High-κ Dielectric (HfO2)/2D Semiconductor (HfSe2) Gate Stack for Low-Power Steep-Switching Computing Devices.

Herein, a high-quality gate stack (native HfO2 formed on 2D HfSe2) fabricated via plasma oxidation is reported, realizing an atomically sharp interface with a suppressed interface trap density (Dit ≈ 5 × 1010 cm-2 eV-1). The chemically converted HfO2 exhibits dielectric constant, κ ≈ 23, resulting in low gate leakage current (≈10-3 A cm-2) at equivalent oxide thickness ≈0.5 nm. Density functional calculations indicate that the atomistic mechanism for achieving a high-quality interface is the possibility of O atoms replacing the Se atoms of the interfacial HfSe2 layer without a substitution energy barrier, allowing layer-by-layer oxidation to proceed. The field-effect-transistor-fabricated HfO2/HfSe2 gate stack demonstrates an almost ideal subthreshold slope (SS) of ≈61 mV dec-1 (over four orders of IDS) at room temperature (300 K), along with a high Ion/Ioff ratio of ≈108 and a small hysteresis of ≈10 mV. Furthermore, by utilizing a device architecture with separately controlled HfO2/HfSe2 gate stack and channel structures, an impact ionization field-effect transistor is fabricated that exhibits n-type steep-switching characteristics with a SS value of 3.43 mV dec-1 at room temperature, overcoming the Boltzmann limit. These results provide a significant step toward the realization of post-Si semiconducting devices for future energy-efficient data-centric computing electronics.

A steep-switching impact ionization-based threshold switching field-effect transistor.

A steep switching device with a low subthreshold swing (SS) that overcomes the fundamental Boltzmann limit (kT/q) is required to efficiently process a continuously increasing amount of data. Recently, two-dimensional material-based impact ionization transistors with various structures have been reported with the advantages of a low critical electric field and a unique quantum confinement effect. However, most of them cannot retain steep switching at room temperature, and device performance degradation issues caused by impact ionization-induced hot carriers have not been structurally addressed. In this study, we presented an impact-ionization-based threshold switching field-effect transistor (I2S-FET) fabricated with a serial connection of a MoS2 FET and WSe2 impact ionization-based threshold switch (I2S). We obtained repetitive operation with low SS (32.8 mV dec-1) at room temperature, along with low dielectric injection efficiency (10-6), through a structural design with separation of the conducting region, which determines on-state carrier transport, and the steep-switching region where the transition from off- to on-state occurs via impact ionization. Furthermore, compared to previously reported threshold-switching devices, our device demonstrated hysteresis-free switching characteristics. This study provides a promising approach for developing next-generation energy-efficient electronic devices and ultralow-power applications.

Anisotropy of impact ionization in WSe2 field effect transistors.

Carrier multiplication via impact ionization in two-dimensional (2D) layered materials is a very promising process for manufacturing high-performance devices because the multiplication has been reported to overcome thermodynamic conversion limits. Given that 2D layered materials exhibit highly anisotropic transport properties, understanding the directionally-dependent multiplication process is necessary for device applications. In this study, the anisotropy of carrier multiplication in the 2D layered material, WSe2, is investigated. To study the multiplication anisotropy of WSe2, both lateral and vertical WSe2 field effect transistors (FETs) are fabricated and their electrical and transport properties are investigated. We find that the multiplication anisotropy is much bigger than the transport anisotropy, i.e., the critical electric field (ECR) for impact ionization of vertical WSe2 FETs is approximately ten times higher than that of lateral FETs. To understand the experimental results we calculate the average energy of the carriers in the proposed devices under strong electric fields by using the Monte Carlo simulation method. The calculated average energy is strongly dependent on the transport directions and we find that the critical electric field for impact ionization in vertical devices is approximately one order of magnitude larger than that of the lateral devices, consistent with experimental results. Our findings provide new strategies for the future development of low-power electric and photoelectric devices.

Structurally Diverse Bench-Stable Nickel(0) Pre-Catalysts: A Practical Toolkit for In Situ Ligation Protocols.

