Lang Jiang

Nanowire crystals of a rigid rod conjugated polymer.

In this paper, we show that well-defined, highly crystalline nanowires of a rigid rod conjugated polymer, a poly(para-phenylene ethynylene)s derivative with thioacetate end groups (TA-PPE), can be obtained by self-assembling from a dilute solution. Structural analyses demonstrate the nanowires with an orthorhombic crystal unit cell wherein the lattice parameters are a approximately = 13.63 A, b approximately = 7.62 A, and c approximately = 5.12 A; in the nanowires the backbones of TA-PPE chains are parallel to the nanowire long axis with their side chains standing on the substrate. The transport properties of the nanowires examined by organic field-effect transistors (OFETs) suggest the highest charge carrier mobility approaches 0.1 cm(2)/(V s) with an average value at approximately 10(-2) cm(2)/(V s), which is 3-4 orders higher than that of thin film transistors made by the same polymer, indicating the high performance of the one-dimensional polymer nanowire crystals. These results are particular intriguing and valuable for both examining the intrinsic properties of PPEs polymer semiconductors and advancing their potential applications in electronic devices.

Sulfonated Graphene for Persistent Aromatic Pollutant Management

Persistent aromatic pollutants are widely found in the effl uents from the pharmaceutical, petrochemical, dyestuff, pesticide, and other industries. Because of their high solubility in water, they transport into the environment widely and do harm to human health. Many studies have focused on the effi cient elimination of organic pollutants from aqueous solutions such as by photocatalysis, [ 1 ] adsorption, [ 2 ] and electrolysis. [ 3 ] Among these methods, adsorption techniques are simple and work effectively because of the preconcentration and solidifi cation of organic pollutants on adsorbents. However, the adsorption capacities of present materials are not high enough. It is important to develop new adsorbents with high adsorption capacities for persistent organic pollutant management in the environment. The high surface area of nanomaterials brings new prospects for the management of organic pollutants, for example, carbon nanotubes are found to work effectively to remove organic contaminants. [ 4 ] Compared with carbon nanotubes, graphene is more exciting. Graphene has a large theoretical specifi c surface area (2620 m 2 g − 1 ), [ 5 ] which indicates its potential for the adsorption of organic pollutants in environmental pollution management. However, to our knowledge, no report has addressed this topic, which is probably attributable to: 1) the strong aggregation of graphene sheets, which reduces the surface area of graphene signifi cantly, and 2) the absence of effective ways to disperse graphene in aqueous solution, which makes it diffi cult to advance in pollution management. Herein, we introduce a kind of sulfonated graphene (around 3 nm thick) with high dispersion properties in aqueous solution capable of absorbing naphthalene and 1-naphthol aromatic pollutants from aqueous solutions. The adsorption capability of the prepared sulfonated

Efficient Light-Emitting Diodes Based on Nanocrystalline Perovskite in a Dielectric Polymer Matrix

Electroluminescence in light-emitting devices relies on the encounter and radiative recombination of electrons and holes in the emissive layer. In organometal halide perovskite light-emitting diodes, poor film formation creates electrical shunting paths, where injected charge carriers bypass the perovskite emitter, leading to a loss in electroluminescence yield. Here, we report a solution-processing method to block electrical shunts and thereby enhance electroluminescence quantum efficiency in perovskite devices. In this method, a blend of perovskite and a polyimide precursor dielectric (PIP) is solution-deposited to form perovskite nanocrystals in a thin-film matrix of PIP. The PIP forms a pinhole-free charge-blocking layer, while still allowing the embedded perovskite crystals to form electrical contact with the electron- and hole-injection layers. This modified structure reduces nonradiative current losses and improves quantum efficiency by 2 orders of magnitude, giving an external quantum efficiency of 1.2%. This simple technique provides an alternative route to circumvent film formation problems in perovskite optoelectronics and offers the possibility of flexible and high-performance light-emitting displays.

Uniform hexagonal graphene flakes and films grown on liquid copper surface

Unresolved problems associated with the production of graphene materials include the need for greater control over layer number, crystallinity, size, edge structure and spatial orientation, and a better understanding of the underlying mechanisms. Here we report a chemical vapor deposition approach that allows the direct synthesis of uniform single-layered, large-size (up to 10,000 μm2), spatially self-aligned, and single-crystalline hexagonal graphene flakes (HGFs) and their continuous films on liquid Cu surfaces. Employing a liquid Cu surface completely eliminates the grain boundaries in solid polycrystalline Cu, resulting in a uniform nucleation distribution and low graphene nucleation density, but also enables self-assembly of HGFs into compact and ordered structures. These HGFs show an average two-dimensional resistivity of 609 ± 200 Ω and saturation current density of 0.96 ± 0.15 mA/μm, demonstrating their good conductivity and capability for carrying high current density.

