Hello everyone,
I have been studying x-ray photoelectron spectroscopy (XPS) for a while. I have studied loads of literature works on XPS. It has already been established that we have to (should) clean the surface before data collection to get rid of the surface contamination, which comes from the contact of the sample with air. Moreover, it is also reported in the literature that the surface chemistry (many other effects are also possible) of your sample might change depending on the etching parameters selection, such as etching particle, energy, angle, and time/rate (depth), which leads to unreliable data. Another thing is that if we successfully etch the sample in any depth without damaging it, it will not show the surface properties but the bulk state of the sample. However, I have not found any solid reference for these parameters yet. In our case, we are using Ar+ ions as an etching particle and etched at different depths with different energies.
What is the suitable etching energy, angle, and time/rate (depth) for studying surface properties correctly?
I have not attached any reference articles since these are summarized information.
Thanks!
That's material-specific.
For graphite or other covalently bound materials, sputter etching will irreversibly damage the surface and thus create new states, so for these, annealing them just below a temperature at which some sort of "intrachemistry" happens has to be enough.
For metal surfaces, 0.5keV for 1min at 90° with subsequent annealing to 100K below the metal melting point did the job for me; at least the surface states became visible for oriented crystals that way.
For ceramics or other ionic compounds, you probably need more energy in order to achieve something, but I've never done that.
Dear Jürgen Weippert
Thank you very much for your prompt reply and useful information.
Best regards,
Dear Dr. Mst. Irin Naher ,
cleaning the surface of a material (before or "during" an analysis) is an extremely critical operation and depends, as the Dr. Jürgen Weippert correctly said, on the type of material you want to analyze but also on the information you want to obtain from the material. the analysis that will be conducted. If I have to characterize a thin film, cleaning the sample before insertion into the analysis chamber must not -theoretically- alter it and if I have to make a depth profile with sputtering I must take into account the existence of a preferential sputtering depending on the elements which I'm going to analyze.
The eminent physicist, Wolfgang Pauli, was therefore right when he said: “God made the bulk; the surface was invented by the devil.” Pauli explained that the diabolical characteristic of surfaces was due to the simple fact that a solid surface shares its border with the external world.
Good work and my best regards, Pierluigi Traverso.
Dear Pierluigi Traverso,
Thank you so much for your kind reply. It has been an interesting and informative discussion Jürgen Weippert and Pierluigi Traverso.
I am studying semiconductors-in powder form. I want to explore phase purity, bonding nature, chemical state, electronic energy diagram, etc. from XPS and UPS studies.
Thank you once again!
Best regards,
Mst. Irin Naher
Powder is hard to handle in this respect because unless you are one of the few lucky people who own an ambient pressure XPS, you need to get the powder in vacuum without getting crumbles into the chamber. Probably you will have to press it into some sort of pellet.
It's questionable whether sputtering that pellet will do any good:
a) Being subjected to the sputtering may cause crumbling in the pellet, and then the chamber is contaminated.
b) Whatever saturates the top surface, of course also saturates the sides of the grains, so its signal contributions will still be there no matter how much you sputter.
Dear Jürgen Weippert, Thanks for your replie. I have similar concerns you mentioned since my samples are in powder form!
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