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

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.

Resistive Switching Memory Performance of Two-Dimensional Polyimide Covalent Organic Framework Films

“…[20][21][22][23] A variety of 2D COFbased organic semiconductors have been constructed from conjugated molecules (such as pyrene, porphyrin, and phthalocyanine) to afford well-defined -arrays with tunable charge transfer. [24][25][26] Among these, fusing the donor and acceptor moieties into 2D frameworks via direct polycondensation gives rise to robust COF materials with tunable electronic properties. 27,28 Growing crystalline COF films at confined interfaces facilitated their integration into devicerelevant settings such as field-effect transistors and photodetector devices.…”

In silico design of 2D polymers containing truxene-based platforms: insights into their structural and electronic properties

“…DFT calculations on the electronic structures of different 2D conjugated polymers have been previously reported, with an emphasis on the role played by the network topology, [29][30][31] lattice symmetry 32 or structural differences between 1D and 2D, [33][34][35] among other structural factors. [36][37][38][39] However, while isolated truxene-based molecules have been amply theoretically explored, a systematic study of their 2D conjugated polymers has not yet been reported. [40][41][42] In this work, we performed an exhaustive investigation of truxene-based 2D conjugated polymers with the aim to explore their chemical structure-electronic property relationships to guide the design of novel optimized 2D materials.…”

Engineering of flat bands and Dirac bands in two-dimensional covalent organic frameworks (COFs): relationships among molecular orbital symmetry, lattice symmetry, and electronic-structure characteristics

“…18 As mentioned already, Dirac and flat bands are known to arise in COFs with specific lattice symmetries. 11,[19][20][21] In addition to lattice symmetry, the frontier molecular orbital (MO) symmetries of the individual core and linker components are also expected to be a key factor determining the nature of the electronic bands near the Fermi level. 22 Benefiting from the diversity of cores and linkers available for COF formation, MO symmetry adds another degree of freedom to engineer the characteristics of the COF bands.…”