Material dimensionality effects on the nanoindentation behavior of Al/a-Si core-shell nanostructures

• Published in: Applied surface science Vol. 412; pp. 96 - 104
• Main Authors: Fleming, Robert A., Goss, Josue A., Zou, Min
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2017
• Subjects: Core confinement; Core-shell nanostructure; Dislocations; Molecular dynamics; Nanoindentation; Molecular dynamics; Core confinement; Nanoindentation; Core-shell nanostructure; Dislocations
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2017.03.221

[Display omitted] •Nanoindentation behavior of Al/a-Si core-shell nanostructures were studied.•3D core confinement enables significant deformation recovery beyond elastic limit.•As the confinement is reduced, the deformation recovery is reduced or suppressed.•Atomistic simulations suggest core confinement affects dislocation dynamics.•3D confinement has the highest percentage of dislocation removal after unloading. The nanoindentation behavior of hemispherical Al/a-Si core-shell nanostructures (CSNs), horizontally-aligned Al/a-Si core-shell nanorods (CSRs) with various lengths, and an Al/a-Si layered thin film has been studied to understand the effects of geometrical confinement of the Al core on the CSN deformation behavior. When loaded beyond the elastic limit, the CSNs have an unconventional load-displacement behavior with no residual displacement after unloading, resulting in no net shape change after indentation. This behavior is enabled by dislocation activities within the confined Al core, as indicated by discontinuous indentation signatures (load-drops and load-jumps) observed in the load-displacement data. When the geometrical confinement of the core is slightly reduced, as in the case of CSRs with the shortest rod length, the discontinuous indentation signatures and deformation resistance are heavily reduced. Further decreases in core confinement result in conventional nanoindentation behavior, regardless of geometry. Supporting molecular dynamics simulations show that dislocations nucleated in the core of a CSN are more effectively removed during unloading compared to CSRs, which supports the hypothesis that the unique deformation resistance of Al/a-Si CSNs are enabled by 3-dimensional confinement of the Al core.