Reactive sputter deposition of metal oxide nanolaminates

Abstract

We discuss the reactive sputter deposition of metal oxidenanolaminates on unheated substrates using four archetypical examples:ZrO2–Al2O3,HfO2–Al2O3,ZrO2–Y2O3, and ZrO2–TiO2. The pseudobinary bulk phase diagrams corresponding to thesenanolaminates represent three types of interfaces. I. Complete immiscibility(ZrO2–Al2O3 andHfO2–Al2O3). II. Completemiscibility (ZrO2–Y2O3). III. Limited miscibility without a common end-member lattice(ZrO2–TiO2). We found that, although reactive sputter deposition is a far-from-equilibrium process,thermodynamic considerations strongly influence both phase formation within layers and atinterfaces. We show that pseudobinary phase diagrams can be used to predict interfacialcation mixing in the nanolaminates. However, size effects must be considered to predictspecific structures. In the absence of pseudoepitaxy, size effects play a significant role indetermining the nanocrystalline phases that form within a layer (e.g. tetragonalZrO2, tetragonalHfO2, and orthorhombicHfO2) and at interfaces(e.g. monoclinic (Zr,Ti)O2). These phases are not bulk standard temperature and pressure phases. Their formation isunderstood in terms of self-assembly into the lowest energy structure in individual criticalnuclei.