Showing papers by "Nanyang Technological University published in 2015"
TL;DR: DIAMOND is introduced, an open-source algorithm based on double indexing that is 20,000 times faster than BLASTX on short reads and has a similar degree of sensitivity.
Abstract: The alignment of sequencing reads against a protein reference database is a major computational bottleneck in metagenomics and data-intensive evolutionary projects. Although recent tools offer improved performance over the gold standard BLASTX, they exhibit only a modest speedup or low sensitivity. We introduce DIAMOND, an open-source algorithm based on double indexing that is 20,000 times faster than BLASTX on short reads and has a similar degree of sensitivity.
7,164 citations
TL;DR: This paper presents an overview of the RF-EHNs including system architecture, RF energy harvesting techniques, and existing applications, and explores various key design issues according to the network types, i.e., single-hop networks, multiantenna networks, relay networks, and cognitive radio networks.
Abstract: Radio frequency (RF) energy transfer and harvesting techniques have recently become alternative methods to power the next-generation wireless networks As this emerging technology enables proactive energy replenishment of wireless devices, it is advantageous in supporting applications with quality-of-service requirements In this paper, we present a comprehensive literature review on the research progresses in wireless networks with RF energy harvesting capability, which is referred to as RF energy harvesting networks (RF-EHNs) First, we present an overview of the RF-EHNs including system architecture, RF energy harvesting techniques, and existing applications Then, we present the background in circuit design as well as the state-of-the-art circuitry implementations and review the communication protocols specially designed for RF-EHNs We also explore various key design issues in the development of RF-EHNs according to the network types, ie, single-hop networks, multiantenna networks, relay networks, and cognitive radio networks Finally, we envision some open research directions
2,352 citations
Boston Children's Hospital1, Harvard University2, King's College London3, Lund University4, Massachusetts Eye and Ear Infirmary5, University of São Paulo6, University of California, San Diego7, Imperial College London8, Brigham and Women's Hospital9, Partners In Health10, Royal North Shore Hospital11, Medical College of Wisconsin12, Nanyang Technological University13, Monash University14, University of Sierra Leone15, University of Oxford16, Mongolian National University17, Flinders University18, University of Malawi19, Beth Israel Deaconess Medical Center20, Bhabha Atomic Research Centre21, Royal Australasian College of Surgeons22, Stanford University23, University of California, San Francisco24
TL;DR: The need for surgical services in low- and middleincome countries will continue to rise substantially from now until 2030, with a large projected increase in the incidence of cancer, road traffic injuries, and cardiovascular and metabolic diseases in LMICs.
2,209 citations
TL;DR: The properties and synthesis methods of these carbon nanodots are reviewed and emphasis is placed on their biological (both fundamental and theranostic) applications.
Abstract: The emerging graphene quantum dots (GQDs) and carbon dots (C-dots) have gained tremendous attention for their enormous potentials for biomedical applications, owing to their unique and tunable photoluminescence properties, exceptional physicochemical properties, high photostability, biocompatibility, and small size. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments. We comparatively review the properties and synthesis methods of these carbon nanodots and place emphasis on their biological (both fundamental and theranostic) applications.
1,665 citations
TL;DR: The state of the art in the development of ultrathin 2D nanomaterials is reviewed and their unique advantages are highlighted, together with some personal insights on the challenges in this research area.
Abstract: The past decade has witnessed an extraordinary increase in research progress on ultrathin two-dimensional (2D) nanomaterials in the fields of condensed matter physics, materials science, and chemistry after the exfoliation of graphene from graphite in 2004. This unique class of nanomaterials has shown many unprecedented properties and thus is being explored for numerous promising applications. In this Perspective, I briefly review the state of the art in the development of ultrathin 2D nanomaterials and highlight their unique advantages. Then, I discuss the typical synthetic methods and some promising applications of ultrathin 2D nanomaterials together with some personal insights on the challenges in this research area. Finally, on the basis of the current achievement on ultrathin 2D nanomaterials, I give some personal perspectives on potential future research directions.
