Field Emission Patterns from Single-Walled Carbon Nanotubes

Saito, Yahachi; Hamaguchi, Koji; Nishino, Tetsuo; Hata, Kenji; Tohji, Kazuyuki; Kasuya, A.

doi:10.1143/jjap.36.l1340

Cited by 146 publications

(59 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Numerous papers investigating the field enhancement factor of an individual CNT have attempted to further the understanding of the emission process through experimental and computational investigations into geometric enhancement factor. [4][5][6][7][8][9] It has long been assumed that the effect of field screening is negated when adjacent emitters are at a separation of twice their height. 6 In this letter, we investigate the effect of field screening on arrays of CNT by means of three-dimensional ͑3D͒ simulations and show the impact on device performance.…”

mentioning

confidence: 99%

Maximizing the electron field emission performance of carbon nanotube arrays

Smith

Silva

2009

Applied Physics Letters

View full text Add to dashboard Cite

The field emission screening effect is one of great importance when aiming to design efficient and powerful cathodes. It has long been assumed that the degrading effect is at a minimum when neighboring emitters are at least twice their height from each other. In this work, we show that the screening effect is underestimated and diminishes at far greater separations of five times the height of the emitter. We further observe that to achieve maximum emission efficiency in an array, one requires a trade off between screening and emitter number, resulting in a separation of three times their height. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3097239͔The use of carbon nanotubes ͑CNTs͒ as electron sources for field emission ͑FE͒ applications 1,2 has generated a wide interest since their identification in 1991. 3 The ability to grow ordered arrays of aligned CNT on a range of substrates has made it possible for designers to specify height, radius, separation, etc., and for these requirements to be accurately fabricated. However, the exact process of electron emission from CNTs is still not fully understood. Numerous papers investigating the field enhancement factor of an individual CNT have attempted to further the understanding of the emission process through experimental and computational investigations into geometric enhancement factor. 4-9 It has long been assumed that the effect of field screening is negated when adjacent emitters are at a separation of twice their height. 6 In this letter, we investigate the effect of field screening on arrays of CNT by means of three-dimensional ͑3D͒ simulations and show the impact on device performance.CNTs were simulated in 3D in SIMION 8.0 software. 10 The software solves the Laplace equation using finite difference with optimized linear time solving to allow extraction of potential and electric field at any point around the structure. An initial calibration simulation was that of a hemisphere on a grounded plane, beneath an anode at a positive potential. Numerically, the solution to the Laplacian equation in 3D for such a structure gives a local field above the hemisphere of three times that of the applied field placed infinitely far away. It was found that as long as the anode electrode was maintained sufficiently afar as not to incur anode proximity effects, 8,9 the enhancement factor simulated was 3.01. Figure 1͑a͒ shows a schematic of the simulated array of CNT. Vertically aligned CNTs of uniform height h and radius r are placed on a grounded cathode that is separated from the positive anode by distance D. To simulate a realistic CNT array the impact of the size of the array on screening was examined. We simulated five different conditions. Firstly, a single CNT of height 3 m and radius 50 nm was placed at the center of the simulation work space. The simulation package has a maximum of 200ϫ 10 6 calculation points. This places an upper limit on the array dimensions for simulation to ensure that the anode was sufficiently far away from the CNT and that the CNT ...

show abstract

mentioning

confidence: 99%

Maximizing the electron field emission performance of carbon nanotube arrays

Smith

Silva

2009

Applied Physics Letters

View full text Add to dashboard Cite

show abstract

“…To date, various studies have been performed on field emission from a single CNT. [11][12][13] Measurements of field emission often attempts to quantify the behavior in terms of the applied electric field and the local electric field at the tip, via ␤. For an emitter not operating in the high current space charge regime, the local electric field required for emission should not be a function of the electrode separation, D, and one would expect that measurements of the applied threshold field not to be dependent on the relative separation of the electrodes, with the applied electric field given simply as V / D, where V is the applied potential difference.…”

