Gap State-Modulated Van Der Waals Short-Term Memory with Broad Band Negative Photoconductance.

Floating gate memory (FGM), composed of van der Waals (vdW) junctions with an atomically thin floating layer for charge storage, is widely employed to develop logic-in memories and in-sensor computing devices. Most research efforts of FGM are spent on achieving long-term charge storage and fast reading/writing for flash and random-access memory. However, dynamic modulation of memory time via a tunneling barrier and vdW interfaces, which is critical for synaptic computing and machine vision, is still lacking. Here, a van der Waals short-term memory with tunable memory windows and retention times from milliseconds to thousands of seconds is reported, which is approximately exponentially proportional to the thickness h-BN (hexagonal boron nitride) barrier. The specific h-BN barrier with fruitful gap states provides charge release channels for trapped charges, making the vdW device switchable between positive photoconductance and negative photoconductance with a broadband light from IR to UV range. The dynamic short-term memory with tunable photo response highlights the design strategy of novel vdW memory vis interface engineering for further intelligent information storage and optoelectronic detection.

Ultrathin Ruddlesden-Popper Perovskite Heterojunction for Sensitive Photodetection.

Thanks to their unique optical and electric properties, 2D materials have attracted a lot of interest for optoelectronic applications. Here, the emerging 2D materials, organic-inorganic hybrid perovskites with van der Waals interlayer interaction (Ruddlesden-Popper perovskites), are synthesized and characterized. Photodetectors based on the few-layer Ruddlesden-Popper perovskite show good photoresponsivity as well as good detectivity. In order to further improve the photoresponse performance, 2D MoS2 is chosen to construct the perovskite-MoS2 heterojunction. The performance of the hybrid photodetector is largely improved with 6 and 2 orders of magnitude enhancement for photoresponsivity (104 A W-1 ) and detectivity (4 × 1010 Jones), respectively, which demonstrates the facile charge separation at the interface between perovskite and MoS2 . Furthermore, the contribution of back gate tuning is proved with a greatly reduced dark current. The results demonstrated here will open up a new field for the investigation of 2D perovskites for optoelectronic applications.

Giant Enhancement of Cathodoluminescence of Monolayer Transitional Metal Dichalcogenides Semiconductors.

Monolayer two-dimensional transitional metal dichalcogenides, such as MoS2, WS2, and WSe2, are direct band gap semiconductors with large exciton binding energy. They attract growing attentions for optoelectronic applications including solar cells, photodetectors, light-emitting diodes and phototransistors, capacitive energy storage, photodynamic cancer therapy, and sensing on flexible platforms. While light-induced luminescence has been widely studied, luminescence induced by injection of free electrons could promise another important applications of these new materials. However, cathodoluminescence is inefficient due to the low cross-section of the electron-hole creating process in the monolayers. Here for the first time we show that cathodoluminescence of monolayer chalcogenide semiconductors can be evidently observed in a van der Waals heterostructure when the monolayer semiconductor is sandwiched between layers of hexagonal boron nitride (hBN) with higher energy gap. The emission intensity shows a strong dependence on the thicknesses of surrounding layers and the enhancement factor is more than 500-fold. Strain-induced exciton peak shift in the suspended heterostructure is also investigated by the cathodoluminescence spectroscopy. Our results demonstrate that MoS2, WS2, and WSe2 could be promising cathodoluminescent materials for applications in single-photon emitters, high-energy particle detectors, transmission electron microscope displays, surface-conduction electron-emitter, and field emission display technologies.

Investigation on the interaction of letrozole with herring sperm DNA through spectroscopic and modeling methods.

The interaction of letrozole, an efficient and safe aromatase inhibitor, with herring sperm DNA (hsDNA) was investigated in vitro through spectroscopy analysis and molecular modeling to elucidate the binding mechanism of anticancer drugs and DNA. The binding constant and the number of binding sites were 2.13 × 10(4) M(-1) and 1.09, respectively, at 298 K. Thermodynamic parameters (ΔG, ΔH and ΔS) exhibited negative values, which indicated that binding was spontaneous and Van der Waals forces and hydrogen bond were the main interaction forces. Fourier transform infrared spectroscopy and other spectroscopy analysis methods illustrated that letrozole could intercalate into the phosphate backbone of hsDNA and interact with the nitrogenous bases. Consistent with the experimental findings, molecular modeling results demonstrated that the interaction was dominated by intercalation and hydrogen bonding. Copyright © 2015 John Wiley & Sons, Ltd.

Chemical compounds from Osmunda japonica and their NO inhibitory activity.

