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uh I'm curious again regarding the theories of reflection.

This is known that

Metals contain free electrons that absorb energy and vibrate when they come in contact with light. Later, they release the energy back in the form of light.

But what if we polish a transparent conductive oxide glass (transparent glass which is electrically conductive). It doesn't seem to be acting like a mirror. So is it really just the electrons which decide the reflection?

Do correct me if I'm wrong. I'm just a stupid kid :)
My previous post

enter image description here

Qmechanic
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44yu5h
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  • Yes. For metals it is mostly simple (with horrible corrections due to surface smoothness and other special properties of each element). For other materials there are other things to consider. It is really ironic that the picture of the glass that you posted, showed a rather bright reflection. – naturallyInconsistent May 25 '23 at 04:19

2 Answers2

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But what if we polish a transparent conductive oxide glass (transparent glass which is electrically conductive). It doesn't seem to be acting like a mirror. So is it really just the electrons which decide the reflection?

For metals it is the first order effect, under specific treatement. If the metal face is is rough there is no mirror though the electrons are there.

In general , solids are modeled with a mathematical model of a lattice , which predicts well the behavior of impinging radiation. One needs a course in quantum mechanics in order to really understand the model. Quantum mechanics models interactions of light with what are transparent lattices.

anna v
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  • Hi, Thanks for answering.. but this doesn't answer my question. Irregularity of surface is not in the scope of the question. And I don't think lattice structure plays an important role for the most part of it. Mostly reflections happen at the surface where electrons interact. And we've seen normal glasses with amorphous structure reflect partially too. I'm asking why doesn't a conductive glass (not normal glass) show the same properties to naked eyes as of metal if they both have free electrons. Does that mean our theory, "reflection happens due to interaction of electrons", is wrong? – 44yu5h May 25 '23 at 05:00
  • Not wrong, just too general, see here for transparency https://en.wikipedia.org/wiki/Transparency_and_translucency#Absorption_of_light_in_solids – anna v May 25 '23 at 05:53
  • "Mostly reflections happen at the surface where electrons interact." but in transparent materials there are not enough surface "free" electrons to interact with , a lot of photons have to get through in order for the material to be transparent. Glass reflects after all, but a lot of the EM radiation goes through – anna v May 25 '23 at 07:44
  • Yeah, I agree but it's the visible spectrum of light that we talking of.. that's what we see as a reflection. I'll have to look at the "thinness" aspect of it as John Rennie stated in his answer. – 44yu5h May 25 '23 at 14:43
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Yes, it is just the electrons.

If I understand your question correctly you are asking how indium tin oxide and similar materials can be both conducting and transparent if the free electrons required for high conductivity act as mirrors.

There are two reasons for this:

  1. the conductivity of indium tin oxide is high but nowhere near as high as a metal. Metals typically have resistivities around $10^{-8}~\Omega.\textrm{m}$ while the resistivity of indium tin oxide is four orders of magnitude higher at about $10^{-4}~\Omega.\textrm{m}$ There are fewer free electrons in indium tin oxide and they interact less strongly with the light.

  2. the indium tin oxide is in the form of a very thin film. The plates in your photograph are just glass with less than a micron of ITO as a film on the surface. This is the main reason for the low reflectivity - the film is simply so thin that most of the light doesn't get the chance to be reflected.

Thin metal films are transparent as well, though due to their high conductivity they have to be very thin. I worked with thin films of silver as part of my PhD and once the thickness falls below $10$ nm the reflectivity falls dramatically. The indium tin oxide films remain transparent at much larger thicknesses simply because their conductivity is $10^4$ times smaller than silver.

John Rennie
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  • Hi, your argument is not correct. Indium oxide has 10^-4 ohm m resistivity but Silicon Carbide (SiC) has a resistivity of 10^-2 ohm m, and there are mirrors made of it. https://www.indiascience.in/videos/silicon-carbide-mirrors-for-space-applications-h – 44yu5h May 25 '23 at 14:31
  • The second reason makes a lot more sense. I'll have to look at this. I have certain questions I'll have to ask some people on Electronics SE. I'll get back if I find something worth sharing. Such a pleasure to be talking to an experienced person. – 44yu5h May 25 '23 at 14:35
  • @44yu5h the reflectivity of SiC mirrors at near IR and visible wavelengths is about 20%. Compare that to a really clean silver surface that has a reflectivity in the high nineties percent. SiC does have a high reflectivity at longer wavelengths and I must admit I'm not sure why that is. – John Rennie May 25 '23 at 15:31