Abstract
For the structural characterization of the polystyrene (PS)-based photonic crystals (PCs), fast and direct imaging capabilities of full field transmission X-ray microscopy (TXM) were demonstrated at soft X-ray energy. PS-based PCs were prepared on an O2-plasma treated Si3N4 window and their local structures and defects were investigated using this label-free TXM technique with an image acquisition speed of ~10 sec/frame and marginal radiation damage. Micro-domains of face-centered cubic (FCC (111)) and hexagonal close-packed (HCP (0001)) structures were dominantly found in PS-based PCs, while point and line defects, FCC (100), and 12-fold symmetry structures were also identified as minor components. Additionally, in situ observation capability for hydrated samples and 3D tomographic reconstruction of TXM images were also demonstrated. This soft X-ray full field TXM technique with faster image acquisition speed, in situ observation, and 3D tomography capability can be complementally used with the other X-ray microscopic techniques (i.e., scanning transmission X-ray microscopy, STXM) as well as conventional characterization methods (e.g., electron microscopic and optical/fluorescence microscopic techniques) for clearer structure identification of self-assembled PCs and better understanding of the relationship between their structures and resultant optical properties.
Highlights
Important characteristics Field of view Sample thickness Acquisition speed Spatial resolution Sample preparation In situ capability
X-ray microscopy has been considered as a promising approach for the characterization of PCs17,18, and those capabilities have been tested in recent studies using scanning transmission X-ray microscopy (STXM)[19,20]
Various local structures and defects of the PS-based PCs were characterized by the soft X-ray TXM endstation at the 10D beamline of the Pohang Light Source (PLS, Pohang, Republic of Korea)
Summary
Important characteristics Field of view (μm) Sample thickness (μm) Acquisition speed (sec/frame) Spatial resolution (nm) Sample preparation In situ capability. These processes may alter the local structures of PCs to a greater extent by exerting the capillary forces on colloidal particles and rendering them unsuitable for the study of self-assembled PCs. To overcome these limitations of optical microscopy (OM), Thijssen et al.[16] used reciprocal space X-ray diffraction technique to identify crystal structure and defects in long-range order.
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