Two new compounds, osmjapterpenoid A (1) and osmunjaponin A (2), along with twenty-six known compounds, were isolated from the roots and rhizomes of Osmunda japonica Thunb. The chemical structures of them were elaborated by extensive spectroscopic means, including 1D, 2D-NMR and HR-ESI-MS. Compound 1 is a diterpenoid derived from cembrane with a novel skeleton of 5/13 dicyclic ring system. The possible biogentic pathway of 1 was deduced. Compounds 3 and 26 exhibited moderate inhibition on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 macrophages with IC50 value of 32.09 and 19.81 µM, respectively.

Spin-Selective Memtransistors with Magnetized Graphene.

Spin-polarized bands in pristine and proximity-induced magnetic materials are promising building blocks for future devices. Conceptually new memory, logic, and neuromorphic devices are conceived based on atomically thin magnetic materials and the manipulation of their spin-polarized bands via electrical and optical methods. A critical remaining issue is the direct probe and the optimized use of the magnetic coupling effect in van der Waals heterostructures, which requires further delicate design of atomically thin magnetic materials and devices. Here, a spin-selective memtransistor with magnetized single-layered graphene on a reactive antiferromagnetic material, CrI3, is reported. The spin-dependent hybridization between graphene and CrI3 atomic layers enables the spin-selective bandgap opening in the single-layered graphene and the electric field control of magnetization in a specific CrI3 layer. The microscopic working principle is clarified by the first-principles calculations and theoretical analysis of the transport data. Reliable memtransistor operations (i.e., memory and logic device-combined operations), as well as a spin-selective probe of Landau levels in the magnetized graphene, are achieved by using the subtle manipulation of the magnetic proximity effect via electrical means.

A Universal Strategy for Synthesis of 2D Ternary Transition Metal Phosphorous Chalcogenides.

The 2D ternary transition metal phosphorous chalcogenides (TMPCs) have attracted extensive research interest due to their widely tunable band gap, rich electronic properties, inherent magnetic and ferroelectric properties. However, the synthesis of TMPCs via chemical vapor deposition (CVD) is still challenging since it is difficult to control reactions among multi-precursors. Here, a subtractive element growth mechanism is proposed to controllably synthesize the TMPCs. Based on the growth mechanism, the TMPCs including FePS3 , FePSe3 , MnPS3 , MnPSe3 , CdPS3 , CdPSe3 , In2 P3 S9 , and SnPS3 are achieved successfully and further confirmed by Raman, second-harmonic generation (SHG), and scanning transmission electron microscopy (STEM). The typical TMPCs-SnPS3 shows a strong SHG signal at 1064 nm, with an effective nonlinear susceptibility χ(2) of 8.41 × 10-11  m V-1 , which is about 8 times of that in MoS2 . And the photodetector based on CdPSe3 exhibits superior detection performances with responsivity of 582 mA W-1 , high detectivity of 3.19 × 1011  Jones, and fast rise time of 611 µs, which is better than most previously reported TMPCs-based photodetectors. These results demonstrate the high quality of TMPCs and promote the exploration of the optical properties of 2D TMPCs for their applications in optoelectronics.

Chemical Vapor Deposition Synthesis of Intrinsic High-Temperature Ferroelectric 2D CuCrSe2.

Ultrathin 2D ferroelectrics with high Curie temperature are critical for multifunctional ferroelectric devices. However, the ferroelectric spontaneous polarization is consistently broken by the strong thermal fluctuations at high temperature, resulting in the rare discovery of high-temperature ferroelectricity in 2D materials. Here, a chemical vapor deposition method is reported to synthesize 2D CuCrSe2 nanosheets. The crystal structure is confirmed by scanning transmission electron microscopy characterization. The measured ferroelectric phase transition temperature of ultrathin CuCrSe2 is about ≈800 K. Significantly, the switchable ferroelectric polarization is observed in ≈5.2 nm nanosheet. Moreover, the in-plane and out-of-plane ferroelectric response are modulated by different maximum bias voltage. This work provides a new insight into the construction of 2D ferroelectrics with high Curie temperature.

Pyroelectric effect in green light-assisted domain reversal of Mg-doped LiNbO3 crystals.

We developed a real-time imaging system to probe the light-assisted domain reversal process of Mg-doped LiNbO(3). An interesting phenomenon was observed where the domain appeared to reverse just after the laser was obscured. An exclusive electric field of about 350 V/mm was measured at 532 nm of light irradiation at an intensity of 6.6 × 10(4) W/cm(2). The exclusive electric field was considered to be produced by a pyroelectric effect owing to a temperature change in the region of irradiation. The temperature change in the light-irradiated region was calculated to be about 2.3°C. Our experimental results indicate that a change of the electric field caused by the pyroelectric effect may play a significant role when LiNbO(3) or other ferroelectric crystals are used under strong light.

