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Organic single crystals (OSCs) have received increasing interest in the last decades for their potential applications in flexible electronics. Although there are various subtractive manufacturing methods of organic electronics, the subtractive manufacturing of OSCs is still a challenge, since OSCs are assembled via weak van-der-Waals interactions which are vulnerable and cannot afford damages and suffer the degradation of performances after the process. Here, we develop an epitaxial etching strategy which clips the OSCs and keeps high-quality crystalline nature of the resulting materials. As a result, high-quality organic micro-ribbon arrays are fabricated which maintains 89% charge mobility in average compared with original OSCs, showing great potential of this subtractive manufacturing method in future organic electronics.

In principle, polymerization tends to produce amorphous or poorly crystalline materials. Efficiently producing high-quality single crystals by polymerization in solvent remains as an unsolved issue in chemistry, especially for covalent organic frameworks (COFs) with highly complex structures. To produce μm-sized single crystals, the growth time is prolonged to >15 days, far away from the requirements in practical applications. Here, we find supercritical CO2 (sc-CO2) accelerates single-crystal polymerization by 10,000,000 folds, and produces two-dimensional (2D) COF single crystals with size up to 0.2 mm within 2~5 min. Although it is the fastest single-crystal polymerization, the growth in sc-CO2 leads to not only the largest crystal size of 2D COFs, but also higher quality with improved photoconductivity performance. This work overcomes traditional concept on low efficiency of single-crystal polymerization, and holds great promise for future applications owing to its efficiency, industrial compatibility, environmental friendliness and universality for different crystalline structures and linkage bonds., Rapid growth of highly crystalline Covalent organic framework (COF) materials remains challenging. Here, the authors accelerate single-crystal polymerization using supercritical CO2 and realize the fabrication of two-dimensional COF single crystals within several minutes.

Metal-air batteries in fiber shape, which are theoretically endowed with high energy densities, have emerged as a versatile platform for the advance of next-generation flexible electronics. The past decade has witnessed the booming development of fiber-shaped metal-air batteries including flexible lithium-air (oxygen) batteries, zinc-air batteries, aluminum-air batteries and lithium-CO2 batteries. Here the recent advances of fiber-shaped metal-air batteries are briefly summarized, with particular emphasis on the fabrication of flexible electrodes, the electrolyte exploitation and encapsulating material optimization. The remaining challenges and promising directions are highlighted to provide clues for the practical implementation of fiber-shaped metal-air batteries.

Recent development of self-healing material has attracted tremendous attention, owing to its biomimetic ability to restore structure and functionality when encountering damages. Here, we develop a three-dimensional (3D) printable self-healing composite conductive polymer by mixing hydrogen-bond-based supramolecular polymer with low-cost carbon black. It has a room-temperature self-healing capability in both conductivity and mechanical property, while its shear-thinning behavior enables fabrication of a self-healable circuit by 3D printing technology. As an application, the circuit shows an excellent temperature-dependent behavior of the resistance, indicating its great potential for practical application in the artificial intelligence field.

A semiconducting photoresist contributes to precise and reliable manufacture of highly integrated organic electronics., Owing to high resolution, reliability, and industrial compatibility, all-photolithography is a promising strategy for industrial manufacture of organic electronics. However, it receives limited success due to the absence of a semiconducting photoresist with high patterning resolution, mobility, and performance stability against photolithography solution processes. Here, we develop a comprehensive semiconducting photoresist with nano-interpenetrating structure. After photolithography, nanostructured cross-linking networks interpenetrate with continuous phases of semiconducting polymers, enabling submicrometer patterning accuracy and compact molecular stacking with high thermodynamic stability. The mobility reaches the highest values of photocrosslinkable organic semiconductors and maintains almost 100% after soaking in developer and stripper for 1000 min. Owing to the comprehensive performance, all-photolithography is achieved, which fabricates organic inverters and high-density transistor arrays with densities up to 1.1 × 105 units cm−2 and 1 to 4 orders larger than conventional printing processes, opening up a new approach toward manufacturing highly integrated organic circuits and systems.

