2D Memory Selectors with Giant Nonlinearity Enabled by Van der Waals Heterostructures.

The integration of one-selector-one-resistor crossbar arrays requires the selectors featured with high nonlinearity and bipolarity to prevent leakage currents and any crosstalk among distinct cells. However, a selector with sufficient nonlinearity especially in the frame of device miniaturization remains scarce, restricting the advance of high-density storage devices. Herein, a high-performance memory selector is reported by constructing a graphene/hBN/WSe2 heterostructure. Within the temperature range of 300-80 K, the nonlinearity of this selector varies from ≈103 - ≈104 under forward bias, and increases from ≈300 - ≈105 under reverse bias, the highest reported nonlinearity among 2D selectors. This improvement is ascribed to direct tunneling at low bias and Fowler-Nordheim tunneling at high bias. The tunneling current versus voltage curves exhibit excellent bipolarity behavior because of the comparable hole and electron tunneling barriers, and the charge transport polarity can be effectively tuned from N-type or P-type to bipolar by simply changing source-drain bias. In addition, the conceptual memory selector exhibits no sign of deterioration after 70 000 switching cycles, paving the way for assembling 2D selectors into modern memory devices.

Study on the Performance of a Surface with Coupled Wettability Difference and Convex-Stripe Array for Improved Air Layer Stability.

The existence of an air layer reduces friction drag on superhydrophobic surfaces. Therefore, improving the air layer stability of superhydrophobic surfaces holds immense significance in reducing both energy consumption and environmental pollution caused by friction drag. Based on the properties of mathematical discretization and the contact angle hysteresis generated by the wettability difference, a surface coupled with a wettability difference treatment and a convex-stripe array is developed by laser engraving and fluorine modification, and its performance in improving the air layer stability is experimentally studied in a von Kármán swirling flow field. The results show that the destabilization of the air layer is mainly caused by the Kelvin-Helmholtz instability, which is triggered by the density difference between gas and liquid, as well as the tangential velocity difference between gas and liquid. When the air layer is relatively thin, tangential wave destabilization occurs, whereas for larger thicknesses, the destabilization mode is coupled wave destabilization. The maximum Reynolds number that keeps the air layer fully covering the surface of the rotating disk (with drag reduction performance) during the disk rotation process is defined as the critical Reynolds number (Rec), which is 1.62 × 105 for the uniform superhydrophobic surface and 3.24 × 105 for the superhydrophobic surface with a convex stripe on the outermost ring (SCSSP). Individual treatments of wettability difference and a convex-stripe array on the SCSSP further improve the air layer stability, but Rec remains at 3.24 × 105. Finally, the coupling of the wettability difference treatment with a convex-stripe array significantly improves the air layer stability, resulting in an increase of Rec to 4.05 × 105, and the drag reduction rate stably maintained around 30%.

Peritoneal Gene Transfection of Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand for Tumor Surveillance and Prophylaxis.

Peritoneal metastasis is very common in gastrointestinal, reproductive, and genitourinary tract cancers in late stages or postsurgery, causing poor prognosis, so effective and nontoxic prophylactic strategies against peritoneal metastasis are highly imperative. Herein, we demonstrate the first gene transfection as a nontoxic prophylaxis preventing peritoneal metastasis or operative metastatic dissemination. Lipopolyplexes of TNF-related-apoptosis-inducing-ligand (TRAIL) transfected peritonea and macrophages to express TRAIL for over 15 days. The expressed TRAIL selectively induced tumor cell apoptosis while exempting normal tissue, providing long-term tumor surveillance. Therefore, tumor cells inoculated in the pretransfected peritoneal cavity quickly underwent apoptosis and, thus, barely formed tumor nodules, significantly prolonging the mouse survival time compared with chemotherapy prophylaxis. Furthermore, lipopolyplex transfection showed no sign of toxicity. Therefore, this peritoneal TRAIL-transfection is an effective and safe prophylaxis, preventing peritoneal metastasis.

