First detection of Bandavirus dabieense in ticks collected from migratory birds in the Republic of Korea.

The causative agent of severe fever with thrombocytopenia syndrome (SFTS) is Bandavirus dabieense, an emerging tick-borne zoonotic pathogen. Migratory birds have often been suggested as potential carriers of ticks that can transmit Bandavirus dabieense; however, their role remains unclear. The Republic of Korea (ROK) holds an important position as a stopover on the East Asian-Australasian Flyway. The present study aimed to investigate the potential involvement of migratory birds in the transmission of the SFTS virus (SFTSV) in the ROK. A total of 4,497 ticks were collected across various regions, including Heuksando and Daecheongdo, in the ROK, from bird migration seasons in 2022 and 2023. Genetic analysis of the SFTSV was performed for 96 ticks collected from 20 different species of migratory birds. Polymerase chain reaction (PCR) fragments of SFTSV were detected in one Haemaphysalis concinna nymph collected from a Black-faced Bunting (Emberiza spodocephala) and one Ixodes turdus nymph collected from an Olive-backed Pipit (Anthus hodgsoni) on Daecheongdo and Heuksando, respectively, during their northward migration in two spring seasons. This finding suggests that migratory birds can be considered as possible carriers and long-distance dispersers of ticks and associated tick-borne diseases. This study highlights the importance of clarifying the role and impact of migratory birds in the rapid expansion of tick-borne diseases, facilitating enhanced preparedness and the development of mitigation measures against emerging SFTS across and beyond East Asia.

Photo-Assisted Ferroelectric Domain Control for α-In2Se3 Artificial Synapses Inspired by Spontaneous Internal Electric Fields.

α-In2Se3 semiconductor crystals realize artificial synapses by tuning in-plane and out-of-plane ferroelectricity with diverse avenues of electrical and optical pulses. While the electrically induced ferroelectricity of α-In2Se3 shows synaptic memory operation, the optically assisted synaptic plasticity in α-In2Se3 has also been preferred for polarization flipping enhancement. Here, the synaptic memory behavior of α-In2Se3 is demonstrated by applying electrical gate voltages under white light. As a result, the induced internal electric field is identified at a polarization flipped conductance channel in α-In2Se3/hexagonal boron nitride (hBN) heterostructure ferroelectric field effect transistors (FeFETs) under white light and discuss the contribution of this built-in electric field on synapse characterization. The biased dipoles in α-In2Se3 toward potentiation polarization direction by an enhanced internal built-in electric field under illumination of white light lead to improvement of linearity for long-term depression curves with proper electric spikes. Consequently, upon applying appropriate electric spikes to α-In2Se3/hBN FeFETs with illuminating white light, the recognition accuracy values significantly through the artificial learning simulation is elevated for discriminating hand-written digit number images.

Ixodid ticks from wild and domestic animals in East and Central Asian flyways.

Tick-borne diseases have a significant impact on human and animal populations, posing an increasing threat to public health, particularly in the context of climate change. Along with the various natural hosts of ticks, birds play a notable role in transmitting ticks and tick-borne pathogens, indicating the importance of monitoring flyways and establishing a cooperative network for comprehensive surveillance and to collect diverse tick samples across various regions. This study aimed to develop an international network for surveillance of disease, collection of sufficient tick samples, and overall identification of the geographical distribution of host and ticks in Asian regions, especially in 11 countries on East Asian and Central Asian flyways. Ticks were collected from wild animals, domestic animals, and vegetation to identify the differences between Ixodid ticks and understand tick distribution. We collected a total 6,624 of ticks from 11 collaborating Asian countries, the Republic of Korea (ROK), Japan, Thailand, Philippines, Indonesia, Cambodia, Vietnam, Taiwan, Hong Kong, Mongolia and Pakistan. We identified 17 host animals and 47 species of both residential and migratory birds. Ticks from birds collected from four countries (ROK, Japan, Hong Kong and Mongolia) belonged to two genera, Haemaphysalis and Ixodes, including Haemaphysalis (H.) longicornis, H. flava, H. concinna, H. hystricis, H. formosensis, Ixodes (I.) nipponensis and I. persulcatus. The potential of migratory birds to cross ecological barriers with ticks and tick-borne diseases indicated the need for further investigations to understand the migration of birds as potential vectors and the new influx of zoonotic diseases along migratory bird flyways. This study suggests the potential risk of spreading tick-borne diseases through birds, thus highlighting the importance of international cooperative networking.

