Quantum Size Effects in Thin Film Stabilities and Properties

Recently, it has been shown that the size quantization of itinerant electrons in an ultra thin metal film plays an important role in the early formation stages and kinetic stabiliy of thin films. This Quantum Size Effect(QSE) also brings about a lot of new interesting physical and chemical properties of thin film. In this paper, I will give a brief introduction to the mechanism of QSE and talk about some practical research examples to the thin film stabilities and properties. 1 Classical film growth modes From a classical point of view, the formation and growth of a thin film is determined by both thermodynamic factors, such as the Gibbs free energy and kinetic factors, such as surface diffusion and deposition rate. In the thermodynamic limit, where the deposited species have enough thermal energy to diffuse and reach energy minimum distribution, the Gibbs free energy plays a key role to determine the morphology of thin film. Or, more precisely speaking, the change of Gibbs free energy in the growth process ∆G = V ·∆GV + ∆(AS · γ) determines the final morphology. Here, V is the volume of thin film and AS is the total surface of the thin film including the interfacial area. ∆GV is the free energy per unit volume of thin film, γ is the surface energy density and ∆(AS · γ) is the corresponding surface energy change before and after deposition. If we only consider film with certain volume like Figure 1 below, Figure 1: Thin film B deposited on substrate A