1,722,573 research outputs found
How the moiré superstructure determines the formation of highly stable graphene quantum dots on Ru(0001) surface
No full text© The Royal Society of Chemistry. Highly stable graphene quantum dots (HSGQDs) are widely observed in the initial stages of graphene chemical vapor deposition (CVD) growth on lattice-mismatched transition metal surfaces, e.g. Ru(0001), but their formation mechanism has so far remained a mystery. Using a combination of density functional theory calculations and theoretical modeling, we show that the sizes and the morphologies of HSGQDs are determined by the interaction of the graphene edge to the metal substrate interaction, which in turn, is modulated by the moiré superstructure, while the relatively weak interaction of the central atoms of graphene (or graphene bulk atoms (GB)) with the substrate plays a secondary role. The theoretical understanding of the effect of moiré superstructure on graphene CVD growth allows us to predict the formation of HSGQDs on various metal surfaces and provides a guideline to select the best catalyst for graphene growth. ©The Royal Society of Chemistry 201
Environment-dependent edge reconstruction of transition metal dichalcogenides: a global search
Full text linkThe properties of an edge of a transition metal dichalcogenide (TMDC) sensitively depend on its atomic structure; therefore, knowing the exact structure is a precondition for predicting the applications of TMDC, such as in catalysis. Although some edge reconstructions of TMDCs have been reported in previous studies, a global search of TMDC edge structures and calculations of their stabilities are still absent. Here, we propose an approach to explore all possible edge reconstructions of a monolayer TMDC by employing the particle swarm optimization algorithm and first-principles calculations. Taking the most studied TMDC material, MoS2, as a representative, we have built a database of the edge structures of TMDCs. Including the five experimentally observed edges, the thirty-four most stable edges with various sulfur concentrations are predicted for the first time. The most stable edge structures of 1H-MoS2 in different environments along both the armchair and zigzag directions have been predicted and agree well with experimental observations. A specific edge of 1H-MoS2 in the database can be stabilized by modulating the chemical composition of the atoms, which offers an efficient way to tune the properties of TMDC nanostructures, such as TMDC quantum dots and/or nanoribbons. (C) 2020 The Author(s). Published by Elsevier Ltd
Theoretical calculation boosting the chemical vapor deposition growth of graphene film
Full text link© 2021 Author(s).Chemical vapor deposition (CVD) is a promising method for the mass production of high-quality graphene films, and great progress has been made over the last decade. Currently, the CVD growth of graphene is being pushed to achieve further advancements, such as super-clean, ultra-flat, and defect-free materials, as well as controlling the layer, stacking order, and doping level during large-scale preparation. The production of high-quality graphene by CVD relies on an in-depth knowledge of the growth mechanisms, in which theoretical calculations play a crucial role in providing valuable insights into the energy-, time-, and scale-dependent processes occurring during high-temperature growth. Here, we focus on the theoretical calculations and discuss the recent progress and challenges that need to be overcome to achieve controllable growth of high-quality graphene films on transition-metal substrates. Furthermore, we present some state-of-the-art graphene-related structures with novel properties, which are expected to enable new applications of graphene-based materials.11Nsciescopu
How a Solid Catalyst Determines the Chirality of the Single-Wall Carbon Nanotube Grown on It
No full textAlthough
the growth of single-wall carbon nanotubes (SWCNTs) with
a chirality selectivity up to 90% has been successfully achieved using
solid catalysts (Yang, F. Nature, 2014, 510, 522; Zhang, S.; Nature, 2017, 543, 234, etc.), the underlying mechanism that governs
the chirality selection is far from clear. Here we propose a mechanism
to understand how a solid catalyst particle determines the structure
of the SWCNT grown on it. The mechanism has to satisfy three criteria:
(i) thermodynamic selection of SWCNTs that possess a structural symmetry
the same as that of the catalyst surface; (ii) kinetic elimination
of the achiral SWCNTs with extremely low growth rates; (iii) rough
control over the catalyst particle size leads to SWCNTs with only
one or a few dominant chiralities. Besides the deep understanding
on the mechanisms of experimentally synthesized (12, 6) and (8, 4)
SWCNTs, the preference growth of other SWCNTs of the (2n, n) family, such as the (10, 5) or (6, 3) SWCNTs,
by using catalyst surface with a 5- or 3-fold symmetry is predicted.
