Graphene has attracted considerable interest as a potential new electronic material [1][2][3][4][5][6][7][8][9][10][11] . With its high carrier mobility, graphene is of particular interest for ultrahigh-speed radio-frequency electronics [12][13][14][15][16][17][18] . However, conventional device fabrication processes cannot readily be applied to produce high-speed graphene transistors because they often introduce significant defects into the monolayer of carbon lattices and severely degrade the device performance [19][20][21] . Here we report an approach to the fabrication of high-speed graphene transistors with a self-aligned nanowire gate to prevent such degradation. A Co 2 Si-Al 2 O 3 core-shell nanowire is used as the gate, with the source and drain electrodes defined through a self-alignment process and the channel length defined by the nanowire diameter. The physical assembly of the nanowire gate preserves the high carrier mobility in graphene, and the selfalignment process ensures that the edges of the source, drain and gate electrodes are automatically and precisely positioned so that no overlapping or significant gaps exist between these electrodes, thus minimizing access resistance. It therefore allows for transistor performance not previously possible. Graphene transistors with a channel length as low as 140 nm have been fabricated with the highest scaled on-current (3.32 mA mm 21 ) and transconductance (1.27 mS mm 21 ) reported so far. Significantly, on-chip microwave measurements demonstrate that the self-aligned devices have a high intrinsic cut-off (transit) frequency of f T 5 100-300 GHz, with the extrinsic f T (in the range of a few gigahertz) largely limited by parasitic pad capacitance. The reported intrinsic f T of the graphene transistors is comparable to that of the very best high-electron-mobility transistors with similar gate lengths 10 .With the highest carrier mobility, exceeding 200,000 cm 2 V 21 s 21 (ref. 8), and many other desirable properties, including a large critical current density (,2 3 10 8 A cm 22 (ref. 22)) and a high saturation velocity (5.5 3 10 7 cm s 21 (ref. 11)), graphene has significant potential for high-speed electronics to offer excellent radio-frequency characteristics with very high cut-off frequency (f T ). Importantly, recent studies have demonstrated graphene transistors operating in the gigahertz regime [12][13][14][16][17][18] with a record of f T 5 100 GHz (ref. 13). However, the reported radio-frequency performance so far is still far from the potential that the graphene transistors may offer, and is primarily limited by two adverse factors in the device fabrication process.The first limitation is associated with the severe mobility degradation resulting from the graphene-dielectric integration process, which introduces substantial defects into pristine graphene lattices 20,23 . To overcome this, we have recently developed a strategy to integrate high-quality, high-dielectric-constant dielectrics with graphene using a physical assembly approach without in...

There is increasing interest in developing artificial systems that can mimic natural photosynthesis to directly harvest and convert solar energy into usable or storable energy resources. Photocatalysis, in which solar photons are used to drive redox reactions to produce chemical fuel, is the central process to achieve this goal. Despite significant efforts to date, a practically viable photocatalyst with sufficient efficiency, stability and low cost is yet to be demonstrated. It is often difficult to simultaneously achieve these different performance metrics with a single material component. The heterogeneous photocatalysts with multiple integrated functional components could combine the advantages of different components to overcome the drawbacks of single component photocatalysts. A wide range of heterostructures, including metal/semiconductor, semiconductor/semiconductor, molecule/semiconductor and multi-heteronanostructures, have been explored for improved photocatalysts by increasing the light absorption, promoting the charge separation and transportation, enhancing the redox catalytic activity and prolonging the functional life-time. The present review gives a concise overview of heterogeneous photocatalysts with a focus on the relationship between the structural architecture and the photocatalytic activity and stability.

We report a series of difluorobenzothiadizole (ffBT) and oligothiophene-based polymers with the oligothiophene unit being quaterthiophene (T4), terthiophene (T3), and bithiophene (T2). We demonstrate that a polymer based on ffBT and T3 with an asymmetric arrangement of alkyl chains enables the fabrication of 10.7% efficiency thick-film polymer solar cells (PSCs) without using any processing additives. By decreasing the number of thiophene rings per repeating unit and thus increasing the effective density of the ffBT unit in the polymer backbone, the HOMO and LUMO levels of the T3 polymers are significantly deeper than those of the T4 polymers, and the absorption onset of the T3 polymers is also slightly red-shifted. For the three T3 polymers obtained, the positions and size of the alkyl chains play a critical role in achieving the best PSC performances. The T3 polymer with a commonly known arrangement of alkyl chains (alkyl chains sitting on the first and third thiophenes in a mirror symmetric manner) yields poor morphology and PSC efficiencies. Surprisingly, a T3 polymer with an asymmetric arrangement of alkyl chains (which is later described as having an "asymmetric bi-repeating unit") enables the best-performing PSCs. Morphological studies show that the optimized ffBT-T3 polymer forms a polymer:fullerene morphology that differs significantly from that obtained with T4-based polymers. The morphological changes include a reduced domain size and a reduced extent of polymer crystallinity. The change from T4 to T3 comonomer units and the novel arrangement of alkyl chains in our study provide an important tool to tune the energy levels and morphological properties of donor polymers, which has an overall beneficial effect and leads to enhanced PSC performance.

Identification on catalytic sites of heterogeneous catalysts at atomic level is important to understand catalytic mechanism. Surface engineering on defects of metal oxides can construct new active sites and regulate catalytic activity and selectivity. Here we outline the strategy by controlling surface defects of nanoceria to create the solid frustrated Lewis pair (FLP) metal oxide for efficient hydrogenation of alkenes and alkynes. Porous nanorods of ceria (PN-CeO2) with a high concentration of surface defects construct new Lewis acidic sites by two adjacent surface Ce3+. The neighbouring surface lattice oxygen as Lewis base and constructed Lewis acid create solid FLP site due to the rigid lattice of ceria, which can easily dissociate H–H bond with low activation energy of 0.17 eV.