Large-Area Bright Emission of Plasmon-Coupled Dark Excitons at Room Temperature.

Brightening dark excitons in transition metal dichalcogenide monolayers (MLs) can provide large-area ultrathin devices for applications in quantum information science and optoelectronics. For practical applications of dark excitons, a robust and bright emission over a wide area at room temperature is desirable; however, no reliable approach has been demonstrated thus far. In this study, an efficient approach is presented for brightening dark excitons at room temperature over a large area of a WSe ML via coupling between plasmons and dark excitons.

Indirect-To-Direct Bandgap Crossover and Room-Temperature Valley Polarization of Multilayer MoS Achieved by Electrochemical Intercalation.

Monolayer (1L) group VI transition metal dichalcogenides (TMDs) exhibit broken inversion symmetry and strong spin-orbit coupling, offering promising applications in optoelectronics and valleytronics. Despite their direct bandgap, high absorption coefficient, and spin-valley locking in K or K' valleys, the ultra-short valley lifetime limits their room-temperature applications. In contrast, multilayer TMDs, with more absorptive layers, sacrifice the direct bandgap and valley polarization upon gaining inversion symmetry from the bilayer structure.

Anomalous Behavior in Dark-Bright Splitting Impacts the Biexciton Binding Energy in (BA)(MA)PbBr ( = 1-3).

Two-dimensional Ruddlesden-Popper series are an excellent system for tuning physical properties of the perovskite by controlling the layer number (). For instance, bandgap and exciton binding energies of the series gradually increase upon reducing via enhanced quantum and dielectric confinements. Here, we present findings that challenge the anticipated trend in electron-hole exchange interaction within (BA)MAPbBr ( = 1-3), which causes spin-dependent exciton level splitting into bright and dark states, where the latter is partially visible near the surface of the Br-based two-dimensional Ruddlesden-Popper series.

Role of Chalcogenides in Sensitive Therapeutic Drug Monitoring Using Laser Desorption and Ionization.

This study investigates the applicability of six transition metal dichalcogenides to efficient therapeutic drug monitoring of ten antiepileptic drugs using laser desorption/ionization-mass spectrometry. We found that molybdenum ditelluride and tungsten ditelluride are suitable for the sensitive quantification of therapeutic drugs. The contribution of tellurium to the enhanced efficiency of laser desorption ionization was validated through theoretical calculations utilizing an integrated model that incorporates transition-metal dichalcogenides and antiepileptic drugs.

Optical grade transformation of monolayer transition metal dichalcogenides encapsulation annealing.

Monolayer transition metal dichalcogenides (TMDs) have emerged as highly promising candidates for optoelectronic applications due to their direct band gap and strong light-matter interactions. However, exfoliated TMDs have demonstrated optical characteristics that fall short of expectations, primarily because of significant defects and associated doping in the synthesized TMD crystals. Here, we report the improvement of optical properties in monolayer TMDs of MoS, MoSe, WS, and WSe, by hBN-encapsulation annealing.

Analysis of -Type Doping in Graphene Induced by Monolayer-Oxidized TMDs.

Doping is one of the most difficult technological challenges for realizing reliable two-dimensional (2D) material-based semiconductor devices, arising from their ultrathinness. Here, we systematically investigate the impact of different types of nonstoichiometric solid MO (M are W or Mo) dopants obtained by oxidizing transition metal dichalcogenides (TMDs: WSe or MoS) formed on graphene FETs, which results in -type doping along with disorders. From the results obtained in this study, we were able to suggest an analytical technique to optimize the optimal UV-ozone (UVO) treatment to achieve high -type doping concentration in graphene FETs (∼2.

Synergetic Enhancement of Quantum Yield and Exciton Lifetime of Monolayer WS by Proximal Metal Plate and Negative Electric Bias.

The efficiency of light emission is a critical performance factor for monolayer transition metal dichalcogenides (1L-TMDs) for photonic applications. While various methods have been studied to compensate for lattice defects to improve the quantum yield (QY) of 1L-TMDs, exciton-exciton annihilation (EEA) is still a major nonradiative decay channel for excitons at high exciton densities. Here, we demonstrate that the combined use of a proximal Au plate and a negative electric gate bias (NEGB) for 1L-WS provides a dramatic enhancement of the exciton lifetime at high exciton densities with the corresponding QY enhanced by 30 times and the EEA rate constant decreased by 80 times.

Polymer-Waveguide-Integrated 2D Semiconductor Heterostructures for Optical Communications.

The demand for high-speed and low-loss interconnects in modern computer architectures is difficult to satisfy by using traditional Si-based electronics. Although optical interconnects offer a promising solution owing to their high bandwidth, low energy dissipation, and high-speed processing, integrating elements such as a light source, detector, and modulator, comprising different materials with optical waveguides, presents many challenges in an integrated platform. Two-dimensional (2D) van der Waals (vdW) semiconductors have attracted considerable attention in vertically stackable optoelectronics and advanced flexible photonics.

