Electron field emission from composite electrodes of carbon nanotubes-boron-doped diamond and carbon felts

Abstract

The electron field emission of carbon nanotube ͑CNT͒/boron-doped diamond ͑BDD͒/carbon felt electrodes ͑CNT/BDD/felt͒ have been investigated. The composite electrode was initially prepared with the growth of BDD on carbon felt and the subsequent growth of CNT by chemical decomposition of methanol. The composite electrodes were characterised using scanning electron microscopy and transmission electron microscopy. For the CNT/BDD/felt samples, the electron field emission was observed at macroscopic fields as low as 1.1 V m −1 . The emission current versus time plot shows significant potential for future field emission applications. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2178247͔ Diamond thin films are a class of carbon materials that have been used for electron field emission devices since 1991. 1 Its electron emission properties depend on several factors, such as the work function, grain boundaries, 2 and small protuberances. [3][4][5][6][7] For example, it has been shown that the boundaries between grains, sites rich in sp 2 hybridization, emit electrons more easily than the diamond facets of boron-doped diamond ͑BDD͒ polycrystalline films. 7 Interestingly, despite boron being an acceptor state in diamond it appears to enhance the electron emission properties of the material. We believe this is based on the substrate playing an important role in the emission process of diamond films. In fact, it has been observed that better emission results from chemical vapor deposited diamond films grown on SnO 2 instead of silicon, suggesting that the electron supply layer or substrates plays an active role in the emission process. 8 However, despite the well-known attractive properties of diamond ͑negative electron affinity, thermal, mechanical, and chemical inertness͒, there are still several problems in the production of field emission devices based on this material associated with obtaining high current densities from emitters, obtaining uniform microstructures, etc., which affect long-term stability. 9 In addition, diamond films, as well as other carbon materials which have been used for emission, are subject to thermal effects at the interface between the substrate and the carbon film. The presence of heating at the interface of the film and substrate generates different mechanical stresses on the film. This will increase the resistance and/or the voltage barrier needed to maintain electron emission at low voltages for an extended periods of time.In order to circumvent the above problem, we present here an approach based on a combination of carbon nanotubes ͑CNTs͒ and BDD films mounted on a carbon felt to obtain reproducible electron emission at low fields. BDD mounts on a carbon felt have previously been explored for electrochemical applications. 10,11 CNTs grown on BDD films, as described in this letter, is a further interesting technique to increase its potential uses.The felt substrate was obtained from carbonization of polyacrinitrile at 2000°C. The obtained carbon fibers have a diameter of around 10...

Field emission from diamond-coated multiwalled carbon nanotube “teepee” structures

“…There are several recent reports on development of such hybrid materials comprising diamond and CNTs. [24][25][26][27][28][29] Although some success has been reported in increasing the time to burn-out by these methods, the FE characteristics were generally not greatly improved due to the fact that the CNTs were randomly oriented and often lying down on the substrate surface. Our approach is to put a thin CVD diamond coating onto vertically aligned CNTs, which requires three stages: (i) deposition of dense vertically aligned CNTs, (ii) seeding the CNT tips with nanodiamond particles to encourage diamond growth, and (iii) depositing CVD diamond sufficient to form a thin coating without completely embedding the CNTs within the diamond film.…”

Composite electrode of carbon nanotubes and vitreous carbon for electron field emission

“…A better dispersion of CNTs in the cavities should reduce the E th of the composite, as observed for the CNT/felt samples already cited in the literature. [9][10][11] Several chemical methods might be used to disperse catalysts used in the CNT growth on VCarbon substrates. The composite can be submitted to chemical treatments for purification or, yet, incorporation of chemical species able to reduce the work functions of CNTs.…”

“…Recently, an electrode structure composed of composites of CNTs based on carbon substrates with a three-dimensional ͑3D͒ structure [9][10][11] has been proposed as a route to avoiding the above-mentioned drawbacks. In this paper we present yet another 3D textured cathode combining CNTs and vitreous carbon ͑VCarbon͒ having microcavities to obtain a reproducible electron emission current at low fields.…”

Carbon Felt/Carbon Nanotubes/Pani as pH Sensor

“…CNTs exhibit very good adsorption properties because they have high specific surface area and a nanoscaled structure that provides a large number of sites for reactions, thus leading to a high sensitivity. However, for many of the mentioned technological applications, CNTs are also needed as electrodes, and carbon nanotubes/carbon felt composites (CNTs/felt) appears as interesting candidates for the development of several devices [4][5][6]. In the hundreds of studies carried out about CNTs, it is possible see that this material is an excellent support to several kinds of chemical species since it can be metallic or semiconductor, and can be submitted to several types of chemical and thermal treatments.…”