Work function estimate for electrons emitted from nanotube carbon cluster films

Abstract

Relying on the obtained theoretical and expenmental results the electron work function from the nanotube carbon film was &mated. It was shown that these structures have a low work function, substantially lower than for graphite. Under estimation we regarded the influence of the film surface relief on its emission ability.Even first investigation results for electron field emission from the thin films containing nanotube carbon structures we developed [l] have shown that these films are promising for emission electronics [l-31. In the present paper we assess the work function of electrons from this material on the base of analyzing the experimentai results for field and thermal emission from the surface of thin nanotube carbon cluster (tubelene) films [4-51 and theoretical calculations.The studies of the nanotube film surface disclose [l-51 that they have an extremely appropriate geometry to construct field emitters when tubelenes are aligned orthogonally to the substrate surface. We have investigated two tubelene types [3-61. The former tubelenes are one-layer tubes of 8 A -1 1 A diameter which are twisted into 100 A -300 A diameter ropes. The letters represent multilayer tubes of 100 A -300 A diameter closed with the cap at the top. We call them, by convention, A and B tubelenes. The mean height of a single tubelene is 100 A .Since the tubelene conductivity is great (about 100 S. cm-1) and the tip radius is very small, a strong electric field arises at the top of the tubelene with applying the potential difference. between the anode and the film under study. This circumstance seems to be one of the factors defining the onset of electron field emission from these carbon films with comparatively low accelerating voltages. Numerical experiments were conducted to study the geometry of the tubelene film. The conductivity of electric field at the emitting surface of the tubelene was calculated using the method of finite elements [7]. So, we estimate, for example, the gain at the tubelene top for a height of a single tubelene of 100 A , its diaqeter of 30 A and an anode-cathode spacing of 20 mkm. With a zero potential at the cathode and the accelerating voltage at the anode U,=lOOO V the maximum field intensity at the top of the tubelene is 0.4 107 V/cm-3. Thus, with a specified geometry of the tubelene film a maximum gain makes up 10. This gain is insufficient to account for the experimentally obtained values of field emission current [4] (in experiment the current was 100 mkm with Ua=lOO V and the anode diameter was 0.6 mkm).Consequently the emission ability of the carbon tubelene film is due to one further factor, and namely, a low work function.In connection with this the Fowler-Nordheim formula was used to calculate the work function versus the number of tubelenes placed at the 0.6 mm diameter cathode. Computation was performed with regard to experimental field emission currents for a theoretically calculated gain at the tubelene tops. Figure 1 presents the work function cp versus Zn (N,JN) where N,, is the maxim...

Three behavioral states observed in field emission from single-walled carbon nanotubes

“…This trend is observed on all tested samples. Field emission from refractory metals with work functions Ͼ3.5 eV is practically temperature independent below 1000 K. The observed strong thermal dependence at low temperatures indicates a different mechanism, such as work function less than 1.3 eV, as reported by Gulyaev et al 8 The temperature dependence of field emission has a different functionality with the work function ͑͒ and field enhancement factor ͑␤͒ than is produced from FowlerNordhiem fits. 23 Thus, it is theoretically possible to determine the and ␤ independently with I -V and I -T data provided a metallic electron tunneling model is followed.…”

“…1, 6 On the other hand, Collins and Zettl 2,7 and Bonard et al 4 observe changes in the slope of the current-voltage behavior in several nanotube samples which they claim suggest a more complicated model than Fowler-Nordheim tunneling. Furthermore, both Gulyaev et al 8 and Rinzler et al 9 have reported unusual temperature-driven changes in field emission current from carbon nanotubes. Gulyaev et al conclude that the strong thermal dependence indicates that both SWNTs and MWNTs are low work function emitters.…”

Aligned carbon nanotube films for cold cathode applications

“…[1][2][3] Carbon nanotube ͑CNT͒ material can be produced in macroscopic quantities by using graphite evaporation in the course of arc discharge or laser ablation or by using thermal decomposition of hydrocarbons. [1][2][3] Carbon nanotube ͑CNT͒ material can be produced in macroscopic quantities by using graphite evaporation in the course of arc discharge or laser ablation or by using thermal decomposition of hydrocarbons.…”

“…[1][2][3] Carbon nanotube ͑CNT͒ material can be produced in macroscopic quantities by using graphite evaporation in the course of arc discharge or laser ablation or by using thermal decomposition of hydrocarbons. 1,[6][7][8][9] From the viewpoint of the field emission ͑FE͒ applications, there is another imperfection of oriented CNT material -a very dense packing of nanotubes. This restrict both the investigations of nanotube's properties and their applications.…”

Work function estimate for electrons emitted from nanotube carbon cluster films

“…[1][2][3] In the present article we assess the electronic work function from this material by analyzing experimental results obtained for field and thermal emission from the surface of thin nanotube carbon cluster ͑tubelene͒ films 4,5 and theoretical calculations. [1][2][3] In the present article we assess the electronic work function from this material by analyzing experimental results obtained for field and thermal emission from the surface of thin nanotube carbon cluster ͑tubelene͒ films 4,5 and theoretical calculations.…”