Energy distributions of field emitted electrons from a multi-wall carbon nanotube

Evolution of the Field‐Emission Properties of Individual Multiwalled Carbon Nanotubes Submitted to Temperature and Field Treatments

“…First, the spectra at low voltage and current are considered. In agreement with previous work on clean MWNTs, [30] the form of the TEDs at low current and voltage are found to follow Equation 1 to first order. That is, the TEDs are composed of a single asymmetric peak fixed at E F that widens principally on the low energy side as the increasing electric field increases the slope of the tunneling barrier.…”

“…That is, the TEDs are composed of a single asymmetric peak fixed at E F that widens principally on the low energy side as the increasing electric field increases the slope of the tunneling barrier. Looking more closely it is seen that: 1) there is a hump in the spectra at about 0.5-1.2 eV below the Fermi level similar to TEDs observed previously [30] on highly ordered MWNTs; 2) the fitted E F is 70 meV below that expected for the voltage applied to the tip; 3) the temperatures found from the fitting are about 100 K higher than the true temperature of about 300 K; and 4) the full width at half maxima (FWHMs) are wider than usual for metal emitters. These second-order effects can be caused by the deviation of the electron density from that of a free electron model which is common even for clean metals.…”

“…The values here are larger than previously measured, [30,51] reaching 0.8 eV because of the inclusion of measurements going to higher field and temperature that widen the spectra further. The FWHM is of technical importance because it is an important parameter for point electron sources and in particular chromatic aberration.…”

“…[31] (It has also been suggested that a larger than expected high-energy side is due to field penetration. [30] ) From a practical point of view this sets a limit on the accuracy of the temperature measurement, particularly at low temperature. Much better agreement was found for W<111> FE tips in the same experimental configuration, and hence it is not due to a poor resolution of the energy analyzer.…”

“…[27] The total energy distributions (TEDs) may show very narrow energy spreads [19,26] and multiple peaks, [26,28] or be those that approach standard theory. [29,30] The community may have been looking for something new in FE specifically related to the novel crystalline or electronic structure of CNTs; however, views are now converging to the idea that the I(V) curves and TEDs from properly cleaned MWNTs are governed to first order by the FN theory. The very strong measured FE effects are not specific to CNT electronic structure but to a variety of secondary effects, particularly: 1) nanometer-scale adsorbate-like structures on the emitter zones; 2) emitter evolution during I(V) measurements; 3) temperature increases during I(V) measurements; and 4) contact resistances.…”