No abstract

The field emission from aligned multiwalled carbon nanotubes prepared by thermal chemical vapor deposition of Fe-phthalocyanine is reported, with emphasis on the current–voltage characteristics and current fluctuation. By running of a pristine emitter at high current and/or voltage for a long time, the onset voltage is lowered from 400 to 125 V and the field-enhancement factor increases from 360 to 1110, demonstrating geometrical reconstruction of the nanotube apex. Deviation from the Fowler–Nordheim relation is caused at a constant local electric field of ∼4×103 V/μm and is related to high-field conditioning. Electron emission current under a high current density condition (>10 mA/cm2) is stable and noiseless. The reason for current noise in the lower current density is discussed.

Microstructures of bamboo-like multiwalled carbon nanotubes prepared by pyrolysis of Ni-phthalocyanine are studied by high-resolution transmission electron microscopy. The intershell spacings of graphitic shells in these nanotubes are estimated. From pristine nanotubes with a tube diameter of 40–260 nm, the spacing values of 0.339–0.342 nm are obtained almost independent of their tube diameters. However, after heat treatment at 2800 °C they are reduced to a value equivalent to the interlayer spacing of graphite, and tube walls with a clear polygonal cross section come to be observed. The heat treatment of samples is also a very useful method to prepare metal-free nanotubes. The bamboo-like graphitic shells are interpreted to be determined by a cone-shaped Ni nanoparticle included at the base of the multiwalled carbon nanotube.

Buckminsterfullerene (C60) is effectively doped in poly(3-alkylthiophene). However, the characteristics of C60-doped poly(3-alkylthiophene) are different from the typical behavior observed in the case of conventional dopants. Electrical conductivity of poly(3-alkylthiophene) increases upon C60 doping and decreases again at higher concentration of C60. Its temperature dependence is also anomalous. The absorption spectrum changes markedly upon C60 doping. ESR linewidth decreases from 7.1 G to 1.9 G upon C60 doping. Spin density, evaluated by ESR, is enhanced upon C60 doping. These doping characteristics are tentatively explained by taking electronic energy diagrams of both poly(3-alkylthiophene) and C60 into consideration.

Electron field emission has been studied with diamond-like carbon (DLC) films deposited from a liquid phase. The DLC films were deposited on Si substrate by electrolysis of methanol liquid. The field emission measurements were carried out with a parallel plate configuration using the deposited DLC films on Si substrate as a cathode, and an indium tin oxide (ITO) coated glass plate as an anode. We found several bright spots on a luminescent screen mounted on the ITO anode, indicating that the electrons are emitted from the isolated emission sites on the deposited DLC film. The emission current density is more than 10−7 A/cm2 at the electric field as low as 1.2 V/μm. This result suggests that the DLC film deposited from the liquid phase has a potential advantage for field emitter applications.