Wetting Regimes for Residual-Layer-Free Transfer Molding at Micro- and Nanoscales

Abstract

Transfer molding offers a low-cost approach to large-area fabrication of isolated structures in a variety of materials when recessed features of the open-faced mold are filled without leaving a residual layer on the plateaus of the mold. Considering both macroscale dewetting and microscale capillary flow, a proposed map of wetting regimes for blade meniscus coating provides a guide for achieving discontinuous dewetting at maximum throughput. Dependence of meniscus morphology on the azimuthal orientation of the stamp provides insight into the dominant mechanisms for discontinuous dewetting of one-dimensional (1-D) patterns. Critical meniscus velocity is measured and residual-layer-free filling is demonstrated for 1-D patterned soft molds (stamps) with periods ranging from 140 nm to 6 μm. Transfer of isolated lines, and multilayer woodpile structures were achieved through plasma bonding. These results are relevant to other roll-to-roll compatible processes for scalable production of high-resolution structures across large areas.

Thickness/morphology of functional material patterned by topographical discontinuous dewetting

“…The proposed model supported by the data is important to obtain good control of the thickness and morphology of the deposited layers patterned using the novel TDD patterning technique. [ 1,2,4,6 ] Control of all the dimensions during patterning of materials is critical for manufacturing to improve the quality and reliability of the technique and devices manufactured from it. Previous studies have only briefly outlined the colloidal ink printing mechanism [ 1,7 ] or the conditions to ensure accurate filling of the microchannels.…”

“…Previous studies have only briefly outlined the colloidal ink printing mechanism [ 1,7 ] or the conditions to ensure accurate filling of the microchannels. [ 6 ] The findings of this work are, therefore, critical to better understand the technique so it can mature into a commercially‐viable advanced nanoscale printing technology. The discovered viscosity dampening effect is unique to TDD of microchannels, which has not previously been observed in thin film blade coating of colloidal dispersions in the evaporative regime [ 40,41,50 ] or surface chemistry‐based discontinuous dewetting patterning.…”

“…This transition into leaving of a residual film at higher inking speeds is essentially the onset of the Landau–Levich deposition regime, [ 40–42 ] which is to be avoided during TDD to ensure effective patterning. [ 6 ] Maximum inking speed may still result in some minimum but non‐zero amount of evaporation‐driven flow, depending on other conditions.…”

“…Topographical discontinuous dewetting (TDD) is being explored by researchers as an effective template‐guided, self‐assembly, nanoscale/microscale patterning and 2D printing technique for a variety of different functional materials including nanomaterials, [ 1–4 ] polymers, [ 5,6 ] biomaterials, [ 7 ] organic single crystals, [ 1,8–13 ] and perovskite. [ 14 ] Discontinuous dewetting occurs due to variations in the wettability of a substrate surface.…”

“…has explained and tested conditions that ensure effective TDD for rectangular open microchannel cavities that avoids residual films on the non‐cavity substrate surface (unwanted Landau–Levich deposition regime) and uncontrolled ink depinning from the microchannels. [ 6 ] While the lateral dimensions of the deposited layers are firmly controlled by the channel dimensions, the z thickness and top surface curvature depend directly on the conditions of the patterning process. However, how these conditions affect the z thickness and top surface curvature for patterns has not been explored and determined, even though controlling these is critical for different applications.…”