Using MXene as a Chemically Induced Initiator to Construct High-Performance Cathodes for Aqueous Zinc-Ion Batteries.

MXene usually exhibits weak pseudo-capacitance behavior in aqueous zinc-ion batteries, which cannot provide sufficient reversible capacity, resulting in the decline of overall capacity when used as the cathode materials. Taking inspiration from polymer electrolyte engineering, we have conceptualized an in-situ induced growth strategy based on MXene materials. Herein, 5.25 % MXene was introduced into the nucleation and growth process of vanadium oxide (HVO), providing the heterogeneous nucleation site and serving as an initiator to regulate the morphology and structural of vanadium oxide (T-HVO). The resulted materials can significantly improve the capacity and rate performance of zinc-ion batteries. The growth mechanism of T-HVO was demonstrated by both characterizations and DFT simulations, and the improved performance was systematically investigated through a series of in-situ experiments related to dynamic analysis steps. Finally, the evaluation and comparison of various defect introduction strategies revealed the efficient, safety, and high production output characteristics of the in-situ induced growth strategy. This work proposes the concept of in-situ induced growth strategy and discloses the induced chemical mechanism of MXene materials, which will aid the understanding, development, and application of cathode in aqueous zinc-ion batteries.

Large enhancement of thermoelectric performance in MoS2/h-BN heterostructure due to vacancy-induced band hybridization.

Local impurity states arising from atomic vacancies in two-dimensional (2D) nanosheets are predicted to have a profound effect on charge transport due to resonant scattering and can be used to manipulate thermoelectric properties. However, the effects of these impurities are often masked by external fluctuations and turbostratic interfaces; therefore, it is challenging to probe the correlation between vacancy impurities and thermoelectric parameters experimentally. In this work, we demonstrate that n-type molybdenum disulfide (MoS2) supported on hexagonal boron nitride (h-BN) substrate reveals a large anomalous positive Seebeck coefficient with strong band hybridization. The presence of vacancies on MoS2 with a large conduction subband splitting of 50.0 ± 5.0 meV may contribute to Kondo insulator-like properties. Furthermore, by tuning the chemical potential, the thermoelectric power factor can be enhanced by up to two orders of magnitude to 50 mW m-1 K-2 Our work shows that defect engineering in 2D materials provides an effective strategy for controlling band structure and tuning thermoelectric transport.

Hydrovoltaic technology: from mechanism to applications.

Water is a colossal reservoir of clean energy as it adsorbs thirty-five percent of solar energy reaching the Earth's surface. More than half of the adsorbed energy turns into latent heat for water evaporation, driving the water cycle of the Earth.1 Yet, only very limited energy in the water cycle is harvested by current industrial technologies. The past decade has witnessed the emergence of hydrovoltaic technology, which generates electricity from nanomaterials by direct interaction with water and enables energy harvesting from the water cycle such as from rain, waves, flows, moisture and natural evaporation. Years of efforts have been committed to improve the conversion efficiency of hydrovoltaic devices through chemical synthesis of advanced nanomaterials and innovative design of device structures. Further development of this field, however, still requires in-depth understanding of hydrovoltaic mechanisms and boosting of the electrical outputs for wider applications. Here, we present a tutorial review of different mechanisms of generating electricity from droplets, flows, natural evaporation and ambient moisture by analyzing basic interactions at various water-material interfaces. Key aspects in raising the output power of hydrovoltaic devices are then discussed in terms of material synthesis, structural design, and device optimization. We also provide an outlook on the potential applications of this technology ranging from sensors, power suppliers to multifunctional systems as well as on the scientific and technological challenges in transforming its potential into practical utility. The prospects of this emerging field are considered for future endeavor.

Metal-free alkylation of quinoxalinones with aryl alkyl ketones.

The first metal-free method for alkylation of quinoxalinones using cheap and stable aryl alkyl ketones as nucleophilic alkylation reagents is reported. This strategy greatly broadens the application channels of aryl alkyl ketones through carbon-carbon bond activation. In addition, the protocol has the advantages of simple operation, broad substrate scope, and good functional group tolerance.

