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Nanoscale characterization of local structures and defects in photonic crystals using synchrotron-based transmission soft X-ray microscopy.

Nho HW, Kalegowda Y, Shin HJ, Yoon TH - Sci Rep (2016)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, College of Natural Sciences, Hanyang University, Seoul, 04763, Republic of Korea.

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.

No MeSH data available.


Related in: MedlinePlus

(A) Schematic illustration of TXM setup. (B) TXM transmission image of self-assembled polystyrene photonic crystals (scale bar of 1 μm). (b-1) Triple- and (b-2) quadruple- layer of FCC indicated by green and dark blue dashed boxes, respectively. (b-3) Triple- and (b-4) quadruple- layer of HCP indicated by pink and brown dashed boxes, respectively. (b-5) Point and (b-6) line defects represented as red solid line arrows with red dashed circles and a light blue arrow with a light blue dashed box, respectively. (C) CAD drawn model structures. (c-1) Triple- layered FCC, (c-2) quadruple- layered FCC, (c-3) triple- layered HCP, and (c-4) quadruple- layered HCP crystal structures. (D) Comparison of line profiles between FCC (green and blue colored dot lines in d-1 and d-2) and HCP (pink and brown colored dot lines in d-3 and c-4) structures in TXM image and CAD model FCC (black solid lines in d-1 and d-2) and HCP (black solid lines in d-3 and d-4) structures. The position and direction of line profiles of (D) are indicated with yellow arrows in (B,C).
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f1: (A) Schematic illustration of TXM setup. (B) TXM transmission image of self-assembled polystyrene photonic crystals (scale bar of 1 μm). (b-1) Triple- and (b-2) quadruple- layer of FCC indicated by green and dark blue dashed boxes, respectively. (b-3) Triple- and (b-4) quadruple- layer of HCP indicated by pink and brown dashed boxes, respectively. (b-5) Point and (b-6) line defects represented as red solid line arrows with red dashed circles and a light blue arrow with a light blue dashed box, respectively. (C) CAD drawn model structures. (c-1) Triple- layered FCC, (c-2) quadruple- layered FCC, (c-3) triple- layered HCP, and (c-4) quadruple- layered HCP crystal structures. (D) Comparison of line profiles between FCC (green and blue colored dot lines in d-1 and d-2) and HCP (pink and brown colored dot lines in d-3 and c-4) structures in TXM image and CAD model FCC (black solid lines in d-1 and d-2) and HCP (black solid lines in d-3 and d-4) structures. The position and direction of line profiles of (D) are indicated with yellow arrows in (B,C).

Mentions: In this study, PS-based PCs were grown on an O2 plasma treated, 100 nm thick Si3N4 window via self-assembly method. Then, 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). As illustrated in Fig. 1A, the condenser zone plate (CZP) was used to focus incident X-ray on the sample, and the objective zone plate (OZP) was used to magnify the projected image on the charge-coupled device (CCD). When assessing the performance of PCs, the degree of crystal perfection is one of the key parameters. Although the complete details of self-assembly growth mechanisms of PCs are not fully understood yet, it is well recognized that crystal structures and defects are determined by the size ratios, size distributions and volume fractions of each particle, ionic strength of solvent, and the flow rates of solvent compensating for the evaporation from the crystal surface21. For instance, the colloidal spheres with minimal ionic interaction are known to arrange in a hexagonally close-packed fashion parallel to the substrate22, while further stacking of subsequent hexagonally close-packed layers defines whether the resultant crystal structure is FCC or HCP. Due to the small free energy difference between FCC and HCP crystal structures, it has been reported that the self-assembled growth of PCs often results in a mixture of both structures. However, since it is difficult to distinguish FCC and HCP structures by SEM observing top surface layer without cross-sectional characterizations of the sample, these colloidal crystal structures could be often misinterpreted.


Nanoscale characterization of local structures and defects in photonic crystals using synchrotron-based transmission soft X-ray microscopy.

Nho HW, Kalegowda Y, Shin HJ, Yoon TH - Sci Rep (2016)

(A) Schematic illustration of TXM setup. (B) TXM transmission image of self-assembled polystyrene photonic crystals (scale bar of 1 μm). (b-1) Triple- and (b-2) quadruple- layer of FCC indicated by green and dark blue dashed boxes, respectively. (b-3) Triple- and (b-4) quadruple- layer of HCP indicated by pink and brown dashed boxes, respectively. (b-5) Point and (b-6) line defects represented as red solid line arrows with red dashed circles and a light blue arrow with a light blue dashed box, respectively. (C) CAD drawn model structures. (c-1) Triple- layered FCC, (c-2) quadruple- layered FCC, (c-3) triple- layered HCP, and (c-4) quadruple- layered HCP crystal structures. (D) Comparison of line profiles between FCC (green and blue colored dot lines in d-1 and d-2) and HCP (pink and brown colored dot lines in d-3 and c-4) structures in TXM image and CAD model FCC (black solid lines in d-1 and d-2) and HCP (black solid lines in d-3 and d-4) structures. The position and direction of line profiles of (D) are indicated with yellow arrows in (B,C).
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Related In: Results  -  Collection

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f1: (A) Schematic illustration of TXM setup. (B) TXM transmission image of self-assembled polystyrene photonic crystals (scale bar of 1 μm). (b-1) Triple- and (b-2) quadruple- layer of FCC indicated by green and dark blue dashed boxes, respectively. (b-3) Triple- and (b-4) quadruple- layer of HCP indicated by pink and brown dashed boxes, respectively. (b-5) Point and (b-6) line defects represented as red solid line arrows with red dashed circles and a light blue arrow with a light blue dashed box, respectively. (C) CAD drawn model structures. (c-1) Triple- layered FCC, (c-2) quadruple- layered FCC, (c-3) triple- layered HCP, and (c-4) quadruple- layered HCP crystal structures. (D) Comparison of line profiles between FCC (green and blue colored dot lines in d-1 and d-2) and HCP (pink and brown colored dot lines in d-3 and c-4) structures in TXM image and CAD model FCC (black solid lines in d-1 and d-2) and HCP (black solid lines in d-3 and d-4) structures. The position and direction of line profiles of (D) are indicated with yellow arrows in (B,C).
Mentions: In this study, PS-based PCs were grown on an O2 plasma treated, 100 nm thick Si3N4 window via self-assembly method. Then, 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). As illustrated in Fig. 1A, the condenser zone plate (CZP) was used to focus incident X-ray on the sample, and the objective zone plate (OZP) was used to magnify the projected image on the charge-coupled device (CCD). When assessing the performance of PCs, the degree of crystal perfection is one of the key parameters. Although the complete details of self-assembly growth mechanisms of PCs are not fully understood yet, it is well recognized that crystal structures and defects are determined by the size ratios, size distributions and volume fractions of each particle, ionic strength of solvent, and the flow rates of solvent compensating for the evaporation from the crystal surface21. For instance, the colloidal spheres with minimal ionic interaction are known to arrange in a hexagonally close-packed fashion parallel to the substrate22, while further stacking of subsequent hexagonally close-packed layers defines whether the resultant crystal structure is FCC or HCP. Due to the small free energy difference between FCC and HCP crystal structures, it has been reported that the self-assembled growth of PCs often results in a mixture of both structures. However, since it is difficult to distinguish FCC and HCP structures by SEM observing top surface layer without cross-sectional characterizations of the sample, these colloidal crystal structures could be often misinterpreted.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, College of Natural Sciences, Hanyang University, Seoul, 04763, Republic of Korea.

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.

No MeSH data available.


Related in: MedlinePlus