ConspectusSince the rise of two-dimensional (2D) materials, synthetic methods including mechanical exfoliation, solution synthesis, and chemical vapor deposition (CVD) have been developed. Mechanical exfoliation prepares randomly shaped materials with small size. Solution synthesis introduces impurities that degrade the performances. CVD is the most successful one for low-cost scalable preparation. However, when it comes to practical applications, disadvantages such as high operating temperature (∼1000 °C), probable usage of metal catalysts, contamination, defects, and interstices introduced by postgrowth transfer are not negligible. These are the reasons why plasma-enhanced CVD (PECVD), a method that enables catalyst-free in situ preparation at low temperature, is imperatively desirable.In this Account, we summarize our recent progress on controllable preparation of 2D materials by PECVD and their applications. We found that there was a competition between etching and nucleation and deposition in PECVD, making it highly controllable to obtain desired materials. Under different equilibrium states of the competition, various 2D materials with diverse morphologies and properties were prepared including pristine or nitrogen-doped graphene crystals, graphene quantum dots, graphene nanowalls, hexagonal boron nitride (h-BN), B-C-N ternary materials (BCxN), etc. We also used mild plasma to modify or treat 2D materials (e.g., WSe2) for desired properties.PECVD has advantages such as low temperature, transfer-free process, and industrial compatibility, which enable facile, scalable, and low-cost preparation of 2D materials with clean surfaces and interfaces directly on noncatalytic substrates. These merits significantly benefit the as-prepared materials in the applications. Field-effect transistors with high motilities were directly fabricated on graphene and nitrogen-doped graphene. By use of h-BN as the dielectric interfacial layer, both mobilities and saturated power densities of the devices were improved owing to the clean, closely contacted interface and enhanced interfacial thermal dissipation. High-quality materials and interfaces also enabled promising applications of these materials in photodetectors, pressure sensors, biochemical sensors, electronic skins, Raman enhancement, etc. To demonstrate the commercial applications, several prototypical devices were studied such as distributed pressure sensor arrays, touching module on a robot hand for braille recognition, and smart gloves for recording sign language. Finally, we discuss opportunities and challenges of PECVD as a comprehensive preparation methodology of 2D materials for future applications beyond traditional CVD.

Self-healing materials have been developed over the past decade with the recovery ability after damage. However, most researches focused on the self-healing process at three-dimension. Herein, we prepare monolayer self-healing hydrogen-bond-based supramolecular polymer film and explore the self-healing process at the two-dimensional limit. The healing process, which can be reversibly repeated for at least three times, is influenced by the temperature, the molecule-substrate interaction and the substrate roughness. In the application, the monolayer self-healing polymer film can be used to modify the SiO2 dielectric for copper phthalocyanine field effect transistor with improved mobility. This work will be valuable for developing two-dimensional functional self-healing materials in the future.

Three-dimensional (3D) graphene has attracted increasing attention in electrochemical devices. However, the existing preparation technologies usually involve a solvent process, which introduces defects and functional groups into the 3D network. Here, we find the defects and functional groups influence the electrochemical stability of graphene. After an electrochemical process, the current decreases by more than 1 order of magnitude, indicating remarkable etching of graphene. To improve the electrochemical stability, we develop a solvent-free preparation process to produce 3D graphene for the first time. After growth on a 3D microporous copper by chemical vapor deposition (CVD), the copper template is removed by a high temperature evaporation process, resulting in 3D graphene network without any solvent process involved. The samples exhibit remarkably improved stability with durable time 2 times, compared with normal CVD samples, and 55 times, compared with reduced graphite oxide, and no obvious etching is...

As a recently developed detection technique, photoelectrochemical (PEC) measurement has received extensive attention. However, owing to the lack of a comprehensive approach to engineer the photo-generated carriers, the performance is still limited. As an example, a significant use of PEC measurement might be in understanding the roles of glutathione in physiological and pathological processes. Here, we developed a new approach for engineering the photo-generated carriers with the aid of the synergic effect of self-doping, surface plasmon resonance, electrical field amplification effect, etc. Thus, a highly sensitive multicomponent PEC platform has been developed, in which Au nanorods are decorated on the surface of self-doped TiO2 nanowires, followed by surface receptor functionalization with hemin for capturing glutathione. The synergic effect effectively increases generation, separation and transfer kinetics of the photo-generated carriers, which can be further increased by using a mixture of Au nanorods with different aspect ratios to tune the absorption wavelength to the entire UV-visible region. As a result, this system exhibits a broad linear range from 10 nM to 17.5 μM and low detection limit down to 8.6 nM for detecting glutathione, about 1–2 orders of magnitude lower than most existing PEC sensors.