Orbital Gating Driven by Giant Stark Effect in Tunneling Phototransistors.

Conventional gating in transistors uses electric fields through external dielectrics that require complex fabrication processes. Various optoelectronic devices deploy photogating by electric fields from trapped charges in neighbor nanoparticles or dielectrics under light illumination. Orbital gating driven by giant Stark effect is demonstrated in tunneling phototransistors based on 2H-MoTe2 without using external gating bias or slow charge trapping dynamics in photogating. The original self-gating by light illumination modulates the interlayer potential gradient by switching on and off the giant Stark effect where the dz 2-orbitals of molybdenum atoms play the dominant role. The orbital gating shifts the electronic bands of the top atomic layer of the MoTe2 by up to 100 meV, which is equivalent to modulation of a carrier density of 7.3 × 1011 cm-2 by electrical gating. Suppressing conventional photoconductivity, the orbital gating in tunneling phototransistors achieves low dark current, practical photoresponsivity (3357 AW-1 ), and fast switching time (0.5 ms) simultaneously.

Harnessing Thermoelectric Puddles via the Stacking Order and Electronic Screening in Graphene.

Thermoelectricity has been investigated mostly on the macroscopic scale despite the fact that its origin is linked to the local electronic band structure of materials. While the role of thermopower from microscopic structures (e.g., surfaces or grain boundaries) increases for emerging thermoelectric materials, manipulating thermoelectric puddles, spatially varying levels of thermoelectric power on the nanometer scale, remains unexplored. Here, we illustrate thermoelectric puddles that can be harnessed via the stacking order and electronic screening in graphene. The local thermoelectric elements were investigated by gate-tunable scanning thermoelectric microscopy on the atomic scale, revealing the roles of local lattice symmetry, impurity charge scatterings, and mechanical strains in the thermopower system. The long-range screening of electrons at the Dirac point in graphene, which could be reached by in-operando spectroscopy, allowed us to unveil distinct thermoelectric puddles in the graphene that are susceptible to the stacking order and external strain. Thus, manipulating thermoelectric puddles via a lattice symmetry and electronic engineering will realize practical thermopower systems with low-dimensional materials.

Robust Quantum Oscillation of Dirac Fermions in a Single-Defect Resonant Transistor.

The massless nature of Dirac Fermions produces large energy gaps between Landau levels (LLs), which is promising for topological devices. While the energy gap between the zeroth and first LLs reaches 36 meV in a magnetic field of 1 T in graphene, exploiting the quantum Hall effect at room temperature requires large magnetic fields (∼30 T) to overcome the energy level broadening induced by charge inhomogeneities in the device. Here, we report a way to use the robust quantum oscillations of Dirac Fermions in a single-defect resonant transistor, which is based on local tunneling through a thin (∼1.4 nm) hexagonal boron nitride (h-BN) between lattice-orientation-aligned graphene layers. A single point defect in the h-BN, selected by the orientation-tuned graphene layers, probes local LLs in its proximity, minimizing the energy broadening of the LLs by charge inhomogeneity at a moderate magnetic field and ambient conditions. Thus, the resonant tunneling between lattice-orientation-aligned graphene layers highlights the potential to spectroscopically locate the atomic defects in the h-BN, which contributes to the study on electrically tunable single photon source via defect states in h-BN.

In-sensor reservoir computing for language learning via two-dimensional memristors.

The dynamic processing of optoelectronic signals carrying temporal and sequential information is critical to various machine learning applications including language processing and computer vision. Despite extensive efforts to emulate the visual cortex of human brain, large energy/time overhead and extra hardware costs are incurred by the physically separated sensing, memory, and processing units. The challenge is further intensified by the tedious training of conventional recurrent neural networks for edge deployment. Here, we report in-sensor reservoir computing for language learning. High dimensionality, nonlinearity, and fading memory for the in-sensor reservoir were achieved via two-dimensional memristors based on tin sulfide (SnS), uniquely having dual-type defect states associated with Sn and S vacancies. Our in-sensor reservoir computing demonstrates an accuracy of 91% to classify short sentences of language, thus shedding light on a low training cost and the real-time solution for processing temporal and sequential signals for machine learning applications at the edge.