Longitudinal resting-state functional connectivity and regional brain atrophy-based biomarkers of preclinical cognitive impairment in healthy old adults.

BACKGROUND: Intervention against age-related neurodegenerative diseases may be difficult once extensive structural and functional deteriorations have already occurred in the brain. AIM: Investigating 6-year longitudinal changes and implications of regional brain atrophy and functional connectivity in the triple-network model as biomarkers of preclinical cognitive impairment in healthy aging. METHODS: We acquired longitudinal cognitive scores and magnetic resonance imaging (MRI) data from 74 healthy old adults. Resting-state functional MRI (rs-fMRI) analysis was conducted using FSL6.0.1 to examine functional connectivity changes and regional brain morphometries were quantified using FreeSurfer5.3. Finally, we cross-validated and compared two support vector machine (SVM) regression models to predict future 6-year cognition score from the baseline regional brain atrophy and resting-state functional connectivity (rs-FC) measures. RESULTS: After a 6-year follow-up, our results (P < 0.05-corrected) indicated significant connectivity reduction within all the three brain networks, significant differences in regional brain volumes and cortical thickness. We also observed significant improvement in episodic memory and significant decline in executive functions. Finally, comparing the two models, we observed that regional brain atrophy predictors were more efficient in approximating future 6-year cognitive scores (R = 0.756, P < 0.0001) than rs-FC predictors (R = 0.6, P < 0.0001). CONCLUSION: This study used longitudinal data to keep subject variability low and to increase the validity of the results. We demonstrated significant changes in structural and functional MRI over 6 years. Our findings present a potential neuroimaging-based biomarker to detect cognitive impairment and prevent risks of neurodegenerative diseases in healthy old adults.

[Key technology of brain-computer interaction based on speech imagery].

Speech expression is an important high-level cognitive behavior of human beings. The realization of this behavior is closely related to human brain activity. Both true speech expression and speech imagination can activate part of the same brain area. Therefore, speech imagery becomes a new paradigm of brain-computer interaction. Brain-computer interface (BCI) based on speech imagery has the advantages of spontaneous generation, no training, and friendliness to subjects, so it has attracted the attention of many scholars. However, this interactive technology is not mature in the design of experimental paradigms and the choice of imagination materials, and there are many issues that need to be discussed urgently. Therefore, in response to these problems, this article first expounds the neural mechanism of speech imagery. Then, by reviewing the previous BCI research of speech imagery, the mainstream methods and core technologies of experimental paradigm, imagination materials, data processing and so on are systematically analyzed. Finally, the key problems and main challenges that restrict the development of this type of BCI are discussed. And the future development and application perspective of the speech imaginary BCI system are prospected.

White matter hyperintensities induce distal deficits in the connected fibers.

White matter hyperintensities (WMH) are common in elderly individuals and cause brain network deficits. However, it is still unclear how the global brain network is affected by the focal WMH. We aimed to investigate the diffusion of WMH-related deficits along the connecting white matters (WM). Brain magnetic resonance imaging data and neuropsychological evaluations of 174 participants (aged 74 ± 5 years) were collected and analyzed. For each participant, WMH lesions were segmented using a deep learning method, and 18 major WM tracts were reconstructed using automated quantitative tractography. The diffusion characteristics of distal WM tracts (with the WMH penumbra excluded) were calculated. Multivariable linear regression analysis was performed. We found that a high burden of tract-specific WMH was related to worse diffusion characteristics of distal WM tracts in a wide range of WM tracts, including the forceps major (FMA), forceps minor (FMI), anterior thalamic radiation (ATR), cingulum cingulate gyrus (CCG), corticospinal tract (CST), inferior longitudinal fasciculus (ILF), superior longitudinal fasciculus-parietal (SLFP), superior longitudinal fasciculus-temporal (SLFT), and uncinate fasciculus (UNC). Furthermore, a higher mean diffusivity (MD) of distal tracts was linked to worse attention and executive function in the FMI, right CCG, left ILF, SLFP, SLFT, and UNC. The effect of WMH on the microstructural integrity of WM tracts may propagate along tracts to distal regions beyond the penumbra and might eventually affect attention and executive function.

