Influence of Grain Boundary Structure on Nanocrystalline Thin Film Stress States
Technical Report,15 Sep 2013,01 Mar 2018
University of Alabama - Tuscaloosa Tuscaloosa United States
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Thin films are a vital subset of material structures that are relevant in several technologically important applications, including information storage, optical devices, and tribological coatings. It has been well documented that the intrinsic stress associated with thin films plays a fundamental role in tuning its physical and mechanical properties. In these material systems, the stresses are often generated from the crystallographic interfaces and their evolutionary response to minimize this energy. To date, most experimental research has focused on the in situ stress evolution of a thin film consisting of a single element. This research explored some of these elemental systems, both computationally and experimentally as well as alloy films. Unlike single element films, these multi-species systems have the added complexity of interactions between different atom types, which can lead to chemical partitioning at various interfaces. Although this can be complex, it does offer several tantalizing opportunities to engineer the growth and subsequent stress conditions of thin films. Work conducted in the grant has shown how the stress state in an alloy film is regulated by the segregation of particular species to the grain boundaries, even when that species is the lower concentration component, and how the solute controls the grain size of the film. The role of grain boundary character evolution, including its structure and chemistry, in response to these changes was quantified using precession enhanced electron diffraction and atom probe tomography. The novelty of this research resided in coupling in situ stress measurements with high fidelity structural characterization to elucidate how chemical segregation at nanocrystalline interfaces alters stress behavior.