Interpretation of the photoelectric effect

[edguy99]

Remember, we were restricting it to within the UV range. In this range of photon energy, there is a significantly higher probability of emission from predominantly the conduction band. You can see this if you look at ARPES data using UV light sources. The photoemission spectrum shows no such "bound" states to the atoms .

In contract, x-ray photoemission spectroscopy (XPS) will cause emission from the "core level", which is not from the conduction band. But this is not the typical photoelectric effect that is in question in this thread.

So what I say is based on not just the theory, but also from experimental observations that I've performed.

Zz.

My google lookup of ARPES pulls up this pdf as the first item.

In an effort to understand this better, I assume the hv jump from the bonded electrons (EB) are distinct and pretty clear. I also assume the jump from EF to a broader area is the conduction band you are talking about.

I am unclear on this:
1/ the electrons in the conduction band when hit with a specific wavelength will have somewhat diffuse energy because of their kinetic motion in the conduction band and that is why we see a broad area?
or 2/ the electron will be ejected with the same energy as the wavelength that hit it subject to the work function? (ie. for each specific wavelength used, you see only a very narrow energy line)

Thanks

 

[Dadface]

In terms of the practical applications of photo cathodes and the like are there any advantages in using the more modern theories? Are the theories good, for example, at showing how the rate of electron emission depends on the intensity of the incident radiation and what factors affect the efficiency of the cathode? Thank you.

 

[ZapperZ]

My google lookup of ARPES pulls up this pdf as the first item.
View attachment 143118
In an effort to understand this better, I assume the hv jump from the bonded electrons (EB) are distinct and pretty clear. I also assume the jump from EF to a broader area is the conduction band you are talking about.

I am unclear on this:
1/ the electrons in the conduction band when hit with a specific wavelength will have somewhat diffuse energy because of their kinetic motion in the conduction band and that is why we see a broad area?
or 2/ the electron will be ejected with the same energy as the wavelength that hit it subject to the work function? (ie. for each specific wavelength used, you see only a very narrow energy line)

Thanks

What you have cited is a basic photoemission spectroscopy that measures the energy spectrum. ARPES technique goes beyond that by also measuring the momentum of the photoelectrons. That picture also does not indicate the energy scale, i.e. what are the photon energies that will cause a noticeable emission from the core level?

Remember what I pointed out to be the issue with your post - that you were not aware that in a standard photoelectric effect experiment, using as high as UV photons, that the overwhelming signal will come from photoelectrons emitted from the conduction band, not from electrons bounded or localized at the various atoms of the metal. That figure already shows that because the energy band that crosses the Fermi energy is just from the conduction band.

To answer your specific question:

1. I don't what you mean by "diffuse energy". One can easily get very sharp "peaks" in the energy spectrum in ARPES experiments. BTW, here's an example of an ARPES spectra in which both energy and momentum are captured (i.e. the band structure).

You'll notice the very bright and well-defined dispersion curves, especially near the Fermi energy, which will be the dominant emission in this case. This is an example of a conduction band of a metal.

2. Er... electrons do not get "... ejected with the same energy as the wavelength that hit it subject to the work function..." Only the ones from the Fermi energy do. Electrons get ejected with a RANGE OF ENERGY, depending from which part of the band it came from. I stated the word "binding energy" already in this thread. This is the energy state of the electrons in the solid below the Fermi energy. In fact, this can be clearly seen in your own diagram. Those from well before the Fermi energy will have to overcome not just the work function, but the binding energy of the solid.

Zz.

 

[edguy99]

... One can easily get very sharp "peaks" in the energy spectrum in ARPES experiments. BTW, here's an example of an ARPES spectra in which both energy and momentum are captured (i.e. the band structure).

View attachment 145109

You'll notice the very bright and well-defined dispersion curves, especially near the Fermi energy, which will be the dominant emission in this case. This is an example of a conduction band of a metal...

Thank you for the post. I have read a lot about ARPES experiments in the last 2 days and hope to learn more. What do the 3 labeled dispersion curves/bandlines say to you?

 

[ZapperZ]

Thank you for the post. I have read a lot about ARPES experiments in the last 2 days and hope to learn more. What do the 3 labeled dispersion curves/bandlines say to you?

They are just different bands.

The band structure of a material isn't just a simple parabolic curve. Many of us in this field often call it the spaghetti lines. For example, look at the calculated band structure of gold:

ARPES experiments can directly measure such bands, especially close to the Fermi energy. It can also (with reconstruction) map out the Fermi surfaces.

But we're now going very far off the topic here.

Zz.