2D helium atom diffraction from a microscopic spot

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von Jeinsen, Nick 
Bergin, Matthew 
Radic, Aleksandar 
Liu, Boyao 

A method for measuring helium atom diffraction with micron-scale spatial resolution is demonstrated in a scanning helium microscope (SHeM) and applied to study a micron-scale spot on the (100) plane of a lithium fluoride (LiF) crystal. The positions of the observed diffraction peaks provide an accurate measurement of the local lattice spacing, while a combination of close-coupled scattering calculations and Monte-Carlo ray-tracing simulations reproduce the main variations in diffracted intensity. Subsequently, the diffraction results are used to enhance image contrast by measuring at different points in reciprocal space. The results open up the possibility for using helium micro-diffraction to characterize the morphology of delicate or electron-sensitive materials on small scales. These include many fundamentally and technologically important samples which cannot be studied in conventional atom scattering instruments, such as small grain size exfoliated 2D materials, polycrystalline samples, and other surfaces that do not exhibit long-range order.

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Physical Review Letters
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American Physical Society
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Engineering and Physical Sciences Research Council (EP/R008272/1)
EPSRC (EP/T00634X/1)
The work was supported by EPSRC grant EP/R008272/1. The authors acknowledge support by the Cambridge Atom Scattering Centre (https://atomscattering.phy.cam.ac.uk) and EPSRC award EP/T00634X/1. The work was performed in part at the Materials and NSW node of the Australian National Fabrication Facility, a company established under the National Collaborative Research Infrastructure Strategy to provide nano and microfabrication facilities for Australia’s researchers. SML acknowledges funding from MathWorks Ltd. BL acknowledges financial support from the CSC and the Cambridge Trust. We would also like to acknowledge constructive discussions with Bill Allison and Paul Dastoor.
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