A flurry of recent research has centered on harnessing the power of nickel catalysis in organic synthesis. These efforts have been bolstered by contemporaneous development of well-defined nickel (pre)catalysts with diverse structure and reactivity. In this report, we present ten different bench-stable, 18-electron, formally zero-valent nickel-olefin complexes that are competent pre-catalysts in various reactions. Our investigation includes preparations of novel, bench-stable Ni(COD)(L) complexes (COD=1,5-cyclooctadiene), in which L=quinone, cyclopentadienone, thiophene-S-oxide, and fulvene. Characterization by NMR, IR, single-crystal X-ray diffraction, cyclic voltammetry, thermogravimetric analysis, and natural bond orbital analysis sheds light on the structure, bonding, and properties of these complexes. Applications in an assortment of nickel-catalyzed reactions underscore the complementary nature of the different pre-catalysts within this toolkit.

Putting Vision and Touch into Conflict: Results From a Multimodal Mixed Reality Setup.

What happens if we put vision and touch into conflict? Which modality "wins"? Although several previous studies have addressed this topic, they have solely focused on integration of vision and touch for low-level object properties (such as curvature, slant, or depth). In the present study, we introduce a multimodal mixed-reality setup based on real-time hand-tracking, which was used to display real-world, haptic exploration of objects in a virtual environment through a head-mounted-display (HMD). With this setup we studied multimodal conflict situations of objects varying along higher-level, parametrically-controlled global shape properties. Participants explored these objects in both unimodal and multimodal settings with the latter including congruent and incongruent conditions and differing instructions for weighting the input modalities. Results demonstrated a surprisingly clear touch dominance throughout all experiments, which in addition was only marginally influenceable through instructions to bias their modality weighting. We also present an initial analysis of the hand-tracking patterns that illustrates the potential for our setup to investigate exploration behavior in more detail.

Three-Component Asymmetric Ni-Catalyzed 1,2-Dicarbofunctionalization of Unactivated Alkenes via Stereoselective Migratory Insertion.

An asymmetric 1,2-dicarbofunctionalization of unactivated alkenes with aryl iodides and aryl/alkenylboronic esters under nickel/bioxazoline catalysis is disclosed. A wide array of aryl and alkenyl nucleophiles are tolerated, furnishing the products in good yield and with high enantioselectivity. In addition to terminal alkenes, 1,2-disubstituted internal alkenes participate in the reaction, establishing two contiguous stereocenters with high diastereoselectivity and moderate enantioselectivity. A combination of experimental and computational techniques shed light on the mechanism of the catalytic transformation, pointing to a closed-shell pathway with an enantiodetermining migratory insertion step, where stereoinduction arises from synergistic interactions between the sterically bulky achiral sulfonamide directing group and the hemilabile bidentate ligand.

A steep switching WSe2 impact ionization field-effect transistor.

The Fermi-Dirac distribution of carriers and the drift-diffusion mode of transport represent two fundamental barriers towards the reduction of the subthreshold slope (SS) and the optimization of the energy consumption of field-effect transistors. In this study, we report the realization of steep-slope impact ionization field-effect transistors (I2FETs) based on a gate-controlled homogeneous WSe2 lateral junction. The devices showed average SS down to 2.73 mV/dec over three decades of source-drain current and an on/off ratio of ~106 at room temperature and low bias voltages (<1 V). We determined that the lucky-drift mechanism of carriers is valid in WSe2, allowing our I2FETs to have high impact ionization coefficients and low SS at room temperature. Moreover, we fabricated a logic inverter based on a WSe2 I2FET and a MoS2 FET, exhibiting an inverter gain of 73 and almost ideal noise margin for high- and low-logic states. Our results provide a promising approach for developing functional devices as front runners for energy-efficient electronic device technology.

Electrophilic Sulfur Reagent Design Enables Directed syn-Carbosulfenylation of Unactivated Alkenes.

