Electron emission and structural characterization of a rope of single-walled carbon nanotubes

Abstract

The electron emission and structural properties of an isolated ''rope'' comprised of ϳ70 individual singlewalled nanotubes ͑SWNT's͒ were investigated by measuring the field-emission energy distributions and by using field-ion microscopy ͑FIM͒. Field-emission energy distributions, obtained under ultrahigh-vacuum conditions, revealed that the emitting nanotube has a large density of states near the Fermi energy, with an energy distribution of emitted electrons close to that predicted by the free-electron theory. Two small features located on the trailing edge of the energy distributions are attributed to localized features in the density of states of a SWNT. FIM studies were also performed on the same rope in an attempt to provide structural information about the emitting nanotube. Initial FIM micrographs showed an uneven distribution of atoms. Eventually, rings of atoms were imaged. The atom placement around an individual ring structure is analyzed and found to be consistent with that expected from a single ͑19,13͒ SWNT.

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

“…The results showed a wide spectrum of behavior, particularly in the few years following the first FE experiments of 1995. As examples, the I(V) characteristics may, more or less, follow the FN law, [19,20,23] or tend either to bend up or to saturate at high currents. [24] FE microscopy (FEM) may show complicated emission patterns, [25,26] or those that come from well-specified closed CNTs whose apexes approach ideal structures.…”

“…[24] FE microscopy (FEM) may show complicated emission patterns, [25,26] or those that come from well-specified closed CNTs whose apexes approach ideal structures. [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.…”

“…Within this topic we discuss here a rather extensive set of FE experiments on MWNTs using most of the standard FE techniques. A considerable body of FE studies now exist in the literature, including several extensive articles [19,20] and reviews, [21,22] with measurements on many aspects of FE from ensembles and individual CNTs of varying structural perfection, apex cleanliness, and degree of ex situ characterization. The results showed a wide spectrum of behavior, particularly in the few years following the first FE experiments of 1995.…”

A carbon nanotube field emission multipixel x-ray array source for microradiotherapy application

“…A proportionality constant ␤ relates the applied voltage V to the resulting electric field E by E = ␤V. Ultimately, ␤ can be related to the tip geometry ͑␥ tip ͒ and a field compress factor k, 14 using ␤ =1/ ͑k␥ tip ͒. The corresponding FowlerNordheim plot of the emitted current versus applied voltage ͓ln ͑I / V 2 ͒ versus 1/V͔ from our CNT cathode is nearly linear ͓see Fig.…”

Electronic mean free path in as-produced and purified single-wall carbon nanotubes

“…Lovall et al reported that a single nanotube protrudes from the tip of a SWNT-rope. 12 Our measurements, which provide the transport properties of a single SWNT, were made using a piezo-driven nanopositioning system at room temperature in air (Fig. 2a).…”