Assumptions
<h2>There are several assumptions inherent to ARXPS experiments :</h2> <h2 class='liste'>1) Any effects of the sample crystallinity on the variation of the signal with changes in the photoemission angle can be ignored. </h2> <h2>Certain ARXPS experiments specifically look at the variation in peak intensity with photoemission angle due to shadowing effects, channeling and so on. In our treatment, however, we shall consider the sample to be effectively amorphous.</2> <h2 class='liste'>2) The effect of elastic collisions can be ignored.</h2> <h2>Photoelectrons that suffer elastic collisions do not lose energy, although they might change direction. Therefore, some photoelectrons may be knocked into, or out of, the analyzer acceptance cone. Such photoelectrons account for a few percent of the total signal in typical experiments.</h2> <h2 class='liste'>3) The refraction of emerging photoelectrons at the surface can be ignored.</h2> <h2>This assumption is reasonable at typical photoelectron energies and photoemission angles below 85 degrees.</h2> <h2 class='liste'>4) The sample's surface is perfectly smooth.</h2> <h2>This is likely to be true only in the most careful experiments.</h2> <h2 class='liste'>5) The analyzer acceptance angle is small, essentially zero.</h2> <h2>More realistic values are on the order of 12-16 degrees.</h2> <h2 class='liste'>6) The sample is uniform in composition on the x-y plane, at least within the analysis area.</h2> <h2>This assumption reasonable if the sample is carefully prepared.</h2> <h2 class='liste'>7) Data manipulation does not introduce any artifacts or errors.</h2> <h2 class='liste'>8) The inelastic mean free path for a given photoelectron is independent of the composition of the material through which it emerges from the sample.</h2> <h2>Sometimes, one can postulate a known composition for a sample, or for a layer therein, and obtain the appropriate photoelectron mean free path from the literature. Other times, it may be necessary to use an estimate.</h2> <h2 class='liste'>9) The total atom density in function of depth is a constant. </h2> <br /> <h2>That's a lot of assumptions and an optimistic idealization of the sample and the experiment. It is therefore wise to exercise caution in the interpretation of ARXPS data and to take the results with a pinch of salt.</h2>