Revealing the Local Electronic Structure of a Single-Layer Covalent Organic Framework through Electronic Decoupling

Daniel J Rizzo; Qingqing Dai; Christopher Bronner; Gregory Veber; Brian J Smith; Michio Matsumoto; Simil Thomas; Giang D Nguyen; Patrick R Forrester; William Zhao; Jakob H Jørgensen; William R Dichtel; Felix R Fischer; Hong Li; Jean-Luc Bredas; Michael F Crommie

doi:10.1021/acs.nanolett.9b03998

Revealing the Local Electronic Structure of a Single-Layer Covalent Organic Framework through Electronic Decoupling

Nano Lett. 2020 Feb 12;20(2):963-970. doi: 10.1021/acs.nanolett.9b03998. Epub 2020 Jan 15.

Authors

Daniel J Rizzo¹, Qingqing Dai^{2

3}, Christopher Bronner¹, Gregory Veber⁴, Brian J Smith⁵, Michio Matsumoto^{6

7}, Simil Thomas^{2

3}, Giang D Nguyen¹, Patrick R Forrester¹, William Zhao¹, Jakob H Jørgensen⁸, William R Dichtel⁶, Felix R Fischer^{4

9

10}, Hong Li^{2

3}, Jean-Luc Bredas^{2

3}, Michael F Crommie^{1

9

10}

Affiliations

¹ Department of Physics , University of California at Berkeley , Berkeley , California 94720 , United States.
² Laboratory for Computational and Theoretical Chemistry of Advanced Materials, Physical Science and Engineering Division , King Abdullah University of Science and Technology , Thuwal 23955-6900 , Kingdom of Saudi Arabia.
³ School of Chemistry and Biochemistry & Center for Organic Photonics and Electronics , Georgia Institute of Technology , 901 Atlantic Drive NW , Atlanta , Georgia 30332-0400 , United States.
⁴ Department of Chemistry , University of California at Berkeley , Berkeley , California 94720 , United States.
⁵ Department of Chemistry , Bucknell University , Lewisburg , Pennsylvania 17837 , United States.
⁶ Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , United States.
⁷ WPI Research Center for Materials Nanoarchitectonics (MANA) , National Institute for Materials Science (NIMS) , 1-1 Namiki, Tsukuba , Ibaraki 305-0044 , Japan.
⁸ Department of Physics and Astronomy and Interdisciplinary Nanoscience Center iNANO , Aarhus University , Aarhus C DK-8000 , Denmark.
⁹ Materials Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.
¹⁰ Kavli Energy NanoSciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.

PMID: 31910625
DOI: 10.1021/acs.nanolett.9b03998

Abstract

Covalent organic frameworks (COFs) are molecule-based 2D and 3D materials that possess a wide range of mechanical and electronic properties. We have performed a joint experimental and theoretical study of the electronic structure of boroxine-linked COFs grown under ultrahigh vacuum conditions and characterized using scanning tunneling spectroscopy on Au(111) and hBN/Cu(111) substrates. Our results show that a single hBN layer electronically decouples the COF from the metallic substrate, thus suppressing substrate-induced broadening and revealing new features in the COF electronic local density of states (LDOS). The resulting sharpening of LDOS features allows us to experimentally determine the COF band gap, bandwidths, and the electronic hopping amplitude between adjacent COF bridge sites. These experimental parameters are consistent with the results of first-principles theoretical predictions.

Keywords: 2D polymer; Covalent organic frameworks (COFs); Kagome lattice; biphenyl COF (BP-COF); density functional theory (DFT); scanning tunneling microscopy (STM); scanning tunneling spectroscopy (STS).