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When we see atoms under an electron microscope, what exactly are we seeing? I mean, these spheres that we know as atoms are electron clouds and that is what we are seeing, am I right?

https://www.youtube.com/watch?v=pGWSX6pStd0

Can you please explain to me, how exactly our eyes are able to see those spheres that we know as atoms? Like photons are hitting those constantly moving electrons and then they reflect back and hit the retina of our eyes where it gets absorbed. That’s fine. But I want to know, how exactly photons are interacting with those constantly moving electrons of an atom of an object from which they are being reflected?

Dale
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  • @Emilio Pisanty Ok, your answer at that post helps me a bit. Because i had misunderstanding that when a photon hits an atom (electron cloud), it bounces back. I was assuming this phenomenon like a boy throwing a ball at a wall and the ball bounces back at him. But my assumption was wrong! Now i know that when a photon hits a reflective material, each atom located on the surface of that reflective material will absorb and re-emit photons. And that is called reflection of light, am i right? BUT i still want to know, what exactly happens between a photon is being absorbed and then re-emitted? –  Jan 04 '20 at 09:18
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    These might help you: 1) What is happening at a atomic level when light hits an object?, 2)Principle of Reflection on atomic level,3) How can reflection and refraction be explained classically and microscopically?. –  Jan 04 '20 at 14:17
  • As the first answer said (below), the link you show is an electron microscope. Electrons are shone onto the sample, not light. Electrons behave as waves and have much smaller wavelenghts, small enough to resolve atomic surface structures. Electrons hit the sample, generate other electrons, which hit a screen where they are detected. The number of secondary electron hits is given a false colour scale, which is what you see in the picture. – SuperCiocia Jan 06 '20 at 07:56
  • @SuperCiocia Ok, i get what you and ‘Hari’ wants to explain. That explanation is related to the video. But what i want to know is, what exactly is reflection at atomic & subatomic level? Look, here comes a photon of visible spectrum, it has certain wavelength which is larger than the size of a gold atom. So it can not hit a single atom, instead it hits a plane which has grid of atoms. Now that photon interacts with grid of atoms. But what exactly happens next?... –  Jan 06 '20 at 08:12
  • ...Does it interacts with only those electrons which are in outermost orbit or does it also interacts with those electrons which are in lower orbits? And when we say, a photon excites an electron and bring it to higher energy state/orbit, what exactly it’s doing? I mean, is it pushing an electron to move into higher orbit or is it doing anything else? –  Jan 06 '20 at 08:14
  • I don’t really understand you question. The inner electrons are usually bound more strongly than outermost ones, so you’d need higher frequencies (higher energies) to excite them. But the reflection off surfaces depends on the material at hand. For example in metals you have metallic bonds and a sea of electrons, which as essentially free charges are very good at cancelling the incoming field and result in near perfect speculation reflection. – SuperCiocia Jan 06 '20 at 16:06
  • The frequency of the photon just relates to its energy. Not size. – SuperCiocia Jan 06 '20 at 16:07

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The linked video shows a TEM image. In transmission electron microscopy, you have a parallel beam of electrons incident on the material, which gets scattered by the atoms in the material. Note that, it is not just the electron cloud, but the potential formed by the atomic core (nucleus+ core electrons) and the valence electrons together, that scatter the incident electrons. To visually see the image one can use a scintillator to capture the electrons, which results in the emission of photons. One can also use a CCD system for this purpose and get a digital image.

Since electrons have a wavelength much lower than visible light, they can be used to probe extremely small length scales and can achieve atomic resolution in the images.

During the scattering process, there are both elastically and inelastically scattered electrons. The elastically scattered electrons are useful in forming diffraction patterns, which can be used to study atomic structures. The inelastically scattered electrons can be used for characterization of the material in EELS, EDX etc.

Hari
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