Analysis of High-Current Yield of Diamond-Based Field Emitters
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find a new source is in itself no great advance unless it be less expensive to make, offers superior performance or (we) gain new physical insights (Ivor Brodie [1])
The history of "unconventional" field emission sources is as long as the history of field emission. Several were recently rediscovered, e.g. compare the original discoveries described in the publications in Table I with breakdown-induced emission from flat diamond films or emission from carbon fibers with its most recent rebirth as carbon nanotubes. If any conclusions about the usefulness of such new emitters is to be made, practical emission measurements must be performed, not just sophisticated structural and surface analyses. If we compare today's emission measurements to those published 20- 30 years ago, and if they are not significantly better, it isn't necessary to proceed further. Fortunately, such practical comparisons can be made, because the early papers (such as those in Table I) contain more useful information about the emission characteristics then today's longer, more scientific papers. Table I. Year [Ref]
Title
1967 [2]
A High-Density Field-Emitting Semiconductor Cathode Produced by a Voltage-Breakdown Process
1972 [3]
Field Emission from Carbon Fibres: A New Electron Source
1985 [4]
Improved electron emission by use of a cloth fiber cathode
Description The cathode consists of a large number of miron-size emitting projections on a smooth semiconductor (Ge, Si) surface. These projections are generated by a voltage-breakdown 2 process. Current densities - 2A/cm' from 1 mm Operation pressure range 10' - 10" torr, max current 400 pA / tip, divergency angle 5-30'. Operation as e-source in SEM Cloth fiber cold cathode were found to be superior to many other types of cold cathode emitters. Peak current 690 A, microwave mode
2. We Need Higher Current[
2
Spindt arrays have demonstrated up to 2000 A/cm and well over 100 microamps per tip. No other material or technology has yet been able to approach these values but it is appropriate that we should continue to try to improve on this record (I. Brodie [I]
The potential for high currents have always been an attractive feature of field emitters. For some applications, such as microwave vacuum electronics, the current and current density are major requirements. So far, highest total current, obtained from a Mo field emitter array has been 180 mA from a cathode with a 1.5 mm diameter and the maximum current density achieved from a small array was about 2000 A/cm 2 .[1] At present, useful high emission current data from Mo and
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Mat. Res. Soc. Symp. Proc. Vol. 558 @2000 Materials Research Society
Si arrays only has been presented in the literature. There is almost no useful data on high current emission from other materials. Two clarifications must be made to prevent misunderstanding. 1. High current densities. Reports of high current density from unconventional emitters (e.g. planar diamond films, carbon nanotubes etc.) can be found in recent publications. But all these data were obt
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