Controlled Formation of Surface Patterns in Metal Films Deposited on Elasticity-Gradient PDMS Substrates

Abstract

Controlled surface patterns are useful in a wide range of applications including flexible electronics, elastomeric optics, fluidic channels, surface engineering, measurement technique, biological templates, stamps, and sensors. In this work, we report on the controlled formation of surface patterns in metal films deposited on elasticity-gradient polydimethylsiloxane (PDMS) substrates. Because of the temperature gradient during the curing process, the PDMS substrate in each sample successively changes from a purely liquid state at one side to a purely elastic state at the opposite side. It is found that surface folds appear in the liquid or viscous PDMS region while wrinkles form in the elastic region. In the transition region from the liquid to elastic PDMS, a nested pattern (i.e., the coexisting of folds and wrinkles) can be observed. The folding wave is triggered by the intrinsic stress during the film deposition and its wavelength is independent of the film thickness. The wrinkling wave is induced by the thermal compression after deposition and its wavelength is proportional to the film thickness. The report in this work could promote better understanding of the effect of substrate elasticity on the surface patterns and fabrication of such patterns (folds and wrinkles) by tuning the substrate property.

Inorganic Thin Film Deposition and Application on Organic Polymer Substrates

“…With the growing interest from several sectors to replace common hard substrates by lightweight and flexible ones, polymers are more frequently used as substrates in PVD processes and limit the capabilities to increase the temperature during the thin film deposition drastically. [34] Regardless of chemistry, molecular weight, and substrate type (be it a μm thick foil [46] or mm to cm thick solid polymer bulk, [41b,47] a spin-coated thin layer, [41a,48] a polymer melt, [49] in liquid phase, [50] partially reticulated elastomer, [51] or a chemically grafted polymer brush onto another substrate [52] ), the inherent properties of polymers might represent a challenge during PVD. The heat distortion and glass transition temperatures of most polymers are well below the melting point of most inorganic materials (indium and tin being the most commonly used low melting point sputtered materials with T m of around 150 and 230 C, respectively).…”

“…Being able to define and control the location of nucleation points at on the surface and modify the subsequent growth of a film represents the first step toward a 'low-cost nanofabrication process". [34] Regardless of chemistry, molecular weight, and substrate type (be it a μm thick foil [46] or mm to cm thick solid polymer bulk, [41b,47] a spin-coated thin layer, [41a,48] a polymer melt, [49] in liquid phase, [50] partially reticulated elastomer, [51] or a chemically grafted polymer brush onto another substrate [52] ), the inherent properties of polymers might represent a challenge during PVD. A general summary of these complications is presented in Figure 7.…”

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.…”

“…[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. [50] In this case, the effect of metal particle bombardment is very strong, especially for very soft material surfaces such as ionic liquids.…”

Controlled evolution of surface patterns for ZnO coated on stretched PMMA upon thermal and solvent treatments

“…The presence of cracks alleviates this compressive stress to a certain extent and changes the stress field near the cracks. In the vicinity of the crack, the isotropic compressive stress is converted to a uniaxial compressive stress parallel to the edge of the crack [53,54]. Consequently, some wrinkles are perpendicular to the edge of the crack near the cracks (as shown in Fig.…”