Ba3.5Cu7.55In1.15Se9: A Wide-Bandgap Copper Indium Selenide Reveals Strong Luminescence and Third-Harmonic Generation.

A new copper indium selenide, Ba3.5Cu7.55In1.15Se9, was synthesized by the KBr flux reaction at 800 °C. The compound crystallizes with orthorhombic Pnma, a = 46.1700(12) Å, b = 4.26710(10) Å, c = 19.8125(5) Å, and Z = 8. The structural framework mainly consists of four sites of cubane-type defective M4Se3 (M = Cu, Cu/In) units with disordered Cu+/In3+ ions present at the part corner of each unit. The single crystal emits intense photoluminescence at 657 nm with a relative quantum yield (RQY) 0.2 times that of rhodamine 6G powder. The compound belongs to a direct band gap at 1.91 eV, analyzed by Tauc's plot, and the energy is close to the PL position. The Hall effect measurement on a pressed pellet reveals an n-type conductivity with a carrier concentration of 3.358 × 1017 cm-3 and a mobility of 24.331 cm2 V-1 s-1. Furthermore, the compound produces a strong nonlinear third-harmonic generation (THG), with an χS(3) value of 1.3 × 105 pm2/V2 comparable to 1.6 × 105 pm2/V2 for AgGaSe2 measured at 800 nm.

Gate-Tuned Gas Molecule Sensitivity of a Two-Dimensional Semiconductor.

In this work, we develop a gate-tunable gas sensor based on a MoS2/hBN heterostructure field effect transistor. Through experimental measurements and numerical simulations, we systematically reveal a principle that relates the concentration of the target gas and sensing signals (ΔI/I0) as a function of gate bias. Because a linear relationship between ΔI/I0 and the gas concentration guarantees reliable sensor operation, the optimal gate bias condition for linearity was investigated. Taking NO2 and NH3 as target molecules, it is clarified that the bias condition greatly depends on the electron accepting/donating nature of the gas. The effects of the bandgap and polarity of the transition metal dichalcogenides (TMDC) channel are also discussed. In order to achieve linearly increasing signals that are stable with respect to the gas concentration, a sufficiently large VBG within VBG > 0 is required. We expect this work will shed light on a way to precisely design reliable semiconducting gas sensors based on the characteristics of TMDC and target gas molecules.

Structure Tuning, Strong Second Harmonic Generation Response, and High Optical Stability of the Polar Semiconductors Na1-xKxAsQ2.

The mixed cation compounds Na1-xKxAsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 crystallize in the polar noncentrosymmetric space group Cc. The AAsQ2 (A = alkali metals, Q = S, Se) family features one-dimensional (1D) 1/∞[AQ2-] chains comprising corner-sharing pyramidal AQ3 units in which the packing of these chains is dependent on the alkali metals. The parallel 1/∞[AQ2-] chains interact via short As···Se contacts, which increase in length when the fraction of K atoms is increased. The increase in the As···Se interchain distance increases the band gap from 1.75 eV in γ-NaAsSe2 to 2.01 eV in Na0.35K0.65AsSe2, 2.07 eV in Na0.2K0.8AsSe2, and 2.18 eV in Na0.1K0.9AsS2. The Na1-xKxAsSe2 (x = 0.8, 0.65) compounds melt congruently at approximately 316 °C. Wavelength-dependent second harmonic generation (SHG) measurements on powder samples of Na1-xKxAsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 suggest that Na0.2K0.8AsSe2 and Na0.1K0.9AsS2 have the highest SHG response and exhibit significantly higher laser-induced damage thresholds (LIDTs). Theoretical SHG calculations on Na0.5K0.5AsSe2 confirm its SHG response with the highest value of d33 = 22.5 pm/V (χ333(2) = 45.0 pm/V). The effective nonlinearity for a randomly oriented powder is calculated to be deff = 18.9 pm/V (χeff(2) = 37.8 pm/V), which is consistent with the experimentally obtained value of deff = 16.5 pm/V (χeff(2) = 33.0 pm/V). Three-photon absorption is the dominant mechanism for the optical breakdown of the compounds under intense excitation at 1580 nm, with Na0.2K0.8AsSe2 exhibiting the highest stability.

