Carbon Nano-Tube Electron Emission Devices

Abstract

A leading UK university has developed a method that uses highly aligned carbon nanotubes (CNT) to emit electrons at high current density (60mAcm-2) and ultra-low power. The CNTs are grown in a highly aligned carpet in order to maximise the electron emission. These are particularly suited for applications where size and power need to be kept to a minimum.

Description

Carbon nanotubes are attractive for neutraliser devices because they have low emission threshold potentials, high current densities, stable field emission over prolonged time periods and are simpler to manufacture than silicon field emission arrays. As field electron emission is principally a function of applied electric field, the CNT alignment optimises geometrical field enhancement and reduces operating power.

It is well established that field emission does not occur at electric fields <108V/m, however, the CNTs were observed to emit at an unenhanced field of 105V/m. Therefore, the enhancement in the field from the tube geometry must be substantial and of the order 103V/m. During the course of endurance tests it was noted that there was no significant change in the current to the mesh, but the change in voltage was +0.05V/h (0.02%/h). This represents a substantial improvement in perfomance when compared to the silicon FEAs that were tested. In lifetime tests the CNT field emitters lasted in excess of 1400 hours. This is lower than the 6000 hours logged by some of the silicon FEAs available. However, there has been much iteration in the manufacturing process of Si FEAs which has not yet been done with the CNT counterparts. Once this has been completed a more realisic lifetime value can be expected

Innovations and advantages of the offer

  • The CNT are grown to be highly aligned which maximises electron emission.
  • The CNT are secured to a substrate which allows for safe working.
  • The CNT can be produced in whatever format is needed (e.g. with integral micro-machined electrodes)

Application

  • Generation of electrons in vacuum (<10-2 torr) for a variety of purposes
    • Microscopy, X-ray generation, and microwave tubes
    • Particularly suited for applications where size and power need to be kept to a minimum
  • Potential for generation of electrons or atmospheric ions at air pressure
    • More work needs to be conducted to confirm this

Space Heritage

Method for electronic propulsion for satellites in space.

Broker comments

At a quite low TRL so a collaborative development project is probably the most effective route to transfer.

Category
Other Technologies
Reference No.
TDO0015
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