2020 New's Items

Amidation, Esterification, and Thioesterification of a Carboxyl-Functionalized Covalent Organic Framework

Guo L
Jia S
Diercks CS
Yang X
Alshmimri SA
Yaghi OM
2020

Three new post-synthetic modification reactions, namely amidation, esterification, and thioesterification, were demonstrated on a novel highly crystalline two-dimensional covalent organic framework (COF), COF-616, bearing pre-installed carboxyl groups. The strategy can be used to introduce a large variety of functional groups into COFs and the modifications can be carried out under mild reaction conditions, with high yields, and an easy work-up protocol. As a proof of concept, various chelating functionalities were successfully incorporated into COF-616 to yield a family of...

Aromaticity as a Guide to Planarity in Conjugated Molecules and Polymers

Wood BM
Forse AC
Persson KA
2020

Conjugated molecules and polymers have the ability to be transformative semiconducting materials; however, to reach their full potential a detailed understanding of the factors governing the molecular structure is crucial for establishing design principles for improved materials. Creating planar or “locking” structures is of particular interest for tuning electronic properties. While noncovalent locks are an effective strategy for increasing planarity, the precise interactions leading to these planar structures are often unknown or mischaracterized. In this study, we demonstrate that...

Centimeter-Scale and Visible Wavelength Monolayer Light-Emitting Devices

Cho J
Amani M
Lien DH
Kim H
Yeh M
Wang V
Tan C
Javey A
2020

Monolayer 2D transition metal dichalcogenides (TMDCs) have shown great promise for optoelectronic applications due to their direct bandgaps and unique physical properties. In particular, they can possess photoluminescence quantum yields (PL QY) approaching unity at the ultimate thickness limit, making their application in light-emitting devices highly promising. Here, large-area WS2 grown via chemical vapor deposition is synthesized and characterized for visible (red) light-emitting devices. Detail optical characterization of the synthesized films is performed, which show peak PL QY as...

propnet: A Knowledge Graph for Materials Science

Mrdjenovich D
Horton MK
Montoya JH
Legaspi CM
Dwaraknath S
Tshitoyan V
Jain A
Persson KA
2020

Data-driven materials science is bolstered by the recent growth of online materials databases. However, the current informatics infrastructure has yet to unlock the full knowledge available within existing datasets or to explore connections between different materials science domains. Here, we present a streamlined system for codifying and connecting materials properties in an open-source Python framework: propnet. We demonstrate the capability of this framework to augment existing datasets of materials properties: by consecutively applying a network of physical relationships to...

Reticulating 1D Ribbons into 2D Covalent Organic Frameworks by Imine and Imide Linkages

Nguyen HL
Gropp C
Yaghi OM
2020

The design and synthesis of 2D and 3D crystalline covalent organic frameworks (COFs) from macromolecular and even infinite building units is largely undeveloped. Here, we report a strategy to link molecules and 1D ribbons into 2D cystalline frameworks. Triangular, tris(4-aminophenyl)amine (TAA), and square, 1,3,6,8-tetrakis(p-formylphenyl)pyrene (TFPPy), organic building units are joined substoichiometrically by imine linkages to produce 1D ribbons, termed COF-76, bearing free amines, which are then used to link the ribbons into 2D frameworks COF-77 and COF-78. In...

Reticular Growth of Graphene Nanoribbon 2D Covalent Organic Frameworks

Veber G
Diercks C
Rogers C
Perkins W
Ciston J
Lee K
Llinas J
Liebman-Palaez A
Zhu C
Bokor J
Fischer F
2020

The reticular synthesis of covalent organic frameworks (COFs), extended porous two-dimensional (2D) or three-dimensional (3D) networks held together by strong, highly directional chemical bonds, has thus far been restricted to small, shape-persistent, molecular building blocks. Here, we demonstrate the growth of crystalline 2D COFs from a polydisperse macromolecule derived from single-layer graphene, bottom-up synthesized quasi-one-dimensional (1D) graphene nanoribbons (GNRs). X-ray scattering and transmission electron microscopy reveal that 2D sheets of GNR-COFs self-assembled at a...

Back-End-of-Line Nano-Electro-Mechanical Switches for Reconfigurable Interconnects

Sikder U
Usai G
Yen T
Horace-Herron K
Hutin L
Liu TK
2020

Non-volatile (NV) nano-electro-mechanical (NEM) switches are successfully implemented using multiple metallic layers in a standard 65 nm CMOS back-end-of-line (BEOL) process with no additional lithography steps. Non-volatile operation of a NEM switch as a reconfigurable interconnect to dynamically change CMOS circuit functionality is demonstrated.

Resonant and bound states of charged defects in two-dimensional semiconductors

M. Aghajanian
B. Schuler
K. A. Cochrane
J.-H. Lee
C. Kastl
J. B. Neaton
A. Weber-Bargioni
A. A. Mostofi
J. Lischner
2020

A detailed understanding of charged defects in two-dimensional semiconductors is needed for the development of ultrathin electronic devices. Here, we study negatively charged acceptor impurities in monolayer WS2 using a combination of scanning tunneling spectroscopy and large-scale atomistic electronic structure calculations. We observe several localized defect states of hydrogenic wave function character in the vicinity of the valence band...

Effect of Anisotropic Confinement on Electronic Structure and Dynamics of Band Edge Excitons in Inorganic Perovskite Nanowires

Folie BD
Tan JA
Huang J
Sercel PC
Delor M
Lai M
Lyons JL
Bernstein N
Efros AL
Yang P
Ginsberg NS
2020

Inorganic lead halide perovskite nanostructures show promise as the active layers in photovoltaics, light emitting diodes, and other optoelectronic devices. They are robust in the presence of oxygen and water, and the electronic structure and dynamics of these nanostructures can be tuned through quantum confinement. Here we create aligned bundles of CsPbBr3 nanowires with widths resulting in quantum confinement of the electronic wave functions and subject them to ultrafast microscopy. We directly image rapid one-dimensional exciton diffusion along the...

Tunable valleytronics with symmetry-retaining high polarization degree in SnSxSe1−x model system

Lin S
Fang Z
Hou T
Hsu TW
So CH
Yeoh C
Li R
Liu Y
Chan EM
Chueh Y-L
Tang B
Persson KA
Yao J
2020
SnS has recently been shown to possess unique valleytronic capability with a large polarization degree, where non-degenerate valleys can be accessed using linearly polarized light, bestowed upon by the unique anisotropy and wavefunction symmetry. It is thus of utmost importance to demonstrate the extension of such effects for the IV–VI system in general, thereby elucidating the generality and tunability of such valleytronics. We show the highly tunable valleytronics via gradual compositional control of the tin(II) sulfo-selenide (SnSxSe1x) alloy system with excellent retainment of...