Xinluo Zhao

The smallest carbon nanotube

We report here the discovery of the smallest possible carbon nanotube. This has a diameter of 4 Å, which is the narrowest attainable that can still remain energetically stable, as predicted by theory. These nanotubes are confined inside multiwalled carbon nanotubes and their diameter corresponds to that of a C20 dodecahedron with a single carbon atom at each of its twenty apices. Unlike larger carbon nanotubes, which, depending on their diameter and helicity, can be either metallic or semiconducting, these smallest nanotubes are always metallic.

Production of petal-like graphite sheets by hydrogen arc discharge

By DC arc-discharge evaporation of graphite in the presence of rarefied hydrogen gas, not only carbon nanotubes but also petal-like graphite sheets were produced on the graphite cathode as a carbon deposit. A large number of interlaced petal-like graphite sheets were observed by scanning electron microscopy on the cathode surface which surrounded the region of carbon deposit including multiwalled carbon nanotubes. The crystal structure of these petal-like graphite sheets was confirmed to be stacking of graphene by using a selected area electron diffraction pattern. Here, we propose a mass production method of petal-like graphite sheets by hydrogen arc discharge evaporation.

Growing carbon nanotubes

The discovery of ‘fullerenes’ added a new dimension to the knowledge of carbon science 1 ; and the subsequent discovery of ‘carbon nanotubes’ (CNTs, the elongated fullerene) added a new dimension to the knowledge of technology 2 ;. Today, ‘nanotechnology’ is a hot topic attracting scientists, industrialists, journalists, governments, and even the general public. Nanotechnology is the creation of functional materials, devices, and systems through control of matter on the nanometer scale and the exploitation of novel phenomena and properties of matter (physical, chemical, biological, electrical, etc.) at that length scale. CNTs are supposed to be a key component of nanotechnology. Almost every week a new potential application of CNTs is identified, stimulating scientists to peep into this tiny tube with ever increasing curiosity.

Preparation of high-grade carbon nanotubes by hydrogen arc discharge

Fine and long multiwalled carbon nanotubes attached with less carbon nanoparticles were prepared by d.c. arc discharge plasma of graphite electrodes in hydrogen gas. These high-grade carbon nanotubes grew on the central part of the cathode as a carbon deposit like black soot. They were mainly observed by a scanning electron microscope and subsequently by a high resolution transmission electron microscope. By comparing with helium and methane gases, the predominance of the use of hydrogen gas as the environmental gas is discussed. A new type of carbon allotrope, namely petal-like graphite sheets consisting of a number of interlaced graphene sheets, was also found in the outside region surrounding the central cathode deposit.

Mass production of single-wall carbon nanotubes by the arc plasma jet method

Abstract Single-wall carbon nanotubes (SWNTs) were mass-produced by a newly developed DC arc plasma jet method for the evaporation of a metal-doped carbon anode. The production rate of the cottonlike soot was significantly higher than that by conventional DC arc discharge evaporation, and the highest yield was 1.24 g/min. Investigations by scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy indicated that more than 50% of the cottonlike carbon soot was composed of fibrous bundles of SWNTs. Through analysis of the breathing modes in the Raman spectra of the cottonlike soot, the diameter of each SWNT was determined to range from 1.28 to 1.52 nm.

Spongy carbon nanobeads—A new material

Abstract Spherical carbon nanobeads (solid and hollow) of two sizes of around 500–850 nm (large) and 250 nm (small) were synthesized by pyrolysing camphor vapour at 1000 °C in an argon atmosphere, using ferrocene, as catalyst, for the first time. The EEL spectrum suggests the carbon beads to be non-graphitic and these are covered by a graphitic shell of 80–100 nm, revealed by transmission electron microscopy (TEM) micrographs. The larger beads, more than 10 are interconnected by the outer shell. After covering the train of carbon, the beads take the shape of fibrous graphitic carbon which perhaps gives the spongy elastic character to the material. The average surface area of the nanobeads determined by BET studies is calculated to be 16 m 2 g −1 . It is suggested that this material may be a useful anode for secondary lithium ion batteries.

Radial breathing modes of multiwalled carbon nanotubes

Abstract A number of Raman-active peaks in the low-frequency region (100–600 cm−1) were observed for multiwalled carbon nanotubes (MWNTs). They were confirmed to be the radial breathing modes (RBMs) by using polarized Raman scattering. These RBMs originate from very thin innermost tubes (diameter, d=∼1 nm ) included in MWNTs, and the RBM peak of the smallest carbon nanotubes ( d=0.4 nm ) appears at 570 cm −1 . It has also been found that the innermost-diameter distribution calculated from the RBM frequencies agrees well with the observations of high-resolution transmission electron microscopy. This provides a new Raman-spectroscopy-based method for the determination of the innermost diameter of MWNTs.

Macroscopic oriented web of single-wall carbon nanotubes

Abstract A macroscopic oriented web (30 cm length) of single-wall carbon nanotubes (SWNTs) with purity higher than 70 at.% has been produced by dc arc discharge evaporation of a carbon electrode including 1 at.% Fe catalyst in H 2 –Ar mixture gas. The SWNTs possess high crystallinity and a ‘clean’ surface. Moreover, the coexisting Fe catalyst nanoparticles can be completely eliminated by a two-step purification process (heating in air at 693 K and mild hydrochloric acid treatment). This study provides a simple, inexpensive and efficient method for producing high-quality SWNTs on a large scale, and enables us to investigate the physical properties of SWNTs in bulk.

Multiple splitting of G-band modes from individual multiwalled carbon nanotubes

Surface-enhanced Raman scattering spectra of an individual multiwalled carbon nanotube (MWNT) with the innermost diameter ∼1 nm, prepared by hydrogen arc discharge, show a single peak of radial breathing mode and multiple splitting of the tangential stretching G-band modes. Based on Lorentzian line shape analysis and related theoretical calculations, the G-band modes of MWNT are confirmed to be composed of both G-band modes (linewidth 4 cm−1) from the innermost tube and graphite-like mode (linewidth ∼20 cm−1) from the outer cylinders in MWNT. This observation indicates that MWNTs are unique and possess characteristic Raman spectra different from other sp2 carbon allotropes.

Mass production of multiwalled carbon nanotubes by hydrogen arc discharge

Highly graphitized multiwalled carbon nanotubes (MWNTs) were mass-produced by hydrogen arc discharge with automatic feeding of carbon electrode. Refluxing them first in hydrogen peroxide and then in a mixture of sulfuric and nitric acids was carried out for purification of MWNTs. The purification process of MWNTs was evaluated by scanning electron microscopy. Nanostructure and crystalline perfection of the purified MWNTs were investigated by using high-resolution transmission electron microscopy and Raman spectroscopy. It was found that the purified MWNTs had about 1.3 nm innermost diameter, resulting in the appearance of radial breathing modes in their Raman spectra.