RESUMEN
Two-dimensional materials have emerged as an important research frontier for overcoming the challenges in nanoelectronics and for exploring new physics. Among them, black phosphorus, with a combination of a tunable bandgap and high mobility, is one of the most promising systems. In particular, black phosphorus nanoribbons show excellent electrostatic gate control, which can mitigate short-channel effects in nanoscale transistors. Controlled synthesis of black phosphorus nanoribbons, however, has remained an outstanding problem. Here we report large-area growth of black phosphorus nanoribbons directly on insulating substrates. We seed the chemical vapour transport growth with black phosphorus nanoparticles and obtain uniform, single-crystal nanoribbons oriented exclusively along the [100] crystal direction. With comprehensive structural calculations, we discover that self-passivation at the zigzag edges holds the key to the preferential one-dimensional growth. Field-effect transistors based on individual nanoribbons exhibit on/off ratios up to ~104, confirming the good semiconducting behaviour of the nanoribbons. These results demonstrate the potential of black phosphorus nanoribbons for nanoelectronic devices and also provide a platform for investigating the exotic physics in black phosphorus.
RESUMEN
Although copper oxide high-temperature superconductors constitute a complex and diverse material family, they all share a layered lattice structure. This curious fact prompts the question of whether high-temperature superconductivity can exist in an isolated monolayer of copper oxide, and if so, whether the two-dimensional superconductivity and various related phenomena differ from those of their three-dimensional counterparts. The answers may provide insights into the role of dimensionality in high-temperature superconductivity. Here we develop a fabrication process that obtains intrinsic monolayer crystals of the high-temperature superconductor Bi2Sr2CaCu2O8+δ (Bi-2212; here, a monolayer refers to a half unit cell that contains two CuO2 planes). The highest superconducting transition temperature of the monolayer is as high as that of optimally doped bulk. The lack of dimensionality effect on the transition temperature defies expectations from the Mermin-Wagner theorem, in contrast to the much-reduced transition temperature in conventional two-dimensional superconductors such as NbSe2. The properties of monolayer Bi-2212 become extremely tunable; our survey of superconductivity, the pseudogap, charge order and the Mott state at various doping concentrations reveals that the phases are indistinguishable from those in the bulk. Monolayer Bi-2212 therefore displays all the fundamental physics of high-temperature superconductivity. Our results establish monolayer copper oxides as a platform for studying high-temperature superconductivity and other strongly correlated phenomena in two dimensions.
RESUMEN
Materials research has driven the development of modern nano-electronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7-11 based on atomically thin van der Waals crystals.
RESUMEN
Advanced Organic Chemical Materials Co-constructed Mechanically bonded amphiphiles (MBAs), also known as mechanically interlocked molecules (MIMs), have emerged as an important kind of functional building block for the construction of artificial molecular machines and soft materials. Herein, a novel MBA, i. e., bistable [2]rotaxane H2 was designed and synthesized. In the solution state, H2 demonstrated pH and metal ion-responsive emissions due to the presence of a distance-dependent photoinduced electron transfer (PET) process and the fluorescence resonance energy transfer (FRET) process, respectively. Importantly, the amphiphilic feature of H2 has endowed it with unique self-assembly capability, and nanospheres were obtained in a mixed H2 O/CH3 CN solvent. Moreover, the morphology of H2 aggregates can be tuned from nanospheres to vesicles due to the pH-controlled shuttling motion-induced alternation of H2 amphiphilicity. Interestingly, larger spheres with novel pearl-chain-like structures from H2 were observed after adding stoichiometric Zn2+ . In particular, H2 shows pH-responsive emissions in its aggregation state, allowing the visualization of the shuttling movement by just naked eyes. It is assumed that the well-designed [2]rotaxane, and particularly the proposed concept of MBA shown here, will further enrich the families of MIMs, offering prospects for synthesizing more MIMs with novel assembly capabilities and bottom-up building dynamic smart materials with unprecedented functions.
