Outrun radiation damage with electrons?

Abstract

The diffract-before-destroy method, using 50-to 100-fs x-ray pulses from a free-electron laser, was designed to determine the three-dimensional structure of biological macromolecules in close to their natural state. Here we explore the possibility of using short electron pulses for the same purpose and the related question of whether radiation damage can be outrun with electrons. Major problems include Coulomb repulsion within the incident beam and the need for high lateral coherence, difficulties that are discussed in terms of existing and future electron sources. Using longer pulses of electrons appears to make the attainment of near-atomic resolution more feasible, at least for nanocrystalline particles, whereas obtaining this information from single-molecule particles in an aqueous environment seems a more distant goal. We also consider the possibility of serial crystallography using a liquid jet injector with a continuous electron beam in a transmission electron microscope (TEM).

Imaging Beam‐Sensitive Materials by Electron Microscopy

“…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.…”

“…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. XFELs employ repetitive femtosecond X‐ray pulses (<100 fs) that outrun primary ionization damage,51,185–187 while pulsed electrons can hardly achieve very short period with sufficiently high brightness due to the Coulomb repulsion between the electrons in each bunch 185.…”

“…The timescales and mechanisms for outrunning the radiation damage with either XFELs or pulsed electrons have been compared 51,185. XFELs employ repetitive femtosecond X‐ray pulses (<100 fs) that outrun primary ionization damage,51,185–187 while pulsed electrons can hardly achieve very short period with sufficiently high brightness due to the Coulomb repulsion between the electrons in each bunch 185. Longer electron pulses allow the elimination of relatively slow secondary or tertiary damage processes (e.g., diffusion‐limited processes57) rather than the primary ionization damage,57,185 which would also be important for materials adopting inverse dose‐rate effects57,69,188 or retarded damage upon dose fractionation 159,189–191.…”

Single-shot electron diffraction using a cold atom electron source

“…The emittance and bunch charge for the CAES are therefore approaching the values required for single-shot diffraction of microcrystals 24 , but the pulse duration is possibly still three orders of magnitude too long to avoid degradation of the diffraction pattern due to beam induced damage of such small samples. However recent studies have suggested the constraints on pulse duration due to damage could be relaxed for electrons compared with X-rays, because of the differences between the scattering and damage-inducing processes 25 . To achieve sub-picosecond ultrafast electron diffraction, the ionisation process can be modified to use femtosecond rather than nanosecond laser pulses 18,19 .…”

Hollow cone illumination for fast TEM, and outrunning damage with electrons

“…Allowing 1% displacements per atom would then increase the number of elastically scattered electrons N s by an order of magnitude in both the above estimates. Alternatively, if the method [30] is used, then the displacement probability per atom in crystals becomes 1% using 100 fs pulses (1 MeV beam, 25 eV displacement threshold for diamond, 100 C cm −2 s −1 ), setting an upper limit on pulse duration [31].…”