Ångström-Scale Topography in Neutral Helium Microscopy—Evaluating Thin-Film Coatings over Large Areas

Nanoscale thin film coatings and surface treatments are ubiquitous across industry, science, and engineering; imbuing specific functional or mechanical properties (such as corrosion resistance, lubricity, catalytic activity and electronic behaviour). Non-destructive nanoscale imaging of thin film coatings across large (ca. centimetre) lateral length scales, crucial to a wide range of modern industry, remains a significant technical challenge. By harnessing the unique nature of the helium atom–surface interaction, neutral helium microscopy images these surfaces without altering the sample under investigation. Since the helium atom scatters exclusively from the outermost electronic corrugation of the sample, the technique is completely surface sensitive. Furthermore, with a cross-section that is orders of magnitude larger than that of electrons, neutrons and photons, the probe particle routinely interacts with features down to the scale of surface defects and small adsorbates (including hydrogen). Here, we highlight the capacity of neutral helium microscopy for sub-resolution contrast using an advanced facet scattering model based on nanoscale features. By replicating the observed scattered helium intensities, we demonstrate that sub-resolution contrast arises from the unique surface scattering of the incident probe. Consequently, it is now possible to extract quantitative information from the helium atom image, including localised ångström-scale variations in topography. Its unique ability to observe the effects of sub-nanoscale features upon scattered helium intensity makes the SHeM a powerful tool for the evaluation of nano-coatings and thin films across large areas. Looking ahead, once a material system is well characterised with SHeM, such analysis will readily become a routine part of quality control; a unique tool for improving production yields and throughput.<br/><br/>Reference<br/>Eder, S.D., Fahy, A., Barr, M.G., Manson, J.R., Holst, B. and Dastoor, P.C., Sub-resolution contrast in neutral helium microscopy through facet scattering for quantitative imaging of nanoscale topographies on macroscopic surfaces. <i>Nature Communications</i>, <b>14:904</b>, (2023).