Harnessing fold-to-wrinkle transition and hierarchical wrinkling on soft material surfaces by regulating substrate stiffness and sputtering flux

Abstract

Strain-induced complex surface patterns such as wrinkles, folds and hierarchical structures are quite useful in a wide range of practical applications. Although various surface patterns have been extensively investigated, precisely controlling the coexistence and transition of multimodal structures is still a challenge. In this work, we report on a facile technique to harness fold-to-wrinkle transition and hierarchical wrinkling on soft material surfaces by regulating substrate stiffness and sputtering flux. It is found that as the substrate stiffness or sputtering flux increases, the surface patterns successively evolve from networked folds to isolated folds (coexistence of folds and wrinkles) and finally to labyrinth-like wrinkles. For larger sputtering flux, two distinct wrinkling patterns (i.e., G1 wrinkling due to surface instability during sputtering and G2 wrinkling due to thermal compression after deposition) can coexist on the sample surfaces, resulting in the spontaneous formation of hierarchical wrinkles. The report in this work could promote better understanding of the sputtering effect on the spontaneous pattern formation for soft materials and controllable fabrication of multiple complex patterns by simply regulating substrate stiffness and sputtering flux.

Morphology, Structure, and Dynamics of Pentacene Thin Films and Their Nanocomposites with [C2C1im][NTf2] and [C2C1im][OTF] Ionic Liquids

“…These structures are usually observed for metal films deposited on soft substrates and are originated from the surface instability due to atom bombardment onto the material surface during sputtering. [50][51][52][53][54] The magnetron sputtering technique with controllable sputtering flux has been used to trigger surface instability and pattern formation. The wrinkling pattern typically can include stripe, herringbone, labyrinth, and dimple structures.…”

“…The wrinkling pattern typically can include stripe, herringbone, labyrinth, and dimple structures. [50][51][52] The surface patterns are dependent on the sputtering flux and the substrate stiffness. [50] The glow plasma exposure induces a surface change of soft materials since the heat radiation can lead to a rise in temperature along the sputtering process.…”

“…[50][51][52] The surface patterns are dependent on the sputtering flux and the substrate stiffness. [50] The glow plasma exposure induces a surface change of soft materials since the heat radiation can lead to a rise in temperature along the sputtering process. [53,54] Some authors claim a negligible effect of glow plasma exposure for short deposition times.…”

Localized wrinkling of metal films on elastic and liquid substrates

“…Since then, various global and localized wrinkling patterns have been fabricated in different films/substrates by using some effective stress tuning technologies. The global wrinkles with well-defined wavelengths such as herringbone, sinusoidal and labyrinth patterns can be readily fabricated in various film/substrate materials including the metal films/elastic substrates [2,14,24,[28][29][30], the nonmetal stiff films/elastic substrates [34,95,[98][99][100] and the polymer films/elastic substrates [33,[41][42][43]101]. The localized wrinkles such as the radial patterns can be easily formed in the floating polymer films [16,20,22,46,50,51,102] and the surface of modified elastomer [36].…”

“…The dimension and morphology of the cracks can be tuned by altering the film thickness and substrate properties. In the case of continuous compressive stress, the films will form various buckling modes such as wrinkles [6,7,[14][15][16][17][18][19][20][21], folds [22][23][24], creases [23,25] and telephone cord buckles [9,26,27]. The stress magnitude, the film thickness, the substrate elasticity and the adhesion performance between the films and the substrates can determine the wavelength, amplitude and morphology of the buckling.…”