Understanding the Mechanical Behavior of Small-scale Materials: Small for the sake of Big


Monday, November 14, 2022 - 3:30pm to 4:30pm


ESB 1001


Professor Gi-Dong Sim

Abstract: Thin films are widely used as functional and structural elements in micro-electronic devices, large-scale integrated circuits, thin-film solar cells, electrical sensors, and electronic textiles. Understanding the mechanical behavior of thin films at different length scales and environmental conditions is essential for the design of reliable devices. However, it is difficult to precisely measure the properties of small-scale materials with the methods that are employed for bulk materials; probing micro/nano scale samples is challenged by the inherent difficulties associated with fabricating and handling of extremely small specimens. In this presentation, I will introduce experimental studies utilizing micro/nano-scale manufacturing and mechanical characterization techniques to understand the mechanical behavior of small-scale materials. In the first topic, the effect of carbon addition and ultra-thin (≤ 10 nm) passivation layer on the microstructure and mechanical behavior of freestanding metal thin films will be discussed. Tensile specimens with sub-micron thickness are fabricated via sputter deposition followed by standard silicon-based microfabrication techniques. Supersaturated aluminum-carbon (Al-C) thin films containing 10.3at% C exhibit yield strength of about 400 MPa, over three times the yield strength of pure Al thin films. Films passivated with an ultra-thin layer (≤ 10 nm) exhibit significant increase in the failure strain, which is attributed to delay in the strain localization due to constraint imposed by the passivation layer. In the second topic, constant strain rate membrane deflection experiment (MDE) technique that enables high-throughput measurement of in-plane mechanical properties of metal thin films will be introduced. By comparing with micro-tensile tests, it is demonstrated that the stress-strain curve of freestanding metal thin films can be successfully measured via constant strain rate MDE. Finally, I will discuss how these techniques are being used to develop shape memory alloy thin films.

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