Antal Adolf Koós

Large scale production of short functionalized carbon nanotubes

A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of ball-milling in specific atmosphere allows us to introduce functional groups like thiol, amine, amide, carbonyl, chlorine, etc. onto carbon nanotubes. The resulted functional groups are characterized using infrared spectroscopy and X-ray photoelectron spectroscopy.

Controlling the orientation, edge geometry, and thickness of chemical vapor deposition graphene.

We report that the shape, orientation, edge geometry, and thickness of chemical vapor deposition graphene domains can be controlled by the crystallographic orientations of Cu substrates. Under low-pressure conditions, single-layer graphene domains align with zigzag edges parallel to a single <101> direction on Cu(111) and Cu(101), while bilayer domains align to two directions on Cu(001). Under atmospheric pressure conditions, hexagonal domains also preferentially align. This discovery can be exploited to generate high-quality, tailored graphene with controlled domain thickness, orientations, edge geometries, and grain boundaries.

Synthesis and characterization of new polyaniline/nanotube composites

Abstract New polyaniline/nanotube (PANI/NT) composites have been synthesized by “in situ” polymerization processes using both multi-wall carbon nanotubes (MWNTs) and single-wall carbon nanotubes (SWNTs) in concentrations ranging from 2 to 50 wt.%. Although no structural changes are observed using MWNTs above a concentration of 20 wt.%, the in situ synthesis results in electronic interactions between nanotubes and the quinoid ring of PANI leading to enhanced electronic properties and thus to the formation of a genuine PANI/MWNT composite material. On the other hand, using SWNTs favors the formation of inhomogeneous mixtures rather than of a homogeneous composite materials, independent of the SWNT concentration. X-ray diffraction, Raman and transport measurements show the different behavior of both classes of nanotubes in PANI/NT materials. The difficulties in the formation of a true PANI/SWNT composite are related to the far more complex structure of the SWNT material itself, i.e. to the presence of entangled bundles of SWNTs, amorphous carbon and even catalytic metal particles.

Probing the bonding in nitrogen-doped graphene using electron energy loss spectroscopy.

Precise control of graphene properties is an essential step toward the realization of future graphene devices. Defects, such as individual nitrogen atoms, can strongly influence the electronic structure of graphene. Therefore, state-of-the-art characterization techniques, in conjunction with modern modeling tools, are necessary to identify these defects and fully understand the synthesized material. We have directly visualized individual substitutional nitrogen dopant atoms in graphene using scanning transmission electron microscopy and conducted complementary electron energy loss spectroscopy experiments and modeling which demonstrates the influence of the nitrogen atom on the carbon K-edge.

Catalyst traces and other impurities in chemically purified carbon nanotubes grown by CVD

Multiwall carbon nanotubes grown by the catalytic decomposition of acetylene over supported Co catalyst were subjected to wet and dry oxidation in order to remove the unwanted products and the catalyst traces. The effects of the purification treatment on the Co content Ž. Ž . was monitored by physical methods: Rutherford Backscattering Spectrometry RBS , Particle Induced X-Ray Emission PIXE and Ž. X-Ray Fluorescence XRF . The purified products were investigated by microscopic methods: TEM, Scanning Electron Microscopy Ž. Ž . SEM , Energy Dispersive Spectroscopy EDS and STM. The KMnOrH SO aqueous oxidation procedure was found to be effective in 42 4 reducing the Co content while damaging only moderately the outer wall of the nanotubes. Treatment in HNO rH SO yields a 32 4 bucky-paper like product and produces the increase of the Si and S content of the sample. q 2002 Elsevier Science B.V. All rights reserved.

Room temperature growth of single-wall coiled carbon nanotubes and Y-branches

Abstract Straight carbon nanotubes, carbon nanotube “knees,” Y-branches of carbon nanotubes and coiled carbon nanotubes were grown on a graphite substrate held at room temperature by the decomposition of fullerene under moderate heating (450 °C) in the presence of 200-nm Ni particles. The grown structures were investigated without any further manipulation by STM. The growth and the chemical stability of the carbon nanostructures containing nonhexagonal rings are discussed.

Facile, fast, and inexpensive synthesis of monodisperse amorphous nickel-phosphide nanoparticles of predefined size.

Monodisperse, size-controlled Ni-P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(II)acetyl-acetonate. The nanoparticles were amorphous, contained ~30 at% P and their size was controlled between 7-21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth.

Arc-grown Y-branched carbon nanotubes observed by scanning tunneling microscopy (STM)

Scanning tunneling microscopy (STM) observation of Y-branched carbon nanotubes produced by the arc-discharge method is reported. A drilled out graphite rod filled with a nickel/yttrium particle mixture was used as anode in the arc chamber under He atmosphere of 660-mbar pressure. Straight multi-wall nanotubes and asymmetrical Y-branches were found in a sample taken from the cathodic deposit. As measured by STM the Y-junctions have low apparent heights in the range of 1 nm. This may be an indication that these nanotubes have only few walls, or possibly they are single-walled. The asymmetrical Y-branches found in this experiment may be related to the additional use of metals or/and to changed temperature conditions on the cathode side due to the switch-off of the cathode water-cooling.

Rapid epitaxy-free graphene synthesis on silicidated polycrystalline platinum

Large-area synthesis of high-quality graphene by chemical vapour deposition on metallic substrates requires polishing or substrate grain enlargement followed by a lengthy growth period. Here we demonstrate a novel substrate processing method for facile synthesis of mm-sized, single-crystal graphene by coating polycrystalline platinum foils with a silicon-containing film. The film reacts with platinum on heating, resulting in the formation of a liquid platinum silicide layer that screens the platinum lattice and fills topographic defects. This reduces the dependence on the surface properties of the catalytic substrate, improving the crystallinity, uniformity and size of graphene domains. At elevated temperatures growth rates of more than an order of magnitude higher (120 μm min−1) than typically reported are achieved, allowing savings in costs for consumable materials, energy and time. This generic technique paves the way for using a whole new range of eutectic substrates for the large-area synthesis of 2D materials.

STM observation of asymmetrical Y-branched carbon nanotubes and nano-knees produced by the arc discharge method

The scanning tunneling microscopy (STM) observation of arc-grown Y-branched carbon nanotubes and sharp nanotube bends (nano-knees) is reported. A drilled out graphite rod filled with a nickel/yttrium particle mixture was used as the anode in an arc chamber under He atmosphere of 660-mbar pressure. Straight multi-wall nanotubes, Y-branches and nano-knees were found in a sample taken from the cathodic deposit. The asymmetrical Y-branches and complex nano-knees found in this experiment may be related to the additional use of metals or/and to induced changes of the temperature distribution on the cathode side. It is suggested that complex nano-knees could be new examples for carbon quantum dots.