Abstract
The effects of constrained sample dimensions on the mechanical behavior of crystalline materials have been extensively investigated. However, there is no clear understanding of these effects in nano-sized amorphous samples. Herein, nanoindentation together with finite element simulations are used to compare the properties of crystalline and glassy CoNi(Re)P electrodeposited nanowires (ϕ ≈ 100 nm) with films (3 μm thick) of analogous composition and structure. The results reveal that amorphous nanowires exhibit a larger hardness, lower Young's modulus and higher plasticity index than glassy films. Conversely, the very large hardness and higher Young's modulus of crystalline nanowires are accompanied by a decrease in plasticity with respect to the homologous crystalline films. Remarkably, proper interpretation of the mechanical properties of the nanowires requires taking the curved geometry of the indented surface and sink-in effects into account. These findings are of high relevance for optimizing the performance of new, mechanically-robust, nanoscale materials for increasingly complex miniaturized devices.
Highlights
The rapid progress in different fields of nanotechnology has prompted an unprecedented revolution in the methods to synthesize materials with nanoscale lateral dimensions and the procedures to assemble them into miniaturized devices
The CoNi(Re)P NWs were grown inside the pores of anodized aluminium oxide (AAO) templates, as depicted in Fig. 1
While the lateral physical constraints imposed by the reduced sample dimensions of the NWs induce an increase of H and E in the crystalline compositions, opposite trends in E and plasticity are observed in the case of nanoscale glassy specimens
Summary
The rapid progress in different fields of nanotechnology has prompted an unprecedented revolution in the methods to synthesize materials with nanoscale lateral dimensions and the procedures to assemble them into miniaturized devices. The size effects manifest in variations of hardness, H, Young’s modulus, E, or plasticity.[1] In nano-sized crystalline materials an increase of the yield stress occurs as a result of lateral confinement and the need to create the so-called “geometrically-necessary dislocations” in order to accommodate the imposed shear strain.[2,3,4] the reduction of lateral size is usually detrimental in terms of ductility, since dislocations have difficulties nucleating and gliding in small crystals. Plastic flow in these materials is accompanied by the net creation of free volume.[5,6] The excess free volume tends to coalesce into shear bands, leading to inhomogeneous plastic flow and premature fracture.[6,7] It has been suggested that this embrittlement becomes less significant if the sample is smaller than the “process zone size”, i.e
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