Field emission arrays

Field emission displays are VFDs that use field emission cathodes as the electron source. The cathodes can be molybdenum microtips,33-35 carbon films,36,37 carbon nanotubes,38" 16 diamond tips,47 or other nanoscale-emitting materials.48 Niobium silicide applied as a protective layer on silicon tip field emission arrays has been claimed to improve the emission efficiency and stability.49 ZnO Zn is used in monochrome field emission device (FED) displays but its disadvantage is that it saturates at over 200 V.29... 

The use of DLC in field emission displays is growing because of its properties as an electron emitter for field emission array applications. By controlling the sp /(sp + sp ) ratio the activation energy can be... 

Thomas RN, Wickstrom RA, Schroder DK, Nathanson HC. Fabrication and some applications of large-area silicon field emission arrays. Solid State Electron 1974 17 155-IN7. 

Stratakis E, Giorgi R. et al.. Three-dimensional carbon nanowall field emission arrays. Applied Physics Letters, 2010. 96(4) 043110. 

Fig. 2. Behavior of electron-field emission at room temperature from Spindt-type arrays of 5000 tips per mm, beginning and ending with ultrahigh vacuum (UHV), eg, ultracontrol (UC) (a) water (b) hydrogen and (c) oxygen, where the dashed line indicates noise. To convert Pa to torr, divide by 133.3.

Nanocarbon emitters behave like variants of carbon nanotube emitters. The nanocarbons can be made by a range of techniques. Often this is a form of plasma deposition which is forming nanocrystalline diamond with very small grain sizes. Or it can be deposition on pyrolytic carbon or DLC run on the borderline of forming diamond grains. A third way is to run a vacuum arc system with ballast gas so that it deposits a porous sp2 rich material. In each case, the material has a moderate to high fraction of sp2 carbon, but is structurally very inhomogeneous [29]. The material is moderately conductive. The result is that the field emission is determined by the field enhancement distribution, and not by the sp2/sp3 ratio. The enhancement distribution is broad due to the disorder, so that it follows the Nilsson model [26] of emission site distributions. The disorder on nanocarbons makes the distribution broader. Effectively, this means that emission site density tends to be lower than for a CNT array, and is less controllable. Thus, while it is lower cost to produce nanocarbon films, they tend to have lower performance. 

The field emission properties of carbon nanotube forests and single nanotubes are described. Controlled emission is possible for aligned CNT arrays where the spacing is twice the CNT height, as grown by plasma enhanced chemical vapor deposition. This leads to the maximum field enhancement factor. For random forests, the field enhancement obeys an exponential distribution, leading to a lower emission site density and imperfect current sharing. Ballast resistors can help alleviate this problem. Random nanocarbons perform less well than CNTs. Some applications are covered. Elec-... 

Figure 10.12. Atomic force microscope (a) and field-emission scanning electron microscope (b) images of an ordered array of 200-nm silver-coated silica spheres. (With permission from Ref. 37.)...

Han K, Lee Y, Jun D, Lee S, Jung KW, Yang SS (2011) Field Emission Ion Source Using a Carbon Nanotube Array for Micro Time-of-Flight Mass Spectrometer. Japanese Journal of Applied Physics 50 06GM04... 

Fan. S. Chapline, M. C. Franklin. N. R. Tombier, T. W. Cassei, A. M. Dai, H. Self-oriented regular arrays of carbon nanotubes and their field emission devices. Science 1999 283, 512. 

S. Fan, M.G. Chapline, N.R. Franklin, T.W. Tombler, A.M. Cassell, H. Dai, Self-Oriented Regular Array of Carbon Nanotubes and Their Field Emission Properties , Science, 283,512 (1999)... 

So far, we have tried to form very fine dot arrays on Si substrate for quantum devices and optical and magnetic recording media [3-7] since Hosaka et al. introduced the EB drawing system comprised of a field-emission... 

As was shown by Berdinsky et al. [4], due to CNTs deep rooting within the ion tracks, the CNTs should be more stable than others against a mechanical influence. Moreover, any chemical vapour deposition (CVD) process allows to get bended CNTs, which are interlaced that leads to an increase of mechanical stability of the CNTs array. This could prevent decomposition of CNTs during the field emission process. Therefore, the conventional thermal chemical vapor deposition (TCVD) process can give the array of CNTs and randomize location of their tips with different height. 

The third example of field emission from Si-based nanowires is from the aligned SiC nanowires. The field emission measurements [68] were carried out in a vacuum chamber at a pressure of 5 x 10 Torr at room temperature. An oriented SiC nanowire array, which was used as the cathode, was stuck to a stainless steel substrate by silver paste with the bottom end of the nanowires facing upward. A copper plate with a diameter of 1 cm, mounted on a precision linear feedthrough, was used as the anode. Field emission current densities of 10 pA cm were observed at applied fields of 0.7-1.5 V pm and current densities of 10 mA cm were realized at applied fields as low as 2.5-3.5 V pm , as shown in Figure 10.35. These results represent one of the lowest fields ever reported for any field-emitting materials at technologically useful current densities. We attributed this emission... 

Hajra, M. Chubun, N.N. Chakhovskoi, A.G. Hunt, C.E. Liu, K. Murali, A. Risbud, S.H. Tyler, T. Zhirnov, V. Field emission characterization of silicon tip arrays coated with GaN and diamond nanoparticle clusters. Electrical and Computer Engineering Department, University of California, Davis, CA. J. Vacuum Sci. Technol. B Microelectron. Nanometer Struct.—Process. Meas. Phenom. 2003, 2/(1), 458-463. 

PEO/sol-gel film, (b) Field emissive SEM image of Ti02 dot arrays prepared from PS- -PEO films with 35% sol-gel precursor after exposure to UV light at room temperature for 6 hours in air. (c) Field-emissive SEM image of Ti02 prepared from 15% sol-gel precursor. (From Kim et al.94)... 

Figure 3.55 Field emission from carbon nanotubes (a) scheme of an emitter array consisting of carbon nanotubes, (b) emission curve and possible geometries...

Contrary to other field emission displays that consist of arrays of tips generated by mechanical means, carbon nanotubes are stable up to much higher field intensities, while they emit already at a rather low field of <1V(xm . They can also stand high current densities of more than 1 Acm"l Both SWNTs and MWNTs are suitable for the production of field emission devices. The actual absence of defects is a more decisive parameter here. It correlates well with the efficiency of emission. MWNTs are more robust on long-term use, whereas for SWNTs, the small diameter of individual tubes is an attractive feature. 

Watts PCP, Lyth SM, Mendoza E, SUva SRP et al. (2006) Polymer supported carbon nanotube arrays for field emission and sensor devices. Appl. Phys. Lett. 89 103113-103124. 

C. W. Wang, Z. Wang, M. K. Li, and H. L. Li, Well-aligned polyaniUne nano-fibril array membrane and its field emission property, Chem. Phys. Lett, 341,431-434 (2001). 

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