Layering transitions in colloidal crystal thin films between 1 and 4 monolayers

F. Ramiro-Manzano; E. Bonet; I. Rodriguez; F. Meseguer

doi:10.1039/B907441D

Research · Publication & note

Layering transitions in colloidal crystal thin films between 1 and 4 monolayers

Soft Matter · Journal article · 3 September 2009

F. Ramiro-Manzano, E. Bonet, I. Rodriguez and F. Meseguer

Soft Matter

Volume 5 · Issue 21

Pages 4279-4282

2009

Abstract

This paper investigates the sequence of morphological transitions in a nearly hard particle arrangement of colloidal crystals confined in a wedge cell. Earlier studies have shown intermediate particle arrangements, such as the buckling, rhombic, prismatic and hcp-like phases, to account for the drastic changes in filling fraction between triangular and square arrangements. Here we describe particle ordering for films between 1 and 4 layers and present a new hcp(011) intermediate phase for transitions with more than 2 layers.

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Article access and reuse

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Figures

Complete Figure 1 composition with SEM panels, scale bars and structural models — Figure 1. SEM images and structural models for the hcp(100)-like to pre-layer transition.

Complete SEM composition showing the hcp and square colloidal-layer transition — Figure 2. Complete SEM composition of intermediate colloidal-layer arrangements.

Complete model composition for transitions between triangular and square colloidal layers — Figure 3. Complete models of the transition between triangular and square layer arrangements.

Complete filling-fraction phase map with surrounding SEM micrographs — Figure 4. Filling fraction as a function of reduced cell thickness, including all surrounding SEM panels.

Research fields

Bottom-up

A wedge-confined colloidal suspension self-organises through one- to four-monolayer regimes. As the gap grows, the particles introduce rotations and hcp-like intermediates that preserve dense packing between the square and triangular limiting layers.

Simulations & fits

Packing models and filling-fraction curves order the candidate triangular, square, hcp(100)-like and pre-layer structures by reduced cell thickness. The framework identifies continuous structural paths that a simple direct layer jump would miss.

Characterization

Front and cleaved-edge SEM images resolve particle positions through each transition, including the uncommon hcp(011) arrangement. Comparing both views with the models determines the stacking sequence rather than inferring it from a two-dimensional surface image.

RESEARCH TOPICS

MaterialsThe wedge cell continuously changes the available thickness, allowing the complete transition between one and four confined layers to be observed in a single specimen. Figure 4 combines SEM images with calculated filling fraction and distinguishes triangular, square, buckled, rhombic, prismatic and hcp-related arrangements. A new hcp(011) intermediate is identified for the four-layer transition, while the measured interlayer spacings explain how the system accommodates thicknesses that are incommensurate with high-symmetry packing.