6 ms·

Metal will never be transparent. Metal means metal bonds which means free electrons. Free electrons are opaque to visible light.

by dvh 9y ago

tedsanders 9y ago
Just to add on for others reading your comment: Although metals are opaque, conductors can still be transparent. A few techniques: - Very thin layers (like graphene) such that absorption is on the order of a percent - Narrow bandwidth materials that are opaque to infrared but transparent to visible - Bad metals and non-band conductors that have correlated electron hopping from site to site Transparent conductors like ITO are critical materials for displays and solar cells, since light needs to enter/exit one side of the device.
ajuc 9y ago
See this experiment for a real transparent metal. Admitedly, the conditions are kinda extreme :) https://www.youtube.com/watch?v=BIGMfai_ICg https://www.youtube.com/watch?v=BIGMfai_ICg Don't mind the intro, the interesting part starts at around 2:00
pjc50 9y ago
I'd never realised the two were connected. What's a good learning reference for bandgap physics? It's something I've never quite understood properly.
- castle-bravo 9y ago
  You don't need bandgaps to understand why conductors (other than thin films of ITO) don't transmit light. You derive it from Maxwell's equations and the fact that in a conductor, current density = conductivity * electric field. Griffiths' Introduction to Electrodynamics is the standard undergraduate textbook on electromagnetism, and explains this reasonably well. For bandgaps, Ashcroft and Mermin's Introduction to Solid State Physics is what I'm reading from right now, but you don't need it to understand why metals (conductors) don't transmit light.
  - Confusion 9y ago
    Ashcroft and Mermin is only an 'introduction' in the graduate student sense of 'introduction'. I don't think you can make sense of it without previous grounding in both quantum mechanics and solid state physics.
    - castle-bravo 9y ago
      Well, he did ask about band gaps. Is there a way to understand band gaps without quantum mechanics? I think you only need a little Fourier analysis to get the basics of band gaps. Anyway, that text and along with Kittel's are the references for an undergraduate solid state course that I'm taking. No prior exposure to solid state physics for me and only introductory quantum mechanics (first half of Griffiths' QM); I find the text totally approachable.
      - silman 9y ago
        Semiconductor Device Fundamentals by Robert F. Pierret was my go-to for undergraduate text. The diagrams speak a thousand words and Pierret is a funny dude. Builds everything up from basic quantum. Don't mistake it with his graduate text, Advanced Semiconductor Fundamentals, though. That's also a great text, but very short and focuses almost exclusively on the quantum aspect without getting too much into the higher level meat of putting it together to form devices. For a comprehensive guide, though, Physics of Semiconductor Devices by Simon M. Sze was my reference bible. It's big and bulky, very heavy on the first principles math and physics, and has everything from quantum to devices and variants on devices.
dbsvsv 9y ago
I don't think in quite understand. You mean they don't let photons to pass through? In which case do electrons in orbit? Or nuclei for example? Or does this need advanced physics knowledge?
- tim333 9y ago
  Roughly light is electromagnetic radiation and puts force on electrons it comes in contact with. If the electrons are fixed in a non conductor they don't move much and so don't absorb the energy. If they can move as in most metals the force accelerates them and they absorb energy from the radiation, stoping of reducing it.
  - dbsvsv 9y ago
    My physics is only high school level so as I see, in the case of fixed - does the photon not get scattered/reflected or does it pass through the electron? And why no orbital transition?
    - ger_in_no 9y ago
      Reflection on the surface of polished metals occurs because of the collective movement of electrons at the surface, caused by the incoming photons. Light of most wavelengths, especially low-energetic infrared doesn't have enough energy to cause orbital transitions in most elements.
  - agumonkey 9y ago
    What about partial ? or only to some wavelengths ?
    - mannykannot 9y ago
      X-rays penetrate metal to some extent, though they also scatter off the atoms. Radiography of high value/risk metal components (such as the stressed parts of gas turbine engines) is a mainstream non-destructive testing technique.
  - 9y ago
jacquesm 9y ago
If the film is thin enough metal is transparent. See for instance 50/50 mirrors and gold plated windows. Of course you can now argue that if the photons hit the metal they will not pass through, but that's not how it works: the photons will excite an electron to a higher orbit and it may drop back to a lower orbit on the other side of the film making the metal appear transparent or it may reflect. edit: saiya-jin I can't reply to your comment but yes, the direction is preserved. The same happens with a mirror, the photons ejected will be ejected at the correct angle even though the photoelectric effect has absorbed the photons. That's why metals reflect the way they do! https://www.scientificamerican.com/article/how-do-mirrors-reflect-ph/ https://www.scientificamerican.com/article/how-do-mirrors-re... The small fraction of photons that is absorbed will heat up the mirror.
- saiya-jin 9y ago
  that doesn't make sense - if that would be the case, the back-emitted photon would have a random vector, not pertaining the same one as original one (thus preserving the picture beyond the sheet of metal). you are stating somehow the direction of photon is preserved when absorbed by electron - absurd idea even for layman physics (not claiming I know how this works, but this can't be the way)
  - archgoon 9y ago
    > you are stating somehow the direction of photon is preserved when absorbed by electron Well, that is how lasers work :) https://en.wikipedia.org/wiki/Stimulated_emission https://en.wikipedia.org/wiki/Stimulated_emission
  - didgeoridoo 9y ago
    I barely understand even layman-level physics, but it would seem to me that this “absurd” idea is just a natural implication of the conservation of momentum? edit: to all the downvoters of saiya-jin — let the one who has never defended their incorrect intuitions in physics cast the first downvote!
    - 9y ago
wolfi1 9y ago
I'm not so sure about that, ever hard of plasmonics?

