3. Quantum confinement of surface states

Discrete energy states are formed whenever electrons are spatially confined by a potential well, as in atoms and molecules. Localized states also appear in "quantum wells" formed by artificially-created nanoscale structures of varying dimensions and sizes. Recent advances in nanofabrication techniques (self-assembly, growth on nanostructured surfaces, direct manipulation of atoms and molecules by STM or AFM) have made it possible to create a wide variety of more or less elaborate low-dimensional structures on a surface, with at least one nanometer-sized dimension: thin films, of course, but also quantum dots and wires (0D and 1D), quantum enclosures (2D)...