1,582 citations
TL;DR: Selective laser melting (SLM) is a particular rapid prototyping, 3D printing, or additive manufacturing (AM) technique designed to use high power-density laser to melt and fuse metallic powders as mentioned in this paper.
Abstract: Selective Laser Melting (SLM) is a particular rapid prototyping, 3D printing, or Additive Manufacturing (AM) technique designed to use high power-density laser to melt and fuse metallic powders. A component is built by selectively melting and fusing powders within and between layers. The SLM technique is also commonly known as direct selective laser sintering, LaserCusing, and direct metal laser sintering, and this technique has been proven to produce near net-shape parts up to 99.9% relative density. This enables the process to build near full density functional parts and has viable economic benefits. Recent developments of fibre optics and high-power laser have also enabled SLM to process different metallic materials, such as copper, aluminium, and tungsten. Similarly, this has also opened up research opportunities in SLM of ceramic and composite materials. The review presents the SLM process and some of the common physical phenomena associated with this AM technology. It then focuses on the following a...
1,455 citations
TL;DR: This critical review will introduce the recent progress in hybrid nanoarchitectures based on 2D TMD nanosheets, and their synthetic strategies, properties, and applications are systematically summarized and discussed, with emphasis on those new appealing structures, properties and functions.
Abstract: Ultrathin two-dimensional (2D) nanosheets of layered transition metal dichalcogenides (TMDs), such as MoS2, TiS2, TaS2, WS2, MoSe2, WSe2, etc., are emerging as a class of key materials in chemistry and electronics due to their intriguing chemical and electronic properties. The ability to prepare these TMD nanosheets in high yield and large scale via various methods has led to increasing studies on their hybridization with other materials to create novel functional composites, aiming to engineer their chemical, physical and electronic properties and thus achieve good performance for some specific applications. In this critical review, we will introduce the recent progress in hybrid nanoarchitectures based on 2D TMD nanosheets. Their synthetic strategies, properties and applications are systematically summarized and discussed, with emphasis on those new appealing structures, properties and functions. In addition, we will also give some perspectives on the challenges and opportunities in this promising research area.
1,329 citations
TL;DR: In this paper, the authors report the current state of the theoretical research and practical advances on this subject and provide a comprehensive view of these advances in ELM together with its future perspectives.
1,289 citations
TL;DR: A metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbide nano-octahedrons composed of ultrafine nanocrystallites exhibited remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions is demonstrated.
Abstract: Electrochemical water splitting has been considered as a promising approach to produce clean and sustainable hydrogen fuel. However, the lack of high-performance and low-cost electrocatalysts for hydrogen evolution reaction hinders the large-scale application. As a new class of porous materials with tunable structure and composition, metal-organic frameworks have been considered as promising candidates to synthesize various functional materials. Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix. Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions. The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts. There is extensive research into non-platinum electrocatalysts for hydrogen evolution. Here, the authors report a molybdenum carbide catalyst, prepared via the carburization of a copper metal-organic framework host/molybdenum-based polyoxometalates guest system, and demonstrate its catalytic activity.
1,194 citations
TL;DR: Recent evidence for the in vivo presence and function of DNA and RNA G-quadruplexes in various cellular pathways including DNA replication, gene expression and telomere maintenance is summarized.
Abstract: 'If G-quadruplexes form so readily in vitro, Nature will have found a way of using them in vivo' (Statement by Aaron Klug over 30 years ago).During the last decade, four-stranded helical structures called G-quadruplex (or G4) have emerged from being a structural curiosity observed in vitro, to being recognized as a possible nucleic acid based mechanism for regulating multiple biological processes in vivo. The sequencing of many genomes has revealed that they are rich in sequence motifs that have the potential to form G-quadruplexes and that their location is non-random, correlating with functionally important genomic regions. In this short review, we summarize recent evidence for the in vivo presence and function of DNA and RNA G-quadruplexes in various cellular pathways including DNA replication, gene expression and telomere maintenance. We also highlight remaining open questions that will have to be addressed in the future.
