42 research outputs found
Field emission in ordered arrays of ZnO nanowires prepared by nanosphere lithography and extended Fowler-Nordheim analyses
A multistage chemical method based on nanosphere lithography was used to produce hexagonally patterned arrays of ZnO vertical nanowires, with 1 lm interspacing and aspect ratio 20, with a view to study the effects of emitter uniformity on the current emitted upon application of a dc voltage across a 250 lm vacuum gap. A new treatment, based on the use of analytical expressions for the image-potential correction functions, was applied to the linear region below 2000 V of the Fowler-Nordheim (FN) plot and showed the most suitable value of the work function / in the range 3.3–4.5 eV (conduction band emission) with a Schottky lowering parameter y ~ 0.72 and a field enhancement factor c in the 700–1100 range. A modeled c value of 200 was calculated for an emitter shape of a prolate ellipsoid of revolution and also including the effect of nanowire screening, in fair agreement with the experimental value. The Fowler-Nordheim current densities
and effective emission areas were derived as 1011 Am2 and 1017 m2, respectively, showing that field emission likely takes place in an area of atomic dimensions at the tip of the emitter. Possible causes for the observed departure from linear FN plot behavior above 2000 V were discussed
Comments on the continuing widespread and unnecessary use of a defective emission equation in field emission related literature
Field electron emission (FE) has relevance in many different technological
contexts. However, many related technological papers use a physically defective
elementary FE equation for local emission current density (LECD). This equation
takes the tunneling barrier as exactly triangular, as in the original FE theory
of 90 years ago. More than 60 years ago, it was shown that the so-called
Schottky-Nordheim (SN) barrier, which includes an image-potential-energy term
(that models exchange-and-correlation effects) is better physics. For a
metal-like emitter with work-function 4.5 eV, the SN-barrier-related
Murphy-Good FE equation predicts LECD values that are higher than the
elementary equation values by a large factor, often between around 250 and
around 500. By failing to mention/apply this 60-year-old established science,
or to inform readers of the large errors associated with the elementary
equation, many papers (aided by defective reviewing) spread a new kind of
"pathological science", and create a modern research-integrity problem. The
present paper aims to enhance author and reviewer awareness by summarizing
relevant aspects of FE theory, by explicitly identifying the misjudgment in the
original 1928 Fowler-Nