High uniaxial buckling strain for measuring the mechanical properties of nanoporous gold films

Guided Wrinkling of Hierarchically Structured Nanoporous Gold Films for Improved Surface‐Enhanced Raman Scattering Performance

“…Moreover, it should be noted that the selection of organic solvent is critically important in removing PMMA because the common solvent can simultaneously degrade the SMP film and induce deterioration of NPG films formed on the SMP substrate. [37] Thus, we used selective acetic acid at this crucial step to avoid the wanted swelling or degradation of the working SMP substrate. As one of the collected information, the side-cut cross-sectional SEM image obviously reveals the thickness level of each film in the wrinkled structure from surface to bottom (i.e., PMMA/NPG/SMP film in the lower left panel).…”

“…where Ēf and Ēs are the plane-strain moduli of PMMA/NPG film and SMP substrate; here, the plane-strain modulus was defined as Ē = E∕(1 − v 2 ), (E: Young's modulus, 𝜈: the Poisson's ratio). The Poisson's ratio of each SMP substrate and PMMA/NPG film was estimated as ≈0.33 and ≈0.35, respectively, [37] which was collected by the nanoindentation tests and standard micrographic measurements. In this physical condition, the wrinkles of the PMMA/NPG layer attached to the SMP substrate can be spontaneously generated when the shrinkage-induced stress (𝜎) exceeds 𝜎 w .…”

“…In this fabrication setup, we intentionally confined the wrinkled surface area (the original width of SMP: 14-20 mm) where the ordered features were expected, as previously reported. [37] For example, this simple tool controlled the uniaxial compressive force on the laminated films in the thermal shrinkage step that induced wrinkled microstructure with fixed dimensions (vii). In addition, to fully adjust the shrinkable ability of the SMP substrate with mechanically constrained NPG film, three different modes were engaged, depending on the geometrical modulation of the in-plane compressive forces, as illustrated in Figure 1b.…”