We predict two-dimensional Be materials, α- and β-beryllene. In α-beryllene each Be atom binds to six other Be atoms in a planar scheme, whereas β-beryllene consists of two stacked α-beryllene ...monolayers. Both α- and β-beryllene are found to be highly stable, as demonstrated by high cohesive energies close to that of bulk Be, an absence of imaginary phonon modes, and high melting points. Both materials are metallic, indicating potential applications in Na-ion and K-ion batteries, which are explored in detail. The diffusion barriers of Na (K) on α- and β-beryllene are found to be only 9 (3) and 4 (5) meV, respectively. In particular, the diffusion barrier of K on α-beryllene exhibits the lowest ever recorded value in two-dimensional materials, suggesting the possibility of ultrafast charge/discharge. As the theoretical specific capacities of Na/K on α- and β-beryllene are found to be 1487/1322 and 743/743 mA h g–1, respectively, the storage capacity is ultrahigh.
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While the MXene Ti3C2 is well known for its extraordinary material properties with wide applications, it is demonstrated here that it is not the most stable 2D titanium carbide. Evolutionary search ...and first‐principles calculations are employed to predict for Ti3C3 a novel structure prototype with P4/mmm symmetry and tetragonal sandwich structure. The cohesive energy, phonon dispersion, and melting point demonstrate high stability of Ti3C3. The mechanical properties are found to be even better than those of graphene in terms of Young's modulus and fracture strength. The metallicity of Ti3C3 indicates potential in metal‐ion batteries. The diffusion barriers for Li, Na, K, and Ca atoms are found to be as low as 0.15, 0.04, 0.002 (record among the known 2D materials), and 0.14 eV, respectively, suggesting the possibility to realize fast charge and discharge. Importantly, the discovered structure prototype gives rise to a whole family of 2D materials. For example, six thermally and dynamically stable materials with metallic properties, Ti3X3 (X = B, Si, Ge, N, P, and As) are identified. The family is promising not only in the fields of nano‐mechanics and metal‐ion batteries but also can guide the search for further 2D structure prototypes.
Based on evolutionary search and first‐principles calculations, a 2D titanium carbide with tetragonal sandwich structure is predicted, Ti3C3, which is found to be more stable than the well‐studied MXene Ti3C2. The novel 2D structure prototype realized by Ti3C3 turns out to provide access to a whole family of 2D materials.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Auxetic materials (negative Poisson’s ratio) are of exceptional importance for nanomechanical applications. Using first-principles calculations, we propose two-dimensional δ-phase carbon ...monochalcogenides (δ-CS, δ-CSe, and δ-CTe) with very strong auxeticity. In contrast to the known two-dimensional materials, we find that Poisson’s ratio is negative in all crystal directions. In addition, the δ-phase carbon monochalcogenides turn out to be direct or quasi-direct bandgap semiconductors with impressive absorption of solar radiation.
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Efficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as Ni2P have been shown to be active toward water splitting. Our theoretical ...analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present for the first time a novel PH3 plasma-assisted approach to convert NiCo hydroxides into ternary NiCoP. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at −10 mA cm–2 in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm–2 is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm–2 is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting. Moreover, our new synthetic approach can serve as a versatile route to synthesize various bimetallic or even more complex phosphides for various applications.
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5.
Point Defects in Blue Phosphorene Sun, Minglei; Chou, Jyh-Pin; Hu, Alice ...
Chemistry of materials,
10/2019, Volume:
31, Issue:
19
Journal Article
Peer reviewed
Open access
Using first-principles calculations, we investigate selected defects in blue phosphorene (BlueP). For a single-vacancy (SV) defect, a 5–9 structure is energetically favorable, and for a ...double-vacancy defect, a 5–8–5 or 555–777 structure is. A P adatom favors the top adsorption site. Scanning tunneling microscopy images are simulated to aid the experimental identification of the defects. Formation of a Stone–Wales defect is found to be most likely, but it can be reverted by thermal annealing. Calculated migration and transformation barriers show that a SV defect can migrate easily. Both a SV defect and a P adatom induce a magnetic moment, thus turning BlueP into a magnetic semiconductor. It turns out that all of the defects under investigation enhance the ability of BlueP to absorb sunlight.