In recent years, as a new class of two-dimensional polymer, covalent organic frameworks (COFs) have attracted intensive attention and developed rapidly. This review provides an overview of a type of COFs which can be utilized as organic semiconductors. Carefully choosing monomers as the building blocks will bestow different types of semiconducting character on COFs. We summarize the p-type, n-type and ambipolar semiconducting COFs and highlight the effects of π-functional building blocks on the photoconductive behaviors of the semiconducting COFs.

Conformal graphene films have directly been synthesized on the surface of grating microstructured quartz substrates by a simple chemical vapor deposition process. The wonderful conformality and relatively high quality of the as-prepared graphene on the three-dimensional substrate have been verified by scanning electron microscopy and Raman spectra. This conformal graphene film possesses excellent electrical and optical properties with a sheet resistance of2000 Ω·sq(-1) and a transmittance of80% (at 550 nm), which can be attached with a flat graphene film on a poly(dimethylsiloxane) substrate, and then could work as a pressure-sensitive sensor. This device possesses a high-pressure sensitivity of -6.524 kPa(-1) in a low-pressure range of 0-200 Pa. Meanwhile, this pressure-sensitive sensor exhibits super-reliability (≥5000 cycles) and an ultrafast response time (≤4 ms). Owing to these features, this pressure-sensitive sensor based on 3D conformal graphene is adequately introduced to test wind pressure, expressing higher accuracy and a lower background noise level than a market anemometer.

Graphene is regarded as a potential surface-enhanced Raman spectroscopy (SERS) substrate. However, the application of graphene quantum dots (GQDs) has had limited success due to material quality. Here, we develop a quasi-equilibrium plasma-enhanced chemical vapor deposition method to produce high-quality ultra-clean GQDs with sizes down to 2 nm directly on SiO2/Si, which are used as SERS substrates. The enhancement factor, which depends on the GQD size, is higher than conventional graphene sheets with sensitivity down to 1 × 10−9 mol L−1 rhodamine. This is attributed to the high-quality GQDs with atomically clean surfaces and large number of edges, as well as the enhanced charge transfer between molecules and GQDs with appropriate diameters due to the existence of Van Hove singularities in the electronic density of states. This work demonstrates a sensitive SERS substrate, and is valuable for applications of GQDs in graphene-based photonics and optoelectronics., Surface-enhanced Raman spectroscopy (SERS) is a promising technology for sensitive optical sensors, generally using rough metal films. Here, Liu et al. synthesize high-quality graphene quantum dot films which offer a large SERS enhancement due to a strong light-matter interaction with Van Hove singularities.

Nitrogen doping is one of the most promising routes to modulate the electronic characteristic of graphene. Plasma-enhanced chemical vapor deposition (PECVD) enables low-temperature graphene growth. However, PECVD growth of nitrogen doped graphene (NG) usually requires metal-catalysts, and to the best of our knowledge, only amorphous carbon-nitrogen films have been produced on dielectric surfaces by metal-free PECVD. Here, a critical factor for metal-free PECVD growth of NG is reported, which allows high quality NG crystals to be grown directly on dielectrics like SiO2/Si, Al2O3, h-BN, mica at 435 °C without a catalyst. Thus, the processes needed for loading the samples on dielectrics and n-type doping are realized in a simple PECVD, which would be of significance for future graphene electronics due to its compatibility with the current microelectronic processes.

Graphene has attracted tremendous research interest owing to its widespread potential applications. However, these applications are partially hampered by the lack of a general method to produce high-quality graphene at low cost. Here, to the best of our knowledge, we use low-cost solid carbon allotropes as the precursor in plasma-enhanced chemical vapor deposition (PECVD) for the first time, and find that the hydrogen plasma and reaction temperature play a crucial role in the process. Hydrogen plasma etches carbon black, and produces graphene crystals in a high-temperature zone. Based on this finding, a modified PECVD technology is developed, which produces transparent conductive nanographene films directly on various substrates at a temperature as low as 600 °C. For application, the closely packed structure of the nanographene film enables a remarkable temperature-dependent behavior of the resistance with a ratio higher than that previously reported, indicating its great potential for usage in highly sensitive temperature detectors.

