OBSERVATION OF A QUANTUM SIZE EFFECT WITH UNUSUAL LONG PERIOD BY EXPERIMENTS OF ABSORPTION OF LOW-ENERGY ELECTRONS AND BY RHEED - A SIMPLE PHYSICAL MODEL

Absorption experiments of electrons of very low energy (few eV) have been done during deposition, at 80 K, of indium on polycrystalline and textured (111) gold films. The target current, for limited range of the energy (E) of the electrons, versus the indium thickness is modulated by damped oscillations with unexpectedly long period of which the value varies with the electronic energy. These results, as those obtained earlier by electrical resistance and work function measurements, can be well explained by a simple physical picture: an effect of vernier (i.e., a stroboscopic effect) between: (i) the quantization of the transverse electronic states in the indium layer in the case of the free electron model (giving a period of half the de Broglie wavelength for electrons of energy E); (ii) the almost perfect atomic layer by atomic layer growth of indium on the gold substrate (d(101) = 0.271 nm). Oscillations of the same type have been found with RHEED experiments by monitoring the variations of the specular intensity in the diffraction pattern.