It is known that surface measurement by X-ray photoelectron spectroscopy (XPS) is only to a depth of a few nanometers.
Can it be used to measure the chemical content at a depth of a few microns below the surface of a sample object by adjusting the intensity of the incident beam? Does anyone have experience in doing this with other spectroscopic methods?
Please enlighten me...
The penetration depth of XPS is primarily determined by the mean free path of the electrons which are attempting to leave the material, not by the depth to which the x-ray beam extends into the material. As a reference: when you perform an x-ray image of your chest at a hospital, the rays also go through your "soft matter" while the electrons locally excited by that don't leave your body (mostly).
Mild changes to the penetration depth can be achieved by varying the x-ray energy and thus the mean free path of the electrons, but I don't think that goes to the depths you have in mind.
In addition to the answer of Jürgen Weippert ,
I would like to add that, depending on the photo electron energies involved, you may have some electrons, which carry informations from a very few µm below the surface. But these electrons will not be primary photo electrons; they are due to the cascade of multiply scattered electrons, which a) have lost their primary energy and b) which were created by electron collisions.Thus they are useless for XPS analysis.
Increasing the x-ray intensity will not change the energy distribution of the electrons and not change any electron escape depth.
Best regards
G.M.
Dear Fauzan,
I think XPS is not the well-suited for what you want to measure. For chemical properties, you may use XRD, EXAFS, Raman or another spectroscopy technique. For the physical properties of a burried interface (thickness, roughness, SLD) you should use XRR in transmission mode. Here, intensity is needed and you also want to choose an X-ray source (energy) that is suited for the materials you are using.
Best regards,
Elhoucine
I concluded that) all spectroscopic methods for chemical content detection only measure the energy of electrons originating from a few nanometers deep. Except for XRR (mentioned by Elhoucine Hadden ) , which I have no information about yet.
But, how about if the incident beam is directed to the side of the sample and then it is moved for every measurement to a certain distance (as the depth of the layer)? Does this make sense?
No,at least for XPS that doesn't change anything since it's still the mean free path of the exiting electrons which determines the probing depth.
For other methods such as Raman or PL a depth mapping is actually possible, but these of course are not measuring methods for stoichiometry.
no. Intensity of the beam will not influence the results. DPS is more of the energy that is able to escape From the surface of the sample. The energy is so low that only able to leave from about 4-7nm from the surface.
alternatively, you can sue the argon beam to dig to the depth you want and conduct XPS analysis at the given depth (relative to silicon wafer). But it’s a destructive method.
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