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Realization of permanent valley polarization in Cr‐doped monolayer MoS2 is found to be unfeasible because of extended moment formation. Introduction of an additional hole is suggested as a viable ...solution. V‐doped monolayer MoS2 is demonstrated to sustain permanent valley polarization and therefore can serve as a prototype material for valleytronics.
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Based on evolutionary search and first-principles calculations, we predict for B8Si4 structural stability in terms of cohesive energy, phonon spectrum, and melting point. The size of the indirect ...band gap is similar to that of bulk Si, and the electronic transport turns out to be highly anisotropic for both holes and electrons. The predicted structure prototype is shared by B8Ge4, B8Sn4, and B8Pb4. B8Ge4 is an indirect band gap semiconductor, with the hole mobility similar to that of B8Si4. B8Sn4 is an indirect band gap semiconductor with the gap size similar to that of bulk Ge. The hole mobility of B8Sn4 turns out to be as high as ∼106 cm2 V–1 s–1 and the electron mobility as high as ∼105 cm2 V–1 s–1, exceeding the performance of graphene (2 × 105 cm2 V–1 s–1). B8Pb4 is found to be metallic.
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The design of materials meeting the rigorous requirements of photocatalytic water splitting is still a challenge. Anisotropic Janus 2D materials exhibit great potential due to outstandingly high ...photocatalytic efficiency. Unfortunately, these materials are scarce. By means of ab initio swarm-intelligence search calculations, we identify a SiP2 monolayer with Janus structure (i.e., out-of-plane asymmetry). The material turns out to be semiconducting with an indirect band gap of 2.39 eV enclosing the redox potentials of water. Notably, the oxygen and hydrogen evolution half reactions can happen simultaneously at the Si and P atoms, respectively, driven merely by the radiation-induced electrons and holes. The carrier mobility is found to be anisotropic and high, up to 10–4 cm2 V–1 s–1, facilitating fast transport of the photogenerated carriers. The SiP2 monolayer shows remarkably strong optical absorption in the visible-to-ultraviolet range of the solar spectrum, ensuring efficient utilization of the solar energy.
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The performance of an electronic device based on a two-dimensional material is strongly affected by the contact with the metallic electrodes. In this article, we study the electronic properties of ...two-dimensional MoSSe in contact with a germanene electrode by first-principles calculations. The results show that the contact characteristics are significantly different for the two sides of MoSSe. Notably, for both sides in-plane tensile strain induces a transition from Schottky to Ohmic behavior. Increasing the thickness of MoSSe also leads to an Ohmic contact. We propose an effective route to high performance MoSSe electronic devices.
We propose an effective route to high performance MoSSe electronic devices.
The anisotropic Janus materials Pd4S3Se3, Pd4S3Te3, and Pd4Se3Te3 are demonstrated to be stable based on the cohesive energy, the phonon spectrum, and ab initio molecular dynamics simulation. They ...are semiconductors with indirect band gaps of 1.25, 0.78, and 1.32 eV, respectively, and exhibit ultrahigh carrier mobilities of up to 9455 cm2 V–1 s–1. Band edges enclosing the redox potentials of water enable photocatalytic water splitting. Importantly, the large intrinsic electric fields of the Janus structures facilitate the migration of photo-generated carriers, which enhances the carrier utilization and, therefore, the solar-to-hydrogen efficiency. The obtained efficiencies of 30.1% for Pd4S3Se3, 38.6% for Pd4S3Te3, and 23.8% for Pd4Se3Te3 surpass the conventional theoretical limit of 18%. In addition, the materials are predicted to catalyze the hydrogen and oxygen evolution reactions. Application potential is identified in electronics, optoelectronics, and photocatalytic water splitting.
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