A. L. Musatov

Field emission from carbon layers containing very long and sparse nanotubes∕nanofilaments

Field-emission characteristics of carbon layers with very long (up to several mm) and sparse nanotubes (nanofilaments) have been investigated. For such layers field emission current of 10μA is registered at very low average electric field Eav=0.16V∕μm and the values of the field amplification coefficient β reach 45 000. It has been found that, at electric fields corresponding to the onset of the field emission, the emitting nanotubes are stretched towards the anode. At high emission currents (exceeding 30–50μA), one or several luminous filaments have been observed in the gap between the sample and the anode. These luminous filaments are carbon nanotubes (nanofilaments) heated by the emission current.

Field electron emission form single-walled carbon nanotubes with deposited cesium atoms

It has been found that deposition g of cesium atoms on single-walled carbon nanotubes covered with potassium atoms not only drastically increases emission current but also considerably changes the shape of current-voltage characteristics of field electron emission, namely, the characteristics become nonlinear in Fowler-Nordheim coordinates. It has been assumed that this effect is associated with the fact that field electron emission in these layers comes from single-walled carbon nanotubes, which have p-type conductivity after potassium treatment, while deposition of cesium leads to the formation of p-n junctions near nanotube tips. Part of the applied voltage drops in p-n junction, thus causing a nonlinearity of current-voltage characteristics.

Influence of cesium atoms on the field electron emission from multi-walled carbon nanotubes

It has been shown that the deposition of cesium atoms on multi-wall carbon nanotubes abruptly increases the current of the field electron emission, decreases the threshold electric field by a factor of three (to 0.8 V/m), and decreases the work function to 2.1–2.3 eV. It has been found that the flowing of the large emission current I ≥ 2 × 10−6 A leads to a change in the current-voltage characteristics and a decrease in the emission current. This effect has been explained by escape of cesium atoms from the tips of most nanotubes into the nanotube depth due to desorption or intercalation. At the same time, the low work function is retained for some nanotubes, probably, due to the stronger bonding of Cs atoms with these nanotubes.

Field electron emission from carbon nanotubes in the presence of a weak high-frequency electric field

Series of narrow peaks in the frequency range of f ≈ 50–1200 MHz have been revealed in the frequency responses of the emission current from carbon nanotubes in the presence of a weak high-frequency electric field. The analysis makes it possible to attribute these peaks to resonance of the first and second harmonics of forced mechanical vibrations of carbon nanotubes in a high-frequency electric field. The determined Q factor of nanotubes is in the range of 100–300.

Low-voltage nonstationary electron emission from single-walled carbon nanotubes as exoelectron emission

Low-voltage nonstationary electron emission from single-walled carbon nanotubes after the passage of high autoemission current has been observed. This emission is assumed to be exoelectron emission associated with mechanical stresses and defects appearing in nanotubes due to electrostatic forces acting on nanotubes in a strong electric field.

Light emission from carbon nanofilaments/nanotubes at field electron emission

The spatial distribution of light emission has been studied in planar field electron emitters with long and sparse carbon nanofilaments/nanotubes. The photographic recording of light emission of the emitting nanofilaments/nanotubes is shown to be efficient to determine the position of individual nanofilaments/ nanotubes in different emitter surface areas, as well as to highlight the nanofilaments/nanotube agglomerate distribution over the emitter surface, which mainly contributes to its emission.

Frequency characteristics of field electron emission from long carbon nanofilaments/nanotubes in a weak AC electric field

Frequency characteristics of field electron emission from long carbon nanofilaments/nanotubes in strong dc and weak ac electric fields have been investigated. A series of narrow peaks with a quality factor of up to 1100 has been discovered in the frequency range of hundreds of kilohertz. The analysis has shown that these peaks are probably associated with mechanical oscillations of the carbon nanofilaments/nanotubes driven by the ac electric field.

Field electron emission from layers with very long carbon nanotubes/nanofilaments grown by CVD

This paper investigates field emission from layers of long carbon nanotubes/nanofilaments. Such layers are grown by CVD techniques on a silica substrate covered by micro-particles of iron oxalate as the catalyst in a flow of methane-hydrogen mixture at 1050/spl deg/C. The layers are investigated by TEM, SAED and SEM. Results show that at emission currents exceeding 50 mA, one or several luminous filaments stretched from the sample toward the anode are observed. At small E/sub av/ a fine red line is visible. Then as E/sub av/ increased a filament becomes bright white and soon disappeared.