Templated self-assembly of non-close-packed colloidal crystals: Toward diamond cubic and novel heterostructures

Abstract

We demonstrate the formation of non-close-packed binary colloidal structures through a novel layer-by-layer directed self-assembly methodology. In this approach we deposit colloidal suspensions of particle concentration and controlled electrostatic potential onto a planar template with a periodic array of features that is able to trap the particles, nucleating ordered domains with a template-defined symmetry and periodicity that permits subsequent, sequential deposition to produce an ordered heterostructure. Specifically, a silicon template with a hole pattern formed by interference lithography that corresponds to [100] symmetry of a cubic system has been used. At low particle concentrations, and using a Debye length that is on the order of the particle diameter, ordered domains in which polystyrene (PS) particles occupy every other site in the template are formed. The remaining sites on the 2D template are then filled by identically sized silica particles using vertical deposition. This process is repeated to produce a second layer of the same structure. Upon removing the PS particles, a two-layer non-close-packed structure that is a half-unit-cell precursor to the diamond cubic structure is obtained. To our knowledge this is the first demonstration of colloidal self-assembly to obtain a non-close-packed multilayer structure. Challenges that remain in applying the approach to create extended three-dimensional structures are discussed.

Particle selection through topographic templates in nematic colloids

“…Assembling them into mesoscale structures with controlled symmetries is a primary challenge for their use in a wide variety of applications, including responsive devices [3] and photonic band-gap crystals [4]. Among the techniques to grow large scale three-dimensional colloidal crystals [1,5,6] the use of topographic templates, to assist the assembly of colloidal particles, has been shown to effectively control the symmetry and orientation of colloidal crystals [7][8][9][10][11]. This method relies on topographically, or chemically, patterned surfaces, tuned through conventional micro-fabrication techniques such as soft lithography, as templates to drive the nucleation and epitaxial growth of colloidal structures [12].…”

“…4 Among the techniques to grow large scale three-dimensional colloidal crystals 1,5,6 the use of topographic templates, to assist the assembly of colloidal particles, has been shown to effectively control the symmetry and orientation of the colloidal crystals. [7][8][9][10][11] This method relies on topographically, or chemically, patterned surfaces, tuned through conventional micro-fabrication techniques such as so lithography, as templates to drive the nucleation and epitaxial growth of colloidal structures. 12 Template-assisted assembly offers advantages over conventional methods, namely (i) templated structures have fewer defects and longer ranged order and (ii) novel structures may be assembled with the tunable symmetry of the template pattern.…”

Controlling disorder in self-assembled colloidal monolayers via evaporative processes

“…The capillary forces on particles, as they are directed over such pits, trap single particles at precise locations on the substrate. In the literature, these have mostly been realized as a protocol to produce highly ordered non-close packed arrays of particles using a range of morphologies, including spheres, 101,[199][200][201][202][203] rods, 195,204 cubes, [205][206][207] and plates. 207 The greatest potential of this technique, regarding the assembly of disordered monolayers, is that particles can be assembled into any arbitrary two-dimensional spatial distribution.…”

Multifunctional Structured Platforms: From Patterning of Polymer-Based Films to Their Subsequent Filling with Various Nanomaterials

“…PS and silica particles can also be deposited via convective assembly in a non-closely-packed fashion right onto substrates covered with cubic arrays of hole surface relief patterns [ 315 ]. Moreover, at low particle concentrations, arrays of ordered PS particles occupying every other site in the template can be obtained ( Figure 15 d).…”