Fabrication and Light‐Transmission Properties of Monolayer Square Symmetric Colloidal Crystals via Controlled Convective Self‐assembly on 1D Grooves

Abstract

Two-dimensional (2D) colloidal crystals have intriguing properties, which make them quite useful in a wide range of applications. For example, 2D colloidal crystals have been widely used as physical masks in, for example, nanosphere lithography, [1] for preparation of metal nanoparticle arrays with a variety of particle morphologies, [2] as templates for growth of binary colloidal crystals, [3] and recently even as templating substrates for preparation of novel plasmonic crystals. [4] Up to now, several methods have been developed to grow 2D colloidal crystals, including self-assembly by capillary force, [5] spincoating, [2a,6] electrophoretic deposition, [7] and LangmuirBlodgett deposition.[8] Among them, convective self-assembly induced by solvent evaporation has been shown to be an effective approach for self-organizing colloidal beads into 2D crystals with hexagonal close-packing geometry. [5] In a typical process, [5a] immersion capillary force at the suspension drying front tends to bring particles into contact when the liquid suspension thickness becomes comparable with the colloidal sphere diameter. Evaporation-induced flow brings more particles towards the suspension front and the crystal grows larger.A patterned substrate provides an effective way to control the packing symmetry and orientation of colloidal crystallizations, [9,10] which is quite important for further extending colloidal crystal applications. Several research groups have reported using a 2D-patterned substrate to drive the growth of colloidal crystals. [9,10a] Self-assembly in the presence of one-dimensional (1D) patterned substrates has also been studied in combination with thermal equilibrium assembly, [10a] convective assembly, [10b] electrostatic assembly, [10c] and electrophoretic deposition process.[10d] Although 2D centered-rectangular lattice colloidal crystals have been fabricated on a 1D-patterned substrate, high defect densities and short-range ordering were often observed in those previously reported results. [10a,10b,10d] To the best of our knowledge, an efficient method to prepare high-quality monolayer square-lattice colloidal crystals has not been reported yet.In this Communication, we report our study of self-assembly of colloidal polystyrene (PS) spheres on a 1D-patterned substrate. Previous studies showed that colloidal structures formed on a 1D-patterned substrate are highly sensitive to the ratio between sphere diameter (d) and groove period (p).[10a]Here, we explore other factors that could have a key influence on the formation of 2D square symmetric colloidal crystals using a 1D-patterned substrate. By introducing an experimental cell that allows simultaneous actions and strong competition of forces on colloids exerted by the suspension drying front and the patterned substrate, we have identified distinct effects of convective assembly on the growth of colloidal crystal by controlling the angle orientation (a) between the colloidal suspension drying front and 1D template grooves. We find that those experi...

Phase-field crystal modelling of crystal nucleation, heteroepitaxy and patterning

“…Setting λ = σ /2 1/2 , where σ is the inter-particle distance and varying the orientation of the grooves relative to the crystallization (drying) front, patterns seen in the experiments [123] are observed to form in the PFC simulations ( figure 15): For grooves parallel to the front, a frustrated 2D hexagonal structure of randomly alternating double and triple layers, separated by channels appear. When the grooves are perpendicular to the crystallization front, the particles align themselves on a square lattice with the (1 1) orientation lying in the interface, while for a 45° declination of the grooves the same 2D square structure forms, however, now with the (1 0) face lying in the front.…”

Phase-field-crystal models for condensed matter dynamics on atomic length and diffusive time scales: an overview

“…Another problem, exemplifying the abilities of PFC simulations in modelling colloid patterning, is colloidal self-assembly under the effect of capillary-immersion forces acting on the colloid particles in thin liquid layers due to capillarity and a periodically varying depth of the liquid layer due to a wavy substrate surface. Experiments of this kind have been used to produce single and double particle chains [236] and the otherwise unfavourable square-lattice structure [237]. The capillary-immersion forces can often be well represented by a potential of the form U = u 1 cos(kx), where u 1 is a constant, k = 2π/λ, and λ the wavelength of the periodic potential.…”

Colloidal Self‐Assembly Meets Nanofabrication: From Two‐Dimensional Colloidal Crystals to Nanostructure Arrays

“…Colloidal nanospheres have also been selectively deposited in the troughs of relaxation‐wrinkles or buckling patterns of thin polymer films via dip‐coating 25c, 28. The colloidal crystal structures formed on these 1D‐patterned substrate are highly sensitive to the ratio between nanosphere diameter and groove period, as well as the relative orientation of the 1D pattern and the suspension drying front 29…”