"Metal Alloy Pillar design in Vertically Aligned Nanostructures (VAN) towards multifunctionality" 

Abhijeet Choudhury, MSE PhD Candidate 

Advisor: Professor Haiyan Wang

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ABSTRACT

Nanostructures generally have different properties than the bulk materials. This has led to a tremendous rise in the interest to utilize such unique properties in various practical applications. Among the various nanostructures, such as multi-layer and nanoparticles, the nanopillar structures are one of the unique structures where manipulation of the structure allowing for tunability of properties is much easier. Vertically Aligned Nanostructures (VAN) are an emerging class of such nanostructures which have highly anisotropic properties while the structure has vertical strain between the different phases present. The growth mechanism of the VANs is primarily dependent on the factors such as difference between the growth rate of the multiple phases present, surface energy difference of those phases and also the mismatch between the lattice parameters for the phases deposited and the substrate chosen. Thus, when adatoms of different phases arrive on the substrate, they behave differently with some preferring a multilayer growth while the others preferring growth as islands on the substrate due to difference in the surface energies. This understanding has led to many oxide-oxide, oxide -metal, nitride-metal systems being reported with unique optical and magnetic properties. However, currently there is an increasing demand to design nanostructures, where multi-functionality is desired. This has led to the growing interest in alloy-based VAN designs, where different metals with unique properties can be integrated to achieve multifunctionality. Nevertheless, there are very few reports of alloy-based VAN structures as it is an emerging field which requires more study. In this review, the reported alloy-based VANs are discussed along with their unique properties, along with the existing challenges in deposition of such films as well as future perspectives which can enhance the understanding of such films to exploit their multifunctionality.