A multi-component approach to structurally complex organosulfur products is described via the nickel-catalyzed 1,2-carbosulfenylation of unactivated alkenes with organoboron nucleophiles and tailored organosulfur electrophiles. The key to the development of this transformation is the identification of a modular N-alkyl-N-(arylsulfenyl)arenesulfonamide family of sulfur electrophiles. Tuning the electronic and steric properties of the leaving group in these reagents controls pathway selectivity, favoring three-component coupling and suppressing side reactions, as examined via computational studies. The unique syn-stereoselectivity differs from traditional electrophilic sulfenyl transfer processes involving a thiiranium ion intermediate and arises from the directed arylnickel(I) migratory insertion mechanism, as elucidated through reaction kinetics and control experiments. Reactivity and regioselectivity are facilitated by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, alcohols, amines, amides, and azaheterocycles.

Nickel-Catalyzed 1,2-Carboamination of Alkenyl Alcohols.

An alcohol-directed, nickel-catalyzed three-component umpolung carboamination of unactivated alkenes with aryl/alkenylboronic esters and electrophilic aminating reagents is reported. This transformation is enabled by specifically tailored O-(2,6-dimethoxybenzoyl)hydroxylamine electrophiles that suppress competitive processes, including undesired ß-hydride elimination and transesterification between the alcohol substrate and electrophile. The reaction delivers the desired 1,2-carboaminated products with generally high regio- and syn-diastereoselectivity and exhibits a broad scope of coupling partners and alkenes, including complex natural products. Various mechanistic experiments and analysis of the stereochemical outcome with a cyclic alkene substrate, as confirmed by X-ray crystallographic analysis, support alcohol-directed syn-insertion of an organonickel(I) species.

Cyclic (Alkyl)(amino)carbene Ligands Enable Cu-Catalyzed Markovnikov Protoboration and Protosilylation of Terminal Alkynes: A Versatile Portal to Functionalized Alkenes*.

Regioselective hydrofunctionalization of alkynes represents a straightforward route to access alkenyl boronate and silane building blocks. In previously reported catalytic systems, high selectivity is achieved with a limited scope of substrates and/or reagents, with general solutions lacking. Herein, we describe a selective copper-catalyzed Markovnikov hydrofunctionalization of terminal alkynes that is facilitated by strongly donating cyclic (alkyl)(amino)carbene (CAAC) ligands. Using this method, both alkyl- and aryl-substituted alkynes are coupled with a variety of boryl and silyl reagents with high α-selectivity. The reaction is scalable, and the products are versatile intermediates that can participate in various downstream transformations. Preliminary mechanistic experiments shed light on the role of CAAC ligands in this process.

Numerical Analysis of the Contact Behavior of a Polymer-Based Waterproof Membrane for Tunnel Lining.

Waterproof membranes have higher initial strength, faster construction, and better waterproofing than conventional sheet membranes. In addition, their polymer constituents have much higher interfacial adhesion and tensile strength than those of conventional materials. However, despite their advantages, waterproof membranes are not widely used in civil construction. This study evaluates the material properties and interface parameters of a waterproof membrane by considering the results of laboratory experiments and numerical analysis. Since the contact behavior of a membrane at its interface with shotcrete is important for understanding the mechanism of the support it offers known as a shotcrete tunnel lining, modeling should adopt appropriate contact conditions. The numerical analysis identifies the suitability and contact conditions of the waterproof membrane in various conditions.

EEG-Based Prediction of Successful Memory Formation During Vocabulary Learning.

Previous Electroencephalography (EEG) and neuroimaging studies have found differences between brain signals for subsequently remembered and forgotten items during learning of items - it has even been shown that single trial prediction of memorization success is possible with a few target items. There has been little attempt, however, in validating the findings in an application-oriented context involving longer test spans with realistic learning materials encompassing more items. Hence, the present study investigates subsequent memory prediction within the application context of foreign-vocabulary learning. We employed an off-line, EEG-based paradigm in which Korean participants without prior German language experience learned 900 German words in paired-associate form. Our results using convolutional neural networks optimized for EEG-signal analysis show that above-chance classification is possible in this context allowing us to predict during learning which of the words would be successfully remembered later.

Recent developments in nickel-catalyzed intermolecular dicarbofunctionalization of alkenes.

