Jian Zheng

Bio: Jian Zheng is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Difluorocarbene & Graphene. The author has an hindex of 23, co-authored 57 publications receiving 1863 citations. Previous affiliations of Jian Zheng include University of Wisconsin-Madison & The University of Nottingham Ningbo China.

Equiangular hexagon-shape-controlled synthesis of graphene on copper surface.

Abstract: The electric properties and device performance are strongly dependent on the size, shape, crystallinity, layer numbers, and edge structures of pristine graphene. In general, imperfection in these parameters leads to undesired scattering of charge carriers that compromise the high intrinsic mobility of graphene. Controlling these parameters of graphene in synthesis or post-synthesis manipulation is thus critical to achieve tunable properties and optimized device performance. Post-synthesis methods including anisotropic etching, [ 3 , 4 ] scanning probebased lithography [ 5 ] and electron-beam induced edge reorganization of graphene [ 6 ] provide some levels of control on graphene geometric parameters. However, direct growth of graphene with controllable shape and edges by chemical vapor deposition (CVD) [ 7–10 ] or epitaxial growth on metal surfaces [ 11 , 12 ] has met with limited success. Here we report a large scale synthesis of equiangular hexagon-shaped single or multilayer graphene by methane CVD on Cu surface at ambient pressure. The shape refl ects the hexagonal graphene lattice, possessing either zigzag or armchair edges. The hexagon-shaped graphene shows no observable defects confi rmed by Raman spectra, and is formed by nucleation and growth mechanism, thus allowing control of both density and size. Moreover, the shape evolution follows an empirical rule that higher CH 4 fl ow rate leads to shorter nucleation time, higher growth rates and larger deviations from equiangular hexagon shape. Based on these observations, we proposed a growth model that qualitatively establishes a connection between various experimental conditions and the fi nal state of the grown graphene, and is in principle capable of predicting the results from different conditions in the Cu-methane CVD system. Moreover, this system provides direct evidence of layer spatial arrangement in the case of multi-layer graphene

Production of Graphite Chloride and Bromide Using Microwave Sparks

Abstract: Chemically modified graphite is an economical material with promising applications in its own right or as an intermediate in the synthesis of graphene. However, because of its extreme chemical inertness, to date only two methods—oxidation and fluorination—have been found which can modify graphite with high yield and large throughput. Herein, we describe a third chemical approach for the synthesis of large quantities of highly modified graphite which uses a microwave-sparks-assisted halogenation reaction. The resulting graphite halide can easily be exfoliated into monolayer graphene in organic solvents. The structure and electronic properties of the original graphene can be recovered after thermal annealing of the graphene halide. Furthermore, the graphene halide can be further modified by a variety of organic functional groups. Solution-processed field-effect transistors based on the graphene halides resulted in device performances were comparable to, or even better than, that of graphene oxide.

Conversion between Difluorocarbene and Difluoromethylene Ylide

Abstract: The interconversion between difluoromethylene ylide and difluorocarbene is described. The difluoromethylene ylide precursor, Ph3P+CF2CO2-, could be turned into an efficient difluorocarbene reagent, whereas the classical difluorocarbene reagents, HCF2Cl an

High‐Performance Phototransistors Based on Organic Microribbons Prepared by a Solution Self‐Assembly Process

Abstract: Oligoarenes as an alternative group of promising semiconductors in organic optoelectronics have attracted much attention. However, high-performance and low-cost opto-electrical devices based on linear asymmetric oligoarenes with nano/microstructures are still rarely studied because of difficulties both in synthesis and high-quality nano/microstructure growth. Here, a novel linear asymmetric oligoarene 6-methy)-anthra[2,3-b]benzo[d]thiophene (Me-ABT) is synthesized and its high-quality microribbons are grown by a solution process. The solution of Me-ABT exhibits a moderate fluorescence quantum yield of 0.34, while the microribbons show a glaucous light emission. Phototransistors based on an individual Me-ABT microribbon prepared by a solution-phase self-assembly process showed a high mobility of 1.66 cm 2 V ―1 s ―1 , a large photoresponsivity of 12 000 A W ―1 , and a photocurrent/dark- current ratio of 6000 even under low light power conditions (30 μW cm ―2 ). The measured photoresponsivity of the devices is much higher than that of inorganic single-crystal silicon thin film transistors. These studies should boost the development of the organic semiconductors with high-quality microstructures for potential application in organic optoelectronics.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Abstract: Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Chemical doping of graphene

Abstract: Recently, a lot of effort has been focused on improving the performance and exploring the electric properties of graphene. This article presents a summary of chemical doping of graphene aimed at tuning the electronic properties of graphene. p-Type and n-type doping of graphene achieved through surface transfer doping or substitutional doping and their applications based on doping are reviewed. Chemical doping for band gap tuning in graphene is also presented. It will be beneficial to designing high performance electronic devices based on chemically doped graphene.

Heteroatom-doped graphene materials: syntheses, properties and applications

Abstract: Heteroatom doping can endow graphene with various new or improved electromagnetic, physicochemical, optical, and structural properties. This greatly extends the arsenal of graphene materials and their potential for a spectrum of applications. Considering the latest developments, we comprehensively and critically discuss the syntheses, properties and emerging applications of the growing family of heteroatom-doped graphene materials. The advantages, disadvantages, and preferential doping features of current synthesis approaches are compared, aiming to provide clues for developing new and controllable synthetic routes. We emphasize the distinct properties resulting from various dopants, different doping levels and configurations, and synergistic effects from co-dopants, hoping to assist a better understanding of doped graphene materials. The mechanisms underlying their advantageous uses for energy storage, energy conversion, sensing, and gas storage are highlighted, aiming to stimulate more competent applications.

Organic light detectors: photodiodes and phototransistors.

Abstract: While organic electronics is mostly dominated by light-emitting diodes, photovoltaic cells and transistors, optoelectronics properties peculiar to organic semiconductors make them interesting candidates for the development of innovative and disruptive applications also in the field of light signal detection. In fact, organic-based photoactive media combine effective light absorption in the region of the spectrum from ultraviolet to near-infrared with good photogeneration yield and low-temperature processability over large areas and on virtually every substrate, which might enable innovative optoelectronic systems to be targeted for instance in the field of imaging, optical communications or biomedical sensing. In this review, after a brief resume of photogeneration basics and of devices operation mechanisms, we offer a broad overview of recent progress in the field, focusing on photodiodes and phototransistors. As to the former device category, very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, and even though the simultaneous optimization of all these relevant parameters is demonstrated in a limited number of papers, real applications are within reach for this technology, as it is testified by the increasing number of realizations going beyond the single-device level and tackling more complex optoelectronic systems. As to phototransistors, a more recent subject of study in the framework of organic electronics, despite a broad distribution in the reported performances, best photoresponsivities outperform amorphous silicon-based devices. This suggests that organic phototransistors have a large potential to be used in a variety of optoelectronic peculiar applications, such as a photo-sensor, opto-isolator, image sensor, optically controlled phase shifter, and opto-electronic switch and memory.

Organic Optoelectronic Materials: Mechanisms and Applications

Abstract: Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...