A scientific approach to surfaces. Characterization and properties

There are different ways of looking at surfaces, for example in terms of scale or cleanliness. But we can also distinguish between model surfaces and industrial, i.e. real, surfaces. The corresponding characteristics are not necessarily the same. While the solid-state physicist will be interested in the electronic structure of surface atoms and observe this on a nanometric scale, the engineer and technician will look at the surface as an imprint of the tool used to obtain or condition it. The scale of observation will not be the same: from nanometric or even microscopic in the first case, it will be meso- and most often macroscopic in the second [9][10] .

Whatever the discipline, the surface is commonly defined as the part or outer boundary of a solid. Given that any material is generally used in a given environment (air, gas, aqueous medium, condensed phase, lubricant, etc.), the surface must be considered as an interface: solid – gas, solid – liquid, or even solid – solid. In this context, given the compositional or characteristic profiles in the zone adjacent to the surface, we even introduce the notion of interphase, which enables us to introduce that of adaptive properties (refractive index gradient, for example).