Ferroelectric-defined reconfigurable homojunctions for in-memory sensing and computing.

Recently, the increasing demand for data-centric applications is driving the elimination of image sensing, memory and computing unit interface, thus promising for latency- and energy-strict applications. Although dedicated electronic hardware has inspired the development of in-memory computing and in-sensor computing, folding the entire signal chain into one device remains challenging. Here an in-memory sensing and computing architecture is demonstrated using ferroelectric-defined reconfigurable two-dimensional photodiode arrays. High-level cognitive computing is realized based on the multiplications of light power and photoresponsivity through the photocurrent generation process and Kirchhoff's law. The weight is stored and programmed locally by the ferroelectric domains, enabling 51 (>5 bit) distinguishable weight states with linear, symmetric and reversible manipulation characteristics. Image recognition can be performed without any external memory and computing units. The three-in-one paradigm, integrating high-level computing, weight memorization and high-performance sensing, paves the way for a computing architecture with low energy consumption, low latency and reduced hardware overhead.

2D materials-based photodetectors combined with ferroelectrics.

Photodetectors are essential optoelectronic devices that play a critical role in modern technology by converting optical signals into electrical signals, which are one of the most important sensors of the informational devices in current 'Internet of Things' era. Two-dimensional (2D) material-based photodetectors have excellent performance, simple design and effortless fabrication processes, as well as enormous potential for fabricating highly integrated and efficient optoelectronic devices, which has attracted extensive research attention in recent years. The introduction of spontaneous polarization ferroelectric materials further enhances the performance of 2D photodetectors, moreover, companying with the reduction of power consumption. This article reviews the recent advances of materials, devices in ferroelectric-modulated photodetectors. This review starts with the introduce of the basic terms and concepts of the photodetector and various ferroelectric materials applied in 2D photodetectors, then presents a variety of typical device structures, fundamental mechanisms and potential applications under ferroelectric polarization modulation. Finally, we summarize the leading challenges currently confronting ferroelectric-modulated photodetectors and outline their future perspectives.

High-performance ß-Ga2O3 thickness dependent solar blind photodetector.

Gallium oxide (Ga2O3) has been studied as one of the most promising wide bandgap semiconductors during the past decade. Here, we prepared high quality ß-Ga2O3 films by pulsed laser deposition. ß-Ga2O3 films of different thicknesses were achieved and their crystal properties were comprehensively studied. As thickness increases, grain size and surface roughness are both increased. Based on these ß-Ga2O3 films, a series of ultraviolet (UV) photodetectors with interdigital electrodes structure were prepared. These devices embrace an ultralow dark current of 100 fA, and high photocurrent on/off ratio of 10E8 under UV light illumination. The photoresponse time is 4 ms which is faster than most of previous works. This work paves the way for the potential application of Ga2O3 in the field of UV detection.

Investigation on risk factors of haemorrhagic fever with renal syndrome (HFRS) in Xuancheng City in Anhui Province, Mainland China.

Haemorrhagic fever with renal syndrome (HFRS), a rodent-borne disease, is a major public health concern in both developed and developing countries. China is the most severe endemic country in the world, constituting 90% of the cases. Although the incidence of HFRS has substantively decreased in most areas of China, HFRS has rebounded remarkably in some epidemic areas. Xuancheng is one of these areas. In this study, we collected the case data reported recently in Xuancheng and designed a 1:3 case-control study. The Chi-square test, univariate and multivariate logistic regression analysis were performed. In all cases, farmers made up the highest proportion of occupations. And there were 20 variables with statistical significance including indoor hygienic conditions; the surrounding environment; whether bitten by rats at work and other criteria. In addition, exposure to rodents and rats bites is a high-risk factor for HFRS. Rodent density was calculated at 20.9% (159/760), the virus carrier rate was 9.4% (15/159) and the index of rats with a virus was about 2.0%. Exposure to rodents and insect bites is also high-risk factors for HFRS among local residents in Xuancheng. More importantly, during the flood years, the increased density of rodents led to an increased risk of human exposure to rodents. As our statistical analysis proves, targeted strategies should be developed and implemented to reduce the incidence of local diseases in the future.

