Optically stimulated synaptic transistor based on MoS2/quantum dots mixed-dimensional heterostructure with gate-tunable plasticity.

In this Letter, we report an optically stimulated synaptic transistor based on MoS2/quantum dots mixed-dimensional (MD) heterostructure, where the channel conductance shows a non-linear response to the optical stimuli. Paired-pulse facilitation is realized with the index above 200%, and the optical synaptic plasticity can be modulated by adjusting the amplitude, duration time, frequency, and power of light spikes. In addition, the long-term plasticity shows a gate-tunability, which can be attributed to the unique photoelectric coupling in MoS2/quantum dots MD heterostructure. This work opens up a new way to explore optically stimulated synaptic devices based on designed device structure and provides a feasible method to achieve plasticity modulation by gate voltage, which plays an important role in developing neuromorphic devices with complicated functions.

Gate stimulated high-performance MoS2-In(OH) x Se phototransistor.

Two-dimensional (2D) materials such as graphene and MoS2 have shown great potential in photodetection platforms. Photoresponsivity and photoresponse speed are two important parameters illustrating photodetector performances. Although various hybrid structures have been designed, the trade-off between photoresponsivity and photoresponse speed has not been well balanced. In this work, MoS2 film and In(OH) x Se nanoparticles are combined together to form the hybrid phototransistor. Utilizing both the photoconducting and photogating effects, the photoresponsivity increases about one order of magnitude with a value of 102 A W-1. The ratio of photocurrent and dark current increases to a value of 104. Considering the slow photo recovery speed, a 2 ms gate voltage pulse is applied after turning off the light, which results in a complete recovery of current. The photoconducting effect, photogating effect and gate voltage stimulation simultaneously promote the superior comprehensive photoresponse performances. This method can be further explored and utilized for realizing high performance photodetectors.

Locally hydrazine doped WSe2 p-n junction toward high-performance photodetectors.

Two dimensional (2D) materials have shown great potential in the photodetection and other optoelectronic applications. Exploiting 2D materials to form p-n junctions enables effective generation and separation of carriers excited by light, thus creating high-performance optoelectronic devices. This paper demonstrates a lateral WSe2 p-n junction through a locally hydrazine doping method. Good current-rectifying characteristics, including a high rectification ratio of ∼103, have been observed; this indicates that a high-quality p-n junction has been formed by chemical doping. Under light illumination, the device shows improved photoresponse capabilities with a responsivity of 30 mA W-1, a detectivity of 6.18 × 108 Jones, photocurrent/dark current ratio of 103 and a response time of 2 ms. These results suggest an effective way to get a p-n junction and reveal the application potential of the device for next generation photodetectors.

Adjustable hydrazine modulation of single-wall carbon nanotube network field effect transistors from p-type to n-type.

Single-wall carbon nanotube (SWCNT) network field effect transistors (FETs), which show decent p-type electronic properties, have been fabricated. The use of hydrazine as an aqueous solution and a strong n-type dopant for the SWCNTs is demonstrated in this paper. The electrical properties are obviously tuned by hydrazine treatment at different concentrations on the surface of the SWCNT network FETs. The transport behavior of SWCNTs can be modulated from p-type to n-type, demonstrating the controllable and adjustable doping effect of hydrazine. With a higher concentration of hydrazine, more electrons can be transferred from the hydrazine molecules to the SWCNT network films, thus resulting in a change of threshold voltage, carrier mobility and on-current. By cleaning the device, the hydrazine doping effects vanish, which indicates that the doping effects of hydrazine are reversible. Through x-ray photoelectron spectroscopy (XPS) characterization, the doping effects of hydrazine have also been studied.

Warm white light generation from a single phase Dy3+ doped Mg2Al4Si5O18 phosphor for white UV-LEDs.

