Electronics &
Communication Technologies -
Electrical/Electronic Products
Introduction
Field emission leading to the luminance of a brilliant
light has been successfully extracted from a highly
oriented film made of carbon nanotubes. A graphite sheet
coiled in cylindrical form was used as the field emitter
for this joint discovery by Japan Fine Ceramics Centre
and Noritake. Application of strong electric field on
micro-tips of diamond, silicon or molybdenum results
in the emission of electrons at an efficiency much higher
than available with the usual thermal electron emission.
Research on better field emission materials has been
amply complimented by the discovery of the carbon nanotubes
and from the ultra-fine radius of curvature characteristics
of these tapered parts.
In this first practical application of the highly oriented
CNT film for making the prototype FED element, a 3 mm2
sample was used to deliver a light beam of brightness
of 105 cd/m2 with a grid voltage of 2KV and an anode
voltage of 10KV. This level of brightness is almost
the same as that obtained from CNTs produced by other
processes and several times greater than those produced
by the thermal emission. This highly oriented CNT film
was prepared using a surface decomposition process established
by heating a SiC single crystal in a vacuum environment.
Uniformity and the orientation density of these films
are much better than those generated by the arc discharge
method or by the CVD. Their external diameter is several
nm, length is about 1 micron and density of growth is
about 30 billion tubes/mm2.
A problem encountered in using this highly oriented
CNT film as a field emitter comes from the non-conductivity
of SiC. Since it is aligned in a very high concentration,
the electric field will not be concentrated on the individual
CNT and thus extremely high voltage is required for
the emission. The problem was resolved by prolonging
the period of growth and applying a conductive graphite
layer on the surface of SiC. A technique was established
to change the temperature conditions and to control
the growth density. The cap parts at the tips of the
CNTs were cut off with an oxidizing process to promote
electron emission. This technology can offer a new method
for fabricating next generation flat panel displays
replacing the plasma display systems and liquid crystals.
For further information
please contact :
Technology Information, Forecasting
and Assessment Council (TIFAC)
Department of Science and Technology (DST)
'A' Wing, Vishwakarma Bhavan, Shaheed Jeet Singh Marg
New Delhi 110016, India.
Phone: +91-(0)11-26592600, 26867764
Fax: 26961158, 26528227, 26863866
E-mail: tifacinfo@tifac.org.in
