A floating-gate field-effect transistor memory device based on organic crystals with a built-in tunneling dielectric by a one-step growth strategy.

A floating-gate organic field-effect transistor (FG-OFET) memory device is becoming a promising candidate for emerging non-volatile memory applications due to the advantages of its sophisticated data-storage mechanism and reliable long-term data retention capacity. However, a conventional FG-OFET memory device suffers from complex fabrication technologies and poor mechanical flexibility, which limits its practical applications. Here, we propose a facile one-step liquid-surface drag coating strategy to fabricate a layered stack of 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (Dif-TES-ADT) crystals and high-quality insulating polymer polystyrene (PS). The liquid surface enhances the spreading area of an organic solution and facilitates the unidirectional growth of organic crystals. In the bilayer-structured blend, the bottom PS polymer and the top Dif-TES-ADT semiconductor serve as a tunneling dielectric and an active memory layer of an FG-OFET memory device, respectively. Consequently, a flexible FG-OFET memory device with a large memory window of 41.4 V, a long retention time of 5000 s, and a high current ON/OFF ratio of 105 could be achieved, showing the best performance ever reported for organic thin film-based FG-OFET memory devices. In addition, multi-level data storage (3 bits per cell) can be achieved by tuning the gate voltage magnitude. Our work not only provides a general strategy for the growth of high-quality organic crystals, but also paves the way towards high-performance flexible memory devices.

Influence of Morphological Characteristics of Coarse Aggregates on Skid Resistance of Asphalt Pavement.

This research aims to improve the durability of skid resistance of asphalt pavement from the perspective of coarse aggregates based on on-site investigation. Firstly, the skid resistance of six representative actual roads was tested during two years by employing the Dynamic Friction Tester and the attenuation characteristics of skid resistance of different types of asphalt pavements were analyzed. Secondly, core samples were drilled onsite and coarse aggregates were extracted from the surface layer of the core samples. The morphological parameters of coarse aggregates were collected by a "backlighting photography" system and three-dimensional profilometer, and the variation rules of angularity and micro-texture of coarse aggregates were investigated. Finally, the correlation between the morphological characteristics of coarse aggregates and the pavement skid resistance was established based on the grey correlation entropy. The research results show that with the increase in service time, the attenuation rate of skid resistance of asphalt pavement gradually slows down; the angularity of coarse aggregates gradually decreases, and the micro-texture on the wearing surface gradually wears away. The grey correlation entropy between all the micro-texture indexes of coarse aggregates and dynamic friction coefficient, as well as between the roundness and skid resistance is more than 0.7, whereas the correlation between other evaluation indicators and the dynamic friction coefficient is poor, indicating that compared with the angularity of coarse aggregates, the micro-texture affects the skid resistance of actual asphalt pavement more greatly. In engineering applications, the use of coarse gradation, coarse aggregates with high roughness or high anti-wear performance can slow down the attenuation of pavement skid resistance, so that the pavement can maintain superior long-term anti-skidding performance.

Activation of buried p-GaN through nanopipes in large-size GaN-based tunnel junction LEDs.

In GaN-based light-emitting diodes (LEDs), tunnel junctions offer a way of replacing the highly resistive p-type GaN (p-GaN) ohmic contact with a low-resistance n-GaN ohmic contact. However, the p-GaN would be re-passivated by hydrogen atoms during the subsequent growth of n-GaN in a metal-organic chemical vapor deposition (MOCVD) chamber. The n-GaN layer, acting as a hydrogen diffusion barrier, hinders the thermal activation of the underlying p-GaN. Here, we report a method to thermally activate the buried p-GaN in tunnel junction LED (TJ-LED) through vertically aligned nanopipe arrays across the top n-GaN layer, which provides a hydrogen outgassing passage. The fabrication of nanopipes is realized via inductive coupled plasma etching using a mask prepared by self-assembled nanosphere arrays. As a result, we attain large-size TJ-LED chips, exhibiting nearly equivalent p-GaN activation and superior light extraction compared to conventional LEDs. Specifically, the light extraction efficiency is boosted by 44% relative to conventional LEDs at an injection current density of 100 A cm-2.

CaCl2-Promoted Dehydroxytrifluoromethylselenolation of Alcohols with [Me4N][SeCF3].

A direct trifluoromethylselenolation of alcohols with the readily accessible [Me4N][SeCF3] salt has been reported. The reaction is significantly promoted by CaCl2 and proceeds smoothly through unprecedented carbonoselenoate intermediates to form the corresponding alkyl trifluoromethyl selenoethers in good yields. This protocol is also applicable to the late-stage dehydroxytrifluoromethylselenolation of complex alcohols owing to its mildness, good compatibility, high efficiency, and broad functional group tolerance.

High-Performance Nanofloating Gate Memory Based on Lead Halide Perovskite Nanocrystals.