In recent years, as a new class of two-dimensional polymer, covalent organic frameworks (COFs) have attracted intensive attention and developed rapidly. This review provides an overview of a type of COFs which can be utilized as organic semiconductors. Carefully choosing monomers as the building blocks will bestow different types of semiconducting character on COFs. We summarize the p-type, n-type and ambipolar semiconducting COFs and highlight the effects of π-functional building blocks on the photoconductive behaviors of the semiconducting COFs.

Graphene and its derivatives hold a great promise for widespread applications such as field-effect transistors, photovoltaic devices, supercapacitors, and sensors due to excellent properties as well as its atomically thin, transparent, and flexible structure. In order to realize the practical applications, graphene needs to be synthesized in a low-cost, scalable, and controllable manner. Plasma-enhanced chemical vapor deposition (PECVD) is a low-temperature, controllable, and catalyst-free synthesis method suitable for graphene growth and has recently received more attentions. This review summarizes recent advances in the PECVD growth of graphene on different substrates, discusses the growth mechanism and its related applications. Furthermore, the challenges and future development in this field are also discussed.

Because of its atomic thickness, excellent properties, and widespread applications, graphene is regarded as one of the most promising candidate materials for nanoelectronics. The wider use of graphene will require processes that produce this material in a controllable manner. In this Account, we focus on our recent studies of the controllable chemical vapor deposition (CVD) growth of graphene, especially few-layer graphene (FLG), and the applications of this material in electronic devices. CVD provides various means of control over the morphologies of the produced graph ene. We studied several variables that can affect the CVD growth of graphene, including the catalyst, gas flow rate, growth time, and growth temperature and successfully achieved the controlled growth of hexagonal graphene crystals. Moreover, we developed several modified CVD methods for the controlled growth of FLGs. Patterned CVD produced FLGs with desired shapes in required areas. By introducing dopant precursor in the CVD process, we produced substitutionally doped FLGs, avoiding the typically complicated post-treatment processes for graphene doping. We developed a template CVD method to produce FLG ribbons with controllable morphologies on a large scale. An oxidation-activated surface facilitated the CVD growth of polycrystalline graphene without the use of a metal catalyst or a complicated postgrowth transfer process. In devices, CVD offers a controllable means to modulate the electronic properties of the graphene samples and to improve device performance. Using CVD-grown hexagonal graphene crystals as the channel materials in field-effect transistors (FETs), we improved carrier mobility. Substitutional doping of graphene in CVD opened a band gap for efficient FET operation and modulated the Fermi energy level for n-type or p-type features. The similarity between the chemical structure of graphene and organic semiconductors suggests potential applications of graphene in organic devices. We used patterned CVD FLGs as the bottom electrodes in pentacene FETs. The strong π-π interactions between graphene and pentacene produced an excellent interface with low contact resistance and a reduced injection barrier, which dramatically enhances the device performance. We also fabricated reversible nanoelectromechanical (NEM) switches and a logic gate using the FLG ribbons produced using our template CVD method. In summary, CVD provides a controllable means to produce graphene samples with both large area and high quality. We developed several modified CVD methods to produce FLG samples with controlled shape, location, edge, layer, dopant, and growth substrate. As a result, we can modulate the properties of FLGs, which provides materials that could be used in FETs, OFETs, and NEM devices. Despite remarkable advances in this field, further exploration is required to produce consistent, homogeneous graphene samples with single layer, single crystal, and large area for graphene-based electronics.

A general and useful method has been developed to evaluate the metallic-to-semiconducting (M/S) ratio for separated single-walled carbon nanotubes (SWNTs). By virtue of measuring UV−vis−NIR spectra of a variety of solutions with different ratios of metallic-rich to semiconducting-rich SWNTs, the commercial IsoNanotubes samples as well as metallic-rich HiPCO SWNTs (HiPCO-M) separated by an Agarose gel method have been evaluated. Values of 99.5% metallic contents for IsoNanotubes-M, 98.9% semiconducting contents for IsoNanotubes-S, and 1.24 for the absorption coefficient of IsoNanotubes, whereas 80.4% metallic contents for HiPCO-M and 1.05 for the absorption coefficient of HiPCO SWNTs were obtained. This method does not need pure metallic (M-) or semiconducting (S-) SWNTs as references. Furthermore, we found that this method can also be applied to evaluate the M/S ratio for any SWNT samples.

