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Laser-induced electron emission from arrays of carbon nanotubes

University of British Columbia

Recently there has been growing interest in the interaction of light and nanomaterials, especially carbon nanotubes. Although there exist a large number of studies on the physical and chemical properties of nanotubes with various spectroscopic techniques, only a limited number of works have looked at this interaction for electron source applications. The work presented in this thesis demonstrates light-induced electron emission from arrays of nanotubes with a broad range of wavelengths and light intensities. I demonstrate that arrays of nanotubes have a quantum efficiency of > 10-⁵ in the photoelectric regime, which is comparable to that of metal photocathodes such as copper. Nanotubes are also expected to have better operational lifetime than metals because of their complete chemical structure. I also demonstrate that, based on an effect called "Heat Trap", a spot on the surface of a nanotube array can be heated to above 2,000 K using a low-power beam of light with a broad range of wavelengths from ultraviolet to infrared. Light-induced heating of a typical bulk conductor to electron emission temperatures requires high-power lasers. This is because of the efficient dissipation of heat generated at the illuminated spot to the surroundings, since electrical conductors are also typically excellent thermal conductors. I show that the situation can be drastically different in an array of nanotubes. This behaviour has far-reaching implications for electron sources. For example, the fabrication cost of light-induced electron sources can be signicantly reduced since the nanotube-based cathode can be heated to thermionic emission temperatures with inexpensive, low-power, battery-operated handheld lasers as apposed to high-power or pulsed laser sources, which are currently required for metal cathodes. Arrays of nanotubes can also be shape engineered because of their sparse nature. I have demonstrated that the emission current density can be increased by a factor of 4 by densifying the array with a liquid-induced shrinkage that works by pulling the nanotubes closer together. The Implications of the findings reported in this thesis go beyond conventional electronbeam technologies. For instance, they could lead to novel devices such as thermionic solar cells, solar displays and new types of optical modulators and thermoelectrics.

Text

2012-11-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/42076

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/