Coexistence of large conventional and planar spin Hall effect with long spin diffusion length in a low-symmetry semimetal at room temperature.

The spin Hall effect (SHE) is usually observed as a bulk effect in high-symmetry crystals with substantial spin-orbit coupling (SOC), where the symmetric spin-orbit field imposes a widely encountered trade-off between spin Hall angle (θSH) and spin diffusion length (Lsf), and spin polarization, spin current and charge current are constrained to be mutually orthogonal. Here, we report a large θSH of 0.32 accompanied by a long Lsf of 2.2 µm at room temperature in a low-symmetry few-layered semimetal MoTe2, thus identifying it as an excellent candidate for simultaneous spin generation, transport and detection. In addition, we report that longitudinal spin current with out-of-plane polarization can be generated by both transverse and vertical charge current, due to the conventional and a newly observed planar SHE, respectively. Our study suggests that manipulation of crystalline symmetries and strong SOC opens access to new charge-spin interconversion configurations and spin-orbit torques for spintronic applications.

Visualization of Crystallographic Orientation and Twist Angles in Two-Dimensional Crystals with an Optical Microscope.

Recently, twisted two-dimensional (2D) bilayers have attracted intense interest due to the emergence of exotic physics in moiré superlattices arising from strong interactions between electrons in the two misaligned lattices. Accurate determination and control of crystallographic orientation is vital to construct twisted 2D bilayers. Here, we demonstrate a very simple method to visualize crystallographic orientation in various 2D crystals by directly imaging n-tritriacontane crystallites epitaxially grown on 2D crystals using an ordinary optical microscope. The specific orientation of the molecular assembly allows the lattice orientation of the underlying 2D crystals to be determined with a high precision using an optical microscope. When tested on a 2D bilayer comprising staggered stacked MoS2 crystals, the twist angle can also be determined accurately. Our findings offer a nondestructive method for determining the lattice structure of 2D crystals and their bilayers and can also be a metrology tool for establishing large-area surface crystalline order.

Face-to-face transfer of wafer-scale graphene films.

Graphene has attracted worldwide interest since its experimental discovery, but the preparation of large-area, continuous graphene film on SiO2/Si wafers, free from growth-related morphological defects or transfer-induced cracks and folds, remains a formidable challenge. Growth of graphene by chemical vapour deposition on Cu foils has emerged as a powerful technique owing to its compatibility with industrial-scale roll-to-roll technology. However, the polycrystalline nature and microscopic roughness of Cu foils means that such roll-to-roll transferred films are not devoid of cracks and folds. High-fidelity transfer or direct growth of high-quality graphene films on arbitrary substrates is needed to enable wide-ranging applications in photonics or electronics, which include devices such as optoelectronic modulators, transistors, on-chip biosensors and tunnelling barriers. The direct growth of graphene film on an insulating substrate, such as a SiO2/Si wafer, would be useful for this purpose, but current research efforts remain grounded at the proof-of-concept stage, where only discontinuous, nanometre-sized islands can be obtained. Here we develop a face-to-face transfer method for wafer-scale graphene films that is so far the only known way to accomplish both the growth and transfer steps on one wafer. This spontaneous transfer method relies on nascent gas bubbles and capillary bridges between the graphene film and the underlying substrate during etching of the metal catalyst, which is analogous to the method used by tree frogs to remain attached to submerged leaves. In contrast to the previous wet or dry transfer results, the face-to-face transfer does not have to be done by hand and is compatible with any size and shape of substrate; this approach also enjoys the benefit of a much reduced density of transfer defects compared with the conventional transfer method. Most importantly, the direct growth and spontaneous attachment of graphene on the underlying substrate is amenable to batch processing in a semiconductor production line, and thus will speed up the technological application of graphene.

