X-ray laser will ‘film’ chemical reactions in unprecedented detail | Hacker News Reader

X-ray laser will ‘film’ chemical reactions in unprecedented detail

nature.com

76 pointsgmays14 comments

Filming is one really interesting application, the other is imaging of single proteins without the need for crystallisation. I wrote a whole PhD thesis about the idea how to reconstruct the three-dimensional electron density from a lot of extremely noisy single proteins shots. It will make a huge class of proteins experimentally accessible that we couldn't structurally look into before.

Hasn't cryoelectron microscopy pretty much taken over for protein structure determination?

Indeed and it's a really impressive technology. However, there is the cooling involved and a lot of effort goes into sampling "the real deal" without changes of the structure due to the imaging process. In single molecule shots the idea is to form tiny droplets with the natural protein inside and sample them at room temperature. Naturally sample preparation here comes with its own challenges.

Do you have links to related content?

Here you go: https://www.nature.com/articles/s41467-018-04830-4

I don't work on this directly, but I do adjacent stuff in the computer science research group at SLAC.

Feel free to ask me questions, I guess? (I will not be able to say much about the physics.)

Neat! Wouldnt powerful xrays change the reaction to be filmed?

Again, not a physicist. But my understanding is that on a femptosecond timescale (the duration of the x-ray pulse generated by LCLS-II), effectively no reactions occur. The pulse destroys the sample, so that means you have to pump through a steady stream of sample particles to image. So for any given experiment, you'll get a stream of what are effectively snapshots of the reaction occurring at a given moment in time, and then it's up to software post-processing to figure out what you're looking at in a given snapshot and how far progressed the chemical reaction is at that point.

I helped with similar experiments at LCLS-I and the first half of this comment is correct. The chemical reaction is carefully timed on the order of milliseconds, so they get a series of snapshots of the reaction at a specific known state (but previously unknown structure). There isn't enough information in individual snapshots for the processing software to do very much with besides combine it with other snapshots (thousands of them).

Incredible stuff. I can't imagine the undulators are perfectly efficient at extracting all the energy from the electron beams. What do you guys do with the leftovers?

Dumb question here, but can X-Ray lasers be used to make CPUs?

That's not a dumb question at all! They're next in line, but there's a long road ahead!

Modern EUV lithography uses 13.7nm light, barely shy of the 10nm cutoff for X-Rays (and that's debatable). Many of the problems we'll need to solve are already in-play with EUV lithography, but with X-Rays they will be turned up to 11. Directing the light is a huge one, most materials are transparent to X-Rays so lenses aren't going to work, and mirrors are difficult. Building an EUV or X-Ray mirror requires coating stacks tens to hundreds of nano-meter thick layers thick but still can't manage very high reflectivity. Also, at these energies, the light easily ionizes substrate atoms knocking electrons out which travel around and affect nearby atoms, causing weird non-local stochastic effects.

We've barely started EUV production, there's plenty of room for optimization, so I'd bet we're decades away from using X-Rays commercially, but you better believe we're trying!

https://www.asml.com/en/products/euv-lithography-systems

https://www.sciencedirect.com/topics/engineering/x-ray-litho...

100s of nanometers is not what I would call thick...

It's even worse than that! There's hundreds of layers, but the individual layers are only a few nanometers each!

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