Three-Dimensional Patterning of Micro/Nanoparticle Assembly with a Single Droplet of Suspension
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Three-Dimensional Patterning of Micro/Nanoparticle Assembly with a Single Droplet of Suspension Sun Choi1,2, Albert P. Pisano1,2 and Tarek I. Zohdi2 1
Berkeley Sensor and Actuator Center (BSAC)
2
Department of Mechanical Engineering, University of California at Berkeley, Berkeley,
California 94720, USA
ABSTRACT We develop a novel patterning technique to create 3D patterns of micro, nanoparticle assembly via evaporative self-assembly based on confinement/release of micro/nano particles assembly based on the coffee-ring effect of evaporating suspension. Based on the presented technique, we demonstrate that the patterns of 3D assembly of various sizes of microparticles (Silica), metal oxide nanoparticles (TiO2, ZnO) and metallic nanoparticles (Ag) can be successfully generated by low-concentrated particle suspension (1.25 wt % ~ 5 wt %) without additional sintering steps and we also show the geometries of the patterns can be finely controlled by adjusting the parameters of the process. INTRODUCTION Creating regular, repetitive and well-defined three-dimensional patterns of particle assembly in targeted area is a major bottleneck in various applications such as the fabrication of three-dimensional photonic crystals1-3, printed electronics on flexible substrates4-5, colloidal quantum-dot based devices for display6-8, plasmonics9-10 and etc. Previous approaches to pattern particle assembly, however, are required to use entire substrates without selective positioning of particle assembly11, chemically pre-patterned substrates12-14, or use soft-lithographic methods of which applicable particles are largely constrained by molds and substrate15-17. Moreover, most of the previous techniques are grounded on the two-dimensional interaction between the substrate and particle assembly, thus, structuring three-dimensional particle assembly has been a huge challenge with those approaches. Evaporative self-assembly of meso, micro and nano-scale particles18-21 is well-known, interesting physical phenomenon at three-phase boundary (particlemedium-air), however, its applications29-36 have been mainly confined to fabricate planar structures since technical difficulty lies in controlling interaction between medium and particles in three-dimension. In this work, we propose simple and straight-forward idea that the patterns of three-dimensional particle assembly are generated by evaporative self-assembly being assisted by photographically defined templates. The patterns of the three-dimensional assembly of various sizes of micro-particles (Silica), metal oxide nano-particles (TiO2, ZnO) and metallic nano-particles (Ag) have been successfully generated by confinement/release of micro/nano particles assembly based on the coffee-ring effect of evaporating suspension. The geometry of
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patterns was finely controlled by adjusting parameters of process and brief theoretical validation of this process has been also included. We demonstrate that photo-patterns with proper surface treatment can be used as an effective scaffold to structure
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