An ultra energy-efficient hardware platform for neuromorphic computing enabled by 2D-TMD tunnel-FETs.

Brain-like energy-efficient computing has remained elusive for neuromorphic (NM) circuits and hardware platform implementations despite decades of research. In this work we reveal the opportunity to significantly improve the energy efficiency of digital neuromorphic hardware by introducing NM circuits employing two-dimensional (2D) transition metal dichalcogenide (TMD) layered channel material-based tunnel-field-effect transistors (TFETs). Our novel leaky-integrate-fire (LIF) based digital NM circuit along with its Hebbian learning circuitry operates at a wide range of supply voltages, frequencies, and activity factors, enabling two orders of magnitude higher energy-efficient computing that is difficult to achieve with conventional material and/or device platforms, specifically the silicon-based 7 nm low-standby-power FinFET technology. Our innovative 2D-TFET based NM circuit paves the way toward brain-like energy-efficient computing that can unleash major transformations in future AI and data analytics platforms.

The future transistors.

The metal-oxide-semiconductor field-effect transistor (MOSFET), a core element of complementary metal-oxide-semiconductor (CMOS) technology, represents one of the most momentous inventions since the industrial revolution. Driven by the requirements for higher speed, energy efficiency and integration density of integrated-circuit products, in the past six decades the physical gate length of MOSFETs has been scaled to sub-20 nanometres. However, the downscaling of transistors while keeping the power consumption low is increasingly challenging, even for the state-of-the-art fin field-effect transistors. Here we present a comprehensive assessment of the existing and future CMOS technologies, and discuss the challenges and opportunities for the design of FETs with sub-10-nanometre gate length based on a hierarchical framework established for FET scaling. We focus our evaluation on identifying the most promising sub-10-nanometre-gate-length MOSFETs based on the knowledge derived from previous scaling efforts, as well as the research efforts needed to make the transistors relevant to future logic integrated-circuit products. We also detail our vision of beyond-MOSFET future transistors and potential innovation opportunities. We anticipate that innovations in transistor technologies will continue to have a central role in driving future materials, device physics and topology, heterogeneous vertical and lateral integration, and computing technologies.

Quantum-Engineered Devices Based on 2D Materials for Next-Generation Information Processing and Storage.

As an approximation to the quantum state of solids, the band theory, developed nearly seven decades ago, fostered the advance of modern integrated solid-state electronics, one of the most successful technologies in the history of human civilization. Nonetheless, their rapidly growing energy consumption and accompanied environmental issues call for more energy-efficient electronics and optoelectronics, which necessitate the exploration of more advanced quantum mechanical effects, such as band-to-band tunneling, spin-orbit coupling, spin-valley locking, and quantum entanglement. The emerging 2D layered materials, featured by their exotic electrical, magnetic, optical, and structural properties, provide a revolutionary low-dimensional and manufacture-friendly platform (and many more opportunities) to implement these quantum-engineered devices, compared to the traditional electronic materials system. Here, the progress in quantum-engineered devices is reviewed and the opportunities/challenges of exploiting 2D materials are analyzed to highlight their unique quantum properties that enable novel energy-efficient devices, and useful insights to quantum device engineers and 2D-material scientists are provided.

The Amelioration of Detrimental Biochemical Anomalies by Supplementing B, C, and E Vitamins in Subjects with Type 2 Diabetes Mellitus May Reduce the Rate of Development of Diabetic Retinopathy.

Excessive intracellular glucose in insulin-independent tissues including nerve, nephron, lens, and retina invites mishandling of metabolism of glucose resulting in a background of increased oxidative stress, advanced glycation end products (AGE) formation, lipid peroxidation, and failure of antioxidant defense systems in type 2 diabetes mellitus (T2DM). All these detrimental biochemical anomalies ultimately attack biological membranes and especially capillary beds of the retina, resulting in the breakdown of the inner blood-retinal barrier and the initiation of diabetic retinopathy (DR). If these disarrays are corrected to a large extent, the development of DR can be avoided or delayed. In this prospective clinical trial, 185 patients with T2DM who received B vitamins, vitamin C, and vitamin E along with antidiabetic medication for five years demonstrated a slower rate of the development of DR and reduced abnormal biochemical mediators like reactive oxygen species (ROS), malondialdehyde (MDA), AGE, and vascular endothelial growth factor (VEGF) compared to 175 T2DM individuals who were treated with only antihyperglycemic drugs.

Benzimidazole- and Imidazole-Fused Selenazolium and Selenazinium Selenocyanates: Ionic Organoselenium Compounds with Efficient Peroxide Scavenging Activities.