A series of Mg2-xAl4Si5O18:xDy(3+) (0 ≤x≤ 0.18) samples were synthesized, for the first time, by a solid state method both in a reducing atmosphere and in air. XRD, diffuse reflectance spectra, excitation spectra, emission spectra, decay times and thermal quenching were used to investigate the structure, photoluminescence, energy transfer and thermal properties. The results show that Mg2Al4Si5O18:Dy(3+) can efficiently absorb UV light and emit violet-blue light in the range of 400 to 500 nm from oxygen vacancies in the host as well as blue light (∼480 nm) and yellow light (∼576 nm) from the f-f transitions of Dy(3+). The emission intensities of the samples obtained under a reducing atmosphere are far superior to those of the samples obtained in air due to an efficient energy transition from oxygen vacancies in the host to Dy(3+). An analysis of the thermal quenching shows that the phosphor Mg2Al4Si5O18:Dy(3+) has excellent thermal properties. The emission intensities of typical samples synthesized in a reducing atmosphere and in air at 250 °C are 70% and 81% of their initial intensities at 20 °C, respectively. In addition, the emission colors of all of the samples are located in the white light region and the optimal chromaticity coordinates and Correlated Color Temperature are (x = 0.34, y = 0.33) and 5129 K, respectively. Therefore, these white Mg2Al4Si5O18:Dy(3+) phosphors could serve as promising candidates for white-light UV-LEDs.

Variation Patterns of Hemoglobin Levels by Gestational Age during Pregnancy: A Cross-Sectional Analysis of a Multi-Center Retrospective Cohort Study in China.

BACKGROUND: Pregnancy anemia is a global health concern. However, to our knowledge, there still has little consensus on the reference value of hemoglobin levels. Particularly, little evidence from China was accessible in most existing guidelines. OBJECTIVE: To evaluate hemoglobin levels and anemia prevalence of pregnant women in China and offer evidence for anemia and its reference values in China. METHODS: A multi-center retrospective cohort study was conducted among 143,307 singleton pregnant women aged 15-49 at 139 hospitals in China, with hemoglobin concentrations routinely tested at each prenatal visit. Subsequently, a restricted cubic spline was performed to reveal a non-linear variation of hemoglobin concentrations during the gestational week. The Loess model was used to describe the changes in the prevalence of different degrees of anemia with gestational age. Multivariate linear regression model and Logistic regression model were applied to explore influencing factors of gestational changes in hemoglobin level and anemia prevalence, respectively. RESULTS: Hemoglobin varied nonlinearly with gestational age, and the mean hemoglobin levels decreased from 125.75 g/L in the first trimester to 118.71 g/L in the third trimester. By analyzing hemoglobin levels with gestational age and pregnancy period, we proposed new criteria according to 5th percentile hemoglobin concentration in each trimester as a reference for anemia, with 108 g/L, 103 g/L, and 99 g/L, respectively. According to WHO's criteria, the prevalence of anemia sustainably increased with gestational age, with 6.2% (4083/65,691) in the first trimester, 11.5% (7974/69,184) in the second trimester and 21.9% (12,295/56,042) in the third trimester, respectively. In subsequent analysis, pregnant women in non-urban residents, multiparity, and pre-pregnancy underweight tended to have lower hemoglobin levels. CONCLUSIONS: This research, the first large-sample study to present a set of gestational age-specific reference centiles for hemoglobin levels in China, could be used to obtain a better understanding of the overall levels of hemoglobin in Chinese healthy pregnant women and ultimately offer clues for a more precise hemoglobin reference value of anemia in China.

Risk of preeclampsia by gestational weight gain in women with varied prepregnancy BMI: A retrospective cohort study.

