Naked Science Forum

General Science => General Science => Topic started by: katieHaylor on 11/10/2017 11:55:31

Title: How do atomic models correlate with electron microscope observations?
Post by: katieHaylor on 11/10/2017 11:55:31

David says:

When we look at pictures of atoms through an Electron Microscope, we see the atoms as ' blurry spheres ', as if there is a shell or covering over the atom itself. However, the model we present of atoms, as a diagram, is a nucleus with neutrons and the electrons and protons revolving around the nucleus. 

What sub-atomic particles make up this ' shell ' ?

What do you think?

Title: Re: How do atomic models correlate with electron microscope observations?
Post by: chiralSPO on 11/10/2017 14:50:41

Protons and neutrons make up the nucleus. The "shell" is the electrons.

See the attached image which my colleague captured using TEM (transmission electron microscopy). This is about as high resolution as can be achieved using these types of techniques. As far as I understand the physics involved, electron microscopy cannot have the precision required to see the subatomic structure for essentially the same reasons that atoms are the size they are (both are determined by the quantum mechanical properties of electrons). However, the resolution is clear enough to see which parts of my sample are crystalline (where all the atoms are in neat rows) and where it is amorphous (random, but still with more order than the empty field on the right, which just looks kinda like static on an old tv). Note you can also see diffraction patterns appearing as halos around the edge of the particle being looked at.
14 lattice burned.jpg (228.33 kB . 668x692 - viewed 4064 times)

Title: Re: How do atomic models correlate with electron microscope observations?
Post by: syhprum on 11/10/2017 20:10:27

Noting the 2nM bar on the picture it is incredible to think that transistors can be built taking up only 14nM 

Title: Re: How do atomic models correlate with electron microscope observations?
Post by: evan_au on 11/10/2017 20:51:14

An even closer image using a scanning tunneling microscope with individual atoms is shown here:
https://en.wikipedia.org/wiki/IBM_(atoms) (https://en.wikipedia.org/wiki/IBM_(atoms))

Electron microscopes (https://en.wikipedia.org/wiki/Electron_microscope) have been able to produce images down to about 50pm resolution, while a Xenon atom is about 300pm across. This means that the "blur" will be about 17% of the width of the atom. But to achieve these resolutions, they have to use very high accelerating voltages - up to 400,000 Volts (ie very high-energy/short wavelength electrons). This disturbs the sample being examined, punching several atoms deep into the material, and interacting with both electrons and the atomic nucleus (electrons approaching the nucleus produce X-Rays).

The scanning tunneling microscope (https://en.wikipedia.org/wiki/Scanning_tunneling_microscope) is much gentler, using low voltages (eg up to 5V) to examine the surface; this does not disturb the surface so much. This senses the electron density in just the top atom on the surface.