Surface area of solids - Electronic properties

The science of materials has always been a major concern for humanity. Among the various states of matter (gas, liquid, solid), the solid state—and more specifically the crystalline solid state—provided scientists with a broad field of investigation from very early on, leading to fruitful results.

Indeed, the crystalline medium, characterized by the periodic and ordered repetition of an identical pattern composed of ions, atoms, or molecules, exhibits interesting spatial symmetry properties (crystal lattice symmetry). These symmetry properties allow for a relative simplification in understanding collective phenomena in the crystalline medium and also facilitate the modeling of its physical properties. Examples of these advantages can be found in both crystallographic structure studies (article Geometric Crystallography in this section) and electronic structure (article "Electronic Structure of Solids") in this section).

However, every solid is bounded by a surface that defines its volume. This surface plays a crucial role, as it governs the interactions between the surrounding environment and the solid. It is all the more important when the surface-to-volume ratio of a given material is high. This is the case, for example, with aggregates, small particles consisting of a few metal atoms used in catalysis, and ultrathin layers used in optical coatings, passivation or protective layers, microelectronics, etc.

However, the surface of a solid exhibits an arrangement of ions, atoms, or molecules that is significantly disrupted compared to the periodic arrangement found within the bulk of the solid. Furthermore, in the direction perpendicular to the surface, there is a loss of translational symmetry. The physical properties of a crystal’s surface are thus significantly altered compared to its bulk properties. This alteration affects both the crystallographic structure (article Surface of solids. Physisorption. Chemisorption. Segregation [A 244] ) and the surface electronic structure, which is the subject of this article.

Understanding the electronic properties of surfaces requires a solid grasp of the energy band structures of bulk solids, which is not generally easy for non-specialist readers to acquire. In this presentation, we will review, when necessary, the essential results obtained for a bulk solid, justifying them as often as possible with phenomenological arguments rather than sophisticated quantum mechanical calculations, which, in our opinion, risk quickly exceeding the scope of this treatise. For further details, we refer the reader to the articles on Quantum Mechanics ,...