Graphene, a two-dimensional material, is regarded as one of the most promising candidates for future nanoelectronics due to its atomic thickness, excellent properties and widespread applications. As the first step to investigate its properties and finally to realize the practical applications, graphene must be synthesized in a controllable manner. Thus, controllable synthesis is of great significance, and received more and more attention recently. This Progress Report highlights recent advances in controllable synthesis of graphene, clarifies the problems, and prospects the future development in this field. The applications of the controllable synthesis are also discussed.

One-dimensional (1D) nanostructures of the wide band gap semiconductors are promising building blocks for photoelectric nanodevices. However, some problems like strong 1D confinement largely hamper their applications. To avoid these problems, here, we provide another 1D configuration, in which an inner-wire coaxial Schottky junction exists, thus effectively avoiding the recombination of the photoexcited carriers. As an example, we produce ZnS/carbon nanotube nanocables with uniform morphologies by a two-step vapor deposition method and find that they have good conductance, obvious light response, and ohmic contacts with electrodes, avoiding the limitations of both the pristine nanomaterials. We believe that this configuration would be valuable for applying the 1D nanomaterials in photoelectronics.

Single-walled carbon nanotubes (SWNTs) are a promising material for future nanotechnology. However, their applications are still limited in success because of the co-existence of metallic SWNTs and semiconducting SWNTs produced samples. Here, electrochemical etching, which shows both diameter and electrical selectivity, is demonstrated to remove SWNTs. With the aid of a back-gate electric field, selective removal of metallic SWNTs is realized, resulting in high-performance SWNT field-effect transistors with pure semiconducting SWNT channels. Moreover, electrochemical etching is realized on a selective area. These findings would be valuable for research and the application of SWNTs in electrochemistry and in electronic devices.

Controllable and scalable production is of great importance for the application of graphene; however, to date, it is still a great challenge and a major obstacle which hampers its practical applications. Here, we develop a template chemical vapor deposition method for scalable synthesis of few-layer graphene ribbons (FLGRs) with controlled morphologies. The FLGRs have a good conductivity and are ideal for use in nanoelectromechanics (NEM). As an application, we fabricate a reversible NEM switch and a logic gate by using the FLGRs. This work realizes both controllable and scalable synthesis of graphene, provides an application of graphene in NEM switches, and would be valuable for both the scientific studies and the practical applications of graphene.

For the miniaturization of microelectronics, carbon nanotubes (CNTs) are regarded as ideal candidates for the next generation of nanoelectronics because of their excellent properties. To realize CNT-based electronics, intramolecular junctions are required components, which can not only connect different CNTs for integration, but can also act as functional building blocks in the circuit, such as rectifiers, field-effect transistors, switches, amplifiers, photoelectrical devices, etc. Therefore, intense attention has been focused on this topic and many advances have been achieved, especially in recent years. On the other hand, some challenges also exist. To provide researchers with a comprehensive overview of this field, this review discusses the synthesis, properties, and applications of intramolecular junctions of CNTs in detail. Among them, the applications of CNT integration are discussed specially. Furthermore, a brief summary and an outlook of future work are provided.

A simple acid treatment method was applied to remove the catalyst impurities and other residues contaminated in the vertically aligned carbon nanotube arrays. We demonstrated that acid treatment was an efficient approach for aligned carbon nanotube purification. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology of the aligned carbon nanotube arrays and to determine the efficiency of the purification. Using hydrochloric acid could efficiently eliminate catalyst impurities and retain the original structures of the aligned carbon nanotube arrays. The method provided a simple, economical, and effective way to purify the aligned carbon nanotubes, and it would promote the applications of vertically aligned carbon nanotube arrays in electronic field.

Molecular electronics is often limited by the lack of a simple method to fabricate nanoelectrodes with controlled gap size. This is partly attributed to the lack of a real time characterization in the fabrication. Here, we report a new method based on an electron induced deposition process operated in scanning electron microscopy that realizes in situ and real time characterization in the nanoelectrode fabrication; thus the gap size can be controlled easily and precisely. It is a clean and nondestructive process for carbon nanotube (CNT) electrodes. The mechanism is detailed. The nanoelectrodes have a pi-conjugated surface due to the deposition of sp(2)-rich amorphous carbon. As an application, DNA molecules are assembled between the CNT electrodes by pi-stacking interaction for current-voltage measurement. Our result provides a feasible route to prepare nanoelectrodes with controlled gap size, and it will be valuable for current efforts in molecular electronics and nanoelectronics.