Observation of aligned dipoles and angular chromism of exciplexes in organic molecular heterostructures.

The dipole characteristics of Frenkel excitons and charge-transfer excitons between donor and acceptor molecules in organic heterostructures such as exciplexes are important in organic photonics and optoelectronics. For the bilayer of the organic donor 4,4',4''-tris[(3-methylphenyl)phenylamino]triphenylamine and acceptor 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine molecules, the exciplexes form aligned dipoles perpendicular to the Frenkel excitons, as observed in back focal plane photoluminescence images. The angular chromism of exciplexes observed in the 100 meV range indicates possible delocalization and angle-sensing photonic applications.

Incommensurate Antiferromagnetic Order in Weakly Frustrated Two-Dimensional van der Waals Insulator CrPSe.

Although magnetic order is suppressed by a strong frustration, it appears in complex forms such as a cycloid or spin density wave in weakly frustrated systems. Herein, we report a weakly magnetically frustrated two-dimensional (2D) van der Waals material CrPSe. Polycrystalline CrPSe was synthesized at an optimized temperature of 700 °C to avoid the formation of any secondary phases (e.

Temperature Dependence of Excitonic Auger Recombination in Excitonic-Complex-Free Monolayer WS by Considering Auger Broadening and Generation Efficiency.

Monolayer transition metal dichalcogenides (TMDs) have been extensively studied for their optoelectronic properties and applications. However, even at moderate exciton densities, their light-emitting capability is severely limited by Auger-type exciton-exciton annihilation (EEA). Previous work on EEA used oversimplified models in the presence of excitonic complexes, resulting in seriously underestimated values for the Auger coefficient.

Kinetic-Controlled Crystallization of α-FAPbI Inducing Preferred Crystallographic Orientation Enhances Photovoltaic Performance.

Crystallization kinetic controls the crystallographic orientation, inducing anisotropic properties of the materials. As a result, preferential orientation with advanced optoelectronic properties can enhance the photovoltaic devices' performance. Although incorporation of additives is one of the most studied methods to stabilize the photoactive α-phase of formamidinium lead tri-iodide (α-FAPbI ), no studies focus on how the additives affect the crystallization kinetics.

Effect of morphological variation in three-dimensional multiwall carbon nanotubes as the host cathode material for high-performance rechargeable lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) demonstrate potential as next-generation energy storage systems due to the high theoretical capacity and energy density of the sulfur cathode (1672 mAh g and 2600 W h kg, respectively) in addition to the low-cost, natural abundance, and environmentally benign characteristics of sulfur. However, the insulating nature of sulfur requires an efficient conductive and porous host material such as three-dimensional carbon nanotubes (3D CNTs). Identifying parameters that provide high conduction pathways and short diffusion lengths for Li-ions within the CNT structure is essential for a highly efficient CNT-S cathode in a LSB.

Far-Red Interlayer Excitons of Perovskite/Quantum-Dot Heterostructures.

Interlayer excitons (IXs) at the interface of heterostructures (HSs) with a staggered band alignment are fascinating quantum quasi-particles with light-emitting and long-lifetime characteristics. In this study, the energy band alignments (EBAs) of the HS of MAPbI perovskite thin sheets with CdSe-ZnS core-shell quantum dot (QD) layers are modulated by using different diameters of the QDs. Far-red IX emission is observed at 1.

Inductive Effect of Lewis Acidic Dopants on the Band Levels of Perovskite for a Photocatalytic Reaction.

Band-edge modulation of halide perovskites as photoabsorbers plays significant roles in the application of photovoltaic and photochemical systems. Here, Lewis acidity of dopants (M) as the new descriptor of engineering the band-edge position of the perovskite is investigated in the gradiently doped perovskite along the core-to-surface (CsPbBr-CsPbMBr). Reducing M-bromide bond strength with an increase in hardness of acidic M increases the electron ability of basic Br, thus strengthening the Pb-Br orbital coupling in M-Pb-Br, noted as the inductive effect of dopants.

Exciton-dominant photoluminescence of MoS by a functionalized substrate.

Transition metal dichalcogenides (TMDs) have been considered as promising candidates for transparent and flexible optoelectronic devices owing to their large exciton binding energy and strong light-matter interaction. However, monolayer (1L) TMDs exhibited different intensities and spectra of photoluminescence (PL), and the characteristics of their electronic devices also differed in each study. This has been explained in terms of various defects in TMDs, such as vacancies and grain boundaries, and their surroundings, such as dielectric screening and charged impurities, which lead to non-radiative recombination of trions, low quantum yield (QY), and unexpected doping.

Gas-Phase Alkali Metal-Assisted MOCVD Growth of 2D Transition Metal Dichalcogenides for Large-Scale Precise Nucleation Control.