1,100 citations
TL;DR: An anion exchange method is reported to synthesize a complex ternary metal sulfides hollow structure, namely nickel cobalt sulfide ball-in-ball hollow spheres that show long-term cycling performance and potential application in high-performance electrochemical capacitors.
Abstract: While the synthesis of hollow structures of transition metal oxides is well established, it is extremely challenging to fabricate complex hollow structures for mixed transition metal sulfides. Here we report an anion exchange method to synthesize a complex ternary metal sulfides hollow structure, namely nickel cobalt sulfide ball-in-ball hollow spheres. Uniform nickel cobalt glycerate solid spheres are first synthesized as the precursor and subsequently chemically transformed into nickel cobalt sulfide ball-in-ball hollow spheres. When used as electrode materials for electrochemical capacitors, these nickel cobalt sulfide hollow spheres deliver a specific capacitance of 1,036 F g(-1) at a current density of 1.0 A g(-1). An asymmetric supercapacitor based on these ball-in-ball structures shows long-term cycling performance with a high energy density of 42.3 Wh kg(-1) at a power density of 476 W kg(-1), suggesting their potential application in high-performance electrochemical capacitors.
TL;DR: All-inorganic colloidal cesium lead halide perovskite quantum dots are revealed to be a new class of favorable optical-gain materials, which show combined merits of both colloidal quantum dots and halideperovskites.
Abstract: All-inorganic colloidal cesium lead halide perovskite quantum dots (CsPbX3 , X = Cl, Br, I) are revealed to be a new class of favorable optical-gain materials, which show -combined merits of both colloidal quantum dots and halide perovskites. Low-threshold and -ultrastable stimulated emission is -demonstrated under atmospheric conditions with wavelength tunability across the whole -visible spectrum via either size or composition control.
TL;DR: The designed synthesis of novel box-in-box nanocages with different shell compositions, namely, Co3O4/NiCo2O4 double-shelled nanocage (DSNCs) with greatly improved electrochemical performance demonstrates the importance of rational design and synthesis of hollow structures with higher complexity.
Abstract: Hollow structures with high complexity in shell architecture and composition have attracted tremendous interest because of their great importance for both fundamental studies and practical applications. Herein we report the designed synthesis of novel box-in-box nanocages (NCs) with different shell compositions, namely, Co3O4/NiCo2O4 double-shelled nanocages (DSNCs). Uniform zeolitic imidazolate framework-67/Ni–Co layered double hydroxides yolk-shelled structures are first synthesized and then transformed into Co3O4/NiCo2O4 DSNCs by thermal annealing in air. Importantly, this strategy can be easily extended to prepare other complex DSNCs. When evaluated as electrodes for pseudocapacitors, the Co3O4/NiCo2O4 DSNCs show a high specific capacitance of 972 F g–1 at a current density of 5 A g–1 and excellent stability with 92.5% capacitance retention after 12 000 cycles, superior to that of Co3O4 NCs with simple configuration and Co3O4/Co3O4 DSNCs. Besides, the Co3O4/NiCo2O4 DSNCs also exhibit much better elect...
TL;DR: A generally accepted definition for SDN is presented, including decoupling the control plane from the data plane and providing programmability for network application development, and its three-layer architecture is dwelled on, including an infrastructure layer, a control layer, and an application layer.
Abstract: Emerging mega-trends (e.g., mobile, social, cloud, and big data) in information and communication technologies (ICT) are commanding new challenges to future Internet, for which ubiquitous accessibility, high bandwidth, and dynamic management are crucial. However, traditional approaches based on manual configuration of proprietary devices are cumbersome and error-prone, and they cannot fully utilize the capability of physical network infrastructure. Recently, software-defined networking (SDN) has been touted as one of the most promising solutions for future Internet. SDN is characterized by its two distinguished features, including decoupling the control plane from the data plane and providing programmability for network application development. As a result, SDN is positioned to provide more efficient configuration, better performance, and higher flexibility to accommodate innovative network designs. This paper surveys latest developments in this active research area of SDN. We first present a generally accepted definition for SDN with the aforementioned two characteristic features and potential benefits of SDN. We then dwell on its three-layer architecture, including an infrastructure layer, a control layer, and an application layer, and substantiate each layer with existing research efforts and its related research areas. We follow that with an overview of the de facto SDN implementation (i.e., OpenFlow). Finally, we conclude this survey paper with some suggested open research challenges.
