Marta Martins Saraiva

Sputter-deposited Mg-Al-O thin films: linking molecular dynamics simulations to experiments

Using a molecular dynamics model the crystallinity of MgxAlyOz thin films with a variation in the stoichiometry of the thin film is studied at operating conditions similar to the experimental operating conditions of a dual magnetron sputter deposition system. The films are deposited on a crystalline or amorphous substrate. The Mg metal content in the film ranged from 100% (i.e. MgO film) to 0% (i.e. Al2O3 film). The radial distribution function and density of the films are calculated. The results are compared with x-ray diffraction and transmission electron microscopy analyses of experimentally deposited thin films by the dual magnetron reactive sputtering process. Both simulation and experimental results show that the structure of the Mg‐Al‐O film varies from crystalline to amorphous when the Mg concentration decreases. It seems that the crystalline Mg‐Al‐O films have a MgO structure with Al atoms in between. (Some figures in this article are in colour only in the electronic version)

Compositional effects on the growth of Mg(M)O films

The influence of the composition on the crystallographic properties of deposited Mg(M)O (with M=Al, Cr, Ti, Y, and Zr) films is studied. For a flexible control of the composition, dual reactive magnetron sputtering was used as deposition technique. Two different approaches to predict the composition are discussed. The first is an experimental way based on the simple relationship between the deposition rate and the target-substrate distance. The second is a route using a Monte Carlo based particle trajectory code. Both methods require a minimal experimental input and enable the user to quickly predict the composition of complex thin films. Good control and flexibility allow us to study the compositional effects on the growth of Mg(M)O films. Pure MgO thin films were grown with a (111) preferential out-of-plane orientation. When adding M to MgO, two trends were noticed. The first trend is a change in the MgO lattice parameters compared to pure MgO. The second tendency is a decrease in the crystallinity of the MgO phase. The experimentally determined crystallographic properties are shown to be in correspondence with the predicted properties from molecular dynamics simulations.

Texture and microstructure in co-sputtered Mg-M-O (M = Mg, Al, Cr, Ti, Zr, and Y) films

Mg-M-O solid solution films (M = Mg, Al, Cr, Ti, Zr, and Y) with various M contents are grown employing reactive co-sputtering by varying the target-to-substrate distance. It is shown that all films are biaxially aligned. When the two cathodes are equipped with the same target material (Mg), the in-plane alignment is determined by the cathode closest to the substrate, i.e., by the largest material flux. In the case of nearly equal material fluxes from the two cathodes, double in-plane orientation is observed. This is also the case for the Mg-Al-O and Mg-Cr-O films, while the Mg-Ti-O, Mg-Zr-O and Mg-Y-O films exhibit single in-plane orientation. Pole figures indicate that the grains in Mg-M-O (M different than Mg) are titled; in the Mg-Al-O, Mg-Cr-O, and Mg-Ti-O films, the grains tilt towards the Al, Cr, and Ti metal flux, respectively, while the grain tilt of the Mg-Zr-O and Mg-Y-O films is found to be towards the Mg metal flux. Furthermore, SEM cross-sectional images of the Mg-M-O films reveal columnar m...

Sputter deposition of MgxAlyOz thin films in a dual-magnetron device: a multi-species Monte Carlo model

A multi-species Monte Carlo (MC) model, combined with an analytical surface model, has been developed in order to investigate the general plasma processes occurring during the sputter deposition of complex oxide films in a dual-magnetron sputter deposition system. The important plasma species, such as electrons, Ar + ions, fast Ar atoms and sputtered metal atoms (i.e. Mg and Al atoms) are described with the so-called multi-species MC model, whereas the deposition of Mg x AlyOz films is treated by an analytical surface model. Target-substrate distances for both magnetrons in the dual-magnetron setup are varied for the purpose of growing stoichiometric complex oxide thin films. The metal atoms are sputtered from pure metallic targets, whereas the oxygen flux is only directed toward the substrate and is high enough to obtain fully oxidized thin films but low enough to avoid target poisoning. The calculations correspond to typical experimental conditions applied to grow these complex oxide films. In this paper, some calculation results are shown, such as the densities of various plasma species, their fluxes toward the targets and substrate, the deposition rates, as well as the film stoichiometry. Moreover, some results of the combined model are compared with experimental observations. Note that this is the first complete model, which can be applied for large and complicated magnetron reactor geometries, such as dual-magnetron configurations. With this model,

Composition-crystallinity-property relations in Mg-M-O films

The crystallographic properties such as texture and the level of crystallinity are important issues for the application of thin films. A fundamental understanding of the thin film growth mechanism forms the key to tune these properties. To understand the transition from crystalline-to-amorphous noticed when changing the composition of oxide thin films, Mg-M-O thin films (with M = Al, Cr, Ti, Zr, and Y) were deposited using reactive magnetron sputtering. Because substituting Mg by M yields to vacancy formation, the observed transition can be compared to the crystalline-to-liquid transition noticed in the hard sphere model, when the packing density is changed. The hardness and the bang gap of the Mg-M-O were measured. Using the packing density, it is possible to decouple the influence of the crystallinity from the influence of the composition in the hardness and band gap of the thin films.