Nickel-catalyzed three-component alkene difunctionalization has rapidly emerged as a powerful tool for forging two C-C bonds in a single reaction. Building upon the powerful modes of bond construction in traditional two-component cross-coupling, various research groups have demonstrated the versatility of nickel in enabling catalytic 1,2-dicarbofunctionalization using a wide range of carbon-based electrophiles and nucleophiles and in a fully intermolecular fashion. Though this area has emerged only recently, the last few years have witnessed a proliferation of publications on this topic, underscoring the potential of this strategy to develop into a general platform that offers high regio- and stereoselectivity. This minireview highlights the recent progress in the area of intermolecular 1,2-dicarbofunctionalization of alkenes via nickel catalysis and discusses lingering challenges within this reactivity paradigm.

Multifaceted Substrate-Ligand Interactions Promote the Copper-Catalyzed Hydroboration of Benzylidenecyclobutanes and Related Compounds.

A unified synthetic strategy to access tertiary four-membered carbo/heterocyclic boronic esters is reported. Use of a Cu(I) catalyst in combination with a modified dppbz ligand enables regioselective hydroboration of various trisubstituted benzylidenecyclobutanes and carbo/heterocyclic analogs. The reaction conditions are mild, and the method tolerates a wide range of medicinally relevant heteroarenes. The protocol can be conveniently conducted on gram-scale, and the tertiary boronic ester products undergo facile diversification into valuable targets. Reaction kinetics and computational studies indicate that the migratory insertion step is turnover-limiting and accelerated by electron-withdrawing groups on the dppbz ligand. Energy decomposition analysis (EDA) calculations reveal that electron-deficient P-aryl groups on the dppbz ligand enhance the T-shaped π/π interactions with the substrate and stabilize the migratory insertion transition state.

Nickel-Catalyzed 1,2-Diarylation of Alkenyl Carboxylates: A Gateway to 1,2,3-Trifunctionalized Building Blocks.

A nickel-catalyzed conjunctive cross-coupling of alkenyl carboxylic acids, aryl iodides, and aryl/alkenyl boronic esters is reported. The reaction delivers the desired 1,2-diarylated and 1,2-arylalkenylated products with excellent regiocontrol. To demonstrate the synthetic utility of the method, a representative product is prepared on gram scale and then diversified to eight 1,2,3-trifunctionalized building blocks using two-electron and one-electron logic. Using this method, three routes toward bioactive molecules are improved in terms of yield and/or step count. This method represents the first example of catalytic 1,2-diarylation of an alkene directed by a native carboxylate group.

Design, synthesis, and biological evaluation of C7-functionalized DMXAA derivatives as potential human-STING agonists.

STING, a central protein in the innate immune response to cytosolic DNA, has emerged as a hot target for the development of vaccine-adjuvants and anticancer drugs. The discovery of potent human-STING (hSTING) agonist is expected to revolutionize the current cancer immunotherapy. Inspired by the X-ray crystal structure of DMXAA (5,6-dimethylxanthenone-4-acetic acid) and hSTINGG230I complex, we designed various DMXAA derivatives that contain a hydrogen bonding donor/acceptor or a halide at the C7 position. While 7-bromo- and 7-hydroxyl-DMXAA showed notable binding to mouse-STING (mSTING), our newly synthesized C7-functionalized DMXAA derivatives did not bind to hSTING. Nevertheless, our newly developed synthetic protocol for the C7-functionalization of DMXAA would be applicable to access other C7-substituted DMXAA analogues as potential hSTING agonists.

Cu-Catalyzed Hydroboration of Benzylidenecyclopropanes: Reaction Optimization, (Hetero)Aryl Scope, and Origins of Pathway Selectivity.

