Acoustic Crystallization of 2D Colloidal Crystals

Abstract

2D colloidal crystallization provides a simple strategy to produce defined nanostructure arrays over macroscopic areas. Regularity and long‐range order of such crystals is essential to ensure functionality, but difficult to achieve in self‐assembling systems. Here, a simple loudspeaker setup for the acoustic crystallization of 2D colloidal crystals (ACDC) of polystyrene, microgels, and core–shell particles at liquid interfaces is introduced. This setup anneals an interfacial colloidal monolayer and affords an increase in average grain size by almost two orders of magnitude. The order is characterized via the structural color of the colloidal crystal, the acoustic annealing process is optimized via the frequency and the amplitude of the applied sound wave, and its efficiency is rationalized via the surface coverage‐dependent interactions within the interfacial colloidal monolayer. Computer simulations show that multiple rearrangement mechanisms at different length scales, from the local motion around voids to grain boundary movements via consecutive particle rotations around common centers, collude to remove defects. The experimentally simple ACDC process, paired with the demonstrated applicability toward complex particle systems, provides access to highly defined nanostructure arrays for a wide range of research communities.

How Colloidal Lithography Limits the Optical Quality of Plasmonic Nanohole Arrays

“…The smaller the average domain size, the more disordered with more reflective gold areas can be expected. The quality of the colloidal sample is typically already obvious from the macroscopic appearance, where individual crystal grains can be easily distinguished by their structural coloration, while less ordered samples show a more opaque appearance (compare the two areas in Figure c) …”

“…In addition to the fabrication inaccuracies, plasmonic lattices are also sensitive to imperfections of their arrangement. ,,− While the colloidal self-assembly allows for the formation of particle monolayers with high order over macroscopic areas, the presence of defects in such self-assembled structures cannot be avoided. The quality of a sample can fluctuate, and the self-assembly process generally results in polycrystalline samples, where individual grains are separated by grain boundaries visible by their opaque appearance (Figure c, deliberate low order and high order, controllable, for example, by acoustic vibrations of the air/water interface). Using such imperfect masks necessarily creates defects and irregularities, which are transferred to the plasmonic nanohole arrays, leading to typical defects, such as vacancies (1D), line defects, or disorder, especially between grains (2D) in their grain boundaries (Figure f).…”

Massively Scalable Self‐Assembly of Nano and Microparticle Monolayers via Aerosol Assisted Deposition

“…In all testing methods the zeta potential of NP solutions was modified by either adsorption (increases |𝜁|) or desorption (decreases |𝜁|) of anionic sodium dodecyl sulfate (SDS) surfactant molecules as described in Experimental Section and in earlier work. [13] In order to accurately calculate the average monolayer selfassembly rate experimental methods were adapted from Menath et al [52] -whose work defines the closing of the self-assembling NP annulus as the point of highest NP concentration and the largest self-assembled monolayer area. We reason that the time it takes the NP self-assembly to reach this event (the closing of the NP annulus) can be accurately compared between the different tested colloidal solutions.…”

Simultaneous occurrence and compensating effects of multi‐type disorder in two‐dimensional photonic structures

“…The material system for photonically active components is often a two‐dimensional (2D) pattern of variable dielectric constants which includes positional disorder on the subwavelength scale with a variety of symmetries. [ 32,40,44,47,67–72 ]…”

“…The material system for photonically active components is often a two-dimensional (2D) pattern of variable dielectric constants which includes positional disorder on the subwavelength scale with a variety of symmetries. [32,40,44,47,[67][68][69][70][71][72] Theoretical works on one-dimensional (1D) photonic structures showed that deviations in the dielectric constant of individual layers of a stack cause the optical transmission to tend towards zero in case of strong disorder. [73] Within a photonic waveguide of flat cylinders, arranged in a 2D square lattice, arbitrary position changes lead to an increasing reduction in transmission with increasing magnitude of shifts, which was shown by finite-element modeling (FEM) calculations [29,30] and experimental research.…”