Graphene-Based Infrared Position-Sensitive Detector for Precise Measurements and High-Speed Trajectory Tracking.

Noncontact optical sensing plays an important role in various applications, for example, motion tracking, pilotless automobile, precision machining, and laser radars. A device with features of high resolution, fast response, and safe detection (operation wavelength at infrared (IR)) is highly desired in such applications. Here, a near IR position-sensitive detector constructed by graphene-Ge Schottky heterojunction has been demonstrated. The device shows high responsivity (minimum detectable power of ∼10 nW), excellent spatial resolution (<1 µm), fast response time (∼µs), and could operate in a wide spectral range (from visible to ∼1600 nm). Applications of precise angle (∼5 × 10-6 degree) and vibration frequency (up to 10 kHz) measurements, as well as the trajectory tracking of a high-speed infrared target (∼100 km/h), have been realized based on this device. This work therefore provides a promising route for a high-performance noncontact IR optical sensing system.

The Role of Oxygen Atoms on Excitons at the Edges of Monolayer WS2.

We clarify that the chemisorption of oxygen atoms at the edges is a key contributor to the frequently observed edge enhancement and spatial non-uniformities of photoluminescence (PL) in WS2 monolayers. Here we have investigated with momentum- and real-space nanoimaging of the chemical and electronic density inhomogeneity of WS2 flakes. Our finding from a large panoply of techniques together with density functional theory calculation confirms that the oxygen chemisorption leads to the electron accumulation at the edges. This facilitates the trion dominance of PL at the edges of WS2 flakes. Our results highlight and unravel the significance of chemisorbed oxygen at the edges in the PL emission and electronic structure of WS2, providing a viable path to enhance the performance of transition-metal-dichalcogenide-based devices.

Gate-Tunable In-Plane Ferroelectricity in Few-Layer SnS.

Ultrathin ferroelectrics hold great promise for modern miniaturized sensors, memories, and optoelectronic devices. However, in most ferroelectric materials, polarization is destabilized in ultrathin films by the intrinsic depolarization field. Here we report robust in-plane ferroelectricity in few-layer tin sulfide (SnS) 2D crystals that is coupled anisotropically to lattice strain. Specifically, the intrinsic polarization of SnS manifests as nanoripples along the armchair direction due to a converse piezoelectric effect. Most interestingly, such nanoripples show an odd-and-even effect in terms of its layer dependence, indicating that it is highly sensitive to changes in inversion symmetry. Ferroelectric switching is demonstrated in field-effect transistor devices fabricated on ultrathin SnS films, in which a stronger ferroelectric response is achieved at negative gate voltages. Our work shows the promise of 2D SnS in ultrathin ferroelectric field-effect transistors as well as nanoscale electromechanical systems.

Triplet-Triplet Annihilation Upconversion for Photocatalytic Hydrogen Evolution.

The solar generation of hydrogen by water splitting provides a promising path for renewable hydrogen production and solar energy storage. Upconversion of low-energy photons into high-energy photons constitutes a promising strategy to enhance the light harvesting efficiency of artificial hydrogen production systems. In the present study, upconversion micelles are integrated with Cd0.5 Zn0.5 S to construct solar energy conversion systems. The upconversion micelle is employed to upconvert red photons to cyan photons. Cd0.5 Zn0.5 S is sensitized by upconverted cyan light to produce hydrogen, but not by incident red light without triplet-triplet annihilation upconversion (TTA-UC). The performance of the upconversion photocatalytic system was dramatically affected by the concentration of Cd0.5 Zn0.5 S and the irradiation intensity. This novel system was able to produce about 2.3 µL hydrogen after 5 h of red light (629 nm) irradiation (2.4 mW cm-2 ). The present study provides a candidate for applications using low-energy photons for solar hydrogen generation.

Structural and functional abnormalities of vision-related brain regions in cirrhotic patients: a MRI study.