Advances in large-area and high-quality 2D transition metal dichalcogenides (TMDCs) growth are essential for semiconductor applications. Here, the gas-phase alkali metal-assisted metal-organic chemical vapor deposition (GAA-MOCVD) of 2D TMDCs is reported. It is determined that sodium propionate (SP) is an ideal gas-phase alkali-metal additive for nucleation control in the MOCVD of 2D TMDCs.

Boosting quantum yields in two-dimensional semiconductors via proximal metal plates.

Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices. However, the short exciton lifetime due to the defect traps and the strong exciton-exciton interaction in TMDs has significantly limited the efficiency of exciton emission from this class of materials. Here, we show that exciton-exciton interaction in 1L-WS can be effectively screened using an ultra-flat Au film substrate separated by multilayers of hexagonal boron nitride.

Spin-Selective Hole-Exciton Coupling in a V-Doped WSe Ferromagnetic Semiconductor at Room Temperature.

While valley polarization with strong Zeeman splitting is the most prominent characteristic of two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductors under magnetic fields, enhancement of the Zeeman splitting has been demonstrated by incorporating magnetic dopants into the host materials. Unlike Fe, Mn, and Co, V is a distinctive dopant for ferromagnetic semiconducting properties at room temperature with large Zeeman shifting of band edges. Nevertheless, little known is the excitons interacting with spin-polarized carriers in V-doped TMDs.

Charge-Transfer Effect and Enhanced Photoresponsivity of WS- and MoSe-Based Field Effect Transistors with π-Conjugated Polyelectrolyte.

The characteristics of field effect transistors (FETs) fabricated using two-dimensional (2D) transition-metal dichalcogenides (TMDCs) can be modulated by surface treatment of the active layers. In this study, an ionic π-conjugated polyelectrolyte, poly(9,9-bis(4'-sulfonatobutyl)fluorene--1,4-phenylene) potassium (FPS-K), was used for the surface treatment of MoSe and WS FETs. The photoluminescence (PL) intensities of monolayer (1L)-MoSe and 1L-WS clearly decreased, and the PL peaks were red-shifted after FPS-K treatment, suggesting a charge-transfer effect.

Doping-Mediated Lattice Engineering of Monolayer ReS for Modulating In-Plane Anisotropy of Optical and Transport Properties.

ReS exhibits strong anisotropic optical and electrical responses originating from the asymmetric lattice. Here, we show that the anisotropy of monolayer (1L) ReS in optical scattering and electrical transport can be practically erased by lattice engineering lithium (Li) treatment. Scanning transmission electron microscopy revealed that significant strain is induced in the lattice of Li-treated 1L-ReS, due to high-density electron doping and the resultant formation of continuous tiling of nanodomains with randomly rotating orientations of 60°, which produced a nearly isotropic response of polarized Raman scattering and absorption of Li-treated 1L-ReS.

Efficacy of reduced-size short tandem repeat PCR analysis for degraded DNA samples.

Background: Short tandem repeats (STR) typing is an essential analysis method for human identification in forensic field. When DNAs obtained from the field as evidences are severely degraded or in too small amounts, STR analysis often shows allele drop-out.

Objective: To improve STR analysis for degraded DNA or trace DNA, reduced-size STR (rSTR) polymerase chain reaction (PCR) system was devised by selecting relatively large-size STR loci.

Massively parallel sequencing of 25 short tandem repeat loci including the SE33 marker in Koreans.

Background: Massively parallel sequencing (MPS) technology has recently been introduced in research, clinical diagnostics, and forensics. MPS enables determination of the genotypes of multiple short tandem repeat (STR) markers and to determine nucleotide sequence variations, additionally.

Objective: To improve STR analysis and a paternity index, a new, smaller-sized STR panel was designed that includes the SE33 locus.

Static Rashba Effect by Surface Reconstruction and Photon Recycling in the Dynamic Indirect Gap of APbBr (A = Cs, CHNH) Single Crystals.

Recently, halide perovskites have gained significant attention from the perspective of efficient spintronics owing to the Rashba effect. This effect occurs as a consequence of strong spin-orbit coupling under a noncentrosymmetric environment, which can be dynamic and/or static. However, there exist intense debates on the origin of broken inversion symmetry since the halide perovskites typically crystallize into a centrosymmetric structure.

Switchable, Tunable, and Directable Exciton Funneling in Periodically Wrinkled WS.

The extreme elastic strain of monolayer transition metal dichalcogenides provides an ideal platform to achieve efficient exciton funneling via local strain modulation; however, studies conducted thus far have focused on the use of substrates with fixed strain profiles. We prepared 1L-WS on a flexible substrate such that the formation of topographic wrinkles could be switched on or off, and the depth or the direction of the wrinkle could be modified by external strain, thereby providing full control of the periodic undulation of the band gap profile of 1L-WS in the range 0-57 meV. Nanoscale photoluminescence (PL) imaging unambiguously evinced that the photoexcited excitons of 1L-WS were accumulated at the top regions of the wrinkles with less band gap than the valley region.