Three new classes of ionic organoselenium compounds containing cationic benzimidazolium and imidazolium ring systems with selenocyanates as counterions are described. The cyclization of N,N'-disubstituted benzimidazolium and imidazolium bromides having N-(CH2)2-Br and N-(CH2)3-Br groups in the presence of potassium selenocyanate (KSeCN) led to formation of the corresponding selenazolium selenocyanates (21a, 21b, 22a, and 22b) and selenazinium selenocyanates (21c, 21d, 22c, and 22d). However, the open-chain selenocyanates with additional selenocyanate counterions (21e, 21f, 22e, and 22f) were formed from the N,N'-disubstituted benzimidazolium and imidazolium bromides having N-(CH2)6-Br groups. Mechanistic studies were carried out to understand the feasibility of such cyclization processes in the presence of KSeCN. The compounds were studied further for their potencies to catalytically reduce H2O2 in the presence of thiols. Interestingly, the cyclic selenazolium (21a, 21b, 22a, and 22b) and selenazinium compounds (21c, 21d, 22c, and 22d) exhibited significantly higher antioxidant activities than the corresponding acyclic selenocyanates (21f, 22e, and 22f). Selected compounds (22d and 22e) were further evaluated for their potencies in modulating the intracellular level of reactive oxygen species (ROS) in a representative macrophage cell line (RAW 264.7). Owing to the cationic nature of compounds, they may target and scavenge mitochondrial ROS in the cellular medium.

Defect and strain engineering of monolayer WSe2 enables site-controlled single-photon emission up to 150 K.

In recent years, quantum-dot-like single-photon emitters in atomically thin van der Waals materials have become a promising platform for future on-chip scalable quantum light sources with unique advantages over existing technologies, notably the potential for site-specific engineering. However, the required cryogenic temperatures for the functionality of these sources has been an inhibitor of their full potential. Existing methods to create emitters in 2D materials face fundamental challenges in extending the working temperature while maintaining the emitter's fabrication yield and purity. In this work, we demonstrate a method of creating site-controlled single-photon emitters in atomically thin WSe2 with high yield utilizing independent and simultaneous strain engineering via nanoscale stressors and defect engineering via electron-beam irradiation. Many of the emitters exhibit biexciton cascaded emission, single-photon purities above 95%, and working temperatures up to 150 K. This methodology, coupled with possible plasmonic or optical micro-cavity integration, furthers the realization of scalable, room-temperature, and high-quality 2D single- and entangled-photon sources.

Author Correction: Is negative capacitance FET a steep-slope logic switch?

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Is negative capacitance FET a steep-slope logic switch?

The negative-capacitance field-effect transistor(NC-FET) has attracted tremendous research efforts. However, the lack of a clear physical picture and design rule for this device has led to numerous invalid fabrications. In this work, we address this issue based on an unexpectedly concise and insightful analytical formulation of the minimum hysteresis-free subthreshold swing (SS), together with several important conclusions. Firstly, well-designed MOSFETs that have low trap density, low doping in the channel, and excellent electrostatic integrity, receive very limited benefit from NC in terms of achieving subthermionic SS. Secondly, quantum-capacitance is the limiting factor for NC-FETs to achieve hysteresis-free subthermionic SS, and FETs that can operate in the quantum-capacitance limit are desired platforms for NC-FET construction. Finally, a practical role of NC in FETs is to save the subthreshold and overdrive voltage losses. Our analysis and findings are intended to steer the NC-FET research in the right direction.

Trisulfides over disulfides: highly selective synthetic strategies, anti-proliferative activities and sustained H2S release profiles.

Temperature- and solvent-induced selective synthesis of trisulfides and disulfides is demonstrated. A remarkable selectivity was achieved using Na2S as a sulfur-transfer agent under mild, greener, catalyst-free and additive-free conditions. This study reveals trisulfides as a better model than disulfides in general for a sustained release of H2S and potent anti-cancer activities.

Potent anti-proliferative activities of organochalcogenocyanates towards breast cancer.

The pharmacological importance, particularly the anti-cancer and chemopreventive potentials, of organochalcogen compounds has attracted wide research attention recently. Herein we describe the synthesis of a series of organochalcogenocyanates that have one or more selenocyanate or thiocyanate units in a single molecule. The anti-proliferative activity of these organochalcogenocyanates in different breast cancer cells shows that selenocyanates exhibit much higher anti-proliferative activities than thiocyanates in general. Our study reveals that the activity of benzyl selenocyanate (1, BSC) could be significantly enhanced by 4-nitro substitution (12), which was more selective towards triple-negative breast cancer cells (MDA-MB-231) over other ER+ breast cancer cells (MCF-7 and T-47D). Furthermore, to the best of our knowledge, this is the first report on the synthesis of compounds having more than two selenocyanate units with promising anti-proliferative activities. Our studies further indicate that the apoptotic activities of selenocyanates are associated with modulation of cellular morphology and cell cycle arrest at S-phase. Selenocyanates also inhibited cellular migration and exhibited weak antioxidant activities. An effective binding interaction of compound 12 with serum albumin indicates its feasible transport in the bloodstream for its enhanced anti-cancer properties. Mechanistic studies by western blot analysis demonstrate that benzylic selenocyanates exhibit anti-proliferative activities by modulating key cellular proteins such as Survivin, Bcl-2 and COX-2; this was further supported by molecular docking studies. The results of this study would be helpful in designing suitable chemotherapeutic and chemopreventive drugs in the future.

