Quantum confinement theory of ultra-thin films: electronic, thermal and superconducting properties

The miniaturization of electronic devices has led to the prominence, in technological applications, of ultra-thin films with a thickness ranging from a few tens of nanometers to just about 1-2 nm. While these materials are still effectively 3D in many respects, traditional theories as well as ab initio methods struggle to describe their properties as measured in experiments. In particular, standard approaches to quantum confinement rely on hard-wall boundary conditions, which neglect the unavoidable, ubiquitous, atomic-scale irregularities of the interface. Recently, a unified theoretical approach to quantum confinement has been proposed which is able to effectively take the real nature of the interface into account, and can efficiently be implemented in synergy with microscopic theories. Its predictions for the electronic properties such as the electrical conductivity of semiconductor thin films or the critical temperature of superconducting thin films, have been successfully verified in comparison with experimental data. The same confinement principles lead to new laws for the phonon density of states and for the heat capacity of thin films, again in agreement with the available experimental data.