Thread by @AlexFoden, So, I'm waiting for some code to run and thought I'd start [...]

So, I& #39;m waiting for some code to run and thought I& #39;d start a thread that explains who I am and what I do as a PhD student. Feel free to jump into this rabbit warren with me. I have no real idea where it will go or how long it will take. Buckle up!

So, I& #39;m Alex. I& #39;m a PhD student at @imperialcollege in the @ImpMaterials dept. Supervised by Dr. @BMatB.

My PhD focus is electron backscatter diffraction, or EBSD for short. And I& #39;m going to try to explain it in this thread.

I also perform magic and date @DesignsDn. Yay :D

To get started, we need a crystalline material....

Hold up, hold up, what on earth is a crystalline material, Alex?

Well I& #39;m glad you asked. It& #39;s a material where the Atoms (they make up everything!) arrange themselves in regular patterns, like cubes or hexagons.

This means you can be either team #hexmat or #cubmat, much like when you were a teenager and were either #teamjacob or #teamedward (I cannot believe I made a twilight reference here).

A good explaination of how atoms arrange themselves can be found on a few videos by @standupmaths and Steve Mould (who I can& #39;t find on twitter (boo!))

https://www.youtube.com/watch?v=O3RsDIWB7s0">https://www.youtube.com/watch... and https://www.youtube.com/watch?v=3inLMXcetUA">https://www.youtube.com/watch...

But what if the Atoms aren& #39;t arranged in a regular way? Like in a liquid?

Well, sadly, that means that EBSD can& #39;t be done.

So What do you mostly EBSD on, Alex?

Usually I look at metals, or silicon, though you can EBSD rocks, ice or meteorite ( @NatStephen has more on that).

So now we know we need a crystalline material, what next?

We need to get a scanning electron microscope (SEM) and...

A what now?

One of these sexy pieces of metal
https://www.fei.com/products/sem/quanta-sem/

In">https://www.fei.com/products/... fact, that& #39;s the model I& #39;ve been trained to drive. There& #39;s multiple ones at imperial and I have access to one of them. I think it& #39;s a form of damage limitation on Ben& #39;s part. But so far I have broken nothing (Whoop)

These are basically really advanced and uber expensive microscopes that electrons instead of light to look at things really, really close up.

Here& #39;s comes a badly draw diagram to explain

If this looks familiar, it& #39;s because it& #39;s essentially a big, powerful version of what used to make the old cathode ray TVs work, before the fancy days oh plasma, LCD and, more recently, LED TVs.

So the reason it& #39;s called a scanning electron microscope, is because it& #39;s a microscope, it uses electrons, and it scans the electrons across the thing you& #39;re looking at to make a pretty picture. That& #39;s how you get picture of bugs wings.

When you put a metal under one of these, it looks like this. This is actually an Iron sample published in https://journals.iucr.org/j/issues/2018/06/00/nb5225/index.html">https://journals.iucr.org/j/issues/... (a paper I helped write) and was captured @JamesHickey11, who can drive an SEM better than I can

When you put a metal under one of these, it looks like this. This is actually an Iron sample published in https://journals.iucr.org/j/issues/... (a paper I helped write) and was captured @JamesHickey11, who can drive an SEM better than I can

To give a little context on how close up that picture is, that Iron was polished to a mirror finish. If it& #39;s not that polished, EBSD won& #39;t work quite so well. Or at all.

Right, so we have out crystalline material and our SEM, and we know what they both are. What now?

We put the thing we want to look at in the SEM and swear a lot. You swear polishing it, getting it in without damaging it and especially when trying to focus the microscope.

When you& #39;re done swearing you leave it overnight for the computer to gather all the data.

Hang on Alex. What Data are we collecting?

This is the interesting bit and the bit I spend most time on in my PhD. There& #39;s main things we can look for, though if you& #39;re clever you can do much more.

But I mostly look at what shapes the atoms make, and what direction they face.

... What are you on about, Alex?

Ok, let me back up a bit and show some pictures that use things I have on my desk/can
"borrow"o from other people& #39;s desks

So here we have a cube and a hexagon. If these were crystal structures, there would be an atom at each of the corners on each of these shapes.

It& #39;s wonderful what you can find in an office of scientists!

The point is, we want to know if the data we are looking at comes from the cube or the hexagon and where the cube is facing, relative to the other shapes around it.

i.e is it like this?

this?

Or this?

We find this out by looking at what we call Kikuchi patterns. They look like this:

That pattern is also from the Iron data that Jim took that we looked at earlier. I told you he was good!

But Alex, what on earth even is that?

I& #39;m glad you asked. When you shoot the electrons at the thing you want to look at in the SEm that we spoke about earlier, they interact with the atoms at the surface of the whatever.

When they interact they bounce off parallel to the planes of the crystal.

Parallel to the what now? I thought we were talking about microscopes, not flying?

I appear to have reached the limit of this thread so will continue in a second!

https://twitter.com/AlexFoden/status/1222935301116637197">https://twitter.com/AlexFoden...

https://twitter.com/AlexFoden/status/1222935301116637197

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