Direction of Photo Electron Emission

In summary, the photo electrons are emitted in all directions, but the most productive angle is around 70-80 degrees with the beam.
  • #1
Leb
94
0
I was looking for information on how the photo electrons are emitted when under X-ray radiation. In this ancient review paper here http://journals.aps.org/pr/pdf/10.1103/PhysRev.30.488 [Broken] they state that the most common angles for non polarized X-ray beams (of various energies) range roughly at around 70-80 degrees with the beam. It is unclear to me, whether the photo electrons are moving towards the source of the X-ray beam or away from it ? Undergrad texts do not seem to shed light on this matter, the best one gets is pictures with emitted electrons being at a 90 degree angle to the incoming photon. Also, I assume this angle is given for a cone, i.e. it's 70-80 w.r.t. the beam, but with 2pi angle around the beam ?
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
Debends upon whether the beam is incident from the front or the back. I've done a lot of photo-electron generation, mostly in transmission.

The energy reqired to emit an electron is the "work function", which varies with the crystal plane that is encountered: 111, 210, etc. Each has a slightly different work function.

But the liberated electron may shoot off in any most any direction, though there are statistics (which I don't recall the details at the moment; they are in my old notes).

Most interactions don't make it out because of (a) going in a bad direction, or (b) scattering. Thus only interactions within a skin depth might be productive, and even then not many.

If there is an extraction field, the electron paths get straightened out.
 
  • #3
Well, that "any direction" answers seems to conflict with experiments from 1920-30's, I wonder why did they find a preferential angle...
 
  • #5
M Quack said:
There is actually some information that can be extracted from the direction of emission. The technique is called
ARPES (angle-resolved photo-emission spectroscopy)

http://en.wikipedia.org/wiki/Angle-resolved_photoemission_spectroscopy

http://arxiv.org/abs/1303.1438

Since I had done ARPES, I can comment on this.

The OP asked about x-ray photoemission, which is distinctly different than the "standard" ARPES experiment that is done in the UV range.

Secondly, in ARPES, the preferred direction of emission is due to the in-plane momentum of the electrons in the surface, i.e. the "k" in band structure. However, this also means that one must perform the experiment on single-crystal material. A polycrystalline or amorphous crystal will not have such directional emission and all you'll get is a momentum-averaged density of states.

I have not looked at the OP's reference, and thus, don't know if there's something similar here. XPS has other factors involved, and any preferential direction of photoelectron emission can be due to other reasons than what I stated here. Certainly, it could be angle-resolved XPS, which would have the same explanation as what I've given above.

Zz.
 
  • #6
I have a question similar to the original post here. I can't find much information on the direction/momentum and polarization of photo electrons emitted by X-rays. Does anyone know of any good, modern, free references for this? So far the newer references I've found gloss over this topic with one sentence like "electrons scatter mostly in the direction of the E-field of linearly polarized incident X-rays," but I'm interested in learning more details about this.
 

What is photoelectron emission?

Photoelectron emission is a phenomenon in which electrons are emitted from a material when it is exposed to light or other forms of electromagnetic radiation.

What factors affect the direction of photoelectron emission?

The direction of photoelectron emission is influenced by the angle of incidence and the intensity of the incident light, as well as the properties of the material itself, such as its work function and surface structure.

What is the difference between normal and tangential photoelectron emission?

Normal photoelectron emission refers to electrons being emitted perpendicularly to the surface of the material, while tangential photoelectron emission is when electrons are emitted at an angle parallel to the surface.

Can the direction of photoelectron emission be controlled?

Yes, the direction of photoelectron emission can be controlled by adjusting the angle and intensity of the incident light, as well as the properties of the material. This is useful in various applications such as electron microscopy and photovoltaic cells.

What is the significance of studying the direction of photoelectron emission?

Understanding the direction of photoelectron emission can provide valuable insights into the properties of materials and their interaction with light. It also has practical applications in various fields including materials science, surface chemistry, and energy conversion technologies.

Similar threads

  • Atomic and Condensed Matter
Replies
17
Views
7K
  • Introductory Physics Homework Help
Replies
3
Views
1K
Replies
8
Views
2K
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
4
Views
1K
Replies
13
Views
6K
  • Introductory Physics Homework Help
Replies
2
Views
8K
  • Atomic and Condensed Matter
Replies
4
Views
4K
  • Introductory Physics Homework Help
Replies
10
Views
10K
  • Classical Physics
Replies
9
Views
6K
Back
Top