J.L. Hutchison

High-yield production of graphene by liquid-phase exfoliation of graphite

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.

Double-walled carbon nanotubes fabricated by a hydrogen arc discharge method

Abstract Double walled carbon nanotubes (DWNTs) were obtained by the arc discharge technique in an atmosphere of Ar and H 2 mixture (1:1/v:v) at 350 Torr. The catalyst was prepared from a mixture of Ni, Co, Fe and S powders heated in an inert gas atmosphere at 500°C for 1 h. High resolution electron microscopy (HREM) revealed that the dominant type of obtained nanotubes were DWNTs with outer diameter in the range of 1.9–5 nm and inner tube diameters in the range 1.1–4.2 nm. As a rule, the DWNT tubes form into bundles. Occasionally single walled nanotubes (SWNTs) were observed by HREM although Raman spectroscopy did not reveal the presence of significant quantities of these tubules in the bulk product.

Inorganic fullerene-like material as additives to lubricants: structure–function relationship

Abstract Recently, inorganic fullerene-like (IF) supramolecules of metal dichalcogenide MX2 (M=Mo, W, etc.; X=S, Se), materials with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized. The main goal of the present work was to study the tribological properties of IF–WS2 in comparison to 2H–WS2 and MoS2 platelets over a wide range of loads and sliding velocities. The size and shape distributions of the nanoparticles were studied by transmission electron microscopy (TEM). The average size of the IF–WS2 particles was 120 nm, while that of 2H–WS2 and 2H–MoS2 was 0.5 μm and 4 μm. The chemical reactivity of the different powders in an oxygenated atmosphere was verified by heating the powders in ambient atmosphere. The friction experiments were performed in laboratory atmosphere (humidity ∼50%) using a ring-block tester. Complementary information on the state of wear of the powders in the lubricating fluid and on the metal surfaces of the specimens was obtained using a combination of TEM, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It has been established that IF–WS2 nanoparticles appear to have excellent tribological properties in definite loading range in comparison to typical metal dichalcogenides. The oxidation of the IF particles and the wear track was essentially less than with solid lubricants made of platelets of the same chemical compound (WS2). The main advantages of IF nanoparticles lie in their round shape and the absence of dangling bonds.

The size distribution, imaging and obstructing properties of C60 and higher fullerenes formed within arc-grown single walled carbon nanotubes

Abstract The relative size distributions of molecules of C60 and higher fullerenes observed in single walled carbon nanotubes (SWNTs) produced by arc vaporization of carbon in the presence of a mixed Ni/Y catalyst are described. The experimental and calculated imaging properties of the fullerenes, which were observed in ca. 5–10% of SWNTs, are also described. The in situ e-beam irradiation in a 300 kV field emission gun transmission electron microscope causes rapid coalescence of the fullerenes within the SWNTs. The incorporated fullerenes also directly impede crystal growth in SWNTs when their cavities are filled by the liquid phase capillary method.

Carbon nanotubes from polyethylene precursors: Structure and structural changes caused by thermal and chemical treatment revealed by HREM

High resolution electron microscopy (HREM) reveals that carbon nanotubes obtained by heating a polyethylene precursor in the presence of catalytic Ni particles have a structure consisting of stacked conical carbon layers. Two main types of nanotube structures were identified. When the conical angle along the tubes is in the range 16–35 °, “bamboo”-shaped nanotubes are observed, characterized by open carbon edges (OEs) that were assumed to terminate in hydrogen. When the conical angle is in the range 75–85 °, a “fish-bone”-type structure is observed. Following heat treatment in the temperature range 1200–2800 °C, the catalytic Ni particles were removed and the hydrogen content reduced. As a result, the neighboring OEs were linked together, revealed in the HREM by the formation of loops along both the external tube sides and also the insides of the inner channels. Chemically, the pre-heat treated tubes could withstand bromination, but were completely destroyed by treatment with hot concentrated HNO3. Treatment of the pre-heat treated tubes with molten V2O5 revealed no penetration of this material between the OEs along the external wall or into the inner channel. The microstructure of the catalytic Ni particles, present at the tips of the pre-heat treated nanotubes, was also investigated. Outer polycrystalline layers consisting of Ni3C and probably NiO were observed near the periphery of terminal Ni particles not covered with graphitic layers and also near that of open regions of partially covered particles.

Two layer 4:4 co-ordinated KI crystals grown within single walled carbon nanotubes

The formation of ‘all surface’ 4:4 co-ordinated KI crystals within 1.4 nm diameter single walled carbon nanotubes (SWNT) is reported. KI was inserted into the SWNTs by a capillary method [J. Sloan, D.M. Wright, H.G. Woo, S. Bailey, G. Brown, A.P.E. York, K.S. Coleman, J.L. Hutchison, M.L.H. Green, J. Chem. Soc. Chem. Commun. (1999) 699], whereby the nanotubes were combined intimately with the molten halide. The crystals grew withh 001 i (relative to bulk KI) parallel to the tubule axes and were continuous tetragonally distorted bilayer crystals composed of alternating columns of K‐I and I‐K pairs when viewed along h 100 i. ” 2000 Elsevier Science B.V. All rights reserved.

Capillarity and silver nanowire formation observed in single walled carbon nanotubes

Single walled carbon nanotubes (SWNTs) exhibit similar capillarity properties to those exhibited by multiple walled carbon nanotubes (MWNTs); SWNTs, previously filled in low yield (ca. 2%) by solution chemistry techniques, can be filled in high yield (up to ca. 50%) by the liquid phase method; compositions from the KCl–UCl4 and AgCl–AgBr systems were used to fill SWNTs without causing them significant chemical or thermal damage; in the case of the latter, exposure to light or an electron beam resulted in the partial photolytic reduction of SWNT incorporated silver halides to continuous metallic silver ‘nanowires’ within the capillaries.

Experimental characterisation of CCD cameras for HREM at 300 kV

The modulation transfer function, noise transfer function and detection quantum efficiency of both 1k2 and 2k2 cameras attached to the same 300 kV FEGTEM have been measured. The results show that both the MTF and the DQE of the 2k2 camera are lower than for the 1k2 camera at frequencies above a third of the Nyquist limit. This lower per-pixel performance of the 2k2 camera is primarily a result of the use of a thicker phosphor scintillator. However, MTF and DQE of the 2k2 camera operated as an effective 1k2 camera by using 2 x 2 pixel binning are superior to the 1k2 camera in the medium spatial frequency range.

Growth of In2O3(100) on Y-stabilized ZrO2(100) by O-plasma assisted molecular beam epitaxy

Thin films of In2O3 have been grown on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy with a substrate temperature of 650°C. Ordered epitaxial growth was confirmed by high resolution transmission electron microscopy. The position of the valence band onset in the x-ray photoemission spectra of the epitaxial films is found to be inconsistent with the widely quoted value of 3.75eV for the fundamental bandgap of In2O3 and suggests a revised value of 2.67eV.

The metamict transformation in alpha-quartz

Abstract The crystalline→noncrystalline (metamict) transformation in α-quartz under electron irradiation has been studied by transmission electron microscopy (TEM), ultra-high resolution structure imaging (SI) and convergent beam electron diffraction (CBD). The transformation is radiolytic and proceeds in two stages: heterogeneous nucleation of discrete disordered inclusions and slower homogeneous loss of long-range order in the surrounding matrix. Irradiations of dry lunar quartz and of heated synthetic quartz suggest that the heterogeneous component is associated with incorporated water impurity. Analysis of the homogeneous component by CBD and SI suggests a transformation model in which progressive disorder evolves from stochastic relaxations of radio-lytically-damaged [SiO4] coordination units.