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Super Ohtaka®, a fermented beverage of plant extracts, is prepared from approximately 50 kinds of fruits and vegetables. Natural fermentation is mainly performed by lactic acid bacteria (Leuconostoc spp.) and yeast (Zygosaccharomyces spp.). Four water-soluble polysaccharide fractions were obtained from Super Ohtaka® by dialysis, ion exchange chromatography, and gel filtration chromatography; these fractions were designated as OEP1-1, OEP1-2, OEP2, and OEP3. OEP1-1 is a polysaccharide composed solely of glucose. The other fractions contained polysaccharides composed of glucose, galactose, mannose, and a small amount of arabinose. OEP2 and OEP3 contained phosphorus, which was not detected in OEP1-1 and OEP1-2. Furthermore, the immunomodulatory activity of the polysaccharides was investigated in murine macrophage cell lines. OEP2 and OEP3 significantly induced nitric oxide (NO) secretion by macrophages in a dose-dependent manner (concentration range of 4 to 100 µg/mL). When the concentration of OEP3 was 100 µg/mL, NO production was almost identical to lipopolysaccharide (LPS; 10 ng/mL) used as a positive control. Notably, OEP3 induced NO secretion more strongly than OEP2. This trend was also observed for TNF-α, IL-1ß, IL-6, and IL-12 p40 secretion. Overall, our in vitro studies on polysaccharides isolated from Super Ohtaka® suggest that the fermented beverage stimulates macrophages and activates the immune system.
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Silanones (OîSiR2), a heavier congener of ketones (R2CîO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OîSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OîSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OîSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{îSiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.
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Two-dimensional (2D) materials stand as a promising platform for tunnel field-effect transistors (TFETs) in the pursuit of low-power electronics for the Internet of Things era. This promise arises from their dangling bond-free van der Waals heterointerface. Nevertheless, the attainment of high device performance is markedly impeded by the requirement of precise control over the 2D assembly with multiple stacks of different layers. In this study, we addressed a thickness-modulated n/p+-homojunction prepared from Nb-doped p+-MoS2 crystal, where the issue on interface traps can be neglected without any external interface control due to the homojunction. Notably, our observations reveal the existence of a negative differential resistance, even at room temperature (RT). This signifies the successful realization of TFET operation under type III band alignment conditions by a single gate at RT, suggesting that the dominant current mechanism is band-to-band tunneling due to the ideal interface.
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Silicon CMOS-based computing-in-memory encounters design and power challenges, especially in logic-in-memory scenarios requiring nonvolatility and reconfigurability. Here, we report a universal design for nonvolatile reconfigurable devices featuring a 2D/3D heterointegrated configuration. By leveraging the photo-controlled charge trapping/detrapping process and the partially top-gated energy band landscape, the van der Waals heterostacking achieves polarity storage and logic reconfigurable characteristics, respectively. Precise polarity tunability, logic nonvolatility, robustness against high temperature (at 85°C), and near-ideal subthreshold swing (80 mV dec-1) can be done. A comprehensive investigation of dynamic charge fluctuations provides a holistic understanding of the origins of nonvolatile reconfigurability (a trap level of 1013 cm-2 eV-1). Furthermore, we cascade such nonvolatile reconfigurable units into a monolithic circuit layer to demonstrate logic-in-memory computing possibilities, such as high-gain (65 at Vdd = 0.5 V) logic gates. This work provides an innovative 3D heterointegration prototype for future computing-in-memory hardware.
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The photoelectron momentum microscope (PMM) in operation at BL6U, an undulator-based soft x-ray beamline at the UVSOR Synchrotron Facility, offers a new approach for µm-scale momentum-resolved photoelectron spectroscopy (MRPES). A key feature of the PMM is that it can very effectively reduce radiation-induced damage by directly projecting a single photoelectron constant energy contour in reciprocal space with a radius of a few Å-1 or real space with a radius of a few 100 µm onto a two-dimensional detector. This approach was applied to three-dimensional valence band structure E(k) and E(r) measurements ("stereography") as functions of photon energy (hν), its polarization (e), detection position (r), and temperature (T). In this study, we described some examples of possible measurement techniques using a soft x-ray PMM. We successfully applied this stereography technique to µm-scale MRPES to selectively visualize the single-domain band structure of twinned face-centered-cubic Ir thin films grown on Al2O3(0001) substrates. The photon energy dependence of the photoelectron intensity on the Au(111) surface state was measured in detail within the bulk Fermi surface. By changing the temperature of 1T-TaS2, we clarified the variations in the valence band dispersion associated with chiral charge-density-wave phase transitions. Finally, PMMs for valence band stereography with various electron analyzers were compared, and the advantages of each were discussed.