Knowledge, attitudes and practices regarding echinococcosis in Xizang Autonomous Region, China.

BACKGROUND: Echinococcosis is a neglected zoonotic parasitic disease caused echinococcus parasitizes, poseing a significant economic burden on both humans and animals. There are limited studies on echinococcosis in China, especially Xizang Autonomous Region, although the area is endemic area for echinococcosis. The study aimed to provide information for strategic prevention against this disease. METHODS: A cross-sectional survey was conducted among the residents in Xizang Autonomous Region, China to evaluate their knowledge, attitudes and practices on endemicity of echinococcosis. A face-to-face survey was conducted to collect the data using a well-designed questionnaire. The contents included basic personal information, knowledge, attitudes and practices about echinococcosis, personal hygiene and behavior habits, dog feeding and whether they had received the information on echinococcosis, and so on. We surveyed 840 persons in practice. All data analysis was performed using Epi Info 7.2. RESULTS: Of the total particpants, 86.8% had a primary education level or below (including primary and illiterate), and even 45.0% were illiterate. Farmers and herdsmen represent the main occupations in this study. People who know all the echinococcosis-related knowledge in the questionnaire only accounted for 8.7% of the participants. However, none of the participants was aware of routes of echinococcosis infection in human or dogs. The data showed participants with higher educational background had the high awareness rate of echinococcosis-related knowledge or attitudes (chi-square for trend, χ2 = 21.23, p<0.05 & χ2 = 48.43, p<0.05). In addition, The percentage of the participant with awareness of echinococcosis-related practices was associated with their age and principle occupation (χ2 = 52.72, p<0.05 & χ2 = 20.63, p<0.05). CONCLUSIONS: Xizang Autonomous Region is an epidemic area of Echinococcosis. The prevalence of the disease has been largely due to the lack of knowledge, awareness, and poor hygiene practice in local residences. Therefore, effective disease prevention education and awareness campaigns in community will be significantly helpful in prevention and control of echinococcosis.

High-Performance Photovoltaic Detector Based on MoTe2 /MoS2 Van der Waals Heterostructure.

Van der Waals heterostructures based on 2D layered materials have received wide attention for their multiple applications in optoelectronic devices, such as solar cells, light-emitting devices, and photodiodes. In this work, high-performance photovoltaic photodetectors based on MoTe2 /MoS2 vertical heterojunctions are demonstrated by exfoliating-restacking approach. The fundamental electric properties and band structures of the junction are revealed and analyzed. It is shown that this kind of photodetectors can operate under zero bias with high on/off ratio (>105 ) and ultralow dark current (≈3 pA). Moreover, a fast response time of 60 µs and high photoresponsivity of 46 mA W-1 are also attained at room temperature. The junctions based on 2D materials are expected to constitute the ultimate functional elements of nanoscale electronic and optoelectronic applications.

Ultrahigh photoresponsivity MoS2 photodetector with tunable photocurrent generation mechanism.

Photodetectors with two-dimensional (2D) materials on a SiO2/Si substrate have been extensively explored. However, these photodetectors often suffer from a large gate voltage and relatively low photoresponsivity due to the low efficiency light absorption of 2D materials. Here, we develop a MoS2 photodetector based on the Al2O3/ITO (indium tin oxide)/SiO2/Si substrate with ultrahigh photoresponsivity of 2.7 × 104 A W-1. Most of the incident light is reflected by the interface of stacked Al2O3/ITO/SiO2 substrate, which significantly increases the light absorption of 2D materials. With the help of thinner and high-κ Al2O3 dielectric, the current ON/OFF ratio could exceed 109 with a gate voltage no more than 2 V. Enhanced gate regulation also brings about a relatively high mobility of 84 cm2 V-1 s-1 and subthreshold swing of 104 mV dec-1. Additionally, two different photocurrent generation mechanisms have also been revealed by tuning the gate voltage. The reflection-enhancement substrate assisted MoS2 photodetector provides a new idea for improving the performance of 2D material photodetectors, which can be perfectly combined with other methods.

The ambipolar evolution of a high-performance WSe2 transistor assisted by a ferroelectric polymer.

