Atomic Lock-On—Quantitative Electron Beam-Matter Interactions at the Single Atom Level Enabled by Picometer Precision Beam Control

Aberration corrected scanning transmission electron microscopy (STEM) is unmatched for high-resolution imaging and correlative analytical studies down to an individual atom. The sub-Angström focused electron probe is raster scanned, collecting various detector signals in a pixel-by-pixel manner. However, images exhibit unavoidable sample drift and scan distortions due to mechanical and electronic instabilities. While post-processing may correct these distortions, the ability to reliably position the electron probe on a desired atomic site without imparting dose to the surrounding regions has remained out of reach. Moreover, many <i>in situ</i> applications would benefit from undistorted atomic lattice information and dynamic probe placement at specific atomic targets. This ability would enable repeated atomic, site-selective spectroscopic measurements or precise structural modifications such as deterministic defect generation.<br/>In this talk, we describe “atomic lock-on,” an <i>in situ</i> electron beam control algorithm for rapid, minimally invasive, and picometer-precise beam placement [1, 2]. Using a sparse annular scan pattern, which reduces scan distortions, we mathematically reconstruct atomic lattice information from the high angular annular dark-field (HAADF) detector data. Optimizing annular scan parameters, we apply this method to a thick sample (13 nm) of CrSBr [3] achieving a consistent targeting precision of sub-20 pm. The approach avoids exposing the area of interest and demonstrates robustness in low-dose environments, as further demonstrated with a monolayer (&lt; 1 nm thin) of MoS₂ and WS₂. The total execution time, including scan and correction, is under 100 ms, significantly faster than typically relevant specimen drift rates. The high targeting precision and speed make the approach suitable for various <i>in situ</i> experiments. We therefore integrate atomic lock-on into custom-designed automated experimental workflows. We repeatedly track and measure the weak core-loss electron energy loss spectroscopic (EELS) signal of a single V dopant in MoS₂. Moreover, we place the electron beam on different atomic sites in WS₂ to study single atom kinetics and observe ejection, recapture and atomic bistability behavior with sub-millisecond time resolution. Atomic lock-on fills a critical gap in the STEM repertoire, enabling unique high-precision experiments and improved studies of beam-matter interactions.<br/><br/>[1] K. M. Roccapriore, F. M. Ross and J. Klein, <i>under review</i><br/>[2] J. Klein, K. M. Roccapriore, F. M. Ross, <i>U. S. Provisional Pat.</i> Ser. No. 63/601,529, Filed November 21, 2023.<br/>[3] J. Klein et al., <i>Nat. </i><i>Comms. <b>13</b>, </i>5420 (2022)<br/>[4] STEM beam control work was supported by Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.