Solid-Phase Coalescence of Electrochemically Exfoliated Graphene Flakes into a Continuous Film on Copper

The ability to directly synthesize high-quality graphene patterns over large areas is important for many applications such as electronic and optoelectronic devices and circuits. Here, we report a facile and scalable approach to coalesce and recrystallize electrochemically exfoliated graphene flakes into a continuous film by thermal annealing on copper foils. The underlying growth mechanism involves defect mediated decomposition of electrochemically exfoliated graphene flakes into active polycyclic carbon species, followed by coalescence of the active carbon species into a continuous, monolayer film of high material quality. First-principles calculations confirm that the enhanced affinity of the polycyclic carbon species with copper effectively prevents their surface desorption at elevated temperatures, which is distinct from graphene growth based on the decomposition of solid carbon sources into gaseous hydrocarbons. Significantly, the localized supply of active carbon species in our approach enables spatially confined growth of graphene. Combined with stencil printing of the exfoliated flakes, transparent and conductive graphene circuits have been directly synthesized over large areas

Experimental Observation of Fullerene Crystalline Growth from Mesocrystal to Single Crystal

Fullerene hierarchical mesocrystals were first prepared by antisolvent induced precipitation method. Their morphologies and sizes can be controlled by adjusting the antisolvent type and the ratio between the solvent (toluene) and antisolvent (ethyl acetate or tetrahydrofuran). The formation of fullerene mesocrystals and their transformation to single crystal were observed by time-dependent experiments with SEM and TEM. Fullerene mesocrystals can be separated from the solution and are stable for several months. HRTEM revealed that mesocrystals were made up of highly oriented nanoparticles. The formation of fullerene mesocrystals and their transformation to single crystals provide a new way for the construction of fullerene nanostructures with different applications

Oxidation-Resistant Acidic Resins Prepared by Partial Carbonization as Cocatalysts in Synthesis of Adipic Acid

The oxidation-resistant acidic resins are of great importance for the catalytic oxidation systems. In this paper, the oxidatively stable acidic resins are obtained from the cation ion exchange resins (CIERs) through the thermal treatment in N₂ atmosphere. The structure and properties of the thermally treated CIERs were characterized by chemical analysis, Fourier transform infrared (FT–IR) spectra, acid capacity measurement and scanning electron microscope (SEM). The thermally treated CIERs possess high acid capacity up to 4.09 mmol g^–1. A partial carbonization is observed in the thermal treatment process of CIERs, but the morphology of resin spheres maintains well. The as-prepared CIERs are used as solid acids to assist the hydrogen peroxide oxidation of cyclohexene to adipic acid (ADA) with tungstic acid as the catalyst precursor. The improved yields of ADA in the recycling reaction are obtained in the presence of acidic CIERs. Meanwhile, the unproductive decomposition of H₂O₂ is effectively suppressed. The high yields of ADA (about 81%) are kept by the thermally treated CIERs even after the fifth cycle. The thermally treated CIERs exhibit excellent acid-catalytic performance and possess remarkable oxidation-resistant capability

Flexible Micropillar Electrode Arrays for In Vivo Neural Activity Recordings

Tarkista embargo, kun artikkeli julkaistu.Flexible electronics that can form tight interfaces with neural tissues hold great promise for improving the diagnosis and treatment of neurological disorders and advancing brain/machine interfaces. Here, the facile fabrication of a novel flexible micropillar electrode array (µPEA) is described based on a biotemplate method. The flexible and compliant µPEA can readily integrate with the soft surface of a rat cerebral cortex. Moreover, the recording sites of the µPEA consist of protruding micropillars with nanoscale surface roughness that ensure tight interfacing and efficient electrical coupling with the nervous system. As a result, the flexible µPEA allows for in vivo multichannel recordings of epileptiform activity with a high signal-to-noise ratio of 252 ± 35. The ease of preparation, high flexibility, and biocompatibility make the µPEA an attractive tool for in vivo spatiotemporal mapping of neural activity.Peer reviewe

Three-Dimensional Carbon Nanotube Sponge-Array Architectures with High Energy Dissipation

Carbon nanotube sponges and aligned arrays are seamlessly integrated into numerous possible configurations such as series, parallel, package, and sandwich complex structures, leading to significantly broadened stress plateau and enhanced energy dissipation. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Colloidal Antireflection Coating Improves Graphene–Silicon Solar Cells

Carbon nanotube-Si and graphene-Si solar cells have attracted much interest recently owing to their potential in simplifying manufacturing process and lowering cost compared to Si cells. Until now, the power conversion efficiency of graphene-Si cells remains under 10% and well below that of the nanotube-Si counterpart. Here, we involved a colloidal antireflection coating onto a monolayer graphene-Si solar cell and enhanced the cell efficiency to 14.5% under standard illumination (air mass 1.5, 100 mW/cm²) with a stable antireflection effect over long time. The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range. Our results demonstrate a great promise in developing high-efficiency graphene-Si solar cells in parallel to the more extensively studied carbon nanotube-Si structures

Concentric sub-micrometer-sized cables composed of Ni nanowires and sub-micrometer-sized fullerene tubes

Highly ordered arrays of submicrometer-sized coaxial cables composed of submicrometer-sized C-60 and C-70 tubes filled with Ni nanowires are successfully prepared by combining a sol-gel method with an electrodeposition process. The wall thickness of the submicrometer-sized tubes can be adjusted by the concentration of fullerenes and the immersion time. The thermal stability of the submicrometer-sized C-60 tubes is studied by Raman spectroscopy and it is found that these structures can be easily decomposed to form carbon nanotubes at relatively low temperatures (above 573 K) in an alumina template. These novel coaxial cable structures have been characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), field-emission SEM (FESEM), Raman spectroscopy, elemental mapping, energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), vibrating sample magnetometer (VSM) experiments, and superconducting quantum interference device (SQUID) measurements. Magnetic measurements show that these submicrometer-sized cables exhibit enhanced ferromagnetic behavior as compared to bulk nickel. Moreover, submicrometer-sized C-70/Ni cables show uniaxial magnetic anisotropy with the easy magnetic axis being parallel to the long axis of the Ni nanowires. C-70/Ni cables also exhibit a new magnetic transition at ca. 10 K in the magnetization-temperature (M-T) curve, which is not observed for the analogous C-60/Ni structures. The origin of this transition is not yet clear, but might be related to interactions between the Ni nanowires and C-70 molecules. There is no preferred magnetization axis in submicrometer-sized C-60/Ni cables, which implies that the Ni nanocrystals have different packing modes in the two composites. These different crystalline packing modes lead to different magnetic anisotropy in the two composites, although the Ni nanocrystals have the same face-centered cubic (fee) structure in both cases