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Transition metal dichalcogenide heterostructures provide a versatile platform to explore electronic and excitonic phases. As the excitation density exceeds the critical Mott density, interlayer excitons are ionized into an electron-hole plasma phase. The transport of the highly non-equilibrium plasma is relevant for high-power optoelectronic devices but has not been carefully investigated previously. Here, we employ spatially resolved pump-probe microscopy to investigate the spatial-temporal dynamics of interlayer excitons and hot-plasma phase in a MoSe2/WSe2 twisted bilayer. At the excitation density of â¼1014 cm-2, well exceeding the Mott density, we find a surprisingly rapid initial expansion of hot plasma to a few microns away from the excitation source within â¼0.2 ps. Microscopic theory reveals that this rapid expansion is mainly driven by Fermi pressure and Coulomb repulsion, while the hot carrier effect has only a minor effect in the plasma phase.
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For the complementary operation of two-dimensional (2D) material-based field-effect transistors (FETs), high-performance p-type FETs are essential. In this study, we applied surface charge-transfer doping from WOx, which has a large work function of â¼6.5 eV, selectively to the access region of WS2 and WSe2 by covering the channel region with h-BN. By reducing the Schottky barrier width at the contact and injecting holes into the valence band, the p-type conversion of intrinsically n-type trilayer WSe2 FET was successfully achieved. However, trilayer WS2 did not show clear p-type conversion because its valence band maximum is 0.66 eV lower than that of trilayer WSe2. Although inorganic WOx boasts high air stability and fabrication process compatibility due to its high thermal budget, the trap sites in WOx cause large hysteresis during back gate operation of WSe2 FETs. However, by using top gate (TG) operation with an h-BN protection layer as a TG insulator, a high-performance p-type WSe2 FET with negligible hysteresis was achieved.
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In-plane heterostructures of transition metal dichalcogenides (TMDCs) have attracted much attention for high-performance electronic and optoelectronic devices. To date, mainly monolayer-based in-plane heterostructures have been prepared by chemical vapor deposition (CVD), and their optical and electrical properties have been investigated. However, the low dielectric properties of monolayers prevent the generation of high concentrations of thermally excited carriers from doped impurities. To solve this issue, multilayer TMDCs are a promising component for various electronic devices due to the availability of degenerate semiconductors. Here, we report the fabrication and transport properties of multilayer TMDC-based in-plane heterostructures. The multilayer in-plane heterostructures are formed through CVD growth of multilayer MoS2 from the edges of mechanically exfoliated multilayer flakes of WSe2 or NbxMo1-xS2. In addition to the in-plane heterostructures, we also confirmed the vertical growth of MoS2 on the exfoliated flakes. For the WSe2/MoS2 sample, an abrupt composition change is confirmed by cross-sectional high-angle annular dark-field scanning transmission electron microscopy. Electrical transport measurements reveal that a tunneling current flows at the NbxMo1-xS2/MoS2 in-plane heterointerface, and the band alignment is changed from a staggered gap to a broken gap by electrostatic electron doping of MoS2. The formation of a staggered gap band alignment of NbxMo1-xS2/MoS2 is also supported by first-principles calculations.
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We report enhanced interlayer tunneling with reduced linewidth at zero interlayer bias in a twist-controlled double monolayer graphene heterostructure in the quantum Hall regime, when the top (ν_{T}) and bottom (ν_{B}) layer filling factors are near ν_{T}=±1/2,±3/2 and ν_{B}=±1/2,±3/2, and the total filling factor ν=±1 or ±3. The zero-bias interlayer conductance peaks are stable against variations of layer filling factor, and signal the emergence of interlayer phase coherence. Our results highlight twist control as a key attribute in revealing interlayer coherence using tunneling.
