The electron states in a finite one-dimensional crystal are solved in the WKB approximation. No conditions are imposed on the number of atomic levels involved or on the shape of the potential wells and their matrix elements. Explicit conditions for the occurence of surface states as well as bulk...

A monolayer of 4He atoms is treated as a system of hard-sphere bosons in a thin film geometry, with a finite thickness. The method of pseudopotential is used to calculate first the energy spectrum, and then the Helmholtz free energy and other thermodynamic functions of the system. It is found...

The radiative decay of the Wannier exciton in thin crystal films is studied by the method of Heitler and Ma in the resonance approximation. It is shown that, while the broken crystal symmetry opens up the possibility of radiative decay, the correlation brought about by the interaction of the...

The energy levels of an impurity atom in a thin slab of crystal are calculated by the method of equivalent Hamiltonian, which includes potential barriers representing the surfaces. For slab thickness smaller than the Bohr radius of the impurity atom, the atom is found to behave like a two...