To understand the FOs phenomenon in metals, lets consider electron gas(for the reminder see fig. ) density around an impurity or a defect that differs from that of the bulk metallic material. The impurity introduces a boundary condition for the electron wavefunctions because the probability of an electron occupying this point in space becomes zero since it is already occupied. Thus, we obtain the reflection of the electron waves from every impurity, and their mutual interference results in an uneven electron density distribution around the impurity. Such a distribution can be characterized by its oscillatory nature, with the amplitude decaying according to the power law the further away we look.