Abstract
We first verify the critical impact of evaporation on the formation of zigzag hollow cracks by regulating the drying micro-environment of silver nanoparticle film. Uneven evaporation and component segregation contributes to the flows along the surface and inside of droplets. Asymmetric vapor concentration distribution is capable of weakening the surface flow of droplets, thus suppressing the inner compressive stress of nanoparticles and leading to a surface morphology with less cracks. Although defect-free and surface smooth nanoparticle film deposited by a solution-based method remains a big challenge, our work has referential significance to optimize high-quality nanoparticle film with appropriate deposition and curing processes. Moreover, an optimization possibility through the drying micro-environment should be considered in high-end applications due to its enhanced effect on high-resolution patterns.
Highlights
Precursor inks are compatible with flexible fabrication due to their low processing temperature (< 200 °C) [1]
Monodispersed nanoparticles (Additional file 1: Figure S1) tend to be self-assembled and form compact surface film due to the outward Marangoni flow, the evaporation driving up force, and the surface tension
The film thickness decreases from region I to III, making the strains increased under compressive stress, and even radial ripples can be resulted
Summary
Precursor inks (silver, gold, copper, etc.) are compatible with flexible fabrication due to their low processing temperature (< 200 °C) [1]. Crack problem remains unsolved and will deteriorate the conductivity and adhesion properties of the deposited film [2]. The underlying mechanism is worth further exploring, while most previous reports concentrate on some external effect, such as laser [3], intense pulsed light [4], and ions [5]. Uneven evaporation nature is underrated to some extent, the coffee ring effect has been proven in numerous studies [6]. Fast evaporation flux of the periphery area and the pinning of the triple line contribute to the outward compensation flow inside of droplets. Directional surface flow can be induced with component segregation [7]
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