337 — Electron ptychography of 2D materials to deep sub-ångström resolution

An average static-electric shock from wool socks on a carpet is around 4KV, 1.2mJoules (thanks @wbeaty on physics.stackexchange.com!). So that’s around $3\times10^{-7}$ coloumbs:

\[\frac{.0012J}{4,000 V} = 3.0\times 10^{-7} C\]

A single electron’s charge is $1.602\times 10^{-19}C$, which means that there are probably somewhere around:

\[\frac{1}{1.60217733\times 10^{-19}}=\frac{x}{3.0\times 10^{-7}}\] \[1.875 \times 10^{12}\]

…1.8 trillion electrons exchanged in that tiny nuisance spark that bothers you a little bit in the winter, but not enough to do anything about it.

1.8 trillion electrons: Doesn’t bother you even a bit.

But even a small handful of electrons will bother a 2D surface a lot.

One of the great challenges in 2D material engineering is that you can’t see what you’re working on: The act of imaging a 2D surface at high enough resolution using an electron microscope often rockets enough electrons at the sample that it disrupts the material itself.

But if you use fewer electrons, the resolution and contrast of the image is far lower (just like how it’s harder to read in low light) and you can’t see what you’re doing for a different reason.

These researchers used the mathematics of electron ptychography to image samples with much lower-energy waves (and thus, ostensibly, lower-resolution) than previous scanning transmission electron microscopes. Using conventional techniques, this wavelength shouldn’t be able to refine details below one ångström. But ptychography — the process by which the interference patterns of the diffracted, incoherent waves are recorded and reconstituted into a coherent image — enabled the researchers to achieve better-than-state-of-the-art resolution with a fraction of the electron-energy.

The images from this work are stunning: You can see the individual atoms in a 2D molecule, and you can actually measure the atomic bond lengths between them. The images’ pixel-resolution is dramatically smaller than a single ångström, without inherently damaging the material. This has huge implications for defect-detection in 2D material construction — and means that we might be revisiting the “best” achievable EM resolution.