Role of the A-Site Cation in Low-Temperature Optical Behaviors of APbBr3 (A = Cs, CH3NH3).

APbBr3 (A = Cs, CH3NH3) are prototype halide perovskites having bandgaps of 2.30-2.35 eV at room temperature, rendering their apparent color nearly identical (bright orange but opaque). Upon optical excitation, they emit bright photoluminescence (PL) arising from carrier recombination whose spectral features are also similar. At 10 K, however, the apparent color of CsPbBr3 becomes transparent yellow, whereas that of CH3NH3PbBr3 does not change significantly due to the presence of an indirect Rashba gap. With increasing the excitation level, evolution of the PL spectra, which are excitonic at 10 K, reveals the emergence of P-band emission arising from inelastic exciton-exciton scattering. Based on the spectral location of the P-band, exciton binding energies are determined to be 21.6 ± 2.0 and 38.3 ± 3.0 meV for CsPbBr3 and CH3NH3PbBr3, respectively. Intriguingly, upon further increase in the exciton density, electron-hole plasma appears in CsPbBr3 as evidenced by both red-shift and broadening of the PL. This phase, however, does not occur in CH3NH3PbBr3 presumably due to polaronic effects. Although the A-site cation is believed not to directly impact optical properties of APbBr3, our results underscore its critical role, which destines different high-density phases and apparent color at low temperatures.

Static Rashba Effect by Surface Reconstruction and Photon Recycling in the Dynamic Indirect Gap of APbBr3 (A = Cs, CH3NH3) 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. In order to clarify the issue, we examine both dynamic and static effects in the all-inorganic CsPbBr3 and organic-inorganic CH3NH3PbBr3 (MAPbBr3) perovskite single crystals by employing temperature- and polarization-dependent photoluminescence excitation spectroscopy. The perovskite single crystals manifest the dynamic effect by photon recycling in the indirect Rashba gap, causing dual peaks in the photoluminescence. However, the effect vanishes in CsPbBr3 at low temperatures (<50 K) accompanied by a striking color change of the crystal, arising presumably from lower degrees of freedom for inversion symmetry breaking associated with the thermal motion of the spherical Cs cation compared with the polar MA cation in MAPbBr3. We also show that the static Rashba effect occurs only in MAPbBr3 below 90 K, presumably due to surface reconstruction via MA-cation ordering, which likely extends across a few layers from the crystal surface to the interior. We further demonstrate that this static Rashba effect can be completely suppressed upon surface treatment with polymethyl methacrylate (PMMA) coating. We believe that our results provide a rationale for the Rashba effects in halide perovskites.

Layered and Cubic Semiconductors AGaM'Q4 (A+ = K+, Rb+, Cs+, Tl+; M'4+ = Ge4+, Sn4+; Q2- = S2-, Se2-) and High Third-Harmonic Generation.