TL;DR: Host−Guest Supramolecular Chemistry A 1.1.1: Aims to explore the role of “ghostly” particles in the determination of chiral stationary phases and their role in the “spatially modified” states.
Abstract: 1. Host−Guest Supramolecular Chemistry A 1.
TL;DR: The Cu-TCPP nanosheet-based sensor shows excellent fluorescent sensing performance and is used for the simultaneous detection of multiple DNA targets.
Abstract: A facile surfactant-assisted bottom-up synthetic method to prepare a series of freestanding ultrathin 2D M-TCPP (M = Zn, Cu, Cd or Co, TCPP = tetrakis(4-carboxyphenyl)porphyrin) nanosheets with a thickness of sub-10 nm is developed. As a proof-of-concept application, some of them are successfully used as new platforms for DNA detection. The Cu-TCPP nanosheet-based sensor shows excellent fluorescent sensing performance and is used for the simultaneous detection of multiple DNA targets.
30 Sep 2015
TL;DR: This position paper position that a new shift is necessary in computing, taking the control of computing applications, data, and services away from some central nodes to the other logical extreme of the Internet, and refers to this vision of human-centered edge-device based computing as Edge-centric Computing.
Abstract: In many aspects of human activity, there has been a continuous struggle between the forces of centralization and decentralization. Computing exhibits the same phenomenon; we have gone from mainframes to PCs and local networks in the past, and over the last decade we have seen a centralization and consolidation of services and applications in data centers and clouds. We position that a new shift is necessary. Technological advances such as powerful dedicated connection boxes deployed in most homes, high capacity mobile end-user devices and powerful wireless networks, along with growing user concerns about trust, privacy, and autonomy requires taking the control of computing applications, data, and services away from some central nodes (the "core") to the other logical extreme (the "edge") of the Internet. We also position that this development can help blurring the boundary between man and machine, and embrace social computing in which humans are part of the computation and decision making loop, resulting in a human-centered system design. We refer to this vision of human-centered edge-device based computing as Edge-centric Computing. We elaborate in this position paper on this vision and present the research challenges associated with its implementation.
TL;DR: The saturable absorption property of the fabricated BP-SAs at the telecommunication band is characterized and shows that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.
Abstract: Black phosphorus (BP), an emerging narrow direct band-gap two-dimensional (2D) layered material that can fill the gap between the semi-metallic graphene and the wide-bandgap transition metal dichalcogenides (TMDs), had been experimentally found to exhibit the saturation of optical absorption if under strong light illumination. By taking advantage of this saturable absorption property, we could fabricate a new type of optical saturable absorber (SA) based on mechanically exfoliated BPs, and further demonstrate the applications for ultra-fast laser photonics. Based on the balanced synchronous twin-detector measurement method, we have characterized the saturable absorption property of the fabricated BP-SAs at the telecommunication band. By incorporating the BP-based SAs device into the all-fiber Erbium-doped fiber laser cavities, we are able to obtain either the passive Q-switching (with maximum pulse energy of 94.3 nJ) or the passive mode-locking operation (with pulse duration down to 946 fs). Our results show that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.
TL;DR: This tutorial review presents the state-of-the-art developments in ultrafast charging LIBs by the rational design of materials, and several aspects of the intrinsic materials, materials engineering and processing, and electrode materials architecture design towards maximizing both ionic and electronic conductivity in the electrode with a short diffusion length.