Lead halide perovskites have been extensively investigated in a host of optoelectronic devices, such as solar cells, light-emitting diodes, and photodetectors. The halogen vacancy defects arising from the halogen-poor growth environment are normally regarded as an unfavorable factor to restrict the device performance. Here, for the first time, we demonstrate the utilization of the vacancy defects in lead halide perovskite nanostructures for achieving high-performance nanofloating gate memories (NFGMs). CH3NH3PbBr3 nanocrystals (NCs) were uniformly decorated on the CdS nanoribbon (NR) surface via a facile dip-coating process, forming a CdS NR/CH3NH3PbBr3 NC core-shell structure. Significantly, owing to the existence of sufficient carrier trapping states in CH3NH3PbBr3 NCs, the hybrid device possessed an ultralarge memory window up to 77.4 V, a long retention time of 12 000 s, a high current ON/OFF ratio of 7 × 107, and a long-term air stability for 50 days. The memory window of the device is among the highest for the low-dimensional nanostructure-based NFGMs. Also, this strategy shows good universality and can be extended to other perovskite nanostructures for the construction of high-performance NFGMs. This work paves the way toward the fabrication of new-generation, high-capacity nonvolatile memories using lead halide perovskite nanostructures.

Memory phototransistors based on exponential-association photoelectric conversion law.

Ultraweak light detectors have wide-ranging important applications such as astronomical observation, remote sensing, laser ranging, and night vision. Current commercial ultraweak light detectors are commonly based on a photomultiplier tube or an avalanche photodiode, and they are incompatible with microelectronic devices for digital imaging applications, because of their high operating voltage and bulky size. Herein, we develop a memory phototransistor for ultraweak light detection, by exploiting the charge-storage accumulative effect in CdS nanoribbon. The memory phototransistors break the power law of traditional photodetectors and follow a time-dependent exponential-association photoelectric conversion law. Significantly, the memory phototransistors exhibit ultrahigh responsivity of 3.8 × 109 A W-1 and detectivity of 7.7 × 1022 Jones. As a result, the memory phototransistors are able to detect ultraweak light of 6 nW cm-2 with an extremely high sensitivity of 4 × 107. The proposed memory phototransistors offer a design concept for ultraweak light sensing devices.

[Design of longitudinal auto-tracking of the detector on X-ray in digital radiography].

One algorithm is designed to implement longitudinal auto-tracking of the the detector on X-ray in the digital radiography system (DR) with manual collimator. In this study, when the longitudinal length of field of view (LFOV) on the detector is coincided with the longitudinal effective imaging size of the detector, the collimator half open angle ( Ψ), the maximum centric distance ( emax) between the center of X-ray field of view and the projection center of the focal spot, and the detector moving distance for auto-traking can be calculated automatically. When LFOV is smaller than the longitudinal effective imaging size of the detector by reducing Ψ, the emax can still be used to calculate the detector moving distance. Using this auto-tracking algorithm in DR with manual collimator, the tested results show that the X-ray projection is totally covered by the effective imaging area of the detector, although the center of the field of view is not aligned with the center of the effective imaging area of the detector. As a simple and low-cost design, the algorithm can be used for longitudinal auto-tracking of the detector on X-ray in the manual collimator DR.

The Ternary Heterostructures of BiOBr/Ultrathin g-C3N4/Black Phosphorous Quantum Dot Composites for Photodegradation of Tetracycline.

Herein, we synthesized BiOBr/ultrathin g-C3N4/ternary heterostructures modified with black phosphorous quantum dots using a simple water bath heating and sonication method. The ternary heterostructure was then used for the photocatalytic degradation of tetracycline in visible light, with an efficiency as high as 92% after 3 h of irradiation. Thus, the photodegradation efficiency is greatly improved compared to that of ultrathin g-C3N4, BiOBr, and black phosphorous quantum dots alone. The synthesized ternary heterostructure improves the charge separation efficiency, thus increasing the photodegradation efficiency. This work provides a new and efficient method for the degradation of antibiotics in the environment.

Surface Charge Transfer Doping via Transition Metal Oxides for Efficient p-Type Doping of II-VI Nanostructures.

Wide band gap II-VI nanostructures are important building blocks for new-generation electronic and optoelectronic devices. However, the difficulty of realizing p-type conductivity in these materials via conventional doping methods has severely handicapped the fabrication of p-n homojunctions and complementary circuits, which are the fundamental components for high-performance devices. Herein, by using first-principles density functional theory calculations, we demonstrated a simple yet efficient way to achieve controlled p-type doping on II-VI nanostructures via surface charge transfer doping (SCTD) using high work function transition metal oxides such as MoO3, WO3, CrO3, and V2O5 as dopants. Our calculations revealed that these oxides were capable of drawing electrons from II-VI nanostructures, leading to accumulation of positive charges (holes injection) in the II-VI nanostructures. As a result, Fermi levels of the II-VI nanostructures were shifted toward the valence band regions after surface modifications, along with the large enhancement of work functions. In situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy characterizations verified the significant interfacial charge transfer between II-VI nanostructures and surface dopants. Both theoretical calculations and electrical transfer measurements on the II-VI nanostructure-based field-effect transistors clearly showed the p-type conductivity of the nanostructures after surface modifications. Strikingly, II-VI nanowires could undergo semiconductor-to-metal transition by further increasing the SCTD level. SCTD offers the possibility to create a variety of electronic and optoelectronic devices from the II-VI nanostructures via realization of complementary doping.