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