Abstract: Rechargeable lithium-ion batteries (LIBs) are important electrochemical energy storage devices for consumer electronics and emerging electrical/hybrid vehicles. However, one of the formidable challenges is to develop ultrafast charging LIBs with the rate capability at least one order of magnitude (>10 C) higher than that of the currently commercialized LIBs. This tutorial review presents the state-of-the-art developments in ultrafast charging LIBs by the rational design of materials. First of all, fundamental electrochemistry and related ionic/electronic conduction theories identify that the rate capability of LIBs is kinetically limited by the sluggish solid-state diffusion process in electrode materials. Then, several aspects of the intrinsic materials, materials engineering and processing, and electrode materials architecture design towards maximizing both ionic and electronic conductivity in the electrode with a short diffusion length are deliberated. Finally, the future trends and perspectives for the ultrafast rechargeable LIBs are discussed. Continuous rapid progress in this area is essential and urgent to endow LIBs with ultrafast charging capability to meet huge demands in the near future.
TL;DR: A new physical and chemical entrapment strategy is based on a highly efficient sulfur host, namely hollow carbon nanofibers filled with MnO2 nanosheets, which efficiently prevents polysulfide dissolution in Lithium-sulfur batteries.
Abstract: Lithium–sulfur batteries have been investigated as promising electrochemical-energy storage systems owing to their high theoretical energy density. Sulfur-based cathodes must not only be highly conductive to enhance the utilization of sulfur, but also effectively confine polysulfides to mitigate their dissolution. A new physical and chemical entrapment strategy is based on a highly efficient sulfur host, namely hollow carbon nanofibers (HCFs) filled with MnO2 nanosheets. Benefiting from both the HCFs and birnessite-type MnO2 nanosheets, the MnO2@HCF hybrid host not only facilitates electron and ion transfer during the redox reactions, but also efficiently prevents polysulfide dissolution. With a high sulfur content of 71 wt % in the composite and an areal sulfur mass loading of 3.5 mg cm−2 in the electrode, the MnO2@HCF/S electrode delivered a specific capacity of 1161 mAh g−1 (4.1 mAh cm−2) at 0.05 C and maintained a stable cycling performance at 0.5 C over 300 cycles.
TL;DR: The state-of-the-art progress of this dynamically developed material family of 2D-GAs with a particular focus on biomedical applications is summarized and some critical unresolved issues, possible challenges/obstacles are summarized.
Abstract: The increasing demand of clinical biomedicine and fast development of nanobiotechnology has substantially promoted the generation of a variety of organic/inorganic nanosystems for biomedical applications. Biocompatible two-dimensional (2D) graphene analogues (e.g., nanosheets of transition metal dichalcogenides, transition metal oxides, g-C3N4, Bi2Se3, BN, etc.), which are referred to as 2D-GAs, have emerged as a new unique family of nanomaterials that show unprecedented advantages and superior performances in biomedicine due to their unique compositional, structural and physicochemical features. In this review, we summarize the state-of-the-art progress of this dynamically developed material family with a particular focus on biomedical applications. After the introduction, the second section of the article summarizes a range of synthetic methods for new types of 2D-GAs as well as their surface functionalization. The subsequent section provides a snapshot on the use of these biocompatible 2D-GAs for a broad spectrum of biomedical applications, including therapeutic (photothermal/photodynamic therapy, chemotherapy and synergistic therapy), diagnostic (fluorescent/magnetic resonance/computed tomography/photoacoustic imaging) and theranostic (concurrent diagnostic imaging and therapy) applications, especially on oncology. In addition, we briefly present the biosensing applications of these 2D-GAs for the detection of biomacromolecules and their in vitro/in vivo biosafety evaluations. The last section summarizes some critical unresolved issues, possible challenges/obstacles and also proposes future perspectives related to the rational design and construction of 2D-GAs for biomedical engineering, which are believed to promote their clinical translations for benefiting the personalized medicine and human health.
TL;DR: In this paper, a computational screening based on density-functional-theory calculations reveals Ge as a candidate element for replacing Pb in halide perovskite compounds suitable for light harvesting.