In recent years, the electrical characteristics of WSe2 field-effect transistors (FETs) have been widely investigated with various dielectrics. Among them, being able to perfectly tune the polarity of WSe2 is meaningful and promising work. In this work, we systematically study the electrical properties of bilayer WSe2 FETs modulated by ferroelectric polymer poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)). Compared to traditional gate dielectric SiO2, the P(VDF-TrFE) can not only tune both electron and hole concentrations to the same high level, but also improve the hole mobility of bilayer WSe2 to 265.96 cm2 V-1 s-1 under SiO2 gating. Its drain current on/off ratio is also improved to 2 × 105 for p-type and 4 × 105 for n-type driven by P(VDF-TrFE). More importantly, the ambipolar behaviors of bilayer WSe2 are effectively achieved and maintained because of the remnant polarization field of P(VDF-TrFE). This work indicates that WSe2 FETs with P(VDF-TrFE) gating have huge potential for complementary logic transistor applications, and paves an effective way to achieve in-plane p-n junctions.

Graphene Dirac point tuned by ferroelectric polarization field.

Graphene has received numerous attention for future nanoelectronics and optoelectronics. The Dirac point is a key parameter of graphene that provides information about its carrier properties. There are lots of methods to tune the Dirac point of graphene, such as chemical doping, impurities, defects, and disorder. In this study, we report a different approach to tune the Dirac point of graphene using a ferroelectric polarization field. The Dirac point can be adjusted to near the ferroelectric coercive voltage regardless its original position. We have ensured this phenomenon by temperature-dependent experiments, and analyzed its mechanism with the theory of impurity correlation in graphene. Additionally, with the modulation of ferroelectric polymer, the current on/off ratio and mobility of graphene transistor both have been improved. This work provides an effective method to tune the Dirac point of graphene, which can be readily used to configure functional devices such as p-n junctions and inverters.

Historical trends of organochlorine pesticides (OCPs) recorded in sediments across the Tibetan Plateau.

Sediment cores from four lakes across the Tibetan Plateau were used as natural archives to study the time trends of organochlorine pesticides (OCPs). The total concentrations of dichlorodiphenyltrichloroethane (ΣDDT) and hexachlorocyclohexane isomers (ΣHCH) were in the range of 0.04-1.61 and 0.08-1.88 ng/g based on dry weight (dw), while the input fluxes were in the range of 0.3-236 and 0.7-295 pg/cm2/y in the core sediments, respectively. The input fluxes of ΣDDT and ΣHCH generally peaked in sediment layers corresponding to the 1970s-1990s and peaked in top sediment layers. The ratio of α/γ-HCH decreased in the top layer sediments, implying that the contribution of lindane (pure γ-HCH) has been increasing in recent years. In addition, the ratio of o,p'-DDT/p,p'-DDT increased significantly over the last 15-20 years, suggesting that dicofol (characterized by high ratio of o,p'-DDT/p,p'-DDT about 7.0) has recently become a relatively more important source of DDT compared to technical DDT itself. The time trends of OCPs recorded in lake sediments examined the impact on such remote alpine regions by human activities.

Highly sensitive visible to infrared MoTe2 photodetectors enhanced by the photogating effect.

Two-dimensional materials are promising candidates for electronic and optoelectronic applications. MoTe2 has an appropriate bandgap for both visible and infrared light photodetection. Here we fabricate a high-performance photodetector based on few-layer MoTe2. Raman spectral properties have been studied for different thicknesses of MoTe2. The photodetector based on few-layer MoTe2 exhibits broad spectral range photodetection (0.6-1.55 µm) and a stable and fast photoresponse. The detectivity is calculated to be 3.1 × 10(9) cm Hz(1/2) W(-1) for 637 nm light and 1.3 × 10(9) cm Hz(1/2) W(-1) for 1060 nm light at a backgate voltage of 10 V. The mechanisms of photocurrent generation have been analyzed in detail, and it is considered that a photogating effect plays an important role in photodetection. The appreciable performance and detection over a broad spectral range make it a promising material for high-performance photodetectors.

Visible to short wavelength infrared In2Se3-nanoflake photodetector gated by a ferroelectric polymer.

