Mesostructures DOI: 10.1002/ange.200801755 Solving Complex Concentric Circular Mesostructures by Using Electron Tomography** Pei Yuan, Nian Liu, Lingzhi Zhao, Xufeng Zhou, Liang Zhou, GraemeJ. Auchterlonie, Xiangdong Yao, John Drennan, GaoQing (Max) Lu, Jin Zou,* and Chengzhong Yu* In nature, ordered structures may present crystal symmetry and/or unconventional helical symmetry that can not be treated by traditional crystallography. The characterization of nanomaterials with helical symmetry creates an extraordinary challenge because of their complexity. The discovery of mesoporous materials [1] with versatile applications [2] has led nanoscience and nanotechnology research into a new dimen- sion. Understanding the morphosynthesis, that is, the internal structure, the external morphology, and the formation mech- anism of novel mesoporous materials is of scientific impor- tance and technological necessity. [3] Recent developments have greatly increased the interest in helical mesostructures with chiral channels [4–7] and circular mesostructures [8–12] as a result of their unique morphologies and internal architec- tures. However, the determination and differentiation of a closed helical mesostructure with the pitch of several nano- meters [9] from a concentric circular mesostructure [8,12] is a formidable challenge. Both the closed helical and concentric circular mesostructures cannot be solely described by tradi- tional crystallography, such as by space groups and symmetry elements, and thus their mesostructures cannot be determined by either X-ray or electron diffraction. [13] Moreover, the structural difference between two mesostructures is very small (in the range of several nanometers) and is located more distinctly in the interior of the material. As a consequence, conventional transmission electron microscopy (TEM) cannot help in determining the hidden information and, in turn, solving the complex mesostructures. Electron tomography (ET) is a rapidly developing tech- nique that is used to obtain the reconstructed complex 3D structures from a tilt series of TEM images. Electron tomography was first used in biology [14–19] to understand cell organelles, subcellular aggregates, and whole cells. Recently, the technique has been increasingly applied in material science to study the morphology and structure of nano- materials. [20–25] The inherent advantage of the ET technique should be helpful in solving mesostructures with complex symmetries. [5] Herein, we demonstrate that, by using the state-of-the-art ET technique, the complex concentric circular (CC) hexag- onal mesostructure can be successfully differentiated from its closed helical (CH) counterpart. The key step in our approach is to make use of each tomographic slice with a thickness of less than 1 nm so that the structural characteristics “hidden” in the interior of selected mesostructured objects can be captured. To our knowledge, this is the first report of using the ET method to solve a complex structure with both conven- tional crystal structures and unusual geometrical configura- tions. The mesostructured silica employed in this study was synthesized by using octadecyltrimethyl ammonium bromide (C 18 TAB) as a template and perfluorooctanoic acid (PFOA) as an additive (see the Supporting Information for details). A TEM image of a typical CC rod is shown in Figure 1a. Hexagonal closely packed pore arrays can be clearly observed near the edges of the rod, which indicates that the pore channels are nearly perpendicular to the long axis of the rod. The distance between two adjacent pores (cell parameter, a) is 4.6 nm. For this selected rod, a series of tilted TEM images were digitally acquired along two orthogonal axes (see movies S1 and S2 in the Supporting Information). The morphology of the mesostructure does not change in the first tilting series (as shown clearly in movie S1 in the Supporting Information), while the ringlike pattern can be observed in the second tilting series (see movie S2 in the Supporting Information). These results indicate that the hexagonally patterned channels are wrapped circularly around the long axis of the rod. To determine the nature of the channels along the axial direction, an ultramicrotome was employed to prepare thin sections (ca. 50 nm) for TEM observations. As shown in Figure 1b, the cross-section of a rod is a circle and the pore channels are visible as concentric rings. It should be noted that, in conventional helical mesostructured rods where the [*] P. Yuan, N. Liu, L. Zhao, X. Zhou, L. Zhou, Prof. C.Z. Yu Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials Fudan University, Shanghai, 200433 (China) Fax: (+ 86) 21-6564-1740 E-mail: j.zou@uq.edu.au P. Yuan, Prof. J. Zou School of Engineering University of Queensland Queensland, QLD 4072 (Australia) E-mail: czyu@fudan.edu.cn G. J. Auchterlonie, Prof. J. Drennan, Prof. J. Zou Centre for Microscopy and Microanalysis University of Queensland, Queensland, QLD 4072 (Australia) Dr. X. Yao, Prof. G. Q. Lu ARC Centre of Excellence for Functional Nanomaterials University of Queensland, Queensland, QLD 4072 (Australia) [**] We thank the State Key Research Program (2004CB217804, 2006CB932302), the NSFC (20721063, 20573021), SLADP (B108), NCET, and the Australian Research Council for financial support. We thank Dr. Matthias Floetenmeyer (UQ) for help with the ultra- microtome experiments. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.200801755. Zuschriften 6772 # 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2008, 120, 6772 –6775