The first outward atomic layers of the object - i.e. its surface - are particularly important
First of all because they constitute the zone of direct interaction with the environment. Oxidation, corrosion, wear, dissolution, all these and other processes start at the surface.
Another reason is that only the surface is immediately available for modification of certain properties of the the material such as its coupling to another surface by welding or bonding , or its protection by metalisation, implantation, or electrodeposition.
A third reason is that the analytical methods limited to the first layers yields information on the zone which, when perturbed, need to be eliminated (for instance by erosion) before the inner zones, truly representative of the bulk material, can be studied.
Beginners or experienced users of spectrometries surface analyses, (XPS, AES, and UPS) are all welcome to exchange and share data in this forum and disseminate their results by adding them to the data base.
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