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Silanones (OîSiR2) are highly reactive species that readily convert to oligomeric siloxane (O-SiR2)n. The coordination of silanones to transition metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Herein, a pyridine-stabilized silanone molybdenum complex Cp*(OC)2Mo{OîSiMes2(py)}(SiMe3) (2b, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2, and py: pyridine) was synthesized by reacting the silyl(silylene) complex Cp*(OC)2Mo(îSiMes2)(SiMe3) (4b) with pyridine-N-oxide in pyridine. X-ray crystal structure analysis revealed that the geometry of complex 2b is similar to those of the previously synthesized DMAP-stabilized analogue Cp*(OC)2Mo{OîSiMes2(DMAP)}(SiMe3) (2a, DMAP: 4-(dimethylamino)pyridine). The SiîO and Mo-O bond distances in 2b are similar to those observed in 2a, but the N-Si coordination bond of 2b is slightly longer (approximately 0.05 Å) than that of 2a, indicating weaker pyridine coordination than that of DMAP. The reaction of 2a with excess PMe3 in C6D6 at room temperature for 28 h afforded Cp*(OC)2Mo(PMe3)(SiMe3) (5c) in a 43% NMR yield. In contrast, reacting 2b with excess PMe3 in C6D6 at room temperature for 9 h afforded 5c and the five-membered metallacyclic carbene complex Cp*(OC)Mo(îC(SiMe3)OSiMes2O)(PMe3) (6) in 10% and 41% NMR yields, respectively. The reactions of pyridine-stabilized silanone complexes Cp*(OC)2M(OîSiMes2(py))(SiMe3) (M = Mo (2b) and W (1b)) with acetone proceeded via pyridine elimination, coordination of acetone to the Si center in the silanone ligand, and elimination of HSiMe3 to give Cp*(OC)2M{OSiMes2OC(Me)îCH2} (M = Mo (8) and W (9)) in high yields.
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Contact engineering of two-dimensional semiconductors is a central issue for performance improvement of micro-/nanodevices based on these materials. Unfortunately, the various methods proposed to improve the Schottky barrier height normally require the use of high temperatures, chemical dopants, or complex processes. This work demonstrates that diffused electron beam energy (DEBE) treatment can simultaneously reduce the Schottky barrier height and enable the direct writing of electrical circuitry on van der Waals semiconductors. The electron beam energy projected into the region outside the electrode diffuses into the main channel, producing selective-area n-type doping in a layered MoTe2 (or MoS2) field-effect transistor. As a result, the Schottky barrier height at the interface between the electrode and the DEBE-treated MoTe2 channel is as low as 12 meV. Additionally, because selective-area doping is possible, DEBE can allow the formation of both n- and p-type doped channels within the same atomic plane, which enables the creation of a nonvolatile and homogeneous MoTe2 p-n rectifier with an ideality factor of 1.1 and a rectification ratio of 1.3 × 103. These results indicate that the DEBE method is a simple, efficient, mask-free, and chemical dopant-free approach to selective-area doping for the development of van der Waals electronics with excellent device performances.
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Van der Waals (vdW) heterostructures-in which layered materials are purposely selected to assemble with each other-allow unusual properties and different phenomena to be combined and multifunctional electronics to be created, opening a new chapter for the spread of internet-of-things applications. Here, an O2 -ultrasensitive MoTe2 material and an O2 -insensitive SnS2 material are integrated to form a vdW heterostructure, allowing the realization of charge-polarity control for multioperation-mode transistors through a simple and effective rapid thermal annealing strategy under dry-air and vacuum conditions. The charge-polarity control (i.e., doping and de-doping processes), which arises owing to the interaction between O2 adsorption/desorption and tellurium defects at the MoTe2 surface, means that the MoTe2 /SnS2 heterostructure transistors can reversibly change between unipolar, ambipolar, and anti-ambipolar transfer characteristics. Based on the dynamic control of the charge-polarity properties, an inverter, output polarity controllable amplifier, p-n diode, and ternary-state logics (NMIN and NMAX gates) are demonstrated, which inspire the development of reversibly multifunctional devices and indicates the potential of 2D materials.
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Recently, the ultrafast operation (â¼20 ns) of a two-dimensional (2D) heterostructured nonvolatile memory (NVM) device was demonstrated, attracting considerable attention. However, there is no consensus on its physical origin. In this study, various 2D NVM device structures are compared. First, we reveal that the hole injection at the metal/MoS2 interface is the speed-limiting path in the NVM device with the access region. Therefore, MoS2 NVM devices with a direct tunneling path between source/drain electrodes and the floating gate are fabricated by removing the access region. Indeed, a 50 ns program/erase operation is successfully achieved for devices with metal source/drain electrodes as well as graphite source/drain electrodes. This controlled experiment proves that an atomically sharp interface is not necessary for ultrafast operation, which is contrary to the previous literature. Finally, the dielectric breakdown strength (EBD) of h-BN under short voltage pulses is examined. Since a high dielectric breakdown strength allows a large tunneling current, ultrafast operations can be achieved. Surprisingly, an EBD = 26.1 MV/cm for h-BN is realized under short voltage pulses, largely exceeding the EBD = â¼12 MV/cm from the direct current (DC) measurement. This suggests that the high EBD of h-BN can be the physical origin of the ultrafast operation.
