Question: how do you look at atoms?

Dean Whittaker answered on 17 Jun 2010:

There are three main ways to look at atoms in a material. If you’re interested in the surface of something and what the atoms look like then you can use something called a scanning tunnelling microscope (or something similar to that – there’s lots of variations). This is simply running a very small needle over the material and measuring the teeny tiny movements it makes up and down due to the bumps of the atoms. The details are a lot more complicated and it’s very very impressive that these things work. I’m always amazed that we can actually measure that sort of thing. Look here: http://en.wikipedia.org/wiki/Scanning_tunneling_microscope

But if you want to look at the whole thing, then you need a diffraction experiment. Diffraction is when you send a wave into the material. It then reflects off all the atoms. The reflected waves all interfere with each other and you get a pattern of bright and dark parts of the reflected wave. A very clever guy named Bragg worked out that the spacing of the “things” the wave bounces off (which might be big blobs, or atoms, or anything) is linked to the pattern you get. So what you do is you send in one wavelength of something and look at which angles you get bright spots. Then you can work out what the spacing was between whatever the wave bounced off of. So what sort of wave do you put in? – well neutrons are a wave and bounce off the atomic nuclei, so you can look at the spacing between the middle of the atoms. X-rays bounce off the electrons – so you can look at them (and actually that also tells you about where the middle of the atoms are too). Electrons can also be used as the wave and things get a bit complicated.

Red laser light bounces off of lots of objects and you can see a diffraction pattern using something called a diffraction grating – a series of lines spaced 10ths of a mm apart (much bigger than atom spacings – but it’s exactly the same idea). here’s info on that http://en.wikipedia.org/wiki/Bragg's_law

The third way is that you make the atoms vibrate by bumping something into them. You can work out by the way that what you used to bump into them slows down how the atoms are jiggling about. What you bump into them can be a neutron or some infrared light. Then if you’re really clever you can work out what the atoms must look like by the way that they vibrate about – but that’s very hard!

hope that answer wasn’t too complicated