Eighteen new quaternary chalcogenides AGaM'Q4 (A+ = K+, Rb+, Cs+, Tl+; M'4+ = Ge4+, Sn4+; Q2- = S2-, Se2-) have been prepared by solid-state syntheses and structurally characterized using single-crystal X-ray diffraction techniques. These new phases crystallize in a variety of layered structure types. The tin analogues also adopt an extended three-dimensional network structure as polymorphs. The polymorphism and phase-stability in these cases were studied by thermal analysis and high-temperature in situ X-ray powder diffraction. All compounds are semiconductors with the colored selenides absorbing light in the infrared-green region (1.8 eV < Eg < 2.3 eV) and the mostly white sulfides absorbing light in the blue-ultraviolet range (2.5 eV < Eg < 3.6 eV). Based on third-harmonic generation (THG) measurements, the third-order nonlinear optical (NLO) susceptibilities χ(3) of the new and previously reported AGaM'Q4 compounds were determined. These measurements revealed an apparent correlation between the THG response of the sample and its band gap, rather than the crystal structure type. While low-gap materials possess higher nonlinearity in general, we found that layered orthorhombic RbGaGeS4 exhibits an impressive χ(3) value (about four times larger than that of AgGaS2) even with a large band gap and shows stability under ambient conditions with no significant irradiation damage.

Enhanced Stability of MAPbI3 Perovskite Solar Cells using Poly(p-chloro-xylylene) Encapsulation.

We demonstrated an effective poly(p-chloro-xylylene) (Parylene-C) encapsulation method for MAPbI3 solar cells. By structural and optical analysis, we confirmed that Parylene-C efficiently slowed the decomposition reaction in MAPbI3. From a water permeability test with different encapsulating materials, we found that Parylene-C-coated MAPbI3 perovskite was successfully passivated from reaction with water, owing to the hydrophobic behavior of Parylene-C. As a result, the Parylene-C-coated MAPbI3 solar cells showed better device stability than uncoated cells, virtually maintaining the initial power conversion efficiency value (15.5 ± 0.3%) for 196 h.

Synthesis and Characterization of Multiple-Cation Rb(MAFA)PbI3 Perovskite Single Crystals.

We synthesized multiple-cation Rb(MAFA)PbI3 perovskite single crystals for the first time. The effect of Rb+ substitution was systemically investigated, and the addition of 1.5 M 5% RbI was the optimum condition to obtain high-quality Rb(MAFA)PbI3 single crystals. Lattice shrinkage occurred in the Rb(MAFA)PbI3 single crystal because of the small ionic radius of Rb+, resulting in blue-shifted absorption and photoluminescence (PL) peaks. The 1.5 M 5% RbI-added (MAFA)PbI3 single crystal showed the longest carrier lifetime of 18.35 ns, exhibiting the highest photoresponse than other crystals. We believe that this work will provide a basic insight into the mixed-cation perovskite single crystals for the future optoelectronic applications.

Unveiling the irreversible performance degradation of organo-inorganic halide perovskite films and solar cells during heating and cooling processes.

While organo-inorganic halide perovskite solar cells show great potential to meet future energy needs, their thermal instability raises serious questions about their commercialization viability. At present, the stability of perovskite solar cells has been studied under various environmental conditions including humidity and temperature. Nonetheless, understanding of the performance of CH3NH3PbI3-xClx perovskite solar cells is limited. This study reports the irreversible performance degradation of CH3NH3PbI3-xClx perovskite solar cells during the heating and cooling processes under AM 1.5 and unveils what triggers the irreversible performance degradation of solar cells. Particularly, the primary cause of the irreversible performance degradation of CH3NH3PbI3-xClx is quantitatively analyzed by monitoring in real time the development of deteriorated crystallinity, charge trapping/detrapping, trap depth, and the PbI2 phase, namely a critical signal of perovskite degradation while varying the temperature of the perovskite films and solar cells. Most surprisingly, it is revealed that the degradation of both perovskite films and solar cells was triggered at ∼70 °C. Remarkably, even after the device temperature cooled down to room temperature, the degraded performance of the solar cells persisted with increasing charge trapping and further development of the PbI2 phase. Identification of the irreversible performance degradation of perovskite solar cells provides guidance for future development of more stable perovskite solar cells.