Designing artificial 2D crystals with site and size controlled quantum dots.

Ordered arrays of quantum dots in two-dimensional (2D) materials would make promising optical materials, but their assembly could prove challenging. Here we demonstrate a scalable, site and size controlled fabrication of quantum dots in monolayer molybdenum disulfide (MoS2), and quantum dot arrays with nanometer-scale spatial density by focused electron beam irradiation induced local 2H to 1T phase change in MoS2. By designing the quantum dots in a 2D superlattice, we show that new energy bands form where the new band gap can be controlled by the size and pitch of the quantum dots in the superlattice. The band gap can be tuned from 1.81 eV to 1.42 eV without loss of its photoluminescence performance, which provides new directions for fabricating lasers with designed wavelengths. Our work constitutes a photoresist-free, top-down method to create large-area quantum dot arrays with nanometer-scale spatial density that allow the quantum dots to interfere with each other and create artificial crystals. This technique opens up new pathways for fabricating light emitting devices with 2D materials at desired wavelengths. This demonstration can also enable the assembly of large scale quantum information systems and open up new avenues for the design of artificial 2D materials.

Two-stage test of means of unordered pairs.

The problem of testing equality of means of a bivariate normal distribution on the basis of a sample of size n has been considered when the labels of the observations are either missing or not known. The problem may arise in many applied settings, especially in genetics. Classical likelihood ratio test fails here because of identifiability problems. We propose a two-stage testing procedure using a recently developed test in the context of penalized splines. The proposed testing procedure is found to outperform the tests proposed in the literature. Copyright © 2017 John Wiley & Sons, Ltd.

Understanding the Device Physics in Polymer-Based Ionic-Organic Ratchets.

High-performance solution-processed ionic-organic ratchets are fabricated using polymer semiconductors. The devices can provide both high short-circuit current and open-circuit voltage at room temperature, and be driven by AC signals with frequencies up to 13.56 MHz. The effects of trap density, mobility, and rectification ratio in the device on short-circuit current are investigated and clarified.

Intercalation Doped Multilayer-Graphene-Nanoribbons for Next-Generation Interconnects.

Copper-based interconnects employed in a wide range of integrated circuit (IC) products are fast approaching a dead-end due to their increasing resistivity and diminishing current carrying capacity with scaling, which severely degrades both performance and reliability. Here we demonstrate chemical vapor deposition-synthesized and intercalation-doped multilayer-graphene-nanoribbons (ML-GNRs) with better performance (more than 20% improvement in estimated delay per unit length), 25%/72% energy efficiency improvement at local/global level, and superior reliability w.r.t. Cu for the first time, for dimensions (down to 20 nm width and thickness of 12 nm) suitable for IC interconnects. This is achieved through a combination of GNR interconnect design optimization, high-quality ML-GNR synthesis with precisely controlled number of layers, and effective FeCl3 intercalation doping. We also demonstrate that our intercalation doping is stable at room temperature and that the doped ML-GNRs exhibit a unique width-dependent doping effect due to increasingly efficient FeCl3 diffusion in scaled ML-GNRs, thereby indicating that our doped ML-GNRs will outperform Cu even for sub-20 nm widths. Finally, reliability assessment conducted under accelerated stress conditions (temperature and current density) established that highly scaled intercalated ML-GNRs can carry over 2 × 108 A/cm2 of current densities, whereas Cu interconnects suffer from immediate breakdown under the same stress conditions and thereby addresses the key criterion of current carrying capacity necessary for an alternative interconnect material. Our comprehensive demonstration of highly reliable intercalation-doped ML-GNRs paves the way for graphene as the next-generation interconnect material for a variety of semiconductor technologies and applications.

Surface functionalization of two-dimensional metal chalcogenides by Lewis acid-base chemistry.

Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid-base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti(4+) to form planar p-type [Ti(4+)n(InSe)] coordination complexes. Using this strategy, we fabricate planar p-n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B(3+), Al(3+) and Sn(4+)) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid-base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

Amarogentin regulates self renewal pathways to restrict liver carcinogenesis in experimental mouse model.

