is generally much stronger when the trast is very weak, since in the SEM the beam includes a range of incident angles. This has the effect of averaging out diffraction contrast from the different orientations of the grains. This contrast is generally much stronger when the incident beam is an ion beam rather than an electron beam — contrast between the grains is strong in ion-beam images but not in normal SEM images.

Precipitates in GaN epilayers grown on sapphire substrates

Precipitates in GaN epilayers grown on sapphire substrates were investigated by atomic number contrast (ANC), wavelength-dispersive x-ray spectrometry (WDS), energy-dispersive spectrometry (EDS), and cathodoluminescence (CL) techniques. The results showed that the precipitates are mainly composed of gallium and oxygen elements and distribute more sparsely and inhomogeneously in directions in the sample grown on substrate nitridated for a longer period. Yellow luminescence intensity was imaged to be stronger in the precipitates. The results suggest that the precipitates are formed on dislocations and grain boundaries by substituting oxygen onto the nitrogen site, and result in the formations of deep levels nearby.