Discovering Hidden Material Properties of MgCl₂ at Atomic Resolution with Structured Temporal Electron Illumination of Picosecond Time Resolution

Abstract

A combination of atomic resolution phase contrast electron microscopy and pulsed electron beams reveals pristine properties of MgCl 2 at 1.7 Å resolution that were previously masked by air and beam damage. Both the inter-and intra-layer bonding in pristine MgCl 2 are weak, which leads to uncommonly large local orientation variations that characterize this Ziegler-Natta catalyst support. By delivering electrons with 1-10 ps pulses and ≈160 ps delay times, phonons induced by the electron irradiation in the material are allowed to dissipate before the subsequent delivery of the next electron packet, thus mitigating phonon accumulations. As a result, the total electron dose can be extended by a factor of 80-100 to study genuine material properties at atomic resolution without causing object alterations, which is more effective than reducing the sample temperature. In conditions of minimal damage, beam currents approach femtoamperes with dose rates around 1 eÅ −2 s −1 . Generally, the utilization of pulsed electron beams is introduced herein to access genuine material properties while minimizing beam damage.

Imaging Beam‐Sensitive Materials by Electron Microscopy

“…Through the electron optics system (Sections 3.2), the D c values of materials can be modulated by beam energy, beam current density, and imaging modes due to their different beam damage mechanisms and dose‐rate effects 75,158. Even with the same D c values, the beam damages can be effectively minimized or retarded by employing either a sparsely sampled, a pulsed or an aloof electron probe 7,159,160. Similar idea can be extended to high‐fidelity 3D reconstruction by low‐dose orientation sampling.…”

“…Red arrows indicate the position of the g = 0.46 Å −1 scattering vector that is unique to β‐MgCl 2 . Reproduced with permission 7. Copyright 2019, Wiley‐VCH.…”

“…Inspired by the successful applications of high‐intensity X‐ray free‐electron lasers (XFELs) in resolving structures of biological macromolecules through “diffract‐and‐destroy” scheme,181–184 the possibility of using short electron pulses to probe electron beam‐sensitive materials have also been explored 7,51,185. The timescales and mechanisms for outrunning the radiation damage with either XFELs or pulsed electrons have been compared 51,185.…”

“…Both of the two primary beam damage mechanisms, radiolysis and knock‐on displacement, are dose‐dependent and thus have their respective critical doses. For the radiolysis mechanism, despite a few exceptions,7,69,110–117 the beam damage rate in most cases follows the first‐order decay kinetics as below where the “ I 0 ” and “ I D ” refer to initial and remnant intensities of monitored feature at an accumulated electron dose of “ D ”. An accumulated critical dose of “ D c ” at an I D / I 0 ratio of 1/ e is widely used as a benchmark for evaluating the beam sensitivity of materials 59.…”

“…In the aspect of pushing the spatial resolution limits of electron microscopy, advanced aberration correction techniques1 or ptychographic diffractive imaging methods2 nowadays allow the imaging of nanoscale objects down to atomic‐ or even deep sub‐Ångstrom resolution. In addition, modern TEM instruments unite various spectroscopic and in situ (operando) techniques and provide multidimensional correlated structural, chemical and electronic information spanning the spatial,3 time,4–8 energy,9 and momentum dimensions 10. Such high‐resolution and correlated information is important in providing a solid basis for the determination of structure–property relationships in materials.…”