RESUMEN
Two-dimensional materials provide opportunities for developing semiconductor applications at atomistic thickness to break the limits of silicon technology. Black phosphorus (BP), as a layered semiconductor with controllable bandgap and high carrier mobility, is one of the most promising candidates for transistor devices at atomistic thickness1-4. However, the lack of large-scale growth greatly hinders its development in devices. Here, we report the growth of ultrathin BP on the centimetre scale through pulsed laser deposition. The unique plasma-activated region induced by laser ablation provides highly desirable conditions for BP cluster formation and transportation5,6, facilitating growth. Furthermore, we fabricated large-scale field-effect transistor arrays on BP films, yielding appealing hole mobility of up to 213 and 617 cm2 V-1 s-1 at 295 and 250 K, respectively. Our results pave the way for further developing BP-based wafer-scale devices with potential applications in the information industry.
RESUMEN
Memristor devices that exhibit high integration density, fast speed, and low power consumption are candidates for neuromorphic devices. Here, we demonstrate a filament-based memristor using p-type SnS as the resistive switching material, exhibiting superlative metrics such as a switching voltage â¼0.2 V, a switching speed faster than 1.5 ns, high endurance switching cycles, and an ultralarge on/off ratio of 108. The device exhibits a power consumption as low as â¼100 fJ per switch. Chip-level simulations of the memristor based on 32 × 32 high-density crossbar arrays with 50 nm feature size reveal on-chip learning accuracy of 87.76% (close to the ideal software accuracy 90%) for CIFAR-10 image classifications. The ultrafast and low energy switching of p-type SnS compared to n-type transition metal dichalcogenides is attributed to the presence of cation vacancies and van der Waals gap that lower the activation barrier for Ag ion migration.
RESUMEN
The advent of black phosphorus field-effect transistors (FETs) has brought new possibilities in the study of two-dimensional (2D) electron systems. In a black phosphorus FET, the gate induces highly anisotropic 2D electron and hole gases. Although the 2D hole gas in black phosphorus has reached high carrier mobilities that led to the observation of the integer quantum Hall effect, the improvement in the sample quality of the 2D electron gas (2DEG) has however been only moderate; quantum Hall effect remained elusive. Here, we obtain high quality black phosphorus 2DEG by defining the 2DEG region with a prepatterned graphite local gate. The graphite local gate screens the impurity potential in the 2DEG. More importantly, it electrostatically defines the edge of the 2DEG, which facilitates the formation of well-defined edge channels in the quantum Hall regime. The improvements enable us to observe precisely quantized Hall plateaus in electron-doped black phosphorus FET. Magneto-transport measurements under high magnetic fields further revealed a large effective mass and an enhanced Landé g-factor, which points to strong electron-electron interaction in black phosphorus 2DEG. Such strong interaction may lead to exotic many-body quantum states in the fractional quantum Hall regime.
RESUMEN
Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus, the bandgap can be modulated by the number of layers; as a result, few-layer black phosphorus has discrete bandgap values that are relevant for optoelectronic applications in the spectral range from red, in monolayer, to mid-infrared in the bulk limit. Here, we further demonstrate continuous bandgap modulation by mechanical strain applied through flexible substrates. The strain-modulated bandgap significantly alters the density of thermally activated carriers; we for the first time observe a large piezo-resistive effect in black phosphorus field-effect transistors (FETs) at room temperature. The effect opens up opportunities for future development of electromechanical transducers based on black phosphorus, and we demonstrate an ultrasensitive strain gauge constructed from black phosphorus thin crystals.
