Abstract
Strong Coulomb interactions in single-layer transition metal dichalcogenides (TMDs) result in the emergence of strongly bound excitons, trions, and biexcitons. These excitonic complexes ...possess the valley degree of freedom, which can be exploited for quantum optoelectronics. However, in contrast to the good understanding of the exciton and trion properties, the binding energy of the biexciton remains elusive, with theoretical calculations and experimental studies reporting discrepant results. In this work, we resolve the conflict by employing low-temperature photoluminescence spectroscopy to identify the biexciton state in BN-encapsulated single-layer WSe
2
. The biexciton state only exists in charge-neutral WSe
2
, which is realized through the control of efficient electrostatic gating. In the lightly electron-doped WSe
2
, one free electron binds to a biexciton and forms the trion–exciton complex. Improved understanding of the biexciton and trion–exciton complexes paves the way for exploiting the many-body physics in TMDs for novel optoelectronics applications.
Daily travel is an important means for everyone to obtain the right to development. With the development of the economy and the progress of the times, the equalization of public infrastructure has ...become an important concern. The accessibility and fairness of transportation have become a hot topic of research in various fields. To promote transport equity and formulate more reasonable transport planning and policies, this paper takes the Kunshan city as the research object, based on the mobile phone signaling data and the travel time consumption data from the application programming interface (API) of Gaode Map, using weighted average accessibility and the Theil index to investigate the accessibility and equity of public transport and car traffic in the Kunshan city. The study found that the accessibility of public transport is lower than that of car transport in the same research unit, but the equity of public transport is better than that of car transport, that is, the public transport is fair and the efficiency is neglected. In the same mode of transportation, equity presents a high four-week low distribution in the central urban area, and the spatial equity difference is mainly caused by the difference in accessibility levels between cell units. According to the research conclusions, it is recommended that Kunshan further optimize the spatial layout of public transportation infrastructure and adopt measures such as bus speed increase to achieve equity and efficiency and improve the competitiveness of public transportation.
Abstract
Heterobilayers of transition metal dichalcogenides (TMDCs) can form a moiré superlattice with flat minibands, which enables strong electron interaction and leads to various fascinating ...correlated states. These heterobilayers also host interlayer excitons in a type-II band alignment, in which optically excited electrons and holes reside on different layers but remain bound by the Coulomb interaction. Here we explore the unique setting of interlayer excitons interacting with strongly correlated electrons, and we show that the photoluminescence (PL) of interlayer excitons sensitively signals the onset of various correlated insulating states as the band filling is varied. When the system is in one of such states, the PL of interlayer excitons is relatively amplified at increased optical excitation power due to reduced mobility, and the valley polarization of interlayer excitons is enhanced. The moiré superlattice of the TMDC heterobilayer presents an exciting platform to engineer interlayer excitons through the periodic correlated electron states.
Abstract
Tungsten-based monolayer transition metal dichalcogenides host a long-lived “dark” exciton, an electron-hole pair in a spin-triplet configuration. The long lifetime and unique spin ...properties of the dark exciton provide exciting opportunities to explore light-matter interactions beyond electric dipole transitions. Here we demonstrate that the coupling of the dark exciton and an optically silent chiral phonon enables the intrinsic photoluminescence of the dark-exciton replica in monolayer WSe
2
. Gate and magnetic-field dependent PL measurements unveil a circularly-polarized replica peak located below the dark exciton by 21.6 meV, equal to E″ phonon energy from Se vibrations. First-principles calculations show that the exciton-phonon interaction selectively couples the spin-forbidden dark exciton to the intravalley spin-allowed bright exciton, permitting the simultaneous emission of a chiral phonon and a circularly-polarized photon. Our discovery and understanding of the phonon replica reveals a chirality dictated emission channel of the phonons and photons, unveiling a new route of manipulating valley-spin.
Carbon-supported well-dispersed Pd–Ni–P ternary catalyst targeted for ethanol oxidation reaction (EOR) in alkaline media is synthesized in a simple aqueous bath containing Pd(II) and Ni(II) salts ...with sodium hypophosphite as the reducing agent and the source for P and sodium citrate as the complexing agent. XRD analysis on the as-prepared Pd–Ni–P/C reveals that Ni shrinks while P expands the Pd lattice structure, and XPS measurement suggests different electronic effects of the two alloying elements on Pd. Cyclic voltammetry and chronoamperometry indicate that the Pd–Ni–P/C presents a remarkably higher electrocatalytic activity than the state-of-the-art Pd/C, Pd–P/C and Pd–Ni/C catalysts. This may be ascribed to the unique electronic, geometric and bifunctional effects involved in this ternary nanoalloy.
