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Ordered surface structuring of spherical colloids with binary nanoparticle superlattices Fabian Meder, Steffi Suja Thomas, Tobias Bollhorst, and Kenneth A. Dawson Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b00173 • Publication Date (Web): 26 Mar 2018 Downloaded from http://pubs.acs.org on March 26, 2018
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Nano Letters
Ordered surface structuring of spherical colloids with binary nanoparticle superlattices Fabian Meder*,1,†,‡, Steffi S. Thomas1,‡, Tobias Bollhorst2, Kenneth A. Dawson1,* 1
Centre for BioNano Interactions, University College Dublin, School of Chemistry and Chemical
Biology, Belfield, Dublin 4, Ireland 2
Advanced Ceramics, University of Bremen, Department of Production Engineering, Bremen,
Germany KEYWORDS self-assembly, nanostructuring, colloidal crystals, surface functionalization
ABSTRACT Surface patterning colloidal matter in the sub-10 nm regime generates exceptional functionality in biology, photonic and electronic materials. Techniques to artificially generate functional patterns in the small nanoscale advanced fascinatingly in the last years, however, remain often restricted to planar and non-colloidal substrates. Patterning colloidal matter in solution via bottom-up assembly of smaller subunits on larger core particles is highly challenging as it is necessary to force the subunits onto randomly moving objects. Consequently, the non-equilibrium conditions present during nanoparticle self-assembly are difficult to control to eventually achieve desired material structures. Here, we describe the formation of surface patterns with intrinsic periodic repeats of 8.9±0.9 nm and less on hard, amorphous colloidal core
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particles by assembling binary nanoparticle superlattices on the curved particle surface. The colloidal environment is preserved during the entire bottom-up crystallization of variable building blocks (here, monodisperse 5 nm Au and 2.4 nm Pd nanoparticles (NPs) and 230 nm SiO2 core particles) into AB13-like, binary, and isotropic superlattice domains on the amorphous cores. The three-dimensional, bottom-up assembly technique is a new tool to pattern colloidal matter in the sub-10-nm surface regime for gaining access to multicomponent metamaterials for bionanoscience, photonics, and electronics.
Crystal-lattice-like structures, consisting of precisely positioned assorted subunits, trigger specific functionality in nature as well as in technology across many length scales. Natural examples are protein arrangements on virus capsids and on certain cells, crystalline ribosomal assemblies, or binary protein DNA co-assemblies.1 Additionally, the interaction of specifically arranged NPs with electromagnetic radiation introduces the potential to tailor a broad set of properties of photonic and metamaterials.2,3 Systematic combinations of NPs likewise opens new doors to miniaturized electronics4 and in addition to modular drug delivery systems with subunits in specific distance on their surface to potentially match receptor pairs on target cells.5–7 Nanoscale manufacturing techniques to obtain patterned nanostructures, such as electron and ion beam lithography as well as self-assembly of NP subunits, advanced fascinatingly in the last years although most of these techniques are usually only successful on planar substrates. Towards three dimensional miniaturization, however, manufacturing on the surface of colloidal particles is becoming essential for, e.g., on-particle devices, photonic systems, or for creating biologically active patterns for nanomedicine purposes.4,5,8–13 Several well-established techniques for the bottom-up self-assembly of monodisperse NPs intriguingly enable hierarchical structure and sub-10-nm-resolution by creating highly periodic
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Nano Letters
superlattices, outperforming thereby most lithographic and other top-down techniques in terms of process ease and equipment.6,14–20 However, transferring superlattices or other fabricated patterns onto individual colloidal substrate particles in solution is puzzling, especially for sub-10 nm particles, due to continuous particle motion, colloidal interaction potentials of similar order of magnitude as the system’s thermal energy21, as well as curvature-based compressive and shear stress.22 On soft or elastic substrates, such as on droplet surfaces or biological membranes, topological defects in the lattice can form. Mobility of particles enable their collective rearrangement into crystalline domains with grain-boundaries facilitating self-organization into patterned structures.22,23 Defects like dislocations can glide within the lattice22 and balance the entropic confinement given by the curved substrate which is used for instance in templated colloidal capsule production7, but regular and highly periodic sub-10 nm structures of multiple subunits are still challenging to fabricate. A major challenge is that, inelastic, hard spherical particles often need to be the substrates (e.g., when specific mechanical or dielectric properties are required, depending on the application). In this circumstance, inelasticity and interfacial interaction forces further limit the rearrangement and ordering of subunits in addition to the spherical frustration. Here, we show that binary NP superlattices consisting of sub-10 nm subunits can be assembled on hard spherical ~230 nm substrate particles by a dimensional confinement in an evaporating miniemulsion droplet. In contrast to well-known colloidal clusters, which consist entirely of selfassembled NPs24,25, or micro-/macroscale systems that allow curved crystallization on elastic cores22,23,26, our method enables functionalizing a given hard core with building blocks periodic placement in sub-10 nm patterns in a multifunctional assembly. The colloidal nature of the system is preserved throughout the entire process.
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Self-assembly of multi-constituent superlattices on hard colloidal cores. Figure 1 illustrates the procedure which leads to modular colloids consisting of an amorphous core and binary crystalline surface patterns, which are finally well-dispersed in water and stabilized by the emulsifying surfactant. The presented experimental system comprises monodisperse 5 nm Au and 2.4 nm Pd NPs and colloidal SiO2 particles (~230 nm) as hard substrate particles (core diameters determined from TEM, further characteristics of all particles are given in Figure S1). The Au and Pd NPs have size standard deviations of 200 Nm) Suitable for Colloidal Templating and Formation of Ordered Arrays. Langmuir 2008, 24, 1714–1720.
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