Interface-mediated softening and deformation mechanics in amorphous/amorphous nanolaminates

Vivek Devulapalli¹, Fedor F. Klimashin¹, Manuel Bärtschi², Stephan Waldner³, Silvia Schwyn Thöny³, Johann Michler^1,3, Xavier Maeder¹

Interfaces govern the unique mechanical response of amorphous multilayers. Here, we examine nanoindentation hardness and deformation behaviour of amorphous/amorphous Ta₂O₅/SiO₂ nanolaminates with bilayer thickness ranging from 2 nm to 334 nm. While monolithic SiO₂ exhibits catastrophic failure through a single dominant shear band, multilayer architectures demonstrate varied deformation mechanisms. Hardness decreases with reduced bilayer thickness, from 7.7 GPa at 334 nm to 5.5 GPa at 2 nm spacing, contrasting with crystalline systems, which strengthen with decreasing spacing. Cross-sectional transmission electron microscopy reveals that fine bilayer thickness promotes closely spaced vertical shear bands accompanied by bilayer compression, while coarser spacings show fewer, widely spaced shear bands with chemical intermixing. Scanning precession electron diffraction mapping demonstrates significant densification beneath indents. The high interface density facilitates strain accommodation that prevents catastrophic failure typical of brittle amorphous materials.

1 EMPA, Laboratory for Mechanics of Materials & Nanostructures, Feuerwerkstrasse 39, 3602 Thun, Switzerland
2 RhySearch, Optical Coating and Characterization Laboratory, Werdenbergstrasse 4, 9470 Buchs, Switzerland
3 Evatec Ltd., Hauptstrasse 1a, 9477 Truebbach, Switzerland
4 EPFL, Institute of Materials, Lausanne 1015, Switzerland

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