A magnetism-assisted chemical vapor deposition method was developed to synthesize branched or iron-encapsulated carbon nanotubes. In the process, the external magnetic field can promote the coalescence or division of the catalyst particles, causing the formation of branched or encapsulated nanostructures. This finding will extend the understanding of the chemical vapor deposition method in a magnetic field and promote the applications of branched or encapsulated nanostructures.

Supercritical fluids in the presence of metal nitrate are used for the modulating conductivity of carbon nanotubes (CNTs). At the same time, CNTs are coated with discontinuous nanometer thin metal oxide dielectrics. To validate the effect of modulation, we have made multiwalled CNTs (self-coating with gate dielectrics) transistors using electron beam lithography deposition technology and studied their electronic properties. In particular, the method appears promising to improve the performance of existing field-effect transistors consisting of single-walled CNT networks, which display poor switching ratios in normal cases due to the coexistence of metallic and semiconducting tubes. Moreover, the mechanism of the multifarious morphology of a CNT/metal oxide has been discussed.

On the basis of high-density and uniform assembly of Au nanoparticles on carbon nanotube (CNT) surface and subsequently the convenient chemical vapor deposition technique, the nanowires with carbon nanotube core and uniform silica insulating shell were controllably synthesized and then efficiently integrated into top-gated FETs. The study provides a simpler, lower-cost, and more controllable methodology for the uniform coating/functionalizing of CNTs with shell layer materials such as oxide gate-dielectrics. Moreover, the as-synthesized core−shell nanowires, with inherent gate-dielectric shell layer, provide a new opportunity for efficiently and conveniently fabricating of top-gated CNTFETs and other vertical surround-gated CNTFET devices, thus making for the development of more highly integrated circuits.

A simple and versatile approach has been developed to synthesize different carbon nanotube (CNT)-nanoparticle hybrid materials. The strategy is based on the nondestructive (noncovalent) functionalization of pristine CNTs and the subsequent in situ synthesis of a variety of different nanoparticles, including metal, semiconductor, and insulator particles, on the modified CNTs. This strategy has been demonstrated here with Pt, CdS, and silica nanoparticles. It is believe that this technique will provide a simple and convenient route to efficiently assemble a wide variety of nanoscale particles/clusters on the surfaces of CNTs, and will enable the construction of nanoscale heterostructures with novel functionalities in nanotechnology.

