Accelerating the development of oxynitride thin films: A combinatorial investigation of the Al-Si-O-N system

TL;DR

This study develops a high-throughput combinatorial approach to rapidly explore and optimize the composition and properties of oxynitride thin films within the Al-Si-O-N system, enabling efficient material discovery for coatings.

Contribution

It introduces a novel high-throughput synthesis method for combinatorial oxynitride films, covering a wide compositional space with minimal depositions, and demonstrates its application in optimizing properties like hardness and refractive index.

Findings

Achieved a broad compositional range of 2-46% oxygen and 4-44% silicon in thin films.

Identified a hardness up to 25 GPa associated with specific microstructures.

Established a correlation between hardness and refractive index in amorphous regions.

Abstract

Oxynitrides are used in a variety of applications including photocatalysts, high-k dielectrics or wear-resistant coatings and often show intriguing multi-functionality. To accelerate the co-optimization of the relevant material properties of these compositionally complex oxynitride systems, high-throughput synthesis and characterization methods are desirable. In the present work, three approaches were investigated to obtain orthogonal anion and cation gradients on the same substrate by magnetron sputtering. The different approaches included varying positions of the local reactive gas inlets and different combinations of target materials. The best performing approach was applied to screen a large two-dimensional area of the quaternary phase space within the Al-Si-O-N system. This material system is a promising candidate for transparent protective coatings with variable refractive indices. With only five depositions of combinatorial libraries, an anion composition range of 2-46% O/(N+O) and a cation composition range of 4-44% Si/(Al+Si) is covered. For lower oxygen and silicon contents, a region with hardness of up to 25 GPa is observed, where the material exhibits either wurtzite AlN or a composite microstructure. By increasing the deposition temperature to 400 {\deg}C, an extension of this region can be achieved. At higher oxygen and silicon contents, the structure of the samples is X-ray amorphous. In this structural region, an intimate correlation between hardness and refractive index is confirmed. The results of this study introduce a practical approach to perform high-throughput development of mixed anion materials, which is transferable to many materials systems and applications.