Introduction: Despite the important clinical significance, limited data on the joint contribution of prepregnancy body mass index (BMI) and gestational weight gain (GWG) to preeclampsia, the second leading cause of maternal mortality worldwide. This study aimed to estimate the risk of preeclampsia by GWG among women with varied prepregnancy BMI. Methods: We conducted a retrospective cohort study using data of 117 738 singleton pregnant women aged 18-49 years from 150 maternity hospitals in China between 2015 and 2018. GWG was calculated as the measured weight at the time of preeclampsia assessment minus prepregnancy weight; GWG velocity was calculated as the GWG divided by the gestational age at weighing. The non-linear associations of GWG with preeclampsia were examined by restricted cubic spline regression analysis according to prepregnancy BMI. The association of the GWG categories with preeclampsia was further examined by performing robust Poisson regression stratified by the prepregnancy BMI categories. Results: Among participants, 2426 (2.06%) were diagnosed with preeclampsia. Compared to women with normal BMI, those who were overweight and obese had 1.92- fold (95%CI, 1.73-2.14) and 5.06- fold (95%CI, 4.43-5.78) increased risks for preeclampsia, respectively. The association of GWG velocity with preeclampsia was presented as a J-shaped curve with the varied inflexion point (where the rate of preeclampsia was 2%), which was 0.54, 0.38, and 0.25 kg/week in women with normal BMI, overweight, and obesity, respectively; a steep risk rise was observed along with GWG velocity beyond the inflexion points. The overall adjusted relative risk for preeclampsia was calculated among women with the different GWG categories of GWG. Conclusions: The findings highlight that high prepregnancy BMI and exceed GWG contributed to increased risk of preeclampsia with a superimposed effect and underscore the need to optimize the recommendations for GWG for women with different prepregnancy BMI.

Association of Gestational Vitamin E Status With Pre-eclampsia: A Retrospective, Multicenter Cohort Study.

Introduction: Pre-eclampsia is the second leading cause of maternal mortality worldwide. The controversy for the association of vitamin E with pre-eclampsia has raged unabated for two decades. We aimed to determine the association of vitamin E level in the first trimester and the gestational change with pre-eclampsia. Materials and Methods: A retrospective cohort study was conducted among singleton pregnant women aged 15-49 years at 137 hospitals in China. Serum vitamin E concentrations in the first trimester and at pre-eclampsia assessment time were uniformly quantified in a laboratory by high performance liquid chromatography. Logistic regression models with restricted cubic splines were performed to reveal a non-linear association of vitamin E concentrations in the first trimester and the gestational change with pre-eclampsia. Results: We included 73 317 participants (47.8% aged 25-29 years) and 2.28% were diagnosed with pre-eclampsia. Higher risk was observed in those with lower concentration in the first trimester and greater gestational decrease, with a range from 0.81 to 80.60%. A non-linear L-shaped association was observed between vitamin E concentrations in the first trimester and pre-eclampsia, suggesting a threshold at 7.3 mg/L and a ceiling effect: the risk saw a steep rise when the concentrations in the first trimester were < 7.3 mg/L but was relatively flat beyond the inflection point. Sharply increased pre-eclampsia risk was also found in those with gestational vitamin E decrease after accounting for the baseline status in the first trimester. However, gestational vitamin E increase was associated with decreased pre-eclampsia risk when the baseline concentrations were < 7.3 mg/L but did not confer additional benefits when it was above the threshold. Conclusion: We demonstrated alarmingly high pre-eclampsia risk in women with vitamin E concentrations of < 7.3 mg/L in the first trimester and gestational vitamin E decrease. These findings underscore the need to supplement vitamin E among pregnant women with low baseline status.

Severity of Anemia During Pregnancy and Adverse Maternal and Fetal Outcomes.

