AVS 47th International Symposium
    Nanotubes - Science and Applications Monday Sessions
       Session NM+NS-MoA

Paper NM+NS-MoA10
A Carbon Nano-Tube Based Electron Gun for Electron Microscopy

Monday, October 2, 2000, 5:00 pm, Room 309

Session: Carbon Nanotubes: Nanoelectronics and Field Emission
Presenter: J.G. Leopold, Dept. of Appl Phys., Rafael Labs, Israel
Authors: O. Zik, El-Mul Technologies Ltd., Israel
J.G. Leopold, Dept. of Appl Phys., Rafael Labs, Israel
D. Rosenblatt, Rosenblatt Associates
Correspondent: Click to Email
A novel electron gun geometry is proposed with a carbon nano-tube (CNT) grown in a conducting microfabricated crater separated from a gate by an insulating layer. Electron microscopy preferably utilizes point sources. Field enhancement is responsible for the increased emitted current. The field decreases after a very short range to the free space field of the device and the beam diverges. Because the point source and the electron optics are in practice far from ideal, large angular emission density is required with apertures cropping the diverging beam. Thus, a very small portion of the emitted current is useful. Best performance for point sources is gained when the emitter is a rounded, long and very sharp whisker - a 'point on plane' geometry. Such geometry can be realized with CNT's which have exceptional electron emission properties with very low energy spread. However, due to beam divergence, bare CNT's 'on a plane' are inadequate for Scanning Electron Microscopy (SEM) and to miniature SEM's, termed 'microcolumns', in particular. The crater geometry decreases field enhancement on the tip by an order of magnitude so that increased voltage is needed. Due to the excellent field emission of CNT's this voltage is acceptably low so as to obtain about 500nA while not exceeding the breakdown limit of the insulating layer. Our computer simulations support these results. For such geometry the CNT is immersed in a gun which in itself comprises a lens aligning the beam. Almost all the emitted current can be used in a micro-column. In addition to the low energy spread inherent to CNT's, this electron gun has very high brightness which is an advantage for SEM and lithography applications.