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Fructans such as inulin and levan accumulate in certain taxonomic groups of plants and are a reserve carbohydrate alternative to starch. Onion (Allium cepa L.) is a typical plant species that accumulates fructans, and it synthesizes inulin-type and inulin neoseries-type fructans in the bulb. Although genes for fructan biosynthesis in onion have been identified so far, no genes for fructan degradation had been found. In this study, phylogenetic analysis predicted that we isolated a putative vacuolar invertase gene (AcpVI1), but our functional analyses demonstrated that it encoded a fructan 1-exohydrolase (1-FEH) instead. Assessments of recombinant proteins and purified native protein showed that the protein had 1-FEH activity, hydrolyzing the ß-(2,1)-fructosyl linkage in inulin-type fructans. Interestingly, AcpVI1 had an amino acid sequence close to those of vacuolar invertases and fructosyltransferases, unlike all other FEHs previously found in plants. We showed that AcpVI1 was localized in the vacuole, as are onion fructosyltransferases Ac1-SST and Ac6G-FFT. These results indicate that fructan-synthesizing and -degrading enzymes are both localized in the vacuole. In contrast to previously reported FEHs, our data suggest that onion 1-FEH evolved from a vacuolar invertase and not from a cell wall invertase. This demonstrates that classic phylogenetic analysis on its own is insufficient to discriminate between invertases and FEHs, highlighting the importance of functional markers in the nearby active site residues.
Asunto(s)
Cebollas , beta-Fructofuranosidasa , Fructanos/metabolismo , Glicósido Hidrolasas/metabolismo , Inulina , Cebollas/genética , Cebollas/metabolismo , Filogenia , Vacuolas/metabolismo , beta-Fructofuranosidasa/genética , beta-Fructofuranosidasa/metabolismoRESUMEN
Selective fragmentation of α,ß-unsaturated esters into CîC, CîO, and OR fragments was investigated with the assistance of a gallane(pyridyl)iron complex Cp*(OC)Fe{(η1-HGaMes2)(η1-2-C5H4N)} (1, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). The reaction of 1 with methyl acrylate in C7D8 afforded vinyliron complex Cp*(OC)2Fe(CHîCH2) (2) and 4-membered Ga2O2 cyclic gallane [Mes2GaOMe]2 (3). The C-O and C-C bonds in t-butyl acrylate were cleaved by the reaction with complex 1, producing complex 2 and pyridine-coordinated gallane Mes2(t-BuO)Ga(pyridine) (4). The selective bond cleavage reactions proceeded by the reactions of 1 with methyl methacrylate and methyl 2-butenoate to afford Cp*(OC)2Fe(CR1îCHR2) (R1 = Me, R2 = H (5), R1 = H, R2 = Me (6)) and 3. In contrast, compound 3 was formed in 11% NMR yield by the reaction of 1 with methyl 3-butenoate (ß,γ-unsaturated ester), and complex mixtures of unidentified products were obtained by the reaction of 1 with methyl 4-pentenoate (γ,δ-unsaturated ester) and methyl propionate (saturated ester). The treatment of a cyclic ester, α-methylene-γ-butyrolactone, with 1 afforded a 4-membered Ga2O2 cyclic gallane dimer with Cp*(OC)2FeC(îCH2)CH2CH2 substituents on the oxygen atoms, namely [Cp*(OC)2FeC(îCH2)CH2CH2OGaMes2]2 (7). In addition, the bond cleavage reaction occurred by the reaction of 1 with allyl methyl ether to afford the (η3-allyl)iron complex Cp*(OC)Fe(η3-CH2CHCH2) (8) and 3. These results indicate that the existence of the -CîC-C-OR fragment, regardless of the presence or absence of the CîO group between the CîC and OR fragments, is essential for the bond cleavage reaction.
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Molybdenum disulfide (MoS2) mono/bilayer have been systematically investigated using atmospheric-pressure mist chemical vapor deposition (mist CVD) from (NH4)2MoS4dissolved in N-methyl-2-pyrrolidone as a precursor. Film deposition was performed by alternating MoS2mist storage within a closed chamber and mist exhaust, i.e. sequential mist supply mode at different furnace temperatures, storage times of precursor, and repetition cycles of mist supply on thermally grown SiO2(th-SiO2) and mist-CVD grown Al1-xTixOy(ATO) layers coated on p+-Si substrates. The average size of the MoS2flake and their number of stack layers could be controlled by tuning the deposition parameters combined with substrate pretreatment. Field-effect transistors with MoS2atomic mono/bilayer as a channel layer exhibited mobility up to 31-40 (43-55) cm2V-1s-1with a threshold voltage of -1.6 (-0.5) V, subthreshold slope of 0.8 (0.11) V dec.-1, and on/off ratio of 3.2 × 104(3.6 × 105) onth-SiO2(ATO) layers as gate dielectric layers without mechanical exfoliation. These findings imply that mist CVD is available for the synthesis of metal transition metal dichalcogenide and metal oxide layers as channel and gate dielectric layers, respectively.
