Programmable Nanopatterns by Controlled Debonding of Soft Elastic Films

We report a facile patterning technique capable of creating nanostructures with different feature heights (h_S), periodicities (λ_S), aspect ratios (A_R), and duty ratios (D_R), using a single grating stamp with fixed feature height h_P and periodicity λ_P. The proposed method relies on controlling the extent of debonding and morphology of the contact instability features, when a rigid patterned stamp is gradually debonded from a soft elastic film to which it was in initial conformal contact. Depending on whether the instability wavelength (λ_F scales with the film thickness h_F as λ_F ≈ 3h_F) and the periodicity of the stamp feature (λ_P) are commensurate or not, it is possible to obtain features along each stamp protrusion when λ_F ≈ λ_P or patterns that span several stripes of the stamp when λ_F > λ_P. In both cases, the patterns fabricated during debonding are taller than the original stamp features (h_S > h_P). We show that h_S can be modulated by controlling the extent of debonding as well as the shear modulus of the film (μ). Additionally, when λ_F > λ_P, progressive debonding leads to the gradual peeling of replicated features, which, in turn, allows possible tuning of the duty ratio (D_R) of the patterns. Finally we show that by the simultaneous modulation of A_R, D_R, and h_S, it becomes possible to create surfaces with controlled wettability.