TY - JOUR
T1 - Mapping Grains, Boundaries, and Defects in 2D Covalent Organic Framework Thin Films
AU - Castano, Ioannina
AU - Evans, Austin M.
AU - Reis, Roberto Dos
AU - Dravid, Vinayak P.
AU - Gianneschi, Nathan C.
AU - Dichtel, William R.
N1 - Funding Information:
This work was supported by the National Science Foundation (NSF) through the Northwestern Materials Research Science and Engineering Center under NSF Award no. DMR-1720139 and partly under NSF-DMR 1929356 (V.P.D. & RdR). We acknowledge the Army Research Office for a Multidisciplinary University Research Initiatives (MURI) award under grant number W911NF-15-1-0447. I.C. is supported by the NSF Graduate Research Fellowship under Grant no. (DGE-1842165). A.M.E. is supported by the NSF Research Fellowship under grant no. (DGE-1324585). This study made use of the EPIC facility of NUANCE Center at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF-ECCS 2025633), the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the Keck Foundation, the State of Illinois, and International Institute for Nanotechnology (IIN). We acknowledge Gatan Inc., Pleasanton, CA, USA for the use of the K3-IS camera installed at the EPIC facility of Northwestern University’s NUANCE Center. Research reported in this publication was supported in part by instrumentation provided by the Office of The Director, National Institutes of Health of the National Institutes of Health under Award Number S10OD026871. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Publisher Copyright:
© 2021 American Chemical Society.
PY - 2021/2/23
Y1 - 2021/2/23
N2 - To improve their synthesis and ultimately realize the technical promise of two-dimensional covalent organic frameworks (2D COFs), it is imperative that a robust understanding of their structure be developed. However, high-resolution transmission electron microscopy (HR-TEM) imaging of such beam-sensitive materials is an outstanding characterization challenge. Here, we overcome this challenge by leveraging low electron flux imaging conditions and high-speed direct electron counting detectors to acquire high-resolution images of 2D COF films. We developed a Fourier mapping technique to rapidly extract nanoscale structural information from these TEM images. This postprocessing script analyzes the evolution of 2D Fourier transforms across a TEM image, which yields information about polycrystalline domain orientations and enables quantification of average domain sizes. Moreover, this approach provides information about several types of defects present in a film, such as overlapping grains and various types of grain boundaries. We also find that the pre-eminent origin of defects in COF-5 films, a prototypical boronate ester-linked COF, arises as a consequence of broken B-O bonds formed during polymerization. These results suggest that the nanoscale features observed are a direct consequence of chemical phenomena. Taken together, this mapping approach provides information about the fundamental microstructure and crystallographic underpinnings of 2D COF films, which will guide the development of future 2D polymerization strategies and help realize the goal of using 2D COFs in a host of thin-film device architectures.
AB - To improve their synthesis and ultimately realize the technical promise of two-dimensional covalent organic frameworks (2D COFs), it is imperative that a robust understanding of their structure be developed. However, high-resolution transmission electron microscopy (HR-TEM) imaging of such beam-sensitive materials is an outstanding characterization challenge. Here, we overcome this challenge by leveraging low electron flux imaging conditions and high-speed direct electron counting detectors to acquire high-resolution images of 2D COF films. We developed a Fourier mapping technique to rapidly extract nanoscale structural information from these TEM images. This postprocessing script analyzes the evolution of 2D Fourier transforms across a TEM image, which yields information about polycrystalline domain orientations and enables quantification of average domain sizes. Moreover, this approach provides information about several types of defects present in a film, such as overlapping grains and various types of grain boundaries. We also find that the pre-eminent origin of defects in COF-5 films, a prototypical boronate ester-linked COF, arises as a consequence of broken B-O bonds formed during polymerization. These results suggest that the nanoscale features observed are a direct consequence of chemical phenomena. Taken together, this mapping approach provides information about the fundamental microstructure and crystallographic underpinnings of 2D COF films, which will guide the development of future 2D polymerization strategies and help realize the goal of using 2D COFs in a host of thin-film device architectures.
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U2 - 10.1021/acs.chemmater.0c04382
DO - 10.1021/acs.chemmater.0c04382
M3 - Article
C2 - 35296112
AN - SCOPUS:85101003447
VL - 33
SP - 1341
EP - 1352
JO - Chemistry of Materials
JF - Chemistry of Materials
SN - 0897-4756
IS - 4
ER -