Effects of cathode structure on the field emission properties of individual multi-walled carbon nanotube emitters

Abstract

We report the effect of cathode structure on the field emission properties of individual carbon nanotubes. Experimental field emission data are obtained for two well-defined cathode structures: a multi-walled carbon nanotube (MWNT) attached to an etched Ni metal wire and a MWNT attached to a flat Ni-coated Si microstructure. We observed different macroscopic turn-on fields of 1.6 and 2.5 V µm−1, respectively, for the aforementioned experimental structures. This effect is investigated by detailed finite element analysis. We demonstrate that the geometry of the cathode structures significantly affects the microscopic tip field, leading to different turn-on voltages and field distributions for such individual MWNT emitters. Simulations show that changing the support geometry from a hemispherically capped shank to a cylindrical shank produces an increase in the macroscopic threshold field of 0.91 V µm−1. This effect is further investigated by varying the support radius from 0.5 to 30 µm for a cylindrically shaped support structure. The results show that such a variation in the radius of the support structure produces an increase in the macroscopic turn on field from 0.72 to 5.89 V µm−1. We also report quantitative evidence for the nonlinear relationship between the field enhancement factor as a function of support structure radius for nanostructures of three different aspect ratios.

Carbon Nanotube Field Emission Devices with Integrated Gate for High Current Applications

“…Figure 3a shows the field emission I-V characteristics of a CPA with a turn-on voltage of 0.9 V/μm. This low turn-on field of CPAs is comparable to values typically reported for individual CNT emitters [7,8].…”

An empirical study of dynamic properties of an individual carbon nanotube electron source system

“…Previous research has demonstrated that nanotube field emission electron source parameters such as the turn-on voltage, field enhancement factor, and beam profile are greatly influenced by the nanotube tip structure [10][11][12]. Our group and others have also shown that field emission characteristics are strongly dependent on the geometry of the CNT support structure due to electrostatic field screening [4] and on the cathode to anode gap separation [13][14][15]. Hence, the magnitude of R is also affected by the geometry of the devices as well as the structure of the CNT emitter itself.…”

“…Finite element analysis reveals that varying the radius of a cylindrically shaped support structure from 0.5 to 30 lm results in an increase in the macroscopic turn-on field from 0.72 to 5.89 V lm À1 . Furthermore, the field enhancement factor decreases asymptotically for increasing support structure radius [4]. We have also demonstrated an improved fabrication technique for individual CNT emitters based on MEMS technology that enables a high degree of control over the cathode structure [5].…”

“…To this end, we previously presented experimental and device simulation data, which reveal field emission behavior of the CNT itself under an electrostatic field [4,5]. Finite element analysis reveals that varying the radius of a cylindrically shaped support structure from 0.5 to 30 lm results in an increase in the macroscopic turn-on field from 0.72 to 5.89 V lm À1 .…”

Dynamic properties of individual carbon nanotube emitters for maskless lithography

“…PERFORMING ORGANIZATION REPORT NUMBER [2]. Also, our group presented an experimental and simulation investigation of the influence of cathode support structure geometry on the field emission properties of a single CNT emitter [3]. In this paper, we present an empirical study of dynamic behavior of an electron source system which incorporates an individual CNT.…”