Resonant Tunneling Spectroscopy to Probe the Giant Stark Effect in Atomically Thin Materials.

Each atomic layer in van der Waals heterostructures possesses a distinct electronic band structure that can be manipulated for unique device operations. In the precise device architecture, the subtle but critical band splits by the giant Stark effect between atomic layers, varied by the momentum of electrons and external electric fields in device operation, has not yet been demonstrated or applied to design original devices with the full potential of atomically thin materials. Here, resonant tunneling spectroscopy based on the negligible quantum capacitance of 2D semiconductors in resonant tunneling transistors is reported. The bandgaps and sub-band structures of various channel materials could be demonstrated by the new conceptual spectroscopy at the device scale without debatable quasiparticle effects. Moreover, the band splits by the giant Stark effect in the channel materials could be probed, overcoming the limitations of conventional optical, photoemission, and tunneling spectroscopy. The resonant tunneling spectroscopy reveals essential and practical information for novel device applications.

Synthesis and discovery of new compounds bearing coumarin scaffold for the treatment of pulmonary fibrosis.

Idiopathic pulmonary fibrosis, characterized by excess accumulation of extracellular matrix, involved in many chronic diseases or injuries, threatens human health greatly. We have reported a series of compounds bearing coumarin scaffold which potently inhibited TGF-ß-induced total collagen accumulation in NRK-49F cell line and migration of macrophages. Compound 9d also suppressed the TGF-ß-induced protein expression of COL1A1, α-SMA, and p-Smad3 in vitro. Meanwhile, 9d at a dose of 100 mg/kg/day through oral administrations for 4 weeks effectively alleviated infiltration of inflammatory cells in lung tissue and fibrotic degree in bleomycin-induced pulmonary fibrosis model, which may related to its inhibition of TGF-ß/Smad3 pathway and anti-inflammation efficacy. In addition, 9d demonstrated decent bioavailability (F = 39.88%) and suitable eliminated half-life time (T1/2 = 13.09 h), suggesting that 9d could be a potential drug candidate for the treatment of fibrotic diseases.

Design, synthesis and discovery of 2(1H)-quinolone derivatives for the treatment of pulmonary fibrosis through inhibition of TGF-ß/smad dependent and independent pathway.

Idiopathic pulmonary fibrosis (IPF) is a progressive, life-threatening and interstitial lung disease with the median survival of only 3-5 years. However, due to the unclear etiology and problems in accurate diagnosis, up to now only two drugs were approved by FDA for the treatment of IPF and their outcome responses are limited. Numerous studies have shown that TGF-ß is the most important cytokine in the development of pulmonary fibrosis and plays a role through its downstream signaling molecule TGF-binding receptor Smads protein. In this paper, compounds bearing 2(1H)-quinolone scaffold were designed and their anti-fibrosis effects were evaluated. Of these compounds, 20f was identified as the most active one and could inhibit TGF-ß-induced collagen deposition of NRK-49F cells and mouse fibroblasts migration with comparable activity and lower cytotoxicity than nintedanib in vitro. Further mechanism studies indicated that 20f reduced the expression of fibrogenic phenotypic protein α-SMA and collagen Ⅰ by inhibiting the TGF-ß/Smad dependent pathways and ERK1/2 and p38 pathways. Moreover, compared with the nintedanib, 20f (100 mg/kg/day, p.o) more effectively alleviated collagen deposition in lung tissue and delayed the destruction of lung tissue structure both in bleomycin-induced prevention and treatment mice pulmonary fibrosis models. The immunohistochemical experiments further showed that 20f could block the expression level of phosphorylated Smad3 in the lung tissue cells, which resulted in its anti-fibrosis effects in vivo. In addition, 20f demonstrated good bioavailability (F = 41.55% vs 12%, compare with nintedanib) and an appropriate elimination half-life (T1/2 = 3.5 h), suggesting that 20f may be a potential drug candidate for the treatment of pulmonary fibrosis.

Purinostat Mesylate Is a Uniquely Potent and Selective Inhibitor of HDACs for the Treatment of BCR-ABL-Induced B-Cell Acute Lymphoblastic Leukemia.

