High Electron Gain from Forests of Multi-Walled Carbon Nanotubes
- PDF / 208,774 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 88 Downloads / 265 Views
1258-R10-21
High Electron Gain from Forests of Multi-Walled Carbon Nanotubes Mario Michan and Alireza Nojeh Department of Electrical and Computer Engineering, The University of British Columbia, Vancouver BC, V6T 1Z4, Canada ABSTRACT Carbon nanotubes are attractive candidates for electron field-emitters due to their high aspect ratio, mechanical stability, and electrical conductivity. It has previously been shown that an electron beam hitting the tip of a carbon nanotube biased near the threshold of field-emission can stimulate the emission of a large number of electrons from the nanotube tip. Here we report on similar experiments on arrays of free-standing multi-walled carbon nanotubes (nanotube forests) interacting with a scanning electron microscope’s primary beam. Electron gains of up to 19,000 were obtained. This can enable applications such as electron detection and multiplication, and vacuum transistors. INTRODUCTION Carbon nanotubes are tubular structures made entirely of sp2-hybrid-bonded carbon atoms in a honeycomb structure that can be thought of as rolled graphene. The cylindrical structure and particularly strong carbon-carbon bond make nanotubes a highly stable material. Also high aspect ratio nanotubes can be synthesized [1]. These characteristics and their good electrical conductivity make nanotubes attractive candidates as electron sources. An electron source is a material used to generate electrons for vacuum-electron-beam applications such as electron microscopes or accelerators. One group of commonly used electron sources require high temperatures for the extraction of electrons and are called thermionic emitters. Field-emitters, on the other hand, can generate electrons at room temperature, via quantum tunneling through the thinned-down potential barrier that the electrons see as a strong electric field is applied. This type of electron emission produces higher current density with smaller electron energy spread than thermionic emission [2]. Electron beams with these characteristics are usually desired for applications. Carbon nanotubes are excellent field-emitters [3-5]. A particular aspect of carbon nanotubes that we have been investigating is their interaction with electron beams. An electron beam impinging on a material produces several observable by-products that can be detected to provide valuable information about the material. Some of the commonly detected by-products of the scattering event are backscattered electrons, secondary electrons, Auger electrons and x-rays. Scanning electron microscopes (SEMs) use, mostly, secondary electrons to generate an image of the surface of the material. The number of secondary electrons generated during the electron beam-material interaction is a function of the electron beam energy, angle of incidence, surface potential and type of material. This interaction is surprisingly strong in carbon nanotubes. The strength of the interaction is most evident during SEM imaging of single-walled carbon nanotubes (SWNTs): Nanotubes are readily visible despite the
Data Loading...