Photodetectors based on two-dimensional (2D) transition-metal dichalcogenides have been studied extensively in recent years. However, the detective spectral ranges, dark current and response time are still unsatisfactory, even under high gate and source-drain bias. In this work, the photodetectors of In2Se3 have been fabricated on a ferroelectric field effect transistor structure. Based on this structure, high performance photodetectors have been achieved with a broad photoresponse spectrum (visible to 1550 nm) and quick response (200 µs). Most importantly, with the intrinsic huge electric field derived from the polarization of ferroelectric polymer (P(VDF-TrFE)) gating, a low dark current of the photodetector can be achieved without additional gate bias. These studies present a crucial step for further practical applications for 2D semiconductors.

Elemental composition of the topsoil fine fraction at and around the Tibetan plateau.

The <20 µm fractions of crusted topsoils on and around the Tibetan Plateau (TP) were analyzed to take a broad view of the composition of major elements (MEs, Al, Fe, and Mn) and twelve trace elements (TEs, As, Ba, Cd, Co, Cr, Cu, Ni, Pb, Sr, U, V, and Zn) and provide a crustal reference for environmental quality evaluation. The concentrations of most elements were generally higher in the Yarlung Zangbo River watershed (YZRW) and Pamirs but lower in the central Tibetan Plateau (CTP), Qaidam Basin (QB), and Tarim Basin (TB) due to the natural geochemical process. The concentrations of most elements in the five regions were higher than those of the upper continental crust (UCC), which was mainly affected by two natural factors. One was that the wide distribution of shale, schist, and phyllite on the TP led to the high concentrations of As and Cr. The other was that the concentrations of most elements in the <20 µm fractions of crusted topsoils were affected by particle sorting. Cu, Cd, As, and Pb in a few sites of the YZRW were influenced by local traffic emissions, mining operations, and increasing fossil fuel combustion over the past three decades (i.e., the 1980s-2010s). Furthermore, the values of crust‒referenced enrichment factor (EFucc) of most TEs (except Ba and Sr) in different environmental media with a high proportion of fine particles, such as aerosols, snow and ice cores, and river and lake sediments were generally 1.2-24.2 times greater than the values of fine fraction (<20 µm)‒referenced enrichment factor (EF < 20 µm), suggesting that the degree of anthropogenic effects on the TP environment should be overestimated in previous assessments using the UCC as the reference.

Short-term synaptic plasticity in emerging devices for neuromorphic computing.

Neuromorphic computing is a promising computing paradigm toward building next-generation artificial intelligence machines, in which diverse types of synaptic plasticity play an active role in information processing. Compared to long-term plasticity (LTP) forming the foundation of learning and memory, short-term plasticity (STP) is essential for critical computational functions. So far, the practical applications of LTP have been widely investigated, whereas the implementation of STP in hardware is still elusive. Here, we review the development of STP by bridging the physics in emerging devices and biological behaviors. We explore the computational functions of various STP in biology and review their recent progress. Finally, we discuss the main challenges of introducing STP into synaptic devices and offer the potential approaches to utilize STP to enrich systems' capabilities. This review is expected to provide prospective ideas for implementing STP in emerging devices and may promote the construction of high-level neuromorphic machines.

Dissolved inorganic carbon budget of two alpine catchments in the central Tibetan Plateau: Glaciation matters.

