[labmembers] Invitation to my PhD orals

Alireza Nojeh anojeh at stanford.edu
Fri Nov 4 08:59:21 PST 2005


Dear labmembers,

I would like to invite you all to my PhD defense on Monday at 10 AM. I
hope you can make it.

Best,
Ali

-----------------------------------

Controlled electron emission from single-walled carbon nanotubes

Alireza Nojeh
Department of Electrical Engineering

Advisor: Professor R. Fabian Pease

Monday, November 7, 2005
10 AM (Refreshments served at 9:45 AM)
CIS-X Auditorium

In electron-beam lithography, the brightness, energy spread, and shot
noise of the electron source are critical in determining the resolution
and throughput. Carbon nanotubes, nanometer-diameter tubes of rolled
graphite layers, have demonstrated brightness values of about an order of
magnitude better than traditional electron sources with similar values of
energy spread. Shot noise is due to the random emission of electrons from
the source. In order to reduce shot noise, electron emission must be
controlled in time. The ultimate goal would be to have a turnstile
electron emitter. Such an emitter is also desirable in a free-electron
analog to digital converter.

One way to gain control is to isolate an electron in a quantum dot, and
stimulate its emission by an external agent. Here the challenge is to have
a quantum dot small enough to be sensitive to single electrons at room
temperature. I will demonstrate that a cross structure, made from
single-walled carbon nanotubes, can provide a solution, and describe
progress made toward the fabrication of such a structure. Then I will
present experiments where electron emission from the tip of a
single-walled carbon nanotube is stimulated by another electron beam. An
electron multiplication factor of up to 100 can be obtained. Since the
interaction volume of the primary beam with the nanotube is very small
(only a few cubic nanometers of a hollow structure), traditional beam-bulk
specimen models cannot explain the effect. I will present a model based on
ab-initio calculations to explain this type of interaction. Interestingly,
this phenomenon shows that single-walled carbon nanotubes can be used not
only as controllable emitters, but also as localized (nanometer scale)
electron detectors.




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