Structural colour of unary and binary colloidal crystals probed by scanning transmission X-ray microscopy and optical microscopy

Hyun Woo Nho,Tae Hyun Yoon

doi:10.1038/s41598-017-12831-4

Hyun Woo Nho, Tae Hyun Yoon

Open Access

https://doi.org/10.1038/s41598-017-12831-4

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Journal: Scientific Reports	Publication Date: Sep 29, 2017
Citations: 9	License type: open-access

Affiliation: Hanyang University

Abstract

Colloidal crystals composed of micro- or nano- colloids have been investigated in various fields such as photonics due to their unique optical properties. Binary colloidal crystals have an outstanding potential for fine-tuning material properties by changing the components, concentration, or size of colloids. Because of their tunable optical, electrical, magnetic, and mechanical properties, those materials attracted great attention. However, it has been hard to elucidate internal structures without fluorescent labelling or cross-sectioning. Here, we demonstrate the structural analysis of not only unary but also binary colloidal crystals using scanning transmission x-ray microscopy and compare the results with colloidal structures and optical properties observed by optical microscopy. Based on the comparison of images obtained by these two methods, the domains of colloidal crystals consisting of different structures and colours were directly identified without any additional sample preparation. Therefore, it was possible to investigate the structural colours of local domains of unary and binary colloidal crystals such as the face centred cubic (FCC) structure with different orientations, that is FCC (111) and FCC (001), and hexagonal close-packed structure, HCP (0001).

Highlights

Two- or three- dimensional colloidal crystals have been studied extensively because of their unique optical properties and potential for various industrial applications such as optical devices[1,2,3,4,5,6] and sensors[7,8,9,10,11,12,13]
The aXis2000, a software for x-ray image and spectra analysis, was used to calculate the optical density (OD) of the binary colloidal crystals consisting of PS and SiO2
We demonstrated the correlations between structures and colours of local domains of colloidal crystals using scanning transmission X-ray microscopy (STXM) and optical microscopy (OM)

Summary

Introduction

Two- or three- dimensional colloidal crystals have been studied extensively because of their unique optical properties and potential for various industrial applications such as optical devices (waveguides, flexible polymer colloidal crystal lasers)[1,2,3,4,5,6] and sensors (pH, volatile organic solvent, humidity)[7,8,9,10,11,12,13]. This is the first study reporting the observation of structures of binary colloidal crystals using STXM and directly identifying correlations between their colours and real structures. The internal structures of colloidal crystals were investigated using STXM and the structural colours of different domains were observed with optical microscopy.

Results

Conclusion