Field emission from optimized structure of carbon nanotube field emitter array

Abstract

The authors report a detail study on the emission properties of field emitter array (FEA) of micro-circular emitters of multiwall carbon nanotubes (CNTs). The FEAs were fabricated on patterned substrates prepared with an array of circular titanium (Ti) islands on titanium nitride coated tantalum substrates. CNTs were rooted into these Ti islands to prepare an array of circular emitters. The circular emitters were prepared in different diameters and pitches in order to optimize their structure for acquiring a high emission current. The pitch was varied from 0 to 600 μm, while a diameter of circular emitters was kept constant to be 50 μm in order to optimize a pitch. For diameter optimization, a diameter was changed from 50 to 200 μm while keeping a constant edge-to-edge distance of 150 μm between the circular emitters. The FEA with a diameter of 50 μm and a pitch of 120 μm was found to be the best to achieve an emission current of 47 mA corresponding to an effective current density of 30.5 A/cm2 at 7 V/μm. The excellent emission current was attributed to good quality of CNT rooting into the substrate and optimized FEA structure, which provided a high electric field on a whole circular emitter of 50 μm and the best combination of the strong edge effect and CNT coverage. The experimental results were confirmed with computer simulation.

Field Emission Cathodes to Form an Electron Beam Prepared from Carbon Nanotube Suspensions

“…Hence, changes in the cathode design, from the high aspect ratio lines to the matrix of squares have resulted in more uniform and 1.4 times higher emission current, probably due to the non-uniform distribution of CNT tips from the surface of the film. Further experiments by following researchers [118,119] showed an increase of emission currents with the reduction of the emitter area and the spacing between them (Figure 9a,b). All the results indicated the potential of a microscale design and the importance of the fine patterning for CNT-FE cathodes.…”

“…However, it is difficult to discuss the effect of the treatment on emission due to a lack of data provided for comparison or other aspects influencing FE cathode properties, e.g., technology. Other methods were also investigated, such as the use of liquid elastomer [140], a soft rubber-roller [122,123,[141][142][143], mechanical crush [144], and plasma [119,133,[145][146][147]. The last one is believed not only to make CNTs protrude from the matrix (Figure 14c), but also to clear the cathode surface, improving the uniformity and reducing the cathode aging, and thus improving the FE characteristics (Figure 14d).…”

“…Influence of a design of a cathode on its emission: (a) the graph presenting simulation results for the FE cathode being a flat film and a bundle-the trend in electric field enhancement upon the distance from the center of the cathode, and the inset shows the bundle SEM image (left) and a schematic image (right); (b) the FE characteristic of the cathodes arrays with various distances between them, and the inset shows SEM images of these FE cathodes.Figure 9a,b reprinted with permission from[118,119], respectively.…”

Design and Simulation of a Multi-Sheet Beam Terahertz Radiation Source Based on Carbon-Nanotube Cold Cathode

“…However, the operating voltage can be reduced by shortening the distance between the grid and the emitter, which beneficially reduces the likelihood of vacuum gap breakdown. To further study the effects of increasing the emission current, array arrangements of CNT film emitters were explored following on from reported dramatic improvements in emission characteristic by Li et al [37] and Chouhan et al [38]. A five-sheet-beam electron optical system based on the CNT film emitter was proposed, as shown in Figure 3.…”

“…The distance between two parallel CNT film emitters was G. In order to reduce the probability of breakdown, and at the same time to obtain a larger emission current density, the distance between the grid and the CNT film emitters was minimized to 1.5 mm. According to previous experiments [32], we have found that significant To further study the effects of increasing the emission current, array arrangements of CNT film emitters were explored following on from reported dramatic improvements in emission characteristic by Li et al [37] and Chouhan et al [38]. A five-sheet-beam electron optical system based on the CNT film emitter was proposed, as shown in Figure 3.…”