NANOSCALE DEVICES: APPLICATIONS AND MODELING - Bio-Inspired and Nanoscale Integrated Computing - page 48

(a)
(b)
Figure 2.12. Nanotube cross QD. (a) AFM image of structure. (b) Simulated
structure using molecular dynamics. Reprinted with permission from [38].
(r 2003 American Chemical Society)
workfunction barrier (thermionic emission), by applying a large external electric
field to extract electrons by quantum mechanical tunneling through the potential
barrier (field-emission), or by a combination of heat and external field (Schottky
emission). Another way to provide the necessary escape energy to the electrons is
by using light (photo-emission).
A sharp object enhances an externally applied electric field and makes electron
emission easier. With the advent of nanotechnology and the possibility of
fabricating very small and sharp tips with high aspect ratios, electron emission
research has reached new dimensions and become a very popular subject in the
world of nanodevice applications (Fig. 2.14). In particular, carbon nanotubes,
with their extremely strong mechanical structure, high current carrying capacity
(10 9 A/cm 2 —orders of magnitude higher than copper and silver), and high aspect
ratios, seem like ideal candidates for field-electron emitters [40-44]. Moreover,
their unique structure could lead to interesting electron emission characteristics or
be used to make more controllable electron emitters. In one experiment, electron