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    Item type:Publication, Access status: with files ,
    Mitigating the film-substrate decohesion in nanoporous metals
    (American Institute of Physics (AIP), 2025-09-01)
    Henkelmann, Gideon
    ;
    Wu, Xinyan
    ;
    Weissmüller, Jörg
    Substrate-supported films of dealloyed nanoporous metals spontaneously develop a low-connectivity layer at the film-substrate interface, impairing interfacial adhesion strength. Comparable interfacial degradation has been reported for sintered interconnects in microelectronics. The phenomenon arises from a divergence in the diffusive, curvature-driven flux of the material, normal to the interface. This reduces the local solute fraction and eventually leads to disconnection by a Plateau-Rayleigh-type instability. Comparing dealloying and subsequent coarsening in experiments and kinetic Monte Carlo simulation, this work investigates mitigation strategies and, in particular, the effect of distinct porosity-depth profiles on the interfacial connectivity. Two design principles are suggested: First, the profile should be smooth, avoiding jumps and kinks. Second, steep porosity gradients should be placed in low-porosity regions. Exponential profiles are found preferable for avoiding degradation. In the fields of nanoporous thin films as functional materials and of interconnects in microelectronics joining, the findings provide the basis for materials design toward enhanced adhesion and lifetime.
    Publicationtype: Journal Article
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    Item type:Publication, Access status: with files ,
    Self-detachment and subsurface densification of dealloyed nanoporoust thin films
    (American Chemical Society (ACS), 2022-08-24)
    Henkelmann, Gideon
    ;
    Waldow, Diana
    ;
    Liu, Maowen
    ;
    Lührs, Lukas
    ;
    Li, Yong
    Experiment shows thin films of dealloyed nanoporous gold (NPG) spontaneously detaching from massive gold base layers. NPG can also densify near its external surface. This is naturally reproduced by kinetic Monte Carlo (KMC) simulation of dealloying and coarsening and so appears generic for nanoscale network materials evolving by surface diffusion. Near the porous layer's external surface and near its interface with the base layer, gradients in the depth-profile of a laterally averaged mean surface curvature provide driving forces for diffusion and cause divergences of the net fluxes of matter, leading to accretion/densification or to erosion/disconnection. As a toy model, the morphology evolution of substrate-supported nanopillars by surface diffusion illustrates and confirms our considerations. Contrary to cylindrical nanowires, the ligaments in nanoporous materials exhibit pre-existing gradients in the mean curvature. The Plateau-Rayleigh long-wavelength stability criterion is then not applicable and the disconnection accelerated.
    Publicationtype: Journal Article
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