High resolution large working distance scanning helium microscopy

TL;DR

This paper reports a significant advancement in scanning helium microscopy by achieving sub-micron resolution at large working distances, enabling detailed imaging of delicate surfaces.

Contribution

The authors demonstrate a sixfold improvement in spatial resolution for large-working-distance SHeM through optimized atom optics and a redesigned pinhole system.

Findings

Achieved 340 nm beamwidth at 770-850 μm working distance.

Beamwidth measurements align with the optimization model.

Demonstrated imaging on bacterial specimens and eroded diamond.

Abstract

Scanning helium microscopy (SHeM) is attractive for imaging delicate and insulating surfaces because it combines a non-destructive neutral-atom probe with strong surface sensitivity. However, large-working-distance pinhole instruments have so far been limited in spatial resolution. Here we report sub-micron resolution in a large-working-distance pinhole SHeM, with an intrinsic beamwidth of 340nm achieved at working distances of 770 {\mu}m to 850 {\mu}m. This sixfold improvement over our previous long-working-distance configuration is enabled by constrained optimisation of the atom optics together with a redesigned high-resolution pinhole-plate, a reduced pinhole diameter, an increased source--pinhole distance and a larger detector aperture. Beamwidth measurements agree well with the modified optimisation model and show that geometric, source-size and diffraction terms now contribute on a similar footing, placing the instrument in a near-optimised regime. The resulting combination of sub-micron beam size, useful depth of field and practical sample access is demonstrated on bacterial specimens and eroded diamond. The work establishes large-working-distance pinhole SHeM as a viable sub-micron imaging platform and extends its usefulness for topographic imaging and micro-diffraction applications.