Figure 1

(a) Schematic sketch depicting water-induced siloxane bond breaking in an organosilane NML at a Cu/NML/silica interface. (b) A typical load-relaxation curve from a four-point-bend test with a schematic showing the crack path. A crack initiated at the notch tip on the substrate traverses to the weakest interface and propagates laterally at a constant load corresponding to ${\Gamma }_c$ (green). When displacement is arrested, the crack is driven subcritically by the remnant load (red), which continually decreases until crack growth stops. The remnant load at the crack arrest point corresponds to the equilibrium fracture toughness ${\Gamma }_{\mathrm{FT}}$.Reuse & Permissions

Figure 2

(a) Crack velocity $v$ vs the driving energy Γ plots obtained at $T=278\hspace{0.5em}\mathrm{K}$ at different $a_{{\mathrm{H}}_2\mathrm{O}}$. The red solid line represents the reaction rate kinetics model fit (Ref. 15) for $a_{{\mathrm{H}}_2\mathrm{O}}=0.25$. (b) Plot showing ${\Gamma }_{\mathrm{FT}}$ decrease with $a_{{\mathrm{H}}_2\mathrm{O}}$ (blue) and temperature (green).Reuse & Permissions

Figure 3

(a) Survey XPS spectra from silica fracture surfaces show Si and O peaks with no traces of Cu, while Cu fracture surfaces exhibit prominent Cu peaks (top). (b) Multiplex scans on Cu fracture surfaces show Si 2$p$ signatures of silyl alkyl moieties (∼102.5 eV) in the organosilane, in contrast to the silica band (∼103.5 eV) on silica fracture surfaces (bottom left). This result, and the exclusive presence of S 2$p$ peak on the Cu fracture surface (bottom right), indicate that delamination occurs via siloxane bond fissure at the NML-silica interface (top left: where filled green and red spheres denote Si and S, respectively, in the MPTMS NML). The essentially identical spectral features for $0.05⩽a_{{\mathrm{H}}_2\mathrm{O}}<0.8$ (bottom left) indicate that the delamination path is unchanged. At $a_{{\mathrm{H}}_2\mathrm{O}}~0.8$—the highest water activity in our experiments—Cu fracture surfaces exhibit a silica sub-band along with the prominent silyl alkyl signature, suggesting some fracture-path deviation owing to bond breaking in the silica substrate.Reuse & Permissions

Figure 4

(a) ${\Gamma }_{\mathrm{FT}}$ as a function of $a_{{\mathrm{H}}_2\mathrm{O}}$ at 293 K. Inset schematically illustrates ${\gamma }_a$ and ${\gamma }_p$; plasticity is depicted as wiggles in the delaminated Cu film. (b) Cu yield stress ${\sigma }_y$ extracted from ${\Gamma }_{\mathrm{FT}}-\log \hspace{0.5em}{a}_{{\mathrm{H}}_2\mathrm{O}}$ plots (red) compared with that obtained by nanoindentation (blue), molecular dynamics simulations of nanograined bulk Cu (Ref. 24), and extrapolation of an analytical model developed from nanoindentation of thicker films (Ref. 25). (c) The ${\Gamma }_{\mathrm{FT}}$ increase with Cu film thicknesses at constant $a_{{\mathrm{H}}_2\mathrm{O}}$ where ${\gamma }_p\ne 0$.Reuse & Permissions

Figure 5

(a) Plastic energy ${\gamma }_p$ in copper plotted as a function of the interfacial work of adhesion ${\gamma }_a$, at $T=293\hspace{0.5em}\mathrm{K}$. (b) Deformation mechanism map created from ${\Gamma }_{\mathrm{FT}}$ measurements on structures with Cu/NML/Si$O_2$ interfaces with a 100-nm-thick Cu film for $278\hspace{0.5em}\mathrm{K}⩽T⩽358\hspace{0.5em}\mathrm{K}$ and $0.6⩽a_{{\mathrm{H}}_2\mathrm{O}}⩽0.1$. In yellow-orange-red regions ${\gamma }_p$ is a major contributor, while green and blue regions represent conditions where ${\Gamma }_{\mathrm{FT}}~{\gamma }_a$.Reuse & Permissions