Tunable herringbone patterns in SiO<sub>2</sub> thin films

Ordered zigzag wrinkles, or herringbones, arising from surface instability in biaxially compressed thin films on soft substrates offer significant potential for diverse engineering applications. In this study, we experimentally investigated the formation of herringbone patterns in silicon dioxide (SiO2) thin films bonded to poly(dimethylsiloxane) (PDMS) substrates. Specifically, we examined how the biaxial pre-strain ratio, defined as the ratio of pre-strain applied to the substrate in the second direction to that applied in the first orthogonal direction prior to film formation, and the film thickness influence herringbone geometry. Under equi-biaxial pre-strain ratio, the films developed herringbones with jog angles of approximately 80°, and the wavelength, amplitude, and length of these patterns showed a nearly linear dependence on film thickness. When the biaxial pre-strain ratio was varied from 0.67 to 1.50, the jog angle was tuned from 40°to 100°. Surface roughness analysis showed that the arithmetical mean height ranged from 0.13 to 0.30 μm depending on both film thickness and biaxial pre-strain ratio. These findings provide insights into controlling herringbone formation in SiO2 films and offer design guidelines for engineered surfaces with tailored morphological features.