Importance: Anemia is the most widespread nutritional deficiency among pregnant females in the world. Despite numerous studies on anemia, evidence is limited about the association of severity of anemia with maternal and fetal health. Objective: To investigate the association between severity of anemia during pregnancy and risk of maternal and fetal adverse outcomes. Design, Setting, and Participants: This retrospective cohort study used data from China's Hospital Quality Monitoring System from January 1, 2016, to December 31, 2019, for pregnant females aged 15 to 49 years with birth outcomes reported at 1508 hospitals with maternity services in mainland China. Exposures: Anemia of varying severity during pregnancy was identified from daily standardized electronic inpatient discharge records using corresponding codes of the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision. Mild anemia was defined as a hemoglobin concentration of 100 to 109 g/L (to convert g/L to g/dL, divide by 10.0); moderate anemia, as 70 to 99 g/L; and severe anemia, as less than 70 g/L. Main Outcomes and Measures: The main outcomes included 6 maternal outcomes (placental abruption, preterm birth, severe postpartum hemorrhage, shock, admission to the intensive care unit [ICU], and maternal mortality) and 3 neonatal outcomes (fetal growth restriction, malformation, and stillbirth). Multivariable logistic regression models were used to estimate the odds ratios (ORs) and 95% CIs of these outcomes among pregnant females with varying severity of anemia. Results: Among 18 948 443 pregnant females aged 15 to 49 years (mean [SD] age, 29.42 [4.87] years), 17.78% were diagnosed with anemia during pregnancy, including 9.04% with mild anemia, 2.62% with moderate anemia, 0.21% with severe anemia, and 5.90% with anemia of unknown severity. Compared with no anemia, anemia severity during pregnancy was associated with increased risks of placental abruption (mild: adjusted OR [aOR], 1.36 [95% CI, 1.34-1.38]; moderate: aOR, 1.98 [95% CI, 1.93-2.02]; severe: aOR, 3.35 [95% CI, 3.17-3.54]), preterm birth (mild: aOR, 1.08 [95% CI, 1.07-1.08]; moderate: aOR, 1.18 [95% CI, 1.17-1.19]; severe: aOR, 1.36 [95% CI, 1.32-1.41]), severe postpartum hemorrhage (mild: aOR, 1.45 [95% CI, 1.43-1.47]; moderate: aOR, 3.53 [95% CI, 3.47-3.60]; severe: 15.65 [95% CI, 15.10-16.22]), and fetal malformation (mild: aOR, 1.15 [95% CI, 1.14-1.17]; moderate: aOR, 1.19 [95% CI, 1.16-1.21]; severe: aOR, 1.62 [95% CI, 1.52-1.73]). Compared with no anemia, moderate or severe anemia were associated with increased risks of maternal shock (moderate: aOR, 1.50 [95% CI, 1.41-1.60]; severe: aOR, 14.98 [95% CI, 13.91-16.13]), ICU admission (moderate: aOR, 1.08 [95% CI, 1.01-1.16]; severe: aOR, 2.88 [95% CI, 2.55-3.25]), maternal death (moderate: aOR, 0.45 [95% CI, 0.30-0.65]; severe: aOR, 1.56 [95% CI, 0.97-2.48], fetal growth restriction (moderate: aOR, 0.80 [95% CI, 0.78-0.82]; severe: aOR, 1.08 [95% CI, 1.00-1.17]), and stillbirth (moderate: aOR,0.79 [95% CI, 0.76-0.81]; severe: aOR, 1.86 [95% CI, 1.75-1.98]), and mild anemia was associated with decreased risks (maternal shock: aOR, 0.67 [95% CI, 0.63-0.71]; ICU admission: aOR, 0.80 [95% CI, 0.76-0.84]; maternal death: aOR, 0.37 [95% CI, 0.29-0.49]; fetal growth restriction: aOR, 0.79 [95% CI, 0.77-0.80]; stillbirth: aOR, 0.59 [95% CI, 0.58-0.61]) after adjusting for sociodemographic characteristics and other complications during pregnancy. Conclusions and Relevance: The findings suggest that anemia during pregnancy is associated with maternal and fetal health outcomes and that mild anemia is associated with improved maternal and fetal survival and fetal growth. Further work is needed to validate the concentration of hemoglobin at which optimal maternal and fetal health are achieved.

Reduced Graphene Oxide/Mesoporous ZnO NSs Hybrid Fibers for Flexible, Stretchable, Twisted, and Wearable NO2 E-Textile Gas Sensor.

E-textiles are gaining growing popularity recently due to low cost, light weight, and conformable compatibility with clothes in wearable and portable smart electronics. Here, an easy-handing, low cost, and scalable fabricating strategy is reported to fabricate conductive, highly flexible, and mechanically stretchable/twisted fiber gas sensor with great wearability and knittability. The proposed gas sensor is built using commercially available cotton/elastic threads as flexible/stretchable templates and reduced graphene oxide/mesoporous zinc oxide nanosheets as sensing layers to form conducting fibers. The as-prepared fiber demonstrates sensitive sensing response, excellent long-term stability (84 days), low theoretical detection limit (43.5 ppb NO2), great mechanical deformation tolerance (3000 bending cycles, 1000 twisting cycles and 65% strain strength), and washing durability in room-temperature gas detection. More significantly, scalable wearable characteristics including repairability, reliability, stability, and practicability have been efficiently improved, which are achieved by knotting the fractured fibers, incorporating multiple sensors in series/parallel and weaving multisensor array networks integrated into clothes. The good sensing properties, superior flexibility, and scalable applications of wearable fibers may provide a broad window for widespread monitoring of numerous human activities in personal mobile electronics and human-machine interactions.