RESUMEN
The aimed of this study was to prepare stabilized thiomers to overcome the poor stability character of traditional thiomers. Poly(acrylic acid)-cysteine (PAA-Cys) was synthesized by conjugating cysteine with poly(acrylic acid) and poly(acrylic acid)-cysteine-6-mercaptonicotinic acid (PAA-Cys-6MNA, stabilized thiomers) was synthesized by grafting a protecting group 6-mercaptonicotinic acid (6MNA) with PAA-Cys. The free thiol of PAA-Cys was determined by Ellmann's reagent method and the ratio of 6MNA coupled was determined by glutathione reduction method. The study of permeation enhancement and stabilized function was conducted by using Franz diffusion cell method, with fluorescein isothiocyanate dextran (FD4) used as model drug. The influence of polymers on tight junctions of Caco-2 cell monolayer was detected with laser scanning confocal fluorescence microscope. The results indicated that both PAA-Cys and PAA-Cys-6MNA could promote the permeation of FD4 across excised rat intestine, and the permeation function of PAA-Cys-6MNA was not influence by the pH of the storage environment and the oxidation of air after the protecting group 6MNA was grafted. The distribution of tight junction protein of Caco-2 cell monolayer F-actin was influenced after incubation with PAA-Cys and PAA-Cys-6MNA. In conclusion, stabilized thiomers (PAA-Cys-6MNA) maintained the permeation function compared with the traditional thiomers (PAA-Cys) and its stability was improved. The mechanism of the permeation enhancement function of the polymers might be related to their influence on tight junction relating proteins of cells.
Asunto(s)
Resinas Acrílicas/química , Cisteína/química , Ácidos Nicotínicos/química , Compuestos de Sulfhidrilo/química , Actinas/metabolismo , Animales , Células CACO-2 , Dextranos , Fluoresceína-5-Isotiocianato/análogos & derivados , Glutatión , Humanos , Absorción Intestinal , Mucosa Intestinal/efectos de los fármacos , RatasRESUMEN
BACKGROUND: The gut microbiota-dependent metabolite trimethylamine N-oxide (TMAO) has recently been recognized to be one of the risk factors for cardiovascular disease (CVD). However, there is a scarcity of data on the relationship between circulating TMAO levels and hypertension in patients with CVD. Meta analysis and a dose-response relationship were used in this study to assess the relationship between circulating trimethylamine N-oxide levels and the risk of hypertension in patients with CVD. METHODS: CNKI, Wanfang Database, Pubmed, Embase, Cochrane Library, and Web of Science were searched up to June 01, 2023. Meta-analysis and dose-response analysis of relative risk data from prospective cohort studies reporting on the relationship between circulating TMAO levels and hypertension risk in patients with CVD were conducted. RESULTS: Fifteen studies with a total of 15,498 patients were included in the present meta-analysis. Compared with a lower circulating TMAO level, a higher TMAO level was associated with a higher risk of hypertension in patients with CVD (RRâ =â 1.14,95%CI (1.08, 1.20)). And the higher the TMAO level, the greater the risk of hypertension. The dose-response analysis revealed a linear dose-response relationship between circulating TMAO levels and the risk of hypertension in patients with CVD. The risk of hypertension increased by 1.014% when the circulating TMAO level increased by 1 µ mol/L. CONCLUSION: In patients with CVD, the level of circulating TMAO is significantly related to the risk of hypertension. The risk of hypertension increased by 1.014% for every 1 µ mol/L increase in circulating TMAO levels.
Asunto(s)
Enfermedades Cardiovasculares , Hipertensión , Metilaminas , Humanos , Enfermedades Cardiovasculares/sangre , Enfermedades Cardiovasculares/epidemiología , Hipertensión/sangre , Hipertensión/epidemiología , Metilaminas/sangre , Estudios ProspectivosRESUMEN
Materials showing second-order nonlinear transport under time reversal symmetry can be used for Radio Frequency (RF) rectification, but practical application demands room temperature operation and sensitivity to microwatts level RF signals in the ambient. In this study, we demonstrate that BiTeBr exhibits a giant nonlinear response which persists up to 350 K. Through scaling and symmetry analysis, we show that skew scattering is the dominant mechanism. Additionally, the sign of the nonlinear response can be electrically switched by tuning the Fermi energy. Theoretical analysis suggests that the large Rashba spin-orbit interactions (SOI), which gives rise to the chirality of the Bloch electrons, provide the microscopic origin of the observed nonlinear response. Our BiTeBr rectifier is capable of rectifying radiation within the frequency range of 0.2 to 6 gigahertz at room temperature, even at extremely low power levels of -15 dBm, and without the need for external biasing. Our work highlights that materials exhibiting large Rashba SOI have the potential to exhibit nonlinear responses at room temperature, making them promising candidates for harvesting high-frequency and low-power ambient electromagnetic energy.
