Height Of Carbon Nanotubes Research Articles

Field emission characteristics of a single free standing carbon nanotube with gate electrode

In this paper, we have constructed and analyzed the field emission behavior of a single vertically aligned free standing carbon nanotube (CNT) with a gate electrode in order to verify the feasibility of using a single CNT as the low-voltage field emission electron source. The single vertically aligned CNT with gate electrode was fabricated by combining optical lithography, electron beam lithography (EBL) and inductively coupled plasma chemical vapor deposition (ICP-CVD) processes. A self-aligned process with a single mask was utilized to define the gated structure and the nano-size catalyst for CNT growth. A single vertically aligned CNT was then grown within the gate hole by ICP-CVD. The length-to-diameter ratio of CNT could be varied by adjusting the e-beam exposure time, and the CNT height was controlled to equal to the gate-to-cathode spacing (800) nm in one gated device and less than the spacing (530 nm) in another device. The field emission characteristics of the integrated gate electrode devices were then measured under a scanning electron microscopy (SEM) with a three-axis nano-positioning device. The turn-on field of the gated devices with 800 and 530 nm height CNT were 2.77 and 3.57 V/μm, respectively, with applying − 10 V gate voltage, and 0 V anode voltage.

Electron field emission from a single carbon nanotube: Effects of anode location

Electron field emission from an isolated carbon nanotube (CNT) was performed in situ in a modified scanning electron microscope, over a range of anode to CNT tip separations, D, of 1–60μm. The threshold field required for an emission current of 100 nA was seen to decrease from a value of 42Vμm−1 at an anode to CNT tip separation of 1μm, asymptotically, to approach 4Vμm−1 at a separation of 60μm. It is proposed that at low D, the electric field enhancement factor (β) reduces as the anode electrode approaches the CNT mimicking a parallel plate configuration. Under “far field” conditions, where D>3h, where h is the CNT height, the CNT enhancement factor is no longer dependant on D, as shown by the asymptotic behavior of the threshold field, and is purely a factor of the CNT height and radius. For each CNT to tip separation, measured emission current data together with the threshold field and enhancement, are consistent with a Fowler-Nordheim analysis for the far field conditions, and dispels the need for a novel emission mechanism to explain the results as has been proposed recently.

Modeling and calculation of field emission enhancement factor for carbon nanotubes array

To estimate the apex field enhancement factor associated with carbon nanotubes (CNTs) array on a planar cathode surface, the image model of floated sphere between parallel anode and cathode plates was proposed. Firstly, the field enhancement factor of individual CNT was given as the following expression, β 0 = h / ρ + 3.5 , where h is the height and ρ is the radius of CNTs. Then the field enhancement factor of CNTs array was discussed and the above expression was modified to be β = h / ρ + 3.5 - W , in which W is the function of the intertube distance R and represents the coulomb field interaction between the CNTs. All results show that the intertube distance of CNTs array critically affects the field emission. When the intertube distance is less than the height of tube, the field enhancement factor will decrease rapidly with decreasing the intertube distance. According to the calculated results and considering the field emission current density, the filed emission is optimal theoretically when the intertube distance is comparable with the height of CNTs.

P‐36: Effects of Binder Materials in CNT Paste on Field Emission Properties for CNT‐Cathode Applications

AbstractThe effects of binder materials in carbon nanotube (CNT) paste on field emission properties were investigated with respect to high‐efficient CNT‐cathode applications. The binder materials that bond the CNTs to a cathode electrode were composed of an insulating glass‐frit and a conducting Ag‐paste. The dependence of the electrical conductivity of CNT paste comprised of binder material and CNTs ink on the field enhancement factor was investigated using the Fowler‐Norheim equation. CNT films were prepared via a screen‐printing process using the CNT paste. The emission current from the CNT cathode by an electron tunneling effect was increased with increasing ratio of the dielectric glass‐frit fraction in the CNT paste. The reason for the larger emission current from the CNT cathode containing insulating binder materials is due to the increased effective height of CNTs which protrude over the film in the cathode electrode, which effects the field enhancement factor.