Advanced electrocatalysts with low platinum content, high activity and durability for the oxygen reduction reaction can benefit the widespread commercial use of fuel cell technology. Here, we report ...a platinum-trimer decorated cobalt-palladium core-shell nanocatalyst with a low platinum loading of only 2.4 wt% for the use in alkaline fuel cell cathodes. This ternary catalyst shows a mass activity that is enhanced by a factor of 30.6 relative to a commercial platinum catalyst, which is attributed to the unique charge localization induced by platinum-trimer decoration. The high stability of the decorated trimers endows the catalyst with an outstanding durability, maintaining decent electrocatalytic activity with no degradation for more than 322,000 potential cycles in alkaline electrolyte. These findings are expected to be useful for surface engineering and design of advanced fuel cell catalysts with atomic-scale platinum decoration.
Blue phosphorene (BlueP) is a graphene-like phosphorus nanosheet which was synthesized very recently for the first time Nano Lett., 2016, 16, 4903-4908. The combination of electronic properties of ...two different two-dimensional materials in an ultrathin van der Waals (vdW) vertical heterostructure has been proved to be an effective approach to the design of novel electronic and optoelectronic devices. Therefore, we used density functional theory to investigate the structural and electronic properties of two BlueP-based heterostructures - BlueP/graphene (BlueP/G) and BlueP/graphene-like gallium nitride (BlueP/g-GaN). Our results showed that the semiconducting nature of BlueP and the Dirac cone of G are well preserved in the BlueP/G vdW heterostructure. Moreover, by applying a perpendicular electric field, it is possible to tune the position of the Dirac cone of G with respect to the band edge of BlueP, resulting in the ability to control the Schottky barrier height. For the BlueP/g-GaN vdW heterostructure, BlueP forms an interface with g-GaN with a type-II band alignment, which is a promising feature for unipolar electronic device applications. Furthermore, we discovered that both G and g-GaN can be used as an active layer for BlueP to facilitate charge injection and enhance the device performance.
We theoretically study physical properties of the most promising color center candidates for the recently observed single-photon emissions in hexagonal boron nitride (h-BN) monolayers. Through our ...group theory analysis combined with density functional theory (DFT) calculations we provide several pieces of evidence that the electronic properties of the color centers match the characters of the experimentally observed emitters. We calculate the symmetry-adapted multielectron wave functions of the defects using group theory methods and analyze the spin–orbit and spin–spin interactions in detail. We also identify the radiative and nonradiative transition channels for each color center. An advanced ab initio DFT method is then used to compute energy levels of the color centers and their zero-phonon-line (ZPL) emissions. The computed ZPLs, the profile of excitation and emission dipole polarizations, and the competing relaxation processes are discussed and matched with the observed emission lines. By providing evidence for the relation between single-photon emitters and local defects in h-BN, this work provides the first steps toward harnessing quantum dynamics of these color centers.
Point Defects in Blue Phosphorene Sun, Minglei; Chou, Jyh-Pin; Hu, Alice ...
Chemistry of materials,
10/2019, Letnik:
31, Številka:
19
Journal Article
Recenzirano
Odprti dostop
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.
We implement a theoretical study of the geometry parameters, binding energies, electronic and magnetic properties of 4d series transition metals substituted graphene. Based on a hybridization model, ...the variations of binding energies and magnetic moments size can be well understood. According to the occupation of different vacancy-metal hybridized electronic states, the substituted systems can be divided into three types: (i) for Y and Zr, all the bonding states are completely occupied, and the magnetic moment is zero; (ii) for Nb, Mo and Tc, nonbonding states become occupied, which induce a strong localized magnetic moment with d character of 1 μB, 2 μB and 1 μB, respectively; (iii) for Ru, Rh and Pd, the magnetic moment oscillates between 0 and 1 μB as the antibonding state become occupied. In addition, we found that the Y- and Rh-substituted graphene exhibit metallic behavior, and the semiconducting natures were found in Zr-, Ru- and Pd-substituted systems. More interestingly, half-metallic state were predicted in Nb- and Tc-substituted graphene, while spin-polarized semiconducting state is realized in Mo-substituted system. The Curie temperature of about 83, 354 and 36 K was estimated for Nb-, Mo- and Tc-substituted systems in the mean-field approximation at impurity concentration 3.125%.
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Diamond is not only the hardest material in nature, but is also an extreme electronic material with an ultrawide bandgap, exceptional carrier mobilities, and thermal conductivity. Straining diamond ...can push such extreme figures of merit for device applications. We microfabricated single-crystalline diamond bridge structures with ~1 micrometer length by ~100 nanometer width and achieved sample-wide uniform elastic strains under uniaxial tensile loading along the 100, 101, and 111 directions at room temperature. We also demonstrated deep elastic straining of diamond microbridge arrays. The ultralarge, highly controllable elastic strains can fundamentally change the bulk band structures of diamond, including a substantial calculated bandgap reduction as much as ~2 electron volts. Our demonstration highlights the immense application potential of deep elastic strain engineering for photonics, electronics, and quantum information technologies.
Highly correlated orbitals coupled with phonons in two-dimension are identified for paramagnetic and optically active boron vacancy in hexagonal boron nitride by first principles methods which are ...responsible for recently observed optically detected magnetic resonance signal. Here, we report ab initio analysis of the correlated electronic structure of this center by density matrix renormalization group and Kohn-Sham density functional theory methods. By establishing the nature of the bright and dark states as well as the position of the energy levels, we provide a complete description of the magneto-optical properties and corresponding radiative and non-radiative routes which are responsible for the optical spin polarization and spin dependent luminescence of the defect. Our findings pave the way toward advancing the identification and characterization of room temperature quantum bits in two-dimensional solids.
The nitrogen-vacancy (NV) center in diamond has shown great promise of nanoscale sensing applications, however, near-surface NV suffer from relatively short spin coherence time that limits its ...sensitivity. This is presumably caused by improper surface termination. Using first-principles calculations, we propose that nitrogen-terminated (111) diamond provides electrical inactivity and surface spin noise free properties. We anticipate that the nitrogen-terminated (111) surface can be fabricated by nitrogen plasma treatment. Our findings pave the way toward an improved NV-based quantum sensing and quantum simulation operating at room temperature.
Recent investigations have revealed that some transition-metal dichalcogenides (TMDs), such as MoS2 and WS2, are excellent candidates for high-efficiency photocatalysts for water splitting. However, ...the high recombination rate of photogenerated carriers greatly hinders their practical application. A promising solution involves developing novel TMDs-based van der Waals (vdW) heterostructures with type-II band alignment. In this study, we used first-principles calculations to design two new heterostructuresMoS2/BSe and WS2/BSeas potential photocatalysts and investigated their structures, stabilities, and electronic and optical properties. We found that both MoS2/BSe and WS2/BSe vdW heterostructures are stable and possess inherent type-II band alignment, which significantly suppresses the recombination of photogenerated carriers. Furthermore, their band edges straddle the redox potential of water, making them suitable for use as photocatalysts in water splitting. They also possess significant built-in electric fields, relatively high carrier mobilities, and excellent abilities to absorb sunlight. Our theoretical findings should shed light on the design of novel TMD-based photocatalysts for water splitting and provide useful guidelines for future experiments.
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