Graphene is regarded as one of the most promising candidate materials for future electronics. For usage in electrical devices, high-quality graphene needs to be placed on a dielectric surface. Currently, methods for graphene preparation require graphene to be transferred from scotch tape, metals, or solutions to the dielectric substrate for electrical applications. The transfer process normally induces contamination, wrinkles, or even breakage of the graphene samples and thus hampers the practical application of graphene in electronics. Moreover, chemical vapor deposition (CVD) on a metal catalyst normally requires a growth temperature as high as 800–1000 8C. For industrial-scale production, lowtemperature growth can lead to a decrease in energy consumption and cost, and an increase in compatibility. Therefore, a low-cost, controllable, and reliable method is required for the production of clean high-quality graphene directly on dielectric substrates at low temperature. One pioneering study towards the goal of the catalyst-free growth of graphene on dielectric materials examined the pyrolysis of CH4 on bare SiO2/Si; [5,6] however, this method requires a high growth temperature (1100–1650 8C). Another approach, plasma-enhanced CVD (PECVD), enables the low-temperature growth of graphene on metals, or even on dielectric surfaces (550–650 8C). However, without metal catalysts, structural defects readily form at the edges and terminate graphene growth. As a result, small graphene nanoclusters or noncrystalline samples are formed, the quality of which is lower than that required for electrical applications. Vertically oriented graphene nanosheets can be produced by PECVD; however, most of the products are multilayered. Herein, we describe the development of a critical PECVD (c-PECVD) growth method, in which a H2 plasma is introduced during graphene growth. H2 plasma is known to etch graphene from the edges. Moderate etching by a H2 plasma removes defects generated at the edges and thus keeps the edges atomically smooth and active during the whole process of graphene crystal growth. Therefore, in a critical equilibrium state between H2 plasma etching and CH4 or C2H4 plasma growth, we observed efficient catalyst-free crystal growth of graphene directly on crystalline sapphire, highly oriented pyrolytic graphite (HOPG), and the amorphous surface of Si substrates with a thermally grown 300 nm SiO2 overlayer (SiO2/Si), with crystal sizes up to the micrometer scale for single-layer hexagonal single crystals and up to the centimeter scale for continuous films. The growth temperature could be decreased to as low as 400 8C when C2H4 was used as the carbon source. To the best of our knowledge, this temperature is one of the lowest used for the catalyst-free growth of graphene. In the experiments, a homemade remote radiofrequency (13.56 mHz) PECVD system (80 W) was used (Figure 1a). Figure 1b illustrates the typical procedure for the c-PECVD growth of graphene on bare Si/SiO2 (see the Experimental Section for details). We first used peel-off graphene to clarify the etching, critical edge growth, and nucleation of graphene in PECVD. Figure 1c shows atomic force microscopy (AFM) images of a trilayer peel-off graphene flake before and after cPECVD growth (H2 plasma activation: 250 mTorr, 500 8C; growth: 30% H2, 90 mTorr, 600 8C, 60 min). The edges of the bottom, middle, and upper layer moved by 79, 117, and 158 nm, respectively, thus indicating that continuous growth of the flake took place on the edges, rather than in the plane. The different growth rate of each layer is attributed to the substrate (see Figure S1 in the Supporting Information). Control experiments show that the edge growth is highly dependent on the H2 content, the growth temperature, and the pressure (Figure 1d). Lower temperatures or higher H2 content tend to induce edge etching, whereas the opposite reaction conditions cause the nucleation of graphitic clusters (see Figure S2). For example, after CH4+H2 plasma CVD at a lower temperature (550 8C), instead of growth, the edges of the flakes were etched by about 168 nm (Figure 1e). Upon CH4+H2 plasma CVD at a lower H2 content (20%), besides the edge growth, small graphitic clusters were nucleated on whole surface of the graphene flakes and SiO2/Si surface with heights lower than 1 nm (Figure 1 f); the heights observed indicate the single-layered nature of the nucleated clusters. The edge growth (Figure 1c; see also Figure S3) only takes place at a well-controlled critical temperature between those needed for nucleation and edge etching, and the critical temperature decreases as the H2 content decreases (Figure 1d). When C2H4 was used as the carbon source in cPECVD (0%H2, 48 mTorr), the critical temperature for edge growth decreased to as low as 400 8C (Figure 1d). Moreover, low pressure can lead to a remarkable improvement in the growth rate. The growth rate (30% H2, 600 8C) was about [*] Dr. D. Wei, Dr. Y. Lu, Prof. W. Chen, Prof. A. T. S. Wee Department of Physics, National University of Singapore 2 Science Drive 3, Singapore 117542 (Singapore) E-mail: phyweid@nus.edu.sg phyweets@nus.edu.sg

Graphene is often regarded as one of the most promising candidates for future nanoelectronics. As an indispensable component in graphene-based electronics, the formation of junctions with other materials not only provides utility functions and reliable connexions, but can also improve or alter the properties of pristine graphene, opening up possibilities for new applications. Here we demonstrate an intramolecular junction produced by the controllable unzipping of single-walled carbon nanotubes, which combines a graphene nanoribbon and single-walled carbon nanotube in a one-dimensional nanostructure. This junction shows a strong gate-dependent rectifying behaviour. As applications, we demonstrate the use of the junction in prototype directionally dependent field-effect transistors, logic gates and high-performance photodetectors, indicating its potential in future graphene-based electronics and optoelectronics.

Graphene has attracted much interest in both academia and industry. The challenge of making it semiconducting is crucial for applications in electronic devices. A promising approach is to reduce its physical size down to the nanometer scale. Here, we present the surface-assisted bottom-up fabrication of atomically precise armchair graphene nanoribbons (AGNRs) with predefined widths, namely 7-, 14- and 21-AGNRs, on Ag(111) as well as their spatially resolved width-dependent electronic structures. STM/STS measurements reveal their associated electron scattering patterns and the energy gaps over 1 eV. The mechanism to form such AGNRs is addressed based on the observed intermediate products. Our results provide new insights into the local properties of AGNRs, and have implications for the understanding of their electrical properties and potential applications.

Ring closure of 6-amino-3-oxo-as-triazine-5-thione with α-haloketones provides the thiazino[2,3-e]-1,2,4-triazines which dehydrate via an unusual pathway to give 7-aryl-8H[1,4]thiazino[2,3-e]-1,2,4-triazin-3(2H)-ones.

