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SSL/NUSNNI Seminar Series
2004 No.3
Combined talks (two speakers)
Date: May 18(Tuesday), 2004
Time: 3:30-4:30pm
Venue: Physics Resource Room (Blk S13 # 02-16)
Speaker I: Mr. Zhu Yanwu
Title: Field emission studies on carbon nanotubes and CuO
nanowires
Abstract:
We have exposed aligned multi-wall carbon nanotube (MWCNT) films
to CF4 plasma from Reactive Ion Etching (RIE) system and studied
the corresponding dependence of the field esmission (FE) properties
of the films on the time of exposure. It is found that that after
2 minutes of plasma treatment the emission currents were enhanced
compared with as grown CNTs; however, extended treatment over 2
minutes degraded FE properties of the film. With the help of Characterizations
it is found that the FE enhancement could be attributed to favorable
surface morphologies, open-ended structures and a large number of
defects in the aligned CNT films.
At the same time, we have used a simple method of direct heating
of bulk copper plates in air to synthesize oriented CuO nanowire
films on a large scale. The length and density of nanowires could
be controlled by growth temperature and growth time. FE measurement
of CuO nanowire films show that they have a low turn-on field of
3.5 ~ 4.5 V/mm and a large current density of 0.45 mA/cm2 under
an applied field of about 7 V/mm. Verified with finite element calculation,
the work function of oriented CuO nanowire films was estimated to
be 2.6 ~ 2.8 eV. Moreover, laser-enhanced FE properties have been
observed in our experiments. By direct incidence of green (532nm)
and infrared (1064nm) laser beams, the emission current was largely
improved. The enhancement degree was related to the applied field,
laser power, laser wavelength and shinning time.
Speaker II: Mr.Gohel Amarsinh, Brandon
Title: Optical Limiting and Field Emission Studies of Carbon
Nanotubes
Abstract:
In this talk, we will investigate two of the most popular applications
of carbon nanotubes: optical limiting and field emission.
The first half of the presentation is dedicated to the discussion
of the modification of the optical limiting properties of carbon
nanotubes. Optical limiting measurements were done at 532nm and
1064nm. It was observed that the optical limiting properties for
modified carbon nanotubes were enhanced at 532nm wavelength.
The second half of the presentation will discuss the modification
of field emission of carbon nanotubes using the N2 and Ar plasma
etching. Randomly aligned carbon nanotubes were grown using the
plasma enhanced chemical vapour deposition system and then etched
with N2 or Ar plasma. SEM imaging showed structural modifications
to the carbon nanotubes after plasma etching treatment. Field emission
measurements showed that carbon nanotubes etched with N2 plasma
showed a large increase in emission current as compared to as-grown
carbon nanotubes under the same applied voltage, while Ar showed
no enhancements. We attempt to provide an explanation for this observation
using data obtained from XPS, UPS and Raman Spectroscopy.
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