Low Temperature Growth of Highly Nitrogen-Doped Single Crystal Graphene Arrays by Chemical Vapor Deposition

The ability to dope graphene is highly important for modulating electrical properties of graphene. However, the current route for the synthesis of N-doped graphene by chemical vapor deposition (CVD) method mainly involves high growth temperature using ammonia gas or solid reagent melamine as nitrogen sources, leading to graphene with low doping level, polycrystalline nature, high defect density and low carrier mobility. Here, we demonstrate a self-assembly approach that allows the synthesis of single-layer, single crystal and highly nitrogen-doped graphene domain arrays by self-organization of pyridine molecules on Cu surface at temperature as low as 300 °C. These N-doped graphene domains have a dominated geometric structure of tetragonal-shape, reflecting the single crystal nature confirmed by electron-diffraction measurements. The electrical measurements of these graphene domains showed their high carrier mobility, high doping level, and reliable N-doped behavior in both air and vacuum.

High Mobility, Air Stable, Organic Single Crystal Transistors of an n‐Type Diperylene Bisimide

Recently, some impressive progress has been made by functionalization of (hetero-)acenes, thiophenes, and arylenes with electron-defi cient constituents. [ 3–5 ] However, the development of air-stable, high mobility, n-type organic semiconductors for organic electronics is still highly emergent. The mobility of organic semiconductors depends on the effi ciency of charge transport from one molecule to another. Hence, some organic semiconductors with dense molecule packing always give high mobility. [ 6 ] As to the stability of organic compounds, it is believed that the highest occupied molecular orbital (HOMO) of p-type organic semiconductors should be more negative than –5.0 eV, e.g., locating at –5.0 to –6.0 eV, and the lowest unoccupied molecular orbitals (LUMO) of n-type organic semiconductors are best located between –4.0 and –4.5 eV, for anti-oxidation in air. [ 2 , 7 ] We have acknowledged these requirements and believe that perylene bisimides (PBIs) will fi t as candidates because of their reasonable electron acceptor ability, [ 8 ] and have been focusing on the expansion of the chemistry of perylene bisimides (PBIs) by a combination of Ullmann coupling and C–H transformation for some time, and have developed a facile strategy to synthesize fully conjugated, triply linked, diperylene bisimides, [ 8 ] conferring the expanded

Equiangular Hexagon‐Shape‐Controlled Synthesis of Graphene on Copper Surface

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

Synthesizing MnO2 nanosheets from graphene oxide templates for high performance pseudosupercapacitors

A facile method to synthesize layered manganese oxide nanosheets was developed for the first time by using graphene oxide as a template. The in situ replacement of carbon atoms on the graphene oxide framework by edge-shared [MnO6] octahedra provides a new methodology to synthesize graphene-based two-dimensional nanomaterials. The transformation of graphene oxide into δ-type MnO2 nanosheets results in an especially high surface area (157 m2 g−1), which is the highest value amongst todays MnO2 nanomaterials. Moreover, the MnO2 nanosheets demonstrated prominent capacitance (∼1017 F g−1 at a scan rate of 3 mV s−1, and ∼1183 F g−1 at a current density of 5 A g−1) and remarkable rate capability (∼244 F g−1 at a high scan rate of 50 mV s−1 and ∼559 F g−1 at a high current density of 25 A g−1), indicating their promise in high energy and power density pseudosupercapacitors.

Organic single crystal field-effect transistors: advances and perspectives

The perfect molecular order in organic crystals, the absence of grain boundaries and the minimized concentration of charge traps in crystals make them extremely promising for the study of intrinsic properties of organic materials and fabrication of high performance devices and circuits (e.g., high mobility) based on the organic crystals. Recently, enormous efforts have brought significant progresses in the development of new organic semiconductors for single crystals and the fabrication of high performance organic single crystal field-effect transistors (SCFETs). Here, the review will focus on organic semiconductors with high performance for single crystals, the techniques for the fabrication of organic SCFETs, the charge transport process in SCFETs, and the application of SCFETs for the development of novel SCFET arrays and complicate circuits. Finally, the perspectives and opportunities of SCFETs in near future is also addressed.

High mobility emissive organic semiconductor

The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm2 V−1 s−1. Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m−2 and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics.