Growth of two-dimensional covalent organic frameworks on substrates: insight from microsecond atomistic simulations.

While growing two-dimensional covalent organic frameworks (2D COFs) on substrates holds promise for producing functional monolayers, the presence of many defects in the resulting crystals often hinders their practical applications. Achieving structural order while suppressing defect formation necessitates a detailed atomic-level understanding. The key lies in understanding the polymerization process with high nano-scale accuracy, which presents significant challenges.

Organic Higher-Order Topological Insulators: Heterotriangulene-Based Covalent Organic Frameworks.

The ability to design and control the chemical characteristics of covalent organic frameworks (COFs) offers a new avenue for the development of functional materials, especially with respect to topological properties. Based on density functional theory calculations, by varying the core units through the choice of bridging groups [O, C═O, CH, or C(CH)] and the linker units [acetylene, diacetylene, or benzene], we have designed heterotriangulene-based COFs that are predicted to be two-dimensional higher-order topological insulators (TIs). The higher-order TI characteristics of these COFs are identified via their topological invariants and the presence of in-gap topological corner modes and gapped edge states.

Organic self-assembled monolayers on superconducting NbSe: interfacial electronic structure and energetics.

While organic self-assembled monolayers (SAMs) have been widely used to modify the work function of metal and metal-oxide surfaces, their application to tune the critical temperature of a superconductor has only been considered recently when SAMs were deposited on NbSemonolayers (Calavalle et al 2021136-143). Here, we describe the results of density functional theory calculations performed on the experimentally reported organic/NbSesystems. Our objectives are: (i) to determine how the organic layers impact the NbSework function and electronic density of states; (ii) to understand the possible correlation with the experimental variations in superconducting behavior upon SAM deposition.

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.

Two-dimensional covalent organic frameworks (2D-COFs), also referred to as 2D polymer networks, display unusual electronic-structure characteristics, which can significantly enrich and broaden the fields of electronics and spintronics. In this Focus article, our objective is to lay the groundwork for the conceptual description of the fundamental relationships among the COF electronic structures, the symmetries of their 2D lattices, and the frontier molecular orbitals (MOs) of their core and linker components. We focus on monolayers of hexagonal COFs and use tight-binding model analyses to highlight the critical role of the frontier-MO symmetry, in addition to lattice symmetry, in determining the nature of the electronic bands near the Fermi level.

Exotic Topological Bands and Quantum States in Metal-Organic and Covalent-Organic Frameworks.

ConspectusMetal-organic and covalent-organic frameworks (MOFs/COFs) have been extensively studied for fundamental interests and their promising applications, taking advantage of their unique structural properties, i.e., high porosity and large surface-to-volume ratio.

π-Orbital Yin-Yang Kagome bands in anilato-based metal-organic frameworks.

π-Orbital bonding plays an important role not only in traditional molecular science and solid-state chemistry but also in modern quantum physics and materials, such as the relativistic Dirac states formed by bonding and antibonding π-bands in graphene. Here, we disclose an interesting manifestation of π-orbitals in forming the Yin-Yang Kagome bands, which host potentially a range of exotic quantum phenomena. Based on first-principles calculations and tight-binding orbital analyses, we show that the frontier π2- and π3-orbitals in anilato-based metal-organic frameworks form concurrently a conduction and valence set of Kagome bands, respectively, but with opposite signs of lattice hopping to constitute a pair of enantiomorphic Yin and Yang Kagome bands, as recently proposed in a diatomic Kagome lattice.

Magneto-Optical Detection of Photoinduced Magnetism Chirality-Induced Spin Selectivity in 2D Chiral Hybrid Organic-Inorganic Perovskites.

The recent convergence of chiral molecules with metal halide perovskite frameworks gives rise to an interesting family of chiral systems: two-dimensional, chiral hybrid organic-inorganic perovskites (chiral-HOIPs). While possessing photovoltaic properties of traditional HOIPs, this class of materials is endowed with chirality through its organic ligands in which the degeneracy of the electron spin in charge transport is broken. That is, the chirality-induced spin selectivity (CISS) effect manifests, making it a promising platform to bridge opto-spintronic studies and the CISS effect.

A 3D percolation model for multicomponent nanocarbon composites: the critical role of nematic transition.

A three-dimensional (3D) continuum percolation model has been developed on the basis of Monte Carlo simulation to investigate the percolation behavior of an electrically insulating matrix reinforced with multiple conductive fillers of different dimensionalities. Impenetrable fillers of large aspect ratio are found to preferentially align with each other to maximize the packing entropy rather than forming randomly oriented clusters. This entropy-driven transition from isotropic to nematic phase is shown to critically affect the percolation threshold.

Incident wavelength and polarization dependence of spectral shifts in β-GaO UV photoluminescence.

We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped β-GaO bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.

Band gap reduction in van der Waals layered 2D materials via a de-charge transfer mechanism.

A thickness dependent band gap is commonly found in layered two-dimensional (2D) materials. Here, using a C3N bilayer as a prototypical model, we systematically investigated the evolution of a band gap from a single layer to a bilayer using first principles calculations and tight binding modeling. We show that in addition to the widely known effect of interlayer hopping, de-charge transfer also plays an important role in tuning the band gap.

Ubiquitous Spin-Orbit Coupling in a Screw Dislocation with High Spin Coherency.

We theoretically demonstrate that screw dislocation (SD), a 1D topological defect widely present in semiconductors, exhibits ubiquitously a new form of spin-orbit coupling (SOC) effect. Differing from the widely known conventional 2D Rashba-Dresselhaus (RD) SOC effect that typically exists at surfaces or interfaces, the deep-level nature of SD-SOC states in semiconductors readily makes it an ideal SOC. Remarkably, the spin texture of 1D SD-SOC, pertaining to the inherent symmetry of SD, exhibits a significantly higher degree of spin coherency than the 2D RD-SOC.

Intrinsic quantum anomalous hall effect in a two-dimensional anilato-based lattice.

Using first-principles calculations, we predict an intrinsic quantum anomalous Hall (QAH) state in a monolayer anilato-based metal-organic framework M2(C6O4X2)3 (M = Mn and Tc, X = F, Cl, Br and I). The spin-orbit coupling of M d orbitals opens a nontrivial band gap up to 18 meV at the Dirac point. The electron counting rule is used to explain the intrinsic nature of the QAH state.

Bis(aminothiolato)nickel nanosheet as a redox switch for conductivity and an electrocatalyst for the hydrogen evolution reaction.

A π-conjugated coordination nanosheet comprising bis(aminothiolato)nickel () moieties was synthesized by the reaction of Ni(acac) with 1,3,5-triaminobenzene-2,4,6-trithiol at liquid-liquid and gas-liquid interfaces. The sheet thickness could be controlled down to a single layer (0.6 nm).

Monte Carlo simulations of electrical percolation in multicomponent thin films with nanofillers.

We developed a 2D disk-stick percolation model to investigate the electrical percolation behavior of an insulating thin film reinforced with 1D and 2D conductive nanofillers via Monte Carlo simulation. Numerical predictions of the percolation threshold in single component thin films showed good agreement with the previous published work, validating our model for investigating the characteristics of the percolation phenomena. Parametric studies of size effect, i.

Tailoring graphene-based electrodes from semiconducting to metallic to increase the energy density in supercapacitors.

The semiconducting character of graphene and some carbon-based electrodes can lead to noticeably lower total capacitances and stored energy densities in electric double layer (EDL)capacitors. This paper discusses the chemical and electronic structure modifications that enhance the available energy bands, density of states and quantum capacitance of graphene substrates near the Fermi level, therefore restoring the conducting character of these materials. The doping of graphene with p or n dopants, such as boron and nitrogen atoms, or the introduction of vacancy defects that introduce zigzag edges, can significantly increase the quantum capacitance within the potential range of interest for the energy storage applications by either shifting the Dirac point away from the Fermi level or by eliminating the Dirac point.

Structural rearrangements of Ru nanoparticles supported on carbon nanotubes under microwave irradiation.

The structure evolution of twinned Ru nanoparticles supported on carbon nanotubes rearranging into Ru single nanocrystals under the microwave irradiation and the exposed surface of Ru single crystals were observed, which provided new insights into synthesis and application of metal nanoparticle catalysts.