Abstract: Computational screening based on density-functional-theory calculations reveals Ge as a candidate element for replacing Pb in halide perovskite compounds suitable for light harvesting. Experimentally, three AGeI3 (A = Cs, CH3NH3 or HC(NH2)2) halide perovskite materials have been synthesized. These compounds are stable up to 150 °C, and have bandgaps correlated with the A-site cation size. CsGeI3-based solar cells display higher photocurrents, of about 6 mA cm−2, but are limited by poor film forming abilities and oxidising tendencies. The present results demonstrate the utility of combining computational screening and experimental efforts to develop lead-free halide perovskite compounds for photovoltaic applications.
TL;DR: This work develops a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres, and demonstrates the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure.
Abstract: Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities.
27 May 2015
TL;DR: The proposed influence maximization algorithm is a set of estimation techniques based on martingales, a classic statistical tool that provides the same worst-case guarantees as the state of the art, but offers significantly improved empirical efficiency.
Abstract: Given a social network G and a positive integer k, the influence maximization problem asks for k nodes (in G) whose adoptions of a certain idea or product can trigger the largest expected number of follow-up adoptions by the remaining nodes This problem has been extensively studied in the literature, and the state-of-the-art technique runs in O((k+l) (n+m) log n e2) expected time and returns a (1-1 e-e)-approximate solution with at least 1 - 1/n l probability This paper presents an influence maximization algorithm that provides the same worst-case guarantees as the state of the art, but offers significantly improved empirical efficiency The core of our algorithm is a set of estimation techniques based on martingales, a classic statistical tool Those techniques not only provide accurate results with small computation overheads, but also enable our algorithm to support a larger class of information diffusion models than existing methods do We experimentally evaluate our algorithm against the states of the art under several popular diffusion models, using real social networks with up to 14 billion edges Our experimental results show that the proposed algorithm consistently outperforms the states of the art in terms of computation efficiency, and is often orders of magnitude faster
TL;DR: In this article, a comparative study of the catalytic activity of different phosphides towards hydrogen evolution reaction (HER) is conducted, where overpotentials at fixed current density, Tafel slope, turnover frequency, and the Gibbs free energy of hydrogen adsorption are evaluated.
Abstract: Hydrogen evolution by means of electrocatalytic water-splitting is pivotal for efficient and economical production of hydrogen, which relies on the development of inexpensive, highly active catalysts. In addition to sulfides, the search for non-noble metal catalysts has been mainly directed at phosphides due to the superb activity of phosphides for hydrogen evolution reaction (HER) and their low-cost considering the abundance of the non-noble constituents of phosphides. Here, recent research focusing on phosphides is summarized based on their synthetic methodology. A comparative study of the catalytic activity of different phosphides towards HER is then conducted. The catalytic activity is evaluated by overpotentials at fixed current density, Tafel slope, turnover frequency, and the Gibbs free energy of hydrogen adsorption. Based on the methods discussed, perspectives for the various methods of phosphides synthesis are given, and the origins of the high activity and the role of phosphorus on the improved activity towards HER are discussed.
TL;DR: This tutorial review will introduce the latest development of the synthesis of monolayer TMDs by CVD approaches, and shows great promise to generate high-quality TMD layers with a scalable size, controllable thickness and excellent electronic properties.
Abstract: In recent years there have been many breakthroughs in two-dimensional (2D) nanomaterials, among which the transition metal dichalcogenides (TMDs) attract significant attention owing to their unusual properties associated with their strictly defined dimensionalities. TMD materials with a generalized formula of MX2, where M is a transition metal and X is a chalcogen, represent a diverse and largely untapped source of 2D systems. Semiconducting TMD monolayers such as MoS2, MoSe2, WSe2 and WS2 have been demonstrated to be feasible for future electronics and optoelectronics. The exotic electronic properties and high specific surface areas of 2D TMDs offer unlimited potential in various fields including sensing, catalysis, and energy storage applications. Very recently, the chemical vapour deposition technique (CVD) has shown great promise to generate high-quality TMD layers with a scalable size, controllable thickness and excellent electronic properties. Wafer-scale deposition of mono to few layer TMD films has been obtained. Despite the initial success in the CVD synthesis of TMDs, substantial research studies on extending the methodology open up a new way for substitution doping, formation of monolayer alloys and producing TMD stacking structures or superlattices. In this tutorial review, we will introduce the latest development of the synthesis of monolayer TMDs by CVD approaches.