Dissolved inorganic carbon (DIC) fluxes account for over one-third of the total carbon transported in most rivers. The DIC budget for glacial meltwater of the Tibetan Plateau (TP), however, is still poorly understood, despite the fact, the TP has the largest glacier distribution outside of the Poles. In this study, the Niyaqu and Qugaqie catchments in the central TP were selected to examine the influence of glaciation on the DIC budget in vertical evasion (CO2 exchange rate at the water-air interface) and lateral transport (sources and fluxes) from 2016 to 2018. Significant seasonal variation in DIC concentration was found in the glaciated Qugaqie catchment, but was absent in the not glaciated Niyaqu catchment. δ13CDIC showed seasonal changes for both catchments, with more depleted signatures during the monsoon season. The average CO2 exchange rates in river water of Qugaqie were ~8 times lower compared to Niyaqu with values of -1294.6 ± 438.58 mg/m2/h and -163.4 ± 581.2 mg/m2/h, respectively, indicating that proglacial rivers can act as a substantial CO2 sink due to CO2 consumption by chemical weathering. DIC sources were quantified via the MixSIAR model using δ13CDIC and ionic ratios. During the monsoon season, the contribution from carbonate/silicate weathering driven by atmospheric CO2 was 13-15 % lower, while biogenic CO2 involved in chemical weathering was 9-15 % higher, indicating a seasonal control on weathering agents. Carbonate dissolution driven by H2SO4/HNO3 was the most important contributor to DIC in both catchments (40.7 ± 2.2 % in Niyaqu and 48.5 ± 3.1 % in Qugaqie). The net CO2 consumption rate in the not glaciated Niyaqu catchment was close to 0 (-0.07 ± 0.04 × 105 mol/km2/y), indicating the carbon sink effect caused by chemical weathering in this area was weak. The net CO2 consumption rate in the glaciated Qugaqie catchment, however, was much lower than that in the not glaciated catchment with a value of -0.28 ± 0.05 × 105 mol/km2/y. This study highlights that chemical weathering in small glaciated catchments of the central TP plays an active role in releasing CO2 to the atmosphere.

Regional and tele-connected impacts of the Tibetan Plateau surface darkening.

Despite knowledge of the presence of the Tibetan Plateau (TP) in reorganizing large-scale atmospheric circulation, it remains unclear how surface albedo darkening over TP will impact local glaciers and remote Asian monsoon systems. Here, we use a coupled land-atmosphere global climate model and a glacier model to address these questions. Under a high-emission scenario, TP surface albedo darkening will increase local temperature by 0.24 K by the end of this century. This warming will strengthen the elevated heat pump of TP, increasing South Asian monsoon precipitation while exacerbating the current "South Flood-North Drought" pattern over East Asia. The albedo darkening-induced climate change also leads to an accompanying TP glacier volume loss of 6.9%, which further increases to 25.2% at the equilibrium, with a notable loss in western TP. Our findings emphasize the importance of land-surface change responses in projecting future water resource availability, with important implications for water management policies.

Black soot and the survival of Tibetan glaciers.

We find evidence that black soot aerosols deposited on Tibetan glaciers have been a significant contributing factor to observed rapid glacier retreat. Reduced black soot emissions, in addition to reduced greenhouse gases, may be required to avoid demise of Himalayan glaciers and retain the benefits of glaciers for seasonal fresh water supplies.

Different patterns and origins between northwestern and southeastern Tibetan ice core glaciochemical records over the past century.

Atmospheric circulation systems differ between the northern and southern Tibetan Plateau (TP) and are characterized by prevailing westerly winds and the Indian monsoon, respectively. This leads to spatial differences between glaciochemical records in the northwestern and southeastern TP. We compared the spatial differences in major soluble ion concentrations (Ca2+, SO42-, NO3-, NH4+, Cl-, Na+, K+, and Mg2+) during the last century in the Aru (northwestern TP) and East Rongbuk (ER; southeastern TP) ice cores. Ca2+ exhibited the largest difference between the ice cores (2371 ppb in the Aru ice core and 65 ppb in the ER ice core), indicating that crustal processes were more dominant in the Aru ice core. NH4+ accounted for 17% of the total ion concentration in the ER ice core but only 3% in the Aru ice core, which may be related to the Indian monsoon traveling over NH3 emission zones in southern Asia. The major soluble ion concentrations exhibited decreasing trends in the Aru ice core but increasing trends in the ER ice core (P < 0.01). Empirical orthogonal function and backward trajectory analyses indicated that the major soluble ions in the Aru ice core originated from crustal sources in central Asia; those in the ER ice core had crustal, anthropogenic, and oceanic sources from southern Asia. The results from the Aru ice core suggest that dust events and enhanced prevailing westerly winds promoted the deposition of dust aerosols from the Taklamakan Desert and arid and semi-arid regions of central Asia. Contrastingly, the results from the ER ice core suggest that the Indian monsoon transported crustal and anthropogenic sources from southern Asia and oceanic sources from the Bay of Bengal and Arabian Sea. This study contributes to the comprehensive understanding of the differences in glaciochemical records and their causes between the northwestern and southeastern TP.