Vertically-aligned Graphene Research Articles

Vertically-aligned graphene flakes on nanoporous templates: morphology, thickness, and defect level control by pre-treatment

Various morphologies of the vertically-aligned graphene flakes were fabricated on the nanoporous templates treated with metal ions in solutions, as well as coated with a thin gold layer and activated in the low-temperature Ar plasma. The thickness and level of structural defects in the graphene flakes could be effectively controlled by a proper selection of the pre-treatment method. We have also demonstrated that various combinations of the flake thickness and defect levels can be obtained, and the morphology and density of the graphene pattern can be effectively controlled. The result obtained could be of interest for various applications requiring fabrication of large graphene networks with controllable properties.

Fabrication of three-dimensional graphene foam with high electrical conductivity and large adsorption capability

A three-dimensional (3D), free-standing graphene foam was prepared by plasma-enhanced chemical vapor deposition on nickel-foam. The prepared graphene foam was found to consist of few-layered vertically-aligned graphene sheets with highly graphite structure. Owing to the 3D interconnected porous nanostructures, the graphene foam exhibited a high electrical conductivity of 125 S/cm and a large surface area of 625.4 cm2/g. For practical application, we prepared the graphene foam/epoxy composites showing a maximum conductivity of 196 S/m at 2.5 vol.% filler loading, and a rather low percolation threshold of 0.18 vol.%. Furthermore, the derived graphene oxide foam exhibited an excellent absorption capability (177.6 mg/g for As(V), 399.3 mg/g for Pb(II)) and recyclability (above 90% removal efficiency after five cycles) for the removal of heavy metal ions. The present study reveals that the multifunctional graphene foam may broaden the graphene-based materials for the applications in electrically conductive composites and environmental cleanup.

Self-assembled growth of Sn@CNTs on vertically aligned graphene for binder-free high Li-storage and excellent stability

Although widely used, the current Li-ion battery (LIB) technology still suffers from a lack of suitable electrodes with enhanced energy and power density, cycling stability, energy efficiency and cycling life. As an anode material for LIBs, metallic tin (Sn) has attracted tremendous interest, owing to its high theoretical capacity. Nevertheless, the practical implementation of metallic tin to LIBs is greatly hampered by the poor cyclability, because volume changes that occur during charging and discharging, result in both mechanical failure and loss of electrical contact at the electrode and the tin nanoparticle aggregates during the discharging process. Here, we report for the first time, a new strategy to grow self-assembled Sn@CNT on vertically aligned graphene (VAGN) by the microwave plasma irradiation reduction of SnO2 growth on VAGN and in situ encapsulating all the Sn nanoparticles in CNTs. The composite, as an anode material in lithium ion batteries, exhibits a high reversible capacity of 1026 mA h g−1 at 0.25 C (cycle lives of more than 280 times) and a capacity of 140 mA h g−1 is retained in a discharge time of 12 s, which represents the best performance values attained for a Sn anode to date. We expect the proposed route to be adopted by the rapidly growing energy storage research community.

Growth of the vertically aligned graphene@ amorphous GeOx sandwich nanoflakes and excellent Li storage properties

Germanium oxide is a promising anode material for lithium ion batteries due to its theoretical capacity (1100mAh/g) is 3 times higher than the commercial graphite anode (only 372mAh/g). However, so far only a few studies have reported the application of germanium oxide in LIBs and the cycling performance is unsatisfactory. In this report, we have prepared a unique VAG@ amorphous GeOx sandwich nanostructure by a non-toxic, low temperature CVD method with vertically aligned graphene(VAG) as templates. The graphene sheets form a fast electron transport channel duo to its superior electron conductivity and the vertically aligned sandwich nanoflakes can offer a short pathway for lithium ion thanks to the unified orientation. Additionally, the GeOx sediments that evenly distribute on the surface of graphene flakes have an amorphous structure and their thickness is less than 10nm, which can mitigate the mechanical stress generating in the lithiation/delithiation process. Owing to these advantages, the as-prepared anode shows a stable capacity of 1008mAh/g for 100 cycles (with capacity retention of 96%). Rate performance reveals the anode can maintain a capacity of 545mAh/g even at the rate of 15C. Our results are demonstrated to be so far the most stable performance for germanium oxide anodes.

Low threshold field emission from nitrogen-incorporated carbon nanowalls

Field emission performance of nitrogen-incorporated vertically-aligned graphene layers, so called “carbon nanowalls (CNWs)”, is found to depend upon their electrical conduction properties. The CNW samples with n-type conduction exhibit near-ideal Ohmic contacts with various metals such as Cu, Ti, and Au, regardless of the work function of the metals. The high resistivity CNWs for lower deposition temperatures ( T D ) show semiconducting behavior in the Arrhenius plots, while the low resistivity CNWs for higher T D show semi-metallic behavior. The emission turn-on field versus T D has a very similar trend to the bulk resistivity versus T D , and is reduced down to about 3 V/μm when the resistivity reaches a minimum (3.0 × 10 − 3 Ω cm). The lower turn-on field for semi-metallic CNWs is attributed to an upward shift of the emission level, which is responsible for a decrease in the surface potential barrier height for emission.

Evolution of structure and morphology during plasma-enhanced chemical vapor deposition of carbon nanosheets

The evolution of structure and morphology of carbon nanosheets during radio frequency plasma-enhanced chemical vapor deposition is investigated by X-ray diffraction (XRD) and scanning electron microscopy. Nanosheets consist of mostly vertically-aligned graphene layer stacks, 1 to > 20 layers thick, which attain approximately 5-μm lengths after 120 min of growth. XRD indicates these nanosheets contain both turbostratic and non-turbostratic graphite, and that the average thickness of nanosheets in all orientations increases with deposition time. Increases in thickness are accompanied by decreases in graphene layer spacing, a trend attributed to an increase in long-range attractive interatomic forces as more graphene layers are added. In-plane XRD scans demonstrate that preferred nanosheet orientation changes from parallel to perpendicular, relative to the substrate surface, with increasing deposition time.

Small sensitive hydrophones : Rijnja, H.A.J. 27 (October 1972) 182

A three-dimensional (3D), free-standing graphene foam was prepared by plasma-enhanced chemical vapor deposition on nickel-foam. The prepared graphene foam was found to consist of few-layered vertically-aligned graphene sheets with highly graphite structure. Owing to the 3D interconnected porous nanostructures, the graphene foam exhibited a high electrical conductivity of 125 S/cm and a large surface area of 625.4 cm2/g. For practical application, we prepared the graphene foam/epoxy composites showing a maximum conductivity of 196 S/m at 2.5 vol.% filler loading, and a rather low percolation threshold of 0.18 vol.%. Furthermore, the derived graphene oxide foam exhibited an excellent absorption capability (177.6 mg/g for As(V), 399.3 mg/g for Pb(II)) and recyclability (above 90% removal efficiency after five cycles) for the removal of heavy metal ions. The present study reveals that the multifunctional graphene foam may broaden the graphene-based materials for the applications in electrically conductive composites and environmental cleanup.