Abstract

Bubbles formed in van der Waals (vdW) materials play a crucial role in modulating strain, electronic structure, and optical response, yet their geometries are challenging to quantify using conventional microscopy. Techniques such as AFM , SEM, and PL mapping suffer from issues including surface damage, limited imaging areas, and indirect strain inference. In this seminar, I will present a new quantitative approach for characterising MoS₂ bubble structures using specular contrast in scanning helium microscopy (SHeM). By performing multi-angle imaging and tracking the angular-dependent intensity maxima associated with the local specular scattering condition, we achieve contact-free 3D reconstruction with height precision better than 100 nm, surpassing the nominal 30 μm beam spot size by nearly 300×. I will introduce the physical basis of helium specular scattering, the speculometric-stereo reconstruction scheme, and supporting ray-tracing simulations. The method provides accurate bubble curvature radii (_{10 mm) and apex heights (}1 μm), revealing its capability to resolve extremely low-aspect-ratio deformations. Beyond MoS₂, this work highlights specular-contrast SHeM as a powerful metrology tool for non-invasive, slope-sensitive topography mapping in a broad class of soft, insulating, or delicate 2D materials.