Amarogentin, a secoiridoid glycoside isolated from medicinal plant Swertia chirata, was found to restrict CCl4 /N-nitrosodiethyl amine (NDEA) induced mouse liver carcinogenesis by modulating G1/S cell cycle check point and inducing apoptosis. To understand its therapeutic efficacy on stem cell self renewal pathways, prevalence of CD44 positive cancer stem cell (CSC) population, expressions (mRNA/protein) of some key regulatory genes of self renewal Wnt and Hedgehog pathways along with expressions of E-cadherin and EGFR were analyzed during the liver carcinogenesis and in liver cancer cell line HepG2. It was observed that amarogentin could significantly reduce CD44 positive CSCs in both pre and post initiation stages of carcinogenesis than carcinogen control mice. In Wnt pathway, amarogentin could inhibit expressions of ß-catenin, phospho ß-catenin (Y-654) and activate expressions of antagonists sFRP1/2 and APC in the liver lesions. In Hedgehog pathway, decreased expressions of Gli1, sonic hedgehog ligand, and SMO along with up-regulation of PTCH1 were seen in the liver lesions due to amarogentin treatment. Moreover, amarogentin could up-regulate E-cadherin expression and down-regulate expression of EGFR in the liver lesions. Similarly, amarogentin could inhibit HepG2 cell growth along with expression and prevalence of CD44 positive CSCs. Similar to in vivo analysis, amarogentin could modulate the expressions of the key regulatory genes of the Wnt and hedgehog pathways and EGFR in HepG2 cells. Thus, our data suggests that the restriction of liver carcinogenesis by amarogentin might be due to reduction of CD44 positive CSCs and modulation of the self renewal pathways. © 2015 Wiley Periodicals, Inc.

Electrical contacts to two-dimensional semiconductors.

The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.

A subthermionic tunnel field-effect transistor with an atomically thin channel.

The fast growth of information technology has been sustained by continuous scaling down of the silicon-based metal-oxide field-effect transistor. However, such technology faces two major challenges to further scaling. First, the device electrostatics (the ability of the transistor's gate electrode to control its channel potential) are degraded when the channel length is decreased, using conventional bulk materials such as silicon as the channel. Recently, two-dimensional semiconducting materials have emerged as promising candidates to replace silicon, as they can maintain excellent device electrostatics even at much reduced channel lengths. The second, more severe, challenge is that the supply voltage can no longer be scaled down by the same factor as the transistor dimensions because of the fundamental thermionic limitation of the steepness of turn-on characteristics, or subthreshold swing. To enable scaling to continue without a power penalty, a different transistor mechanism is required to obtain subthermionic subthreshold swing, such as band-to-band tunnelling. Here we demonstrate band-to-band tunnel field-effect transistors (tunnel-FETs), based on a two-dimensional semiconductor, that exhibit steep turn-on; subthreshold swing is a minimum of 3.9 millivolts per decade and an average of 31.1 millivolts per decade for four decades of drain current at room temperature. By using highly doped germanium as the source and atomically thin molybdenum disulfide as the channel, a vertical heterostructure is built with excellent electrostatics, a strain-free heterointerface, a low tunnelling barrier, and a large tunnelling area. Our atomically thin and layered semiconducting-channel tunnel-FET (ATLAS-TFET) is the only planar architecture tunnel-FET to achieve subthermionic subthreshold swing over four decades of drain current, as recommended in ref. 17, and is also the only tunnel-FET (in any architecture) to achieve this at a low power-supply voltage of 0.1 volts. Our device is at present the thinnest-channel subthermionic transistor, and has the potential to open up new avenues for ultra-dense and low-power integrated circuits, as well as for ultra-sensitive biosensors and gas sensors.

Impact of Contact on the Operation and Performance of Back-Gated Monolayer MoS2 Field-Effect-Transistors.

Metal contacts to atomically thin two-dimensional (2D) crystal based FETs play a decisive role in determining their operation and performance. However, the effects of contacts on the switching behavior, field-effect mobility, and current saturation of monolayer MoS2 FETs have not been well explored and, hence, is the focus of this work. The dependence of contact resistance on the drain current is revealed by four-terminal-measurements. Without high-κ dielectric boosting, an electron mobility of 44 cm(2)/(V·s) has been achieved in a monolayer MoS2 FET on SiO2 substrate at room temperature. Velocity saturation is identified as the main mechanism responsible for the current saturation in back-gated monolayer MoS2 FETs at relatively higher carrier densities. Furthermore, for the first time, electron saturation velocity of monolayer MoS2 is extracted at high-field condition.