Thickness Tunable Wedding-Cake-like MoS2 Flakes for High-Performance Optoelectronics.

Atomically thin transition-metal dichalcogenides (TMDCs) have received substantial interest due to their typical thickness-dependent optical and electronic properties and related applications in optoelectronics. However, the large-scale, thickness-tunable growth of such materials is still challenging. Herein, we report a fast growth of thickness-tunable wedding-cake-like MoS2 flakes on 6-in. soda-lime glass by using NaCl-coated Mo foils as metal precursors. The MoS2 thicknesses are tuned from one layer (1L) to >20L by controlling the concentrations of NaCl promoter. To attest to the ultrahigh crystal quality, related devices based on 1L-multilayer MoS2 lateral junctions have been constructed and display a relatively high rectification ratio (∼103) and extra high photoresponsitivity (∼104 A/W). Thanks to the scalable sizes, uniform distributions of the flakes and homogeneous optical properties, the applications in ultraviolet (UV) irradiation filtering eyewear are also demonstrated. Our work should hereby propel the scalable production of layer-controlled TMDC materials as well as their optical and optoelectrical applications.

Light-Enhanced Ion Migration in Two-Dimensional Perovskite Single Crystals Revealed in Carbon Nanotubes/Two-Dimensional Perovskite Heterostructure and Its Photomemory Application.

Two-dimensional (2D) hybrid perovskite sandwiched between two long-chain organic layers is an emerging class of low-cost semiconductor materials with unique optical properties and improved moisture stability. Unlike conventional semiconductors, ion migration in perovskite is a unique phenomenon possibly responsible for long carrier lifetime, current-voltage hysteresis, and low-frequency giant dielectric response. While there are many studies of ion migration in bulk hybrid perovskite, not much is known for its 2D counterparts, especially for ion migration induced by light excitation. Here, we construct an exfoliated 2D perovskite/carbon nanotube (CNT) heterostructure field effect transistor (FET), not only to demonstrate its potential in photomemory applications, but also to study the light induced ion migration mechanisms. We show that the FET I-V characteristic curve can be regulated by light and shows two opposite trends under different CNT oxygen doping conditions. Our temperature-dependent study indicates that the change in the I-V curve is probably caused by ion redistribution in the 2D hybrid perovskite. The first principle calculation shows the reduction of the migration barrier of I vacancy under light excitation. The device simulation shows that the increase of 2D hybrid perovskite dielectric constant (enabled by the increased ion migration) can change the I-V curve in the trends observed experimentally. Finally, the so synthesized FET shows the multilevel photomemory function. Our work shows that not only we could understand the unique ion migration behavior in 2D hybrid perovskite, it might also be used for many future memory function related applications not realizable in traditional semiconductors.

All-Inorganic Perovskite Nanowires-InGaZnO Heterojunction for High-Performance Ultraviolet-Visible Photodetectors.

Inorganic cesium lead halide perovskites have attracted intense interest in optoelectronic applications due to the relatively stable performance in air. However, most reported inorganic perovskite-based optoelectronic devices exhibit low photosensitivity, which greatly hinders their further applications. Here, we first demonstrate a hybrid optical structure, which combines the n-type thin-film InGaZnO and the all-inorganic perovskite nanowires of CsPbBr3 together. By this way, excellent optical and electrical properties such as a low dark current of 10-10 A (at -5 V), a high Iph/Idark of 1.2 × 104, a response time of 2 ms and photoresponsivity of 3.794 A/W have been obtained. It is also found that the photodetector shows good stability in air ambient for 2 months with little reduction in performance. Moreover, such hybrid photodetectors exhibit enhanced photocurrent and Iph/Idark in high-temperature environment. This work paves a new way for high-performance photodetectors and points out the possible application of the inorganic cesium lead halide perovskites in harsh environment.

