The film are grown using PECVD by CH4/Ar/N2 composition. XPS spectra of as grown film is not showing any N-peak, whereas Hall measurement confirmed the n-type carrier concentration. How to explain the facts?
Thanks in advance.
Dear Sir,
in case that the relative amount of N is very small, the small photoemission cross section of the N-1s orbital will prevent the appearance of a distinct N-1s signal in a usual survey scan (or detail spectrum). If it was my experiment, I would probe the N-1s range (e.g. from 390 eV to 410 eV) with the largest pass energy for several hours (e.g. over night) to see whether as signal emerges out of the background.
Sincerely, FM
Dear Subrata,
XPS probes the top 10 nm of the surface only. It may happen that the surface of your sample is either covered with impurities or nitrogen is incorporated in the bulk not on the surface. So you can characterize your sample with TOF-SIMS which would give you information of the bulk.
Dear Sir,
in case that the relative amount of N is very small, the small photoemission cross section of the N-1s orbital will prevent the appearance of a distinct N-1s signal in a usual survey scan (or detail spectrum). If it was my experiment, I would probe the N-1s range (e.g. from 390 eV to 410 eV) with the largest pass energy for several hours (e.g. over night) to see whether as signal emerges out of the background.
Sincerely, FM
XPS investigate just the surface, from 2 to 20 atomic layers, then if nitrogen is not in this region, you can't detect it with this technique.
I totally agree with all the above possible explanations of your "unusual" results. If you wamt to probe the presence of nitrogen in your (apparently very inhomogeneous) films, in addition to XPS you need at least Raman and ATR/FT-IR spectra. This is because addition of N gas within CVD technique leads to a rather significant amorphization of the film with formation of N-rich clusters usually concentrated near the grain boundaries. As a result, nitrogen addition favors a significant increase of the grain (cluster) size which, in turn, contributes to a tangible Hall response. These N-rich clusters may actually form both at the surface and deep in the bulk of the film. A particular configuration (favoring surface or bulk states) depends on the experimental conditions fulfilled during an actual CVD procedure.
As XPS determine the few nm i.e 5-10 nm of the sample so if N is not present in that region so it will not possible to analysis by this technique. You need an other one.
If the other mentioned techniques are not directly on hand but XPS is, you could try to increase the probing depth of the XPS by increasing the takeoff angle towards 90°
Dear Subrata Da:
XPS analysis always gives the chemical compositions up to 10 to 20 nm depending upon the compositions. Most of the cases, the samples are naturally oxidized in atmosphere. Thus, you can try XPS after etching the sample by Ar sputtering if your XPS is not in-situ. In order to confirm the presence of N in bulk, probably you need to think of other spectroscopic technique like Raman or FTIR.
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