mentioning

confidence: 99%

Electron field emission from a single carbon nanotube: Effects of anode location

Smith

Cox

Silva

2005

Applied Physics Letters

104

View full text Add to dashboard Cite

Electron field emission from an isolated carbon nanotube ͑CNT͒ was performed in situ in a modified scanning electron microscope, over a range of anode to CNT tip separations, D, of 1-60 m. The threshold field required for an emission current of 100 nA was seen to decrease from a value of 42 V m −1 at an anode to CNT tip separation of 1 m, asymptotically, to approach 4 V m −1 at a separation of 60 m. It is proposed that at low D, the electric field enhancement factor ͑␤͒ reduces as the anode electrode approaches the CNT mimicking a parallel plate configuration. Under "far field" conditions, where D Ͼ 3 h, where h is the CNT height, the CNT enhancement factor is no longer dependant on D, as shown by the asymptotic behavior of the threshold field, and is purely a factor of the CNT height and radius. For each CNT to tip separation, measured emission current data together with the threshold field and enhancement, are consistent with a Fowler-Nordheim analysis for the far field conditions, and dispels the need for a novel emission mechanism to explain the results as has been proposed recently. Since the identification of carbon nanotubes 1 ͑CNT͒, there has been sustained research academically and industrially into numerous potential applications.2-7 Much effort has been invested in the study of their application for electron sources by the process of electron field emission, 7-9 leading to the fabrication of possible next generation flat panel displays.10 Carbon nanotubes are promising candidates for cold cathode electron field emitters due to their electrical properties, chemical inertness, tensile strength, and high aspect ratio, which enable them to alter the local electric field around the tip due to a field enhancement factor, often denoted by ␤. It is important, therefore, in designing and fabricating field emission displays or future cold cathode sources, to understand fully the emission properties and characteristics of not just arrays and mats of CNT, but of individual CNTs. To date, various studies have been performed on field emission from a single CNT.11-13 Measurements of field emission often attempts to quantify the behavior in terms of the applied electric field and the local electric field at the tip, via ␤. For an emitter not operating in the high current space charge regime, the local electric field required for emission should not be a function of the electrode separation, D, and one would expect that measurements of the applied threshold field not to be dependent on the relative separation of the electrodes, with the applied electric field given simply as V / D, where V is the applied potential difference. In this letter, we report that the position of the anode electrode in field emission from a single CNT is important, and furthermore that redefining the manner in which the applied field is described gives rise to a better understanding of the CNTs field emission properties.Multiwalled carbon nanotubes were synthesized by a plasma arc discharge between two graphite electrodes. The subsequent carb...

show abstract

“…Carbon nanotubes are the signature 1D material that show low electrical resistivity and strong field electron emission at a low applied field (Saito et al, 1997). However, they exhibit a relatively high work function, but in combination with a low work function material such as p-type, B-doped diamond, can provide an ideal configuration for specific emitter applications.…”

Section: Nanotips/1d Materialsmentioning

confidence: 99%

Thermionic Energy Conversion in the Twenty-first Century: Advances and Opportunities for Space and Terrestrial Applications

Haase

George

et al. 2017

Front. Mech. Eng.

View full text Add to dashboard Cite

Thermionic energy conversion (TEC) is the direct conversion of heat into electricity by the mechanism of thermionic emission, the spontaneous ejection of hot electrons from a surface. Although the physical mechanism has been known for over a century, it has yet to be consistently realized in a manner practical for large-scale deployment. This perspective article provides an assessment of the potential of TEC systems for space and terrestrial applications in the twenty-first century, overviewing recent advances in the field and identifying key research challenges. Recent developments as well as persisting research needs in materials, device design, fundamental understanding, and testing and validation are discussed.Keywords: thermal energy conversion, thermionic energy conversion, thermionic emission, heat engine, electron emission iNTRODUCTiON The direct conversion of heat to electricity without any intermediate steps or moving parts remains one of the most promising, yet challenging, methods of power production. The promise of high conversion efficiency, device simplicity, and robust operation continues to push research and technology development at the cutting edge. Furthermore, because of the wide variety of possible heat sources, ranging from combustion of fossil or other fuels, nuclear reactors, solar heat, or even waste heat from the human body, the applications for thermal-to-electric energy convertors are vast, spanning many orders of magnitude of possible temperature and power ranges.Thermionic energy conversion (TEC) for direct conversion of heat to electrical energy occurs when electrons thermally emit from a hot surface, traverse a gap, and are collected by another surface. This process, starting with thermionic emission, produces a current of electrons that can subsequently drive an electrical load to produce work. Particularly well suited for high-temperature applications, since it was first proposed by Schlichter (1915), thermionic emission has been pursued as a power generation method for over a century Gyftopoulos, 1973, 1979), yet has seldom been realized in either space or terrestrial applications. However, recent advances in material science and nanotechnology as well as our evolving understanding of the underlying physical processes afford new opportunities to develop practical thermionic convertors, reinvigorating the field. Thermionic energy conversion has a long and storied history, particularly in the space programs of the United States and the former Soviet Union. However, while the field was vibrant and much progress was made during the 1960s through 1980s, including space flight demonstrations, TEC has largely been supplanted by alternative energy conversion technologies, specifically thermoelectrics and photovoltaics, in both the public and research community consciences. Much of thermionic-based research tapered off after a 2001 report by the National Research Council titled Thermionics Quo Vadis? An Assessment of the DTRA's Advanced Thermionics Research and Development Program (Na...

show abstract

Field Emission Patterns from Single-Walled Carbon Nanotubes

Cited by 146 publications

References 14 publications

Maximizing the electron field emission performance of carbon nanotube arrays

Maximizing the electron field emission performance of carbon nanotube arrays

Electron field emission from a single carbon nanotube: Effects of anode location

Thermionic Energy Conversion in the Twenty-first Century: Advances and Opportunities for Space and Terrestrial Applications

Contact Info

Product

Resources

About