PURPOSE: Previous studies have focused on global cerebral alterations observed in cirrhosis. However, little was known about the specific abnormalities of vision-related brain regions in cirrhotic patients. In this study, we sought to explore neurological alterations of vision-related regions by measuring brain resting-state network connectivity, based on the structural investigation in cirrhotic patients without clinical sign of hepatic encephalopathy (HE). METHODS: Structural and functional magnetic resonance image (MRI) data were collected from 20 hepatitis B virus (HBV)-related cirrhotic patients without clinical sign of HE and from 20 healthy controls (HC). Voxel-based morphometric (VBM) analysis and brain functional network analysis were performed to detect abnormalities in cerebral structure and function. RESULTS: Cirrhotic patients showed regions with the most significant gray matter reduction primarily in vision-related brain regions, including the bilateral lingual gyri, left putamen, right fusiform gyrus, and right calcarine gyrus, and other significant gray matter reductions were distributed in bilateral hippocampus. Based on structural investigation focused on vision-related regions, brain functional network analysis revealed decreased functional connectivity between brain functional networks within vision-related regions (primary visual network (PVN), higher visual network (HVN), visuospatial network (VSN)) in the patient group compared with HC group. CONCLUSION: These results indicate that structural and functional impairment were evident in the vision-related brain regions in cirrhotic patients without clinical sign of hepatic encephalopathy. The physiopathology and clinical relevance of these changes could not be ascertained from the present study, which provided a basis for further evolution of the disease.

Modified-release oral pellets for duodenum delivery of doxycycline hyclate.

To minimize the gastric and esophageal injury effect, a system to deliver doxycycline hyclate (DOXY) to the duodenum area is needed. DOXY-containing modified-release oral pellets (DMOP) coated with hydroxypropyl methylcellulose phthalate HP-55 (HPMCP HP-55) and hydroxypropyl methylcellulose E15 (HPMC E15) appear to be a reasonable choice. This coating layer dissolves at pH 5.5, which is the pH of the duodenum, but not at a gastric pH (1.2). The formulation and preparation of DMOP were optimized, and a scale-up test was performed. The results showed that the production reproducibility was acceptable, and the quality of DMOP well met the standards of Chinese Pharmacopeia (Ch.P, 2015 edition). Notably, the accumulated DOXY release was lower than 50% at pH 1.2 (20 min) and higher than 85% at pH 5.5, which met the USP40-NF35 standard for DOXY modified-release formulations. Moreover, the storage stability of DMOP with different packages was investigated by stress testing, accelerated and long-term testings. The stability of DMOP was maintained up to 12 months, in terms of DOXY content and in vitro release behavior. The results seem to suggest that DMOP could be a promising duodenum delivery system.

Phonon-Mediated Colossal Magnetoresistance in Graphene/Black Phosphorus Heterostructures.

There is a huge demand for magnetoresistance (MR) sensors with high sensitivity, low energy consumption, and room temperature operation. It is well-known that spatial charge inhomogeneity due to impurities or defects introduces mobility fluctuations in monolayer graphene and gives rise to MR in the presence of an externally applied magnetic field. However, to realize a MR sensor based on this effect is hampered by the difficulty in controlling the spatial distribution of impurities and the weak magnetoresistance effect at the monolayer regime. Here, we fabricate a highly stable monolayer graphene-on-black phosphorus (G/BP) heterostructure device that exhibits a giant MR of 775% at 9 T magnetic field and 300 K, exceeding by far the MR effects from devices made from either monolayer graphene or few-layer BP alone. The positive MR of the G/BP device decreases when the temperature is lowered, indicating a phonon-mediated process in addition to scattering by charge impurities. Moreover, a nonlocal MR of >10 000% is achieved for the G/BP device at room temperature due to an enhanced flavor Hall effect induced by the BP channel. Our results show that electron-phonon coupling between 2D material and a suitable substrate can be exploited to create giant MR effects in Dirac semimetals.