Sprayed, Scalable, Wearable, and Portable NO2 Sensor Array Using Fully Flexible AgNPs-All-Carbon Nanostructures.

Flexible chemical sensors usually require transfer of prepared layers or whole device onto special flexible substrates and further attachment to target objects, limiting the practical applications. Herein, a sprayed gas sensor array utilizing silver nanoparticles (AgNPs)-all-carbon hybrid nanostructures is introduced to enable direct device preparation on various target objects. The fully flexible device is formed using metallic single-walled carbon nanotubes as conductive electrodes and AgNPs-decorated reduced graphene oxide as sensing layers. The sensor presents sensitive response ( Ra/ Rg) of 6.0-20 ppm NO2, great mechanical robustness (3000 bending cycles), and obvious sensing ability as low as 0.2 ppm NO2 at room temperature. The sensitivity is about 3.3 and 13 times as that of the sample based on metal electrodes and the sample without AgNP decoration. The fabrication method demonstrates good scalability and suitability on the planar and nonplanar supports. The devices attached on a lab coat or the human body perform stable performance, indicating practicability in wearable and portable fields. The flexible and scalable sensor provides a new choice for real-time monitoring of toxic gases in personal mobile electronics and human-machine interactions.

Hybrid graphene/cadmium-free ZnSe/ZnS quantum dots phototransistors for UV detection.

Graphene-based optoelectronic devices have attracted much attention due to their broadband photon responsivity and fast response time. However, the performance of such graphene-based photodetectors is greatly limited by weak light absorption and low responsivity induced by the gapless nature of graphene. Here, we achieved a high responsivity above 103 AW-1 for Ultraviolet (UV) light in a hybrid structure based phototransistor, which consists of CVD-grown monolayer graphene and ZnSe/ZnS core/shell quantum dots. The photodetectors exhibit a selective photo responsivity for the UV light with the wavelength of 405 nm, confirming the main light absorption from QDs. The photo-generated charges have been found to transfer from QDs to graphene channel, leading to a gate-tunable photo responsivity with the maximum value obtained at V G about 15V. A recirculate 100 times behavior with a good stability of 21 days is demonstrated for our devices and another flexible graphene/QDs based photoconductors have been found to be functional after 1000 bending cycles. Such UV photodetectors based on graphene decorated with cadmium-free ZnSe/ZnS quantum dots offer a new way to build environmental friendly optoelectronics.

Lateral multilayer/monolayer MoS2 heterojunction for high performance photodetector applications.

Inspired by the unique, thickness-dependent energy band structure of 2D materials, we study the electronic and optical properties of the photodetector based on the as-exfoliated lateral multilayer/monolayer MoS2 heterojunction. Good gate-tunable current-rectifying characteristics are observed with a rectification ratio of 103 at V gs = 10 V, which may offer an evidence on the existence of the heterojunction. Upon illumination from ultraviolet to visible light, the multilayer/monolayer MoS2 heterojunction shows outstanding photodetective performance, with a photoresponsivity of 103 A/W, a photosensitivity of 1.7 × 105 and a detectivity of 7 × 1010 Jones at 470 nm light illumination. Abnormal photoresponse under positive gate voltage is observed and analyzed, which indicates the important role of the heterojunction in the photocurrent generation process. We believe that these results contribute to a better understanding on the fundamental physics of band alignment for multilayer/monolayer MoS2 heterojunction and provide us a feasible solution for novel electronic and optoelectronic devices.

Organic Dye-Sensitized CH3NH3PbI3 Hybrid Flexible Photodetector with Bulk Heterojunction Architectures.

A flexible photodetector based on the bulk heterojunction of an organometallic halide perovskites CH3NH3PbI3 and an organic dye Rhodamine B (RhB) has been fabricated via a solution casting process. It showed a high responsivity (Rmax = 43.6 mA/W) to visible lights, short response time (tr ≈ 60 ms, td ≈ 40 ms), high on-off ratio (Ion/Ioff ≈ 287) and satisfactory stability because of its Schottky barrier structure and the dye enhanced light absorption.