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 (lambda(S)), aspect ratios (A(R)), and duty ratios (D-R), using a single grating stamp with fixed feature height h(P) and periodicity lambda(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 (lambda(F) scales with the film thickness h(F) as lambda(F) approximate to 3h(F)) and the periodicity of the stamp feature (lambda(P)) are commensurate or not, it is possible to obtain features along each stamp protrusion when lambda(F) approximate to lambda(P) or patterns that span several stripes of the stamp when lambda(F) > lambda(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 (mu). Additionally, when lambda(F) > lambda(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.