Articles you may be interested inStandardized assessment of new electromagnetic field generators in an interventional radiology setting Med. Phys. 39, 3424 (2012); 10.1118/1.4712222 Vacuum measurement by carbon nanotube field emissiona)Integrally gated carbon nanotube field emission cathodes produced by standard microfabrication techniques A compact electron energy analyzer for measuring field emission energy distributions Rev.Interest in field emission and field emission devices has been renewed in the last 5 yr. This increase has been due to work on several new materials systems, which have shown promising field emission ͑FE͒ behavior. In turn, this interest gives impetus to the search for new FE sources. In order to move the technology ahead at a faster pace, there is a need for common ground rules and a ''standardization'' of the data reported so that it can be compared directly in a meaningful way and thereby accelerate the development process. In this article key factors affecting the FE data will be discussed and several parameters are suggested to initiate the process of developing a set of ''standardized'' FE parameters. A correct, or at least consistent, determination of characteristics such as work function, emission area, and field enhancement form the basis for developing a framework to make meaningful comparisons between different sets of data.

Polycrystalline diamond thin films have been formed on single crystal silicon field emitters using bias-enhanced nucleation in a microwave plasma chemical vapor deposition system. A diamond nucleation density greater than 1010/cm2 with small grain sizes (<25 nm) was achieved on the surfaces of silicon emitters with nanometer scale curvature. Field emission from these diamond coated silicon emitters exhibited significant enhancement compared to the pure Si emitters both in total emission current and stability. Using a Fowler–Nordheim analysis a very large effective emitting area of nearly 10−11 cm2 was obtained from the diamond coated Si emitters compared to that of uncoated Si emitters (10−16 cm2). This area was found to be comparable to the entire tip surface area.

Single crystal silicon field emitters have been modified by surface deposition of diamond using bias-enhanced microwave plasma chemical vapor deposition. Polycrystalline diamond with a high nucleation density ͑10 10 /cm 2 ͒ and small grain size ͑Ͻ20 nm͒ was achieved on silicon field emitters. Field emission from these diamond coated emitters exhibited significant enhancement both in total emission current and stability compared to pure silicon emitters. A large effective emitting area comparable to the tip surface area was obtained from a Fowler-Nordheim analysis. The effective work function of the polycrystalline diamond coated emitter surface was found to be larger than that of a pure silicon emitter surface.

An analysis of wide band gap materials from the point of view of their application in cold emission devices is presented, and criteria of material choice for device application are discussed. Not only material but also technological parameters are taken into consideration. Among the material parameters, the following were found to be the most important; electron affinity, dielectric constant, thermal conductivity, melting point, chemical and physical robustness. The major technological parameter is compatibility of the material deposition process with commercially available facilities and other steps of cathode fabrication. It was shown that wide band gap materials are most effective for emission if deposited on sharp conductive tips. Experimental results from diamond, AlN, c-BN, and SiO2 field emitters are presented and some possible mechanisms explaining their I–V characteristics are discussed.

Noise characteristics of emission current from conductive diamond-like carbon thin films coating on cone shaped silicon field emittersThe data for the maximum emission currents from needle-shaped emitters with differing diamond coatings were empirically analyzed. The coatings studied were chemical vapor deposition diamond, natural diamond, and nanodiamond. Two parameters were chosen to characterize the emissive properties: ͑1͒ the dependence of the maximum current (I max ) on the coating thickness ͑D͒, i.e., I(D)ϭ⌬I max /⌬D, and ͑2͒ the dependence of the threshold voltage V th on ͓(D);⌬V th /⌬D͔. The dependence of I max (D) and I max /V max (D) were determined from the experimental data for the three different diamond coatings. The maximum current I max is very different for these three different coatings and is also a function of the coating thickness, D. Both the maximum current and the transconductance of field emission tips can be increased significantly by diamond coatings. A strong, nearly linear, dependence of I max on diamond thickness was found. An empirical estimate of the thermal conductivity of nanodiamond, based on the field emission data, gave 2.71 W/cm K. The maximum current output from multitip arrays was also analyzed and an optimization procedure was devised that suggested a route to ''engineered coatings.''