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Two-dimensional heterostructures have been extensively investigated as next-generation nonvolatile memory (NVM) devices. In the past decade, drastic performance improvements and further advanced functionalities have been demonstrated. However, this progress is not sufficiently supported by the understanding of their operations, obscuring the material and device structure design policy. Here, detailed operation mechanisms are elucidated by exploiting the floating gate (FG) voltage measurements. Systematic comparisons of MoTe2, WSe2, and MoS2 channel devices revealed that the tunneling behavior between the channel and FG is controlled by three kinds of current-limiting paths, i.e., tunneling barrier, 2D/metal contact, and p-n junction in the channel. Furthermore, the control experiment indicated that the access region in the device structure is required to achieve 2D channel/FG tunneling by preventing electrode/FG tunneling. The present understanding suggests that the ambipolar 2D-based FG-type NVM device with the access region is suitable for further realizing potentially high electrical reliability.
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In van der Waals (vdW) heterostructures formed by stacking two monolayers of transition metal dichalcogenides, multiple exciton resonances with highly tunable properties are formed and subject to both vertical and lateral confinement. We investigate how a unique control knob, the twist angle between the two monolayers, can be used to control the exciton dynamics. We observe that the interlayer exciton lifetimes in MoSe_{2}/WSe_{2} twisted bilayers (TBLs) change by one order of magnitude when the twist angle is varied from 1° to 3.5°. Using a low-energy continuum model, we theoretically separate two leading mechanisms that influence interlayer exciton radiative lifetimes. The shift to indirect transitions in the momentum space with an increasing twist angle and the energy modulation from the moiré potential both have a significant impact on interlayer exciton lifetimes. We further predict distinct temperature dependence of interlayer exciton lifetimes in TBLs with different twist angles, which is partially validated by experiments. While many recent studies have highlighted how the twist angle in a vdW TBL can be used to engineer the ground states and quantum phases due to many-body interaction, our studies explore its role in controlling the dynamics of optically excited states, thus, expanding the conceptual applications of "twistronics".
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Squeezing bubbles and impurities out of interlayer spaces by applying force through a few-layer graphene capping layer leads to van der Waals heterostructures with the ultraflat structure free from random electrostatic potential arising from charged impurities. Without the graphene capping layer, a squeezing process with an AFM tip induces applied-force-dependent charges of Δn â¼ 2 × 1012 cm-2 µN-1, resulting in the significant intensity of trions in photoluminescence spectra of MoSe2 at low temperature. We found that a hBN/MoSe2/hBN prepared with the "graphene-capping-assisted AFM nano-squeezing method" shows a strong excitonic emission with negligible trion peak, and the residual line width of the exciton peak is only 2.2 meV, which is comparable to the homogeneous limit. Furthermore, in this high-quality sample, we found that the formation of biexciton occurs even at extremely low excitation power (Φph â¼ 2.3 × 1019 cm-2 s-1) due to the enhanced collisions between excitons.
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Van der Waals heterostructures are the ideal material platform for tunnel field-effect transistors (TFETs) because a band-to-band tunneling (BTBT) dominant current is feasible at room temperature (RT) because of ideal, dangling bond-free heterointerfaces. However, achieving subthreshold swing (SS) values lower than 60 mV dec-1 of the Boltzmann limit is still challenging. In this work, we systematically studied the band alignment and heterointerface quality in n-MoS2 channel heterostructure TFETs. By selecting a p+-MoS2 source with a sufficiently high doping level, stable gate modulation to a type III band alignment was achieved regardless of the number of MoS2 channel layers. For the gate stack formation, it was found that the deposition of Al2O3 as the top gate introduces defect states for the generation current under reverse bias, while the integration of a hexagonal boron nitride (h-BN) top gate provides a defect-free, clean interface, resulting in the BTBT dominant current even at RT. All 2D heterostructure TFETs produced by combining the type III n-MoS2/p+-MoS2 heterostructure with the h-BN top-gate insulator resulted in low SS values at RT.