RESUMEN
High mobility electron gases confined at material interfaces have been a venue for major discoveries in condensed matter physics. Ultra-high vacuum (UHV) technologies played a key role in creating such high-quality interfaces. The advent of two-dimensional (2D) materials brought new opportunities to explore exotic physics in flat lands. UHV technologies may once again revolutionize research in low dimensions by facilitating the construction of ultra-clean interfaces with a wide variety of 2D materials. Here, we describe the design and operation of a UHV 2D material device fabrication system, in which the entire fabrication process is performed under pressure lower than 5 × 10-10 mbar. Specifically, the UHV system enables the exfoliation of atomically clean 2D materials. Subsequent in situ assembly of van der Waals heterostructures produces high-quality interfaces that are free of contamination. We demonstrate functionalities of this system through exemplary fabrication of various 2D materials and their heterostructures.
RESUMEN
Inonotus obliquus (Pers.:Fr.) Pilát has been traditionally used as a folk remedy for treatment of cancers, cardiovascular disease and diabetes in Russia, Poland, and most of the Baltic countries, but natural reserves of this fungus have nearly been exhausted. This study was designed to investigate the artificial cultivation of I. obliquus and the antitumor activity of its tissues. The ethanol extract of cultivated sclerotium had the highest cell growth inhibitory rate (74.6%) as determined by an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. 78% of the bags produced sclerotia and only 6.17 g/bag of sclerotium was obtained. Extracts of the cultivated fruiting body showed 44.2% inhibitory activity against tumor cells. However, the yield was as high as 18.24 g/bag, and 98% of the bags produced fruiting body. The results of gas chromatography-mass spectroscopy (GC-MS) showed that similar compounds were extracted from the wild and cultivated samples. The principal compounds observed were lanosterol, inotodiol, and ergosterol. Their percentages of the mass fraction were 86.1, 59.9, and 71.8% of the total, for the wild sclerotium, cultivated sclerotium, and cultivated fruiting body, respectively. Ergosterol was found to be much higher (27.32%) in cultivated fruiting body. We conclude that cultivated fruiting body of I. obliquus obtained by inoculation of the substrate with spawn mycelium of the fifth generation could serve as an ideal substitute for the wild I. obliquus.
Asunto(s)
Agaricales/química , Antineoplásicos/farmacología , Productos Biológicos/farmacología , Proliferación Celular/efectos de los fármacos , Agaricales/crecimiento & desarrollo , Antioxidantes/química , Antioxidantes/farmacología , Línea Celular Tumoral , Ensayos de Selección de Medicamentos Antitumorales , Humanos , Neoplasias Pulmonares , Medicina TradicionalRESUMEN
In a magnetic topological insulator, nontrivial band topology combines with magnetic order to produce exotic states of matter, such as quantum anomalous Hall (QAH) insulators and axion insulators. In this work, we probe quantum transport in MnBi2Te4 thin flakes-a topological insulator with intrinsic magnetic order. In this layered van der Waals crystal, the ferromagnetic layers couple antiparallel to each other; atomically thin MnBi2Te4, however, becomes ferromagnetic when the sample has an odd number of septuple layers. We observe a zero-field QAH effect in a five-septuple-layer specimen at 1.4 kelvin, and an external magnetic field further raises the quantization temperature to 6.5 kelvin by aligning all layers ferromagnetically. The results establish MnBi2Te4 as an ideal arena for further exploring various topological phenomena with a spontaneously broken time-reversal symmetry.
RESUMEN
Strong in-plane anisotropy of atomic layer and thin-film black phosphorus (P) offers new device perspectives and stimulates increasing interest and explorations, where precisely determining the black P crystal orientation and anisotropic axes is a necessity. Here, we demonstrate that the crystal orientation and intrinsic in-plane optical anisotropy of black P crystals in a broad thickness range (from â¼5 to â¼300 nm) can be directly and precisely determined, by polarized reflectance measurement alone, in visible range. Combining experiments with modeling of optical anisotropy and multilayer interference effects, we elucidate the underlying principles and validate these measurements. The polarized reflectance method is not only easy to implement but also deterministic, nondestructive, and effective for both on-substrate and suspended black P atomic layers and thin films.
