Electron microscopes are capable of resolving details that small.

Here's a side-on view of what they did. You can see the individual gold atoms.

https://www.nature.com/articles/s44160-024-00518-4/figures/1

And here's a top down view

https://www.nature.com/articles/s44160-024-00518-4/figures/2

Both of these are from the paper describing their process and results

https://www.nature.com/articles/s44160-024-00518-4

Thanks for posting the photos, I don't know why I had this image of perfect square sheet in my mind. Of course it doesn't work like that and they are more like shreds. Very cool to be able to see them.

That side on view is wild and I didn’t know that the resolutions of electron microscopes had gotten that good where you can make out individual atoms. Insane.

They have been that good for a while

Holy crap, I want one.

Scanning electronic microscopes can see and/or manipulate individual atoms. So, the answer to your question is simple: they took a look from the side and confirmed that it's 1 atom thick.

1. https://education.mrsec.wisc.edu/scanning-tunneling-microsco...

Small correction: Scanning tunneling microscopes can do that. They are basically a very sharp tip scanned across the surface.

Scanning electron microscopes, where a beam of electrons is rastered across the surface can not (yet?) resolve atoms.

* cannot resolve atoms on a surface, in transmission mode (STEM) and with the right sample, as in the article it's another story.

> Small correction: Scanning tunneling microscopes can do that.

Thanks! You're correct.

Per the article, an electron microscope.