The copper-catalyzed hydroboration of benzylidenecyclopropanes, conveniently accessed in one step from readily available benzaldehydes, is reported. Under otherwise identical reaction conditions, two distinct phosphine ligands grant access to different products by either suppressing or promoting cyclopropane opening via ß-carbon elimination. Computational studies provide insight into how the rigidity and steric environment of these different bis-phosphine ligands influence the relative activation energies of ß-carbon elimination versus protodecupration from the key benzylcopper intermediate. The method tolerates a wide variety of heterocycles prevalent in clinical and pre-clinical drug development, giving access to valuable synthetic intermediates. The versatility of the tertiary cyclopropylboronic ester products is demonstrated through several derivatization reactions.

Natural Compound Licochalcone B Induced Extrinsic and Intrinsic Apoptosis in Human Skin Melanoma (A375) and Squamous Cell Carcinoma (A431) Cells.

Licochalcone B (Lico B), which is normally isolated from the roots of Glycyrrhiza inflata (Chinese Licorice), generally classified into organic compounds including retrochalcones. Potential pharmacological properties of Lico B include anti-inflammatory, anti-bacterial, anti-oxidant, and anti-cancer activities. However, its biological effects on melanoma and squamous cell carcinoma (SCC) are unknown. Based on these known facts, this study investigated the role of Lico B in apoptosis, through the extrinsic and intrinsic pathways and additional regulation of specificity protein 1 in human skin cancer cell lines. Annexin V/7-aminoactinomycin D staining, western blot analysis, mitochondrial membrane potential assay, and an anchorage-independent cell transformation assay demonstrated that Lico B treatment of human melanoma and SCC cells significantly inhibited cell proliferation and induced apoptotic cell death. More specifically, Lico B induced apoptosis through the regulation of specificity protein 1 and apoptosis-related proteins including CCAAT/enhancer-binding protein homologous protein, death receptors, and poly (ADP-ribose) polymerase. These results indicate that Lico B has apoptotic effect on A375 and A431 skin cancer cells, suggesting the potential value of Lico B for the treatment of human melanoma and SCC. Copyright © 2017 John Wiley & Sons, Ltd.

Six-Step Total Synthesis of Azaspirene.

The total synthesis of (±)-azaspirene (1) was achieved in a total of six steps from commercially available materials. Keys to the conciseness of our synthetic approach were the effective γ-lactam formation from linear precursor 36 and successful tandem epoxidations of γ-lactam 34 to afford α,ß-epoxy-γ-hydroxy-γ-lactam intermediate 14. While our streamlined synthesis of azaspirene (1) sought inspiration from its biogenetic hypothesis, experimentally observed chemical reactivity of biosynthetically relevant precursors conversely provides insights to the biological origin of this natural product.

Licochalcone A Suppresses Specificity Protein 1 as a Novel Target in Human Breast Cancer Cells.

Licochalcone A (LCA), isolated from the root of Glycyrrhiza inflata, are known to have medicinal effect such as anti-oxidant, anti-bacterial, anti-viral, and anti-cancer. Though, as a pharmacological mechanism regulator, anti-cancer studies on LCA were not investigated in human breast cancer. We investigated the anti-proliferative and apoptotic effect of LCA in human breast cancer cells MCF-7 and MDA-MB-231 through MTS assay, PI staining, Annexin-V/7-AAD assay, mitochondrial membrane potential assay, multi-caspase assay, RT-PCR, Western blot analysis, and anchorage-independent cell transformation assay. Our results showed the little difference between two cells, as MCF-7 cell is both estrogen/progesterone receptor positive, there were only effect on Sp1 protein level, but not in mRNA level. Adversely, estrogen/progesterone/human epidermal growth factor receptor 2 triple negative, MDA-MB-231 showed decreased Sp1 mRNA, and protein levels. To confirm the participation of Sp1 in breast cancer cell viability, siRNA techniques were introduced. Both cells showed dysfunction of mitochondrial membrane potential and mitochondrial ROS production, which reflects it passed intracellular mitochondrial apoptosis pathway. Additionally, LCA showed the anti-proliferative and apoptotic effect in breast cancer cells through regulating Sp1 and apoptosis-related proteins in a dose- and a time-dependent manner. Consequently, LCA might be a potential anti-breast cancer drug substitute. J. Cell. Biochem. 118: 4652-4663, 2017. © 2017 Wiley Periodicals, Inc.