Nanomechanical behavior of optically optimized AlN/SiO2 and AlN/Ag nanomultilayers

Conference Dates

September 29-October 4, 2019


A multilayer is a composite structure of one or more constituent materials, with layer thicknesses ranging from the micro to nanoscale. The repeated distances in the multilayers can be designed to be identical to interaction lengths that are characteristic of important physical properties such as electromagnetic or optical interaction lengths [1, 2]. Additionally, multilayers have been shown to exhibit desirable properties such as corrosion resistance, radiation resistance, and high strength [3-5]. However, research on optical multilayers has been primarily focused on developing transparent conductive oxides or x-ray optics without exploiting the many other capabilities of multilayers. Thus, the possible novel combination of properties, such as transparency and strength, presents an extraordinary area of research with potential applications in optical windows, sensor protection, and numerous other applications which require light penetration for function and a robust barrier for protection.

The overall goal of this study is to synthesize and characterize systems of nanostructured multilayers, leveraging nanoscale features to enhance optical properties while improving mechanical performance. To address this, samples with a range of layer thicknesses and optical performances were synthesized via DC/RF reactive magnetron sputtering. Multilayer configurations of ceramic/metal and ceramic/ceramic systems with improved optical behavior were designed using calculations to predict optical behavior for maximized transmittance, and the as-sputtered experimental transmittance measurements showed good agreement with predicted values. In this work, the transmittance of optically optimized AlN/Ag and AlN/SiO2 multilayers was measured using UV/Vis spectrophotometry and ellipsometry, ranging from 60 to 95% over 300-800 nm. The mechanical properties were determined using nanoindentation and microtensile testing. For example, in the AlN/Ag nanomultilayers, the measured nanoindentation hardness values ranged from 4.9 GPa to 19.4 GPa, and the optically optimized samples exhibited a fourfold increase in hardness and increased %T over the repeated non-optically optimized bilayer samples, despite similar observed deformation behavior. This work presents how the synthesis and microstructural features influence the mechanical and optically properties of transparent nanomultilayers.

[1] T.W. Barbee Jr., in: L. Chang, B.C. Giessen (Eds.), Synthetic Modulated Structures, Academic Press, New York, 1985, pp. 313-337.

[2] T.W. Barbee Jr., D.L. Keith, Synthesis of metastable materials by sputter deposition techniques, Proceedings of the Fall Meeting of the Metallurgical Society AIME, Pittsburgh, PA, 1980.

[3] E.G. Fu, N. Li, A. Misra, R.G. Hoagland, H. Wang, X. Zhang, Mater. Sci. Eng., A 493(1-2) (2008) 283-287.

[4] J.S. Koehler, Phys Rev B 2(2) (1970) 547-&.

[5] M.N. Polyakov, E. Courtois-Manara, D. Wang, K. Chakravadhanula, C. Kubel, A.M. Hodge, Appl. Phys. Lett. 102(24) (2013).

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