RESUMEN
Phosphorene, a single atomic layer of black phosphorus, has recently emerged as a new two-dimensional (2D) material that holds promise for electronic and photonic technologies. Here we experimentally demonstrate that the electronic structure of few-layer phosphorene varies significantly with the number of layers, in good agreement with theoretical predictions. The interband optical transitions cover a wide, technologically important spectral range from the visible to the mid-infrared. In addition, we observe strong photoluminescence in few-layer phosphorene at energies that closely match the absorption edge, indicating that they are direct bandgap semiconductors. The strongly layer-dependent electronic structure of phosphorene, in combination with its high electrical mobility, gives it distinct advantages over other 2D materials in electronic and opto-electronic applications.
RESUMEN
Multirod and hierarchically spherical 3D Co(1-x)Mn(x)O (2/3 < or = x < or = 1) nanostructures have been successfully synthesized by the decomposition of acetylacetonate precursors. Their morphologies could be controlled through tuning the heat rating which affects the nucleation. The rods grew along [110] directions to reduce the appearance of high-energy crystallographic {110} planes. The hierarchically spherical superstructures were formed by a three-dimensional oriented-attachment mechanism. Magnetic measurement indicates that the MnO nanomaterials with hierarchically spherical superstructures show an antiferromagnetic transition temperature at 121 K, similar to that of bulk, and a ferromagnetic ordering exists at low temperature. Such anomalous magnetic properties arise plausibly from their microstructure characteristics.
RESUMEN
Electron-electron and electron-phonon interactions are two major driving forces that stabilize various charge-ordered phases of matter. In layered compound 1T-TaS2, the intricate interplay between the two generates a Mott-insulating ground state with a peculiar charge-density-wave (CDW) order. The delicate balance also makes it possible to use external perturbations to create and manipulate novel phases in this material. Here, we study a mosaic CDW phase induced by voltage pulses, and find that the new phase exhibits electronic structures entirely different from that of the original Mott ground state. The mosaic phase consists of nanometre-sized domains characterized by well-defined phase shifts of the CDW order parameter in the topmost layer, and by altered stacking relative to the layers underneath. We discover that the nature of the new phase is dictated by the stacking order, and our results shed fresh light on the origin of the Mott phase in 1T-TaS2.
Asunto(s)
Electrones , Fonones , Sulfuros/química , Tantalio/química , Electrónica , Transición de Fase , TemperaturaRESUMEN
A previous study demonstrated that birds that are exposed to light at night develop advanced reproductive systems. However, spectrum might also affect the photoperiodic response of birds. The present study was aimed to investigate the effects of spectral composition on the growth and reproductive physiology of female breeders, using pure light-emitting diode spectra. A total of 1,000 newly hatched female avian breeders (Gallus gallus) were equally allocated to white-, red-, yellow-, green- and blue-light treated groups. We found that blue-light treated birds had a greater and faster weight gain than did red- and yellow-light treated birds (P = 0.02 and 0.05). The red light expedited the sexual maturation of the chicks, whose age at sexual maturity was 7 and 14 days earlier than that of the green- and blue-light treated birds, respectively. The accumulative egg production of the red-light treated birds was 9 and 8 eggs more than that of the blue- and green-light treated birds. The peak lay rate of the red-light treated groups was significantly greater than the blue-light treated birds (P = 0.028). In conclusion, exposure to short-wavelength light appears to promote growth of female breeder birds, whereas exposure to long-wavelength light appears to accelerate reproductive performance.
Asunto(s)
Pollos/fisiología , Luz , Fotoperiodo , Reproducción , Animales , Peso Corporal , Pollos/crecimiento & desarrollo , Femenino , Fertilidad , Maduración SexualRESUMEN
There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin-momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observe the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Furthermore, the magnetic field angle dependence of the spin signal is consistent with spin-momentum locking property of surface states of SmB6.