21
$\begingroup$

I've been experimenting with some materials by changing the wavelength of the incident light on the material and detecting photoelectrons, like in the diagram below:

enter image description here

I might get a response that looks like this

enter image description here

Both materials have the same HOMO (organics) / Work Function (metals). For example, I hardly detect any photoelectrons (emitted electrons) from stainless steel, but loads from copper (both roughly 4.5eV). However, I am more interested in organics.

Why might some substances (e.g certain blends of perovskites) emit more photoelectrons than others (even if I have exceeded the energy required to lift an electron from the HOMO to the vacuum level)?

I thought it might be related to Density of States in metals, but this effect is also found in non-lattice molecules.

Could this be related to the reversibility of the reaction? I heard mentioned by a scientist (name now unknown) that molecules that easily lose or win an electron by an outersphere process (?) (which are likely to have a clean reversible CV voltagramm) exhibit a strong response in spectroscopy where an electron is given.

$\endgroup$
6
  • 9
    $\begingroup$ Three words - density of states. $\endgroup$
    – Jon Custer
    Commented Jul 26, 2017 at 13:46
  • 1
    $\begingroup$ I suggest that you google "photocathodes" for a lot more information. Most public university libraries have some public access which will allow you to get articles from many pay sites for free. $\endgroup$
    – MaxW
    Commented Jul 26, 2017 at 15:05
  • 1
    $\begingroup$ Do you mean organic molecules blended with perovskite? You have one perovskite, and you change the organic composition? $\endgroup$
    – Alchimista
    Commented Jul 26, 2017 at 22:36
  • $\begingroup$ Some material emits more photoelectrons because of there low value of work function(minimum amount of energy to be dissipated for photoelectrons to be emitted. $\endgroup$ Commented Feb 27, 2020 at 1:14
  • 1
    $\begingroup$ Is it a simple as the reflectivity of the substance under investigation? If a photon is reflected, it cannot remove an electron. You mention stainless steel, in my experience stainless steel is very reflective and the neutral colour suggests it is reflective over a wide range of frequencies. Copper clearly is less reflective at shorter wavelengths, given its colour. $\endgroup$ Commented Feb 16, 2023 at 8:24

2 Answers 2

1
$\begingroup$

Based on photoelectric effect, the amount of photons emitted is dependent on the intensity of the incident radiation. All factors that would emit for photoelectrons include; Energy of light and potential difference, the nature/ chemistry of material, intensity of light, and the frequency of light. Ive learned that increasing the light frequency increases the Kinetic Energy of photoelectrons and increasing of the light amplitude will increase the current.

$\endgroup$
-1
$\begingroup$

When EM radiation encounters a barrier, it can be reflected/scattered, transmitted, or absorbed. Only absorbed photons can have their energy converted to photoelectrons. But even if the radiation is absorbed then its energy could be converted to many forms that don't involve the emission of a photoelectron.

The photon's energy could be converted to heat, increasing the kinetic energy of particles within the material without changing their mean position or the energy could alter the position of particles with no emission, altering the substance's microstructure. In some cases, chemical bonds can be altered or new photons emitted at a different wavelength. Finally, photons that penetrate through the outermost layers of the material might create photoelectrons that could interact with those layers before escaping.

Chemical properties and physical microstructure at and near the surface would have an impact on all those things.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.