Synthesis of carbon 'onions' in water.

The fabrication of carbon nanomaterials usually calls for expensive vacuum systems to generate plasmas and yields are disappointingly low. Here we describe a simple method for producing high-quality spherical carbon nano-'onions' in large quantities without the use of vacuum equipment. The nanoparticles, which have C60 cores surrounded by onion-like nested particles, are generated by an arc discharge between two graphite electrodes submerged in water. This technique is economical and environmentally benign, and produces uncontaminated nanoparticles which may be useful in many applications.

Surface atomic properties of tetrahedral amorphous carbon

The surface energy and surface atomic structure of tetrahedral amorphous carbon has been calculated by an ab-initio method. The surface atoms are found to reconstruct into sp2 sites often bonded in graphitic rings. Placing the dangling bonds on adjacent surface atoms lower their energy by π-bonding and this is the source of the low surface energy. The even lower surface energy of hydrogenated amorphous carbon (a-C:H) is due to the hydrogenation of all broken surface bonds. © 2005 Elsevier B.V. All rights reserved.

Deposition of carbon nitride films using an electron cyclotron wave resonance plasma source

Hydrogenated amorphous carbon nitride (a-C:N:H) has been synthesized using a high plasma density electron cyclotron wave resonance (ECWR) technique using N2 and C2H2 as source gases, at different ratios and a fixed ion energy (80 eV). The composition, structure and bonding state of the films were investigated and related to their optical and electrical properties. The nitrogen content in the film rises rapidly until the N2/C2H2 gas ratio reaches 2 and then increases more gradually, while the deposition rate decreases steeply, placing an upper limit for the nitrogen incorporation at 30 at%. For nitrogen contents above 20 at%, the band gap and sp3-bonded carbon fraction decrease from 1.7 to 1.1 eV and approximately 65 to 40%, respectively. Films with higher nitrogen content are less dense than the original hydrogenated tetrahedral amorphous carbon (ta-C:H) film but, because they have a relatively high band gap (1.1 eV), high resistivity (109 Ω cm) and moderate sp3-bonded carbon fraction (40%), they should be classed as polymeric in nature.

Analysis of amorphous carbon thin films by spectroscopic ellipsometry

Using spectroscopic ellipsometry (SE), we have measured the optical properties of amorphous carbon (a-C) films ∼ 10-30 nm thick prepared using a filtered beam of C+ ions from a cathodic arc. Such films exhibit a wide range of sp3-bonded carbon contents from 20 to 76 at.% as measured by electron energy loss spectroscopy (EELS), and a range of optical gaps from 0.65 eV (20 at.% sp3 C) to 2.25 eV (76 at.% sp3 C) as measured by SE. SE data from 1.5 to 5 eV have been analyzed by applying the most widely used effective medium theory (EMT) namely that of Bruggeman with isotropic screening, assuming a model of the material as a composite with sp2 C and sp3 C components. Although the atomic fractions of sp3 C deduced by SE with the Bruggeman EMT correlate monotonically with those obtained by EELS, the SE results range from 10 to 25 at.% higher. The possible origins of this discrepancy are discussed within the framework of an optical composite. Improved agreement between SE and EELS is obtained by employing a simple form for the EMT, in which the effective dielectric function is determined as a volume-fraction-weighted average of the dielectric functions of the two components. © 1998 Elsevier Science B.V. All rights reserved.

Carbon onions: Carriers of the 217.5 nm interstellar absorption feature

The UV-VIS characteristics of carbon ions fabricated by an arch discharge in water or liquid nitrogen show characteristics that are similar to the interstellar absorption feature. Thus, high purity and well separated carbon onion samples prepared by annealing the as-fabricated powder in air at 600°C for 60 showed a constant absorption peak at 4.6 μm-1 with a variable width ranging from 1.2-1.6 μm-1. In addition to the UV-VIS data, the origin of the absorption feature at 4.6 μm-1 in carbon onions can be attributed to the collective excitations of π plasmons.

Electrical and field emission investigation of individual carbon nanotubes from plasma enhanced chemical vapour deposition

Plasma enhanced chemical vapour deposition (PECVD) is a controlled technique for the production of vertically aligned multiwall carbon nanotubes for field emission applications. In this paper, we investigate the electrical properties of individual carbon nanotubes which is important for designing field emission devices. PECVD nanotubes exhibit a room temperature resistance of 1-10 kΩ/μm length (resistivity 10-6 to 10-5 Ω m) and have a maximum current carrying capability of 0.2-2 mA (current density 107-108 A/cm2). The field emission characteristics show that the field enhancement of the structures is strongly related to the geometry (height/radius) of the structures and maximum emission currents of ∼ 10 μA were obtained. The failure of nanotubes under field emission is also discussed. © 2002 Elsevier Science B.V. All rights reserved.

Fabrication and bio-functionalization of tetrahedral amorphous carbon thin films for bio sensor applications

Tetrahedral amorphous carbon (ta-C) thin films are a promising material for use as biocompatible interfaces in applications such as in-vivo biosensors. However, the functionalization of ta-C film surface, which is a pre-requisite for biosensors, remains a big challenge due to its chemical inertness. We have investigated the bio-functionalization of ta-C films fabricated under specific physical conditions through the covalent attachment of functional biomolecular probes of peptide nucleic acid (PNA) to ta-C films, and the effect of fabrication conditions on the bio-functionalization. The study showed that the functional bimolecular probes such as protected long-chain ω-unsaturated amine (TFAAD) can be covalently attached to the ta-C surface through a well-defined structure. With the given fabrication process, electrochemical methods can be applied to the detection of biomolecular interaction, which establishes the basis for the development of stable, label-free biosensors. © 2011 Elsevier B.V. All rights reserved.