Proposal for experiments for the direct verification of the size-quantization effect

Based on a simple pictorial construct in E-k→ space, we analyze the interactions of external excitations with electrons in thin films and propose three new experiments for the direct verification of the size-quantization effect. Two of these involve intersubband transitions, and the third is predicted to give results analogous to the giant quantum oscillations observed in solids under the action of a magnetic field. Excitations suitable for these experiments are shown to be ultrasonic waves.