To realize graphene-based electronics, various types of graphene are required; thus, modulation of its electrical properties is of great importance. Theoretic studies show that intentional doping is a promising route for this goal, and the doped graphene might promise fascinating properties and widespread applications. However, there is no experimental example and electrical testing of the substitutionally doped graphene up to date. Here, we synthesize the N-doped graphene by a chemical vapor deposition (CVD) method. We find that most of them are few-layer graphene, although single-layer graphene can be occasionally detected. As doping accompanies with the recombination of carbon atoms into graphene in the CVD process, N atoms can be substitutionally doped into the graphene lattice, which is hard to realize by other synthetic methods. Electrical measurements show that the N-doped graphene exhibits an n-type behavior, indicating substitutional doping can effectively modulate the electrical properties of graphene. Our finding provides a new experimental instance of graphene and would promote the research and applications of graphene.

For the miniaturization of microelectronics, carbon nanotubes (CNTs) are regarded as ideal candidates for the next generation of nanoelectronics because of their excellent properties. To realize CNT-based electronics, intramolecular junctions are required components, which can not only connect different CNTs for integration, but can also act as functional building blocks in the circuit, such as rectifiers, field-effect transistors, switches, amplifiers, photoelectrical devices, etc. Therefore, intense attention has been focused on this topic and many advances have been achieved, especially in recent years. On the other hand, some challenges also exist. To provide researchers with a comprehensive overview of this field, this review discusses the synthesis, properties, and applications of intramolecular junctions of CNTs in detail. Among them, the applications of CNT integration are discussed specially. Furthermore, a brief summary and an outlook of future work are provided.

We report high performance organic field-effect transistors (OFETs) with the modified Cu bottom-contact electrodes. Efficient modification of the Cu electrodes with nanometer-size copper tetracyanoquinodimethane (Cu-TCNQ) increases the electrode/organic layer contact area and reduces contact resistance. We investigated the effect of the Cu-TCNQ morphology on the device performance. The pentacene-based OFETs with the modified Cu bottom-contact electrodes exhibited high device performance. The field-effect mobility up to 0.31 cm(2)/V s was achieved. To the best of our knowledge, this is the highest device performance for the OFETs with the bottom Cu electrodes ever reported. Consequently, our results provide an effective approach to fabricate high performance and low-cost OFETs.

Here we develop a simple method by using flow fluctuation to synthesize arrays of multi-branched carbon nanotubes (CNTs) that are far more complex than those previously reported. The architectures and compositions can be well controlled, thus avoiding any template or additive. A branching mechanism of fluctuation-promoted coalescence of catalyst particles is proposed. This finding will provide a hopeful approach to the goal of CNT-based integrated circuits and be valuable for applying branched junctions in nanoelectronics and producing branched junctions of other materials.

Molecular electronics are considered one of the most promising ways to meet the challenge of micro-electronics facing its scaling down pathway. Molecular devices, especially molecular scale field-effect transistors (MSFET), are key building blocks for molecular electronics. Three major hurdles to device fabrication are yet to be overcome: electrode pairs must be fabricated with a controllable gap size commensurate with the functional molecule size of interest; the molecules of interest must be arranged between the electrodes with precise location and orientation control; and stable, conducting contacts must be made between the molecules and the electrodes. We have combined “top-down” and “bottom-up” approaches to solve these problems. Using photolithography and molecular lithography with self-assembled mono/multiple molecule layer(s) as a resist, we fabricated electrode structures with a controllable molecular-scale gap between source and drain electrodes and a third terminal of a buried gate. For our device, we synthesized a thiolated phthalocyanine derivative molecule, {di-[1-(S-acetylthio)-4-ethynylphenyl]-di-(tert-butyl)phthalocyanato}copper(II), with acetylthio groups on both ends, conjugated with ethynylphenyl groups. The synthesized end-thiolated molecules were assembled between the tailored molecular gap of the as-fabricated FET electrode structures in solution via Au–S bonding, forming stable contacts between the electrodes and the molecules, and a 3 terminal MSFET device was formed. Electrical measurements show that the device has characteristics of a typical FET device. The field-effect mobility of the as-fabricated MS-FET is 0.16 cm2 V−1 s−1.