PURPOSE: This study was to perform preclinical evaluation of a novel class I and IIb HDAC-selective inhibitor, purinostat mesylate, for the treatment of Ph+ B-cell acute lymphoblastic leukemia (B-ALL). EXPERIMENTAL DESIGN: Biochemical assays were used to test enzymatic activity inhibition of purinostat mesylate. Ph+ leukemic cell lines and patient cells were used to evaluate purinostat mesylate activity in vitro. BL-2 secondary transplantation Ph+ B-ALL mouse model was used to validate its efficacy, mechanism, and pharmacokinetics properties in vivo. BCR-ABL(T315I)-induced primary B-ALL mouse model and PDX mouse model derived from relapsed Ph+ B-ALL patient post TKI treatment were used to determine the antitumor effect of purinostat mesylate for refractory or relapsed Ph+ B-ALL. Long-term toxicity and hERG blockade assays were used to safety evaluation of purinostat mesylate. RESULTS: Purinostat mesylate, a class I and IIb HDAC highly selective inhibitor, exhibited robust antitumor activity in hematologic cancers. Purinostat mesylate at low nanomolar concentration induced apoptosis, and downregulated BCR-ABL and c-MYC expression in Ph+ leukemia cell lines and primary Ph+ B-ALL cells from relapsed patients. Purinostat mesylate efficiently attenuated Ph+ B-ALL progression and significantly prolonged the survival both in BL-2 secondary transplantation model with clinical patient symptoms of Ph+ B-ALL, BCR-ABL(T315I)-induced primary B-ALL mouse model, and PDX model derived from patients with relapsed Ph+ B-ALL post TKI treatment. In addition, purinostat mesylate possesses favorable pharmacokinetics and low toxicity properties. CONCLUSIONS: Purinostat mesylate provides a new therapeutic strategy for patients with Ph+ B-ALL, including those who relapse after TKI treatment.

Light-Tunable 1T-TaS2 Charge-Density-Wave Oscillators.

External stimuli-controlled phase transitions are essential for fundamental physics and design of functional devices. Charge density wave (CDW) is a metastable collective electronic phase featured by the periodic lattice distortion. Much attention has been attracted to study the external control of CDW phases. Although much work has been done in the electric-field-induced CDW transition, the study of the role of Joule heating in the phase transition is insufficient. Here, using the Raman spectroscopy, the electric-field-driven phase transition is in situ observed in the ultrathin 1T-TaS2. By quantitative evaluation of the Joule heating effect in the electric-field-induced CDW transition, it is shown that Joule heating plays a secondary role in the nearly commensurate (NC) to incommensurate (IC) CDW transition, while it dominants the IC-NC CDW transition, providing a better understanding of the electric field-induced phase transition. More importantly, at room temperature, light illumination can modulate the CDW phase and thus tune the frequency of the ultrathin 1T-TaS2 oscillators. This light tunability of the CDW phase transition is promising for multifunctional device applications.

Room-temperature electrically driven phase transition of two-dimensional 1T-TaS2 layers.

Due to the strong electron-electron and electron-phonon interactions, the transition metal dichalcogenide 1T-TaS2 exhibits temperature dependent as well as electric field driven charge density wave (CDW) phase transitions (PTs). In this work, we investigate the thickness dependence of the electric field driven PT in 1T-TaS2 two-dimensional (2D) flakes. Electrically driven PT between high- and low-resistance states occurs at temperatures in the range of 60-300 K. For a thin 1T-TaS2 (≤8.8 nm) sample, only one PT is triggered, whereas thick films experience double PTs (13-17 nm) and multiple PTs (≥17.5 nm) until reaching the final low-resistance state. The multiple PTs may imply the existence of hidden nearly-commensurate charge density wave (NCCDW) states. In addition, a threshold electric field is observed, in which the low-resistance state is unable to resume the high-resistance state. Finally, we fabricate a 1T-TaS2/graphene hybrid field effect transistor to achieve a gate-tunable PT at room temperature. Such a hybrid device might provide a new avenue for the construction of CDW-based memories based on 2D materials.

Vacuum level dependent photoluminescence in chemical vapor deposition-grown monolayer MoS 2.

The stronger photoluminescence (PL) in chemical vapor deposition (CVD) grown monolayer MoS2 has been attributed to its high crystal quality compared with that in mechanically exfoliated (ME) crystal, which is contrary to the cognition that the ME crystal usually have better crystal quality than that of CVD grown one and it is expected with a better optical quality. In this report, the reason of abnormally strong PL spectra in CVD grown monolayer crystal is systematically investigated by studying the in-situ opto-electrical exploration at various environments for both of CVD and ME samples. High resolution transmission electron microscopy is used to investigate their crystal qualities. The stronger PL in CVD grown crystal is due to the high p-doping effect of adsorbates induced rebalance of exciton/trion emission. The first principle calculations are carried out to explore the interaction between adsorbates in ambient and defects sites in MoS2, which is consistent to the experimental phenomenon and further confirm our proposed mechanisms.