Experimental study of energy-dependent angular broadening of MeV electron beams for high-resolution imaging in thick samples

Journal Article · Sat Oct 18 00:00:00 UTC 2025 · Ultramicroscopy

DOI: https://doi.org/10.1016/j.ultramic.2025.114260 · OSTI ID:3003347

Yang, Xi  ^[1]; Denham, Paul ^[2]; Kulkarni, Atharva ^[2]; Schaap, Brian ^[2]; Smaluk, Victor ^[1]; Wang, Tianyi ^[1]; Bouet, Nathalie ^[1]; Idir, Mourad ^[1]; Musumeci, Pietro ^[2]

---

1. Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)
2. Univ. of California, Los Angeles, CA (United States)

In scanning transmission electron microscopy (STEM), spatial resolution is primarily influenced by the projected size of the electron probe within the specimen. In thin samples, a large semi-convergence angle enables a tightly focused beam and sub-nanometer resolution. However, in thick specimens, resolution is fundamentally limited by transverse beam broadening from multiple large-angle scattering events—for example, a probe with 10 mrad angular divergence can broaden by ∼100 nm over a 10 μm path. Since this broadening scales inversely with beam energy, MeV-STEM offers a promising route for high-resolution imaging in thick materials. To quantitatively assess this effect, we performed high-precision measurements at UCLA’s PEGASUS beamline, characterizing beam divergence and intensity profiles for 3–8 MeV electrons transmitted through a wedged-silicon sample of varying thickness. Our results reconcile discrepancies among analytical models and validate Monte Carlo simulations. Here, we find that increasing beam energy from 3.0 to 5.8 MeV reduces angular broadening by a factor of 2.6, with diminishing returns observed at 7.6 MeV. These findings provide a quantitative framework for optimizing MeV-STEM parameters in high-resolution imaging of thick biological and microelectronic specimens, and for guiding beam energy selection in other advanced imaging modes beyond STEM.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: SC0012704
• OSTI ID: 3003347
• Report Number(s): BNL--229145-2025-JAAM
• Journal Information: Ultramicroscopy, Journal Name: Ultramicroscopy Vol. 279; ISSN 0304-3991
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English