Metal will never be transparent. Metal means metal bonds which means free electrons. Free electrons are opaque to visible light.

by dvh 9y ago

Metal will never be transparent. Metal means metal bonds which means free electrons. Free electrons are opaque to visible light.

tedsanders 9y ago

Just to add on for others reading your comment: Although metals are opaque, conductors can still be transparent. A few techniques: - Very thin layers (like graphene) such that absorption is on the order of a percent - Narrow bandwidth materials that are opaque to infrared but transparent to visible - Bad metals and non-band conductors that have correlated electron hopping from site to site Transparent conductors like ITO are critical materials for displays and solar cells, since light needs to enter/exit one side of the device.

ajuc 9y ago

See this experiment for a real transparent metal. Admitedly, the conditions are kinda extreme :) https://www.youtube.com/watch?v=BIGMfai_ICg https://www.youtube.com/watch?v=BIGMfai_ICg Don't mind the intro, the interesting part starts at around 2:00

pjc50 9y ago

I'd never realised the two were connected. What's a good learning reference for bandgap physics? It's something I've never quite understood properly.

castle-bravo 9y ago
You don't need bandgaps to understand why conductors (other than thin films of ITO) don't transmit light. You derive it from Maxwell's equations and the fact that in a conductor, current density = conductivity * electric field. Griffiths' Introduction to Electrodynamics is the standard undergraduate textbook on electromagnetism, and explains this reasonably well. For bandgaps, Ashcroft and Mermin's Introduction to Solid State Physics is what I'm reading from right now, but you don't need it to understand why metals (conductors) don't transmit light.
- Confusion 9y ago
  Ashcroft and Mermin is only an 'introduction' in the graduate student sense of 'introduction'. I don't think you can make sense of it without previous grounding in both quantum mechanics and solid state physics.
  - castle-bravo 9y ago
    Well, he did ask about band gaps. Is there a way to understand band gaps without quantum mechanics? I think you only need a little Fourier analysis to get the basics of band gaps. Anyway, that text and along with Kittel's are the references for an undergraduate solid state course that I'm taking. No prior exposure to solid state physics for me and only introductory quantum mechanics (first half of Griffiths' QM); I find the text totally approachable.
    - silman 9y ago
      Semiconductor Device Fundamentals by Robert F. Pierret was my go-to for undergraduate text. The diagrams speak a thousand words and Pierret is a funny dude. Builds everything up from basic quantum. Don't mistake it with his graduate text, Advanced Semiconductor Fundamentals, though. That's also a great text, but very short and focuses almost exclusively on the quantum aspect without getting too much into the higher level meat of putting it together to form devices. For a comprehensive guide, though, Physics of Semiconductor Devices by Simon M. Sze was my reference bible. It's big and bulky, very heavy on the first principles math and physics, and has everything from quantum to devices and variants on devices.

dbsvsv 9y ago

I don't think in quite understand. You mean they don't let photons to pass through? In which case do electrons in orbit? Or nuclei for example? Or does this need advanced physics knowledge?

tim333 9y ago
Roughly light is electromagnetic radiation and puts force on electrons it comes in contact with. If the electrons are fixed in a non conductor they don't move much and so don't absorb the energy. If they can move as in most metals the force accelerates them and they absorb energy from the radiation, stoping of reducing it.
- dbsvsv 9y ago
  My physics is only high school level so as I see, in the case of fixed - does the photon not get scattered/reflected or does it pass through the electron? And why no orbital transition?
  - ger_in_no 9y ago
    Reflection on the surface of polished metals occurs because of the collective movement of electrons at the surface, caused by the incoming photons. Light of most wavelengths, especially low-energetic infrared doesn't have enough energy to cause orbital transitions in most elements.
- agumonkey 9y ago
  What about partial ? or only to some wavelengths ?
  - mannykannot 9y ago
    X-rays penetrate metal to some extent, though they also scatter off the atoms. Radiography of high value/risk metal components (such as the stressed parts of gas turbine engines) is a mainstream non-destructive testing technique.
- 9y ago

jacquesm 9y ago

If the film is thin enough metal is transparent. See for instance 50/50 mirrors and gold plated windows. Of course you can now argue that if the photons hit the metal they will not pass through, but that's not how it works: the photons will excite an electron to a higher orbit and it may drop back to a lower orbit on the other side of the film making the metal appear transparent or it may reflect. edit: saiya-jin I can't reply to your comment but yes, the direction is preserved. The same happens with a mirror, the photons ejected will be ejected at the correct angle even though the photoelectric effect has absorbed the photons. That's why metals reflect the way they do! https://www.scientificamerican.com/article/how-do-mirrors-reflect-ph/ https://www.scientificamerican.com/article/how-do-mirrors-re... The small fraction of photons that is absorbed will heat up the mirror.

saiya-jin 9y ago
that doesn't make sense - if that would be the case, the back-emitted photon would have a random vector, not pertaining the same one as original one (thus preserving the picture beyond the sheet of metal). you are stating somehow the direction of photon is preserved when absorbed by electron - absurd idea even for layman physics (not claiming I know how this works, but this can't be the way)
- archgoon 9y ago
  > you are stating somehow the direction of photon is preserved when absorbed by electron Well, that is how lasers work :) https://en.wikipedia.org/wiki/Stimulated_emission https://en.wikipedia.org/wiki/Stimulated_emission
- didgeoridoo 9y ago
  I barely understand even layman-level physics, but it would seem to me that this “absurd” idea is just a natural implication of the conservation of momentum? edit: to all the downvoters of saiya-jin — let the one who has never defended their incorrect intuitions in physics cast the first downvote!
  - 9y ago

wolfi1 9y ago

I'm not so sure about that, ever hard of plasmonics?