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Tuning the Field Emission Properties of Patterned Carbon Nanotube Films
| Content Provider | Semantic Scholar |
|---|---|
| Author | Weiss, Nicolas Kind, Hannes Stöckli, Thomas Forró, L. Kern, K. |
| Copyright Year | 2001 |
| Abstract | We demonstrate here the possibility of tuning the field emission properties of carbon nanotube film emitters. Patterned nanotube films were realized by chemical vapor deposition (CVD) combined with soft lithography, which allows one to vary the density of nanotubes on the films. We show that the geometrical arrangement has a determining influence on the field emission properties, and has important consequences for the realization of nanotube field emission devices such as displays. In particular, medium density films with nanotubes protruding over the substrate showed the lowest emission fields and reached current densities of 10 mA cm below 4 V/lm. A decrease or increase of the nanotube density resulted in degraded emission properties. The necessity to display information is central to much of modern science and technology, and displays have nowadays become indispensable. Diverse types of flat panel displays are currently in use but are not always satisfying the requirements of demanding applications. Different solutions are under consideration with major concerns on production costs, long-term stability, and scale up. Field emission has been recognized early as an attractive alternative to liquid crystal displays (LCDs). In such a device, electrons are extracted from an emitter or emitter array and bombard a phosphor layer deposited on the counter electrode to produce light. Commercial field emission displays based on Mo tips provide a superior picture quality and higher luminosity than LCDs but show high fabrication costs and extreme sensitivity to contamination by adsorbates. Every effort has been made to develop field emitters based on carbon-containing materials (e.g., diamond, diamond-like carbon, and tetrahedral-amorphous carbon) to circumvent those problems. The high expectations and promises held by these materials, however, have not yet been matched by their performances. Carbon nanotubes (CNTs) have recently emerged as one of the most promising electron field emitters. The power of CNTs as electron sources for displays and lighting devices was amply demonstrated in the last few years. Lighting elements based on CNT cathodes have been presented in 1998 and are commercially available with lifetimes in excess of 8000 h. Samsung developed last year a sealed full-color 92 display. CNT cathodes have been incorporated in gas discharge tubes for overvoltage protections and in microwave tubes. The Samsung CNT displays represent an impressive feat and an important milestone towards a fully functional device. They work up to now in diode configuration, which implies that the brightness of a pixel is controlled by varying the potential between emitter and phosphor screen, which is on the order of several kilovolts. Conversely, a triode configuration incorporates a control electrode located near the emitter, and the brightness of the pixel is then controlled by adjusting the potential between cathode and control electrode. For both diode and triode configuration patterns of CNTs have to be defined on the substrate. This has been demonstrated using different techniques: offset printing, standard lithography, soft lithography, and self-assembly. We use here microcontact printing (lCP) to pattern Si substrates with catalyst and subsequently grow CNTs by CVD of acetylene. The advantage of lCP is that the catalyst is applied in liquid form to an elastomeric stamp prior to the transfer to the substrate. Varying the concentration of catalyst in the solution (also called ainko) influences directly the density of CNTs on the patterned film. We demonstrate here that this approach allows one in turn to tune the electron emission properties of the films. We consider ten patterned (samples A±J) and one continuous (sample K) CNT films obtained with different ink concentrations as summarized in Table 1. Figure 1 displays the effect of ink concentration for five different films and provides an overview of the different samples. Diluted inks (1 mM, sample B) yielded films of low density with very short and thick |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.fkf.mpg.de/52531/ |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
