This invention relates to flexible carbon nanotube based field emitters, and a single step process for the manufacture thereof
The invention relates to a simple process for the synthesis of aligned multiwalled carbon nanotube field emitters over a special flexible substrate, graphitized carbon woven, using water assisted chemical vapor deposition technique.
Ever since their discovery, carbon nanotubes (CNTs) have attracted considerable research interest owing to their exceptional electronic and mechanical properties. Electron field emission from CNTs has been demonstrated as the most promising among their various suggested applications. Due to their natural geometry with high aspect ratio, chemical stability, high mechanical strength, high electrical conductivity and the possibility of large scale production, both vertically aligned and randomly oriented CNTs have been reported as excellent emitters at low operating voltages. A film of single walled nanotubes produced by arc discharge method under static He yields a current density of 10 mA/cm2 at about 4.4 V/um but shows a significant degradation with time. High emission stability has been shown by MWNT, however, a small field enhancement factor has resulted in low emission current. The lack of a suitable stable film fabrication process over a suitable flexible substrate has limited the realization of CNT based vacuum microelectronic devices. Weak, adhesion of CNTs to the substrate often leads to a catastrophic vacuum breakdown or arcing during operation. Moreover, the electronic resistance between the CNTs and substrate results in joule

heating of the interface, thereby damaging the interface and resulting in an increase in the voltage required for emission over extended periods.
It is thus an object of the present invention to provide a process for the manufacture of aligned MWNT field emitters over a specific flexible substrate, which employs the assisted catalytic chemical vapour decomposition of a hydrocarbon over selective alloy hydride film, at optimum temperature and flow rates.
It is also an object of the present invention to provide a process that facilitates the fabrication of a flexible substrate, graphitized carbon woven, which is a double layer structured gas diffusion layer porous carbon woven. It consists of a macroporous layer of carbon fiber woven and a microporous layer of carbon black powder and a hydrophobic agent.
Accordingly, this invention discloses a simple process for the preparation of a flexible substrate, graphitized carbon woven, by deposition of a mixture of carbon black and polytetrafluoroethylene powders onto carbon woven. The present invention employs a process leading to the formation of aligned MWNT field emitters over the flexible graphitized carbon woven by water assisted chemical vapour deposition, where a hydrocarbon, acetylene, is catalytically decomposed over a thin film of a selected rare earth based AB2 alloy coated on the flexible substrate. The decomposition of hydrocarbon is earned out at 700 C by the introduction of acetylene through water, at
a flow rate of 50 seem. The thin film of the alloy containing active metal catalyst, catalyzes (i) hydrocarbon decomposition and (ii) the growth of aligned MWNTs. The field emitters characteristics were

determined using high resolution transmission electron microscopy and scanning electron microscopy. The field emission characteristics were studied. Aligned MWNT field emitters were found to have a turn on field (10uA/cm2) of 1.88 V/μm and a threshold field (0.5mA/cm2) of 2.4 V/um. The current stability of the sample was monitored continuously for a period of 4 h at a constant field of 3.25 V/μm and the emission current remained fairly constant. The fluctuation in emission current was within 1% .
The process proposed herein is intended for making fully carbon
based MWNT field emitters for their potential applications iri display technology and vacuum microelectronics.
In accordance with this invention, the fabrication of the fully carbon based substrate, the graphitized carbon woven, offers high flexibility in the choice of substrate geometry as well as superior control of the structural parameters of the substrate layer.
According to this invention, the prepared emitter and the substrate are of the same material which offers perfect matching between the two and thereby reduces the joule heating.
According to this invention, the presence of the graphitic layer provides better adhesion between the substrate and the emitters.

In the process proposed herein, the alloy thin film catalyst is attached to the substrate and hence the emitting surface of the as-grown aligned MWNT based field emitter is free from catalytic impurities.
The single step process for the manufacture of flexible carbon nanotube based field emitter, according to this invention, comprises the preparation of a flexible substrate, namely, graphitized carbon woven, by deposition of a mixture of carbon black and polytetrafluoroethylene powders on to the said carbon woven; the catalytic decompostion of a preselected hydrocarbon over a thin film of a rare earth based AB2 alloy coated on the said substrate, the decomposition of the hydrocarbon being carried out at 700 C by the introduction of the hydrocarbon through water, at a flow rate of 50 seem., the thin film of the alloy containing active metal catalyst, catalyzing the hydrocarbon decomposition and the growth of aligned MWNTs.

The terms and expressions herein are of description and not of limitation having regard to the scope and ambit of this invention.

We Claim:
1. A single step process for the manufacture of flexible carbon
nanotube based field emitter comprising the preparation of a flexible
substrate, namely, graphitized carbon woven, by deposition of a
mixture of carbon black and polytetrafluoroethylene powders on to the
said carbon woven; the catalytic decompostion of a preselected
hydrocarbon over a thin film of a rare earth based AB2 alloy coated
on the said substrate, the decomposition of the hydrocarbon being
carried out at 700 °C by the introduction of the hydrocarbon through water, at a flow rate of 50 seem., the thiri film of the alloy containing active metal catalyst, catalyzing the hydrocarbon decomposition and the growth of aligned MWNTs.
2. A process as claimed in Claim 1 wherein the hydrocarbon is acetylene.
3. A process as claimed in Claim I wherein the deposition is carried out by water assisted chemical vapour deposition, the current stability being monitored continuously for a period of 4 h at a constant field of 3.25 V/um, the emission current remaining substantially constant, the fluctuation in emission current being within 1 % .
4. A single step process for the manufacture of flexible carbon nanotube based field emitter substantially as herein described and illustrated by the Example.

5. A flexible carbon nanotube based field emitter whenever manufactured by a process as claimed in any one of the preceding