•Initial synthesis of Pd–Ni–P/C ternary nanocatalyst for ethanol electro-oxidation in alkaline media.•Significantly enhanced electrocatalytic performance on Pd–Ni–P/C compared to that on Pd/C, Pd–P/C or Pd–Ni/C.•Electronic, geometric and bifunctional effects assumed to account for the improved performance.
Unlike the vast majority of transition metal dichalcogenides which are semiconductors, vanadium disulfide is metallic and conductive. This makes it particularly promising as an electrode material in ...lithium-ion batteries. However, vanadium disulfide exhibits poor stability due to large Peierls distortion during cycling. Here we report that vanadium disulfide flakes can be rendered stable in the electrochemical environment of a lithium-ion battery by conformally coating them with a ~2.5 nm thick titanium disulfide layer. Density functional theory calculations indicate that the titanium disulfide coating is far less susceptible to Peierls distortion during the lithiation-delithiation process, enabling it to stabilize the underlying vanadium disulfide material. The titanium disulfide coated vanadium disulfide cathode exhibits an operating voltage of ~2 V, high specific capacity (~180 mAh g
@200 mA g
current density) and rate capability (~70 mAh g
@1000 mA g
), while achieving capacity retention close to 100% after 400 charge-discharge steps.
Van der Waals heterostructures have recently emerged as a new class of materials, where quantum coupling between stacked atomically thin two-dimensional layers, including graphene, hexagonal-boron ...nitride and transition-metal dichalcogenides (MX2), give rise to fascinating new phenomena. MX2 heterostructures are particularly exciting for novel optoelectronic and photovoltaic applications, because two-dimensional MX2 monolayers can have an optical bandgap in the near-infrared to visible spectral range and exhibit extremely strong light-matter interactions. Theory predicts that many stacked MX2 heterostructures form type II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. Here, we report the first experimental observation of ultrafast charge transfer in photoexcited MoS2/WS2 heterostructures using both photoluminescence mapping and femtosecond pump-probe spectroscopy. We show that hole transfer from the MoS2 layer to the WS2 layer takes place within 50 fs after optical excitation, a remarkable rate for van der Waals coupled two-dimensional layers. Such ultrafast charge transfer in van der Waals heterostructures can enable novel two-dimensional devices for optoelectronics and light harvesting.
The objective of the present study was to develop a W/O/W nanoemulsion (NE) drug delivery system loaded with punicalagin (PGN) for oral delivery and evaluate its potential in antibacterial therapy. ...The W/O/W PGN-NE was prepared using a two-step process by combining ultrasonic with high-energy emulsification and subsequently characterized by its droplet size, zeta potential, and morphology. The PGN-NE was further evaluated for its pH, in vitro antibacterial activity, drug release property, and cytotoxicity. The results indicated the formation of spherical, nano-sized globules of PGN-NE had a mean particle size of 45.53 ± 2.2 nm, with a PDI value of 0.22 ± 0.028, zeta potential was −4.67 ± 0.88 mV, and pH value was 5.8. In vitro antibacterial activity studies showed a significantly higher antibacterial activity of PGN-NE in comparison to free PGN, suggesting that NE can effectively improve the antibacterial effect of natural pharmaceuticals. The drug release assay demonstrated that PGN was slowly released from the NE preparation and absorbed, helping to prolong the potency and improve the bioavailability of PGN. Cytotoxicity testing showed that PGN had reduced toxicity when encapsulated in NE. Thus, the developed NE formulation of PNG exhibited a greater potential for the slow-release effect delivery and in the treatment of microbial infections with favorable safety profile.
Graphical abstract
Micromorphology of W/O/W PGN nanoemulsion
The W/O/W PGN-NE are uniform in size and non-adhesive, with a size distribution of 28.214 to 141.772 nm and a mean size of 45.53 ± 2.2 nm, respectively, with a PDI value of 0.22 ± 0.028.
Abstract
The heterostructure of monolayer transition metal dichalcogenides (TMDCs) provides a unique platform to manipulate exciton dynamics. The ultrafast carrier transfer across the van der Waals ...interface of the TMDC hetero-bilayer can efficiently separate electrons and holes in the intralayer excitons with a type II alignment, but it will funnel excitons into one layer with a type I alignment. In this work, we demonstrate the reversible switch from exciton dissociation to exciton funneling in a MoSe
2
/WS
2
heterostructure, which manifests itself as the photoluminescence (PL) quenching to PL enhancement transition. This transition was realized through effectively controlling the quantum capacitance of both MoSe
2
and WS
2
layers with gating. PL excitation spectroscopy study unveils that PL enhancement arises from the blockage of the optically excited electron transfer from MoSe
2
to WS
2
. Our work demonstrates electrical control of photoexcited carrier transfer across the van der Waals interface, the understanding of which promises applications in quantum optoelectronics.
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