TL;DR: This special issue is about two-dimensional transition metal dichalcogenides (2D TMDs), a family of materials consisting of over 40 compounds with the generalized formula of MX2, where M is a transition metal typically from groups 4–7, and X is a chalcogens such as S, Se or Te.
Abstract: This special issue is about two-dimensional transition metal dichalcogenides (2D TMDs), a family of materials consisting of over 40 compounds with the generalized formula of MX2, where M is a transition metal typically from groups 4–7, and X is a chalcogen such as S, Se or Te. Bulk TMDs have been widely studied over several decades because it is possible to formulate compounds with disparate electronic structures. In the bulk form, MX2 compounds are layered materials (or van der Waals solids) in which there is strong intralayer bonding and weak interlayer bonding. Each individual layer of the TMDs consists of three atomic layers in which the transition metal is sandwiched by two chalcogens. Furthermore, the chalcogen atoms are saturated and therefore are not highly reactive. These features allow for the attainment of individual layers of the TMDs by several exfoliation or vapor deposition methods. The isolation of monolayers of TMDs leads to the dramatic changes in their properties, primarily due to the confinement of charge carriers in two dimensions (xand y-directions) due to the absence of interactions in the z-direction. Thus, singlelayered nanosheets are two-dimensional materials that possess dramatically different a Materials Science and Engineering, Rutgers University, 607 Taylor Road, Piscataway, NJ 08854, USA. E-mail: manish1@rci.rutgers.edu b Center for Nanochemistry (CNC), Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, People’s Republic of China. E-mail: zfliu@pku.edu.cn c School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. E-mail: hzhang@ntu.edu.sg
TL;DR: Additive manufacturing (AM), commonly known as three-dimensional (3D) printing or rapid prototyping, has been introduced since the late 1980s as discussed by the authors, and a considerable amount of progress has been made in this field.
Abstract: Additive manufacturing (AM), commonly known as three-dimensional (3D) printing or rapid prototyping, has been introduced since the late 1980s. Although a considerable amount of progress has been made in this field, there is still a lot of research work to be done in order to overcome the various challenges remained. Recently, one of the actively researched areas lies in the additive manufacturing of smart materials and structures. Smart materials are those materials that have the ability to change their shape or properties under the influence of external stimuli. With the introduction of smart materials, the AM-fabricated components are able to alter their shape or properties over time (the 4th dimension) as a response to the applied external stimuli. Hence, this gives rise to a new term called ‘4D printing’ to include the structural reconfiguration over time. In this paper, recent major progresses in 4D printing are reviewed, including 3D printing of enhanced smart nanocomposites, shape memory al...
TL;DR: A facile one-pot wet-chemical method is developed to prepare MS2-CdS (M=W or Mo) nanohybrids, which possess a large number of edge sites in the MS2 layers, which are active sites for the HER.
Abstract: Exploration of low-cost and earth-abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition-metal dichalcogenides (TMDs) showed outstanding performance as co-catalysts for the hydrogen evolution reaction (HER), designing TMD-hybridized photocatalysts with abundant active sites for the HER still remains challenge. Here, a facile one-pot wet-chemical method is developed to prepare MS2–CdS (M=W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single-layer MS2 nanosheets with lateral size of 4–10 nm selectively grow on the Cd-rich (0001) surface of wurtzite CdS nanocrystals. These MS2–CdS nanohybrids possess a large number of edge sites in the MS2 layers, which are active sites for the HER. The photocatalytic performances of WS2–CdS and MoS2–CdS nanohybrids towards the HER under visible light irradiation (>420 nm) are about 16 and 12 times that of pure CdS, respectively. Importantly, the MS2–CdS nanohybrids showed enhanced stability after a long-time test (16 h), and 70 % of catalytic activity still remained.