Such a simple three-criteria mechanism deepens our understanding of
the selective growth of SWCNTs and provides a guideline for catalyst
design for controlled SWCNT synthesis
Molecular dynamics simulation of graphene sinking during chemical vapor deposition growth on semi-molten Cu substrate
No full text© 2020, The Author(s).Copper foil is the most promising catalyst for the synthesis of large-area, high-quality monolayer graphene. Experimentally, it has been found that the Cu substrate is semi-molten at graphene growth temperatures. In this study, based on a self-developed C–Cu empirical potential and density functional theory (DFT) methods, we performed systematic molecular dynamics simulations to explore the stability of graphene nanostructures, i.e., carbon nanoclusters and graphene nanoribbons, on semi-molten Cu substrates. Many atomic details observed in the classical MD simulations agree well with those seen in DFT-MD simulations, confirming the high accuracy of the C–Cu potential. Depending on the size of the graphene island, two different sunken-modes are observed: (i) graphene island sinks into the first layer of the metal substrate and (ii) many metal atoms surround the graphene island. Further study reveals that the sinking graphene leads to the unidirectional alignment and seamless stitching of the graphene islands, which explains the growth of large single-crystal graphene on Cu foil. This study deepens our physical insights into the CVD growth of graphene on semi-molten Cu substrate with multiple experimental mysteries well explained and provides theoretic references for the controlled synthesis of large-area single-crystalline monolayer graphen
Stabilization of Black Phosphorene by Edge-Selective Adsorption of C60Molecules
No full textBlack phosphorene (BP) has excellent application prospects in nanoelectronics, optoelectronics, and thermal electronics due to its tunable direct band gap and high carrier mobility. However, BP can be easily oxidized under ambient conditions, making its application challenging. In this work, we applied first-principles theoretical calculations to study the stabilization of BP through C60 passivation at its edge. It is found that C60 functionalization at the zigzag, armchair, and 54 edges moves the conduction band minima (CBMs) of BP below the O2/O2 redox potential, preventing BP from being oxidized. Moreover, the CBM of the functionalized BP changes from the edge P atoms to the adsorbed C60, and the valence band maximum remains on the BP, leading to charge transfer from BP to C60 under light excitation. Furthermore, the light adsorption of C60-passivated BP is enhanced, which provides better performance for BP's application in optoelectronics. Our study provides guidance to find a highly efficient way to improve the stability of BP by edge functionalization.11Nsciescopu
A family of superconducting boron crystals made of stacked bilayer borophenes
No full textMonolayer borophenes tend to be easily oxidized, while thicker borophenes have stronger antioxidation properties. Herein, we proposed four novel metallic boron crystals by stacking the experimentally synthesized borophenes, and one of the crystals has been reported in our previous experiments. Bilayer units tend to act as blocks for crystals as determined by bonding analyses. Their kinetic, thermodynamic and mechanical stabilities are confirmed by our calculated phonon spectra, molecular dynamics and elastic constants. Our proposed allotropes are more stable than the boron α-Ga phase below 1000 K at ambient pressure. Some of them become more stable than the α-rh or γ-B28 phases at appropriate external pressure. More importantly, our calculations show that three of the proposed crystals are phonon-mediated superconductors with critical temperatures of about 5-10 K, higher than those of most superconducting elemental solids, in contrast to typical boron crystals with significant band gaps. Our study indicates a novel preparation method for metallic and superconducting boron crystals dispensing with high pressure. © 2022 The Royal Society of Chemistry11Nsciescopu
Anomalous twin boundaries in two dimensional materials
Full text linkTwin boundary defects form in virtually all crystalline materials as part of their response to applied deformation or thermal stress. For nearly six decades, graphite has been used as a textbook example of twinning with illustrations showing atomically sharp interfaces between parent and twin. Using state-of-the-art high-resolution annular dark-field scanning transmission electron microscopy, we have captured atomic resolution images of graphitic twin boundaries and find that these interfaces are far more complex than previously supposed. Density functional theory calculations confirm that the presence of van der Waals bonding eliminates the requirement for an atomically sharp interface, resulting in long-range bending across multiple unit cells. We show these remarkable structures are common to other van der Waals materials, leading to extraordinary microstructures, Raman-active stacking faults, and sub-surface exfoliation within bulk crystals. © 2018, The Author(s
Mechanism of Corrugated Graphene Moir?? Superstructures on Transition-Metal Surfaces
No full textA graphene layer on a transition-metal (TM) surface can be either corrugated or flat, depending on the type of the substrate and its rotation angle with respect to the substrate. It was broadly observed that the degree of corrugation generally decreases with the increase of rotation angle or the decrease of Moir?? pattern size. In contrast to a flat graphene on a TM surface, a corrugated graphene layer has an increased binding energy to the substrate and a concomitant elastic energy. Here, we developed a theoretical model about the competition between the binding energy increase and the elastic energy of corrugated graphene layers on TM surfaces in which all the parameters can be calculated by density functional theory (DFT) calculations. The agreement between the theoretical model and the experimental observations of graphene on various TM surfaces, for example, Ru(0001), Rh(111), Pt(111), and Ir(111), substantiated the applicability of this model for graphene on other TM surfaces. Moreover, the morphology of a graphene layer on an arbitrary TM surface can be theoretically predicted through simple DFT calculations based on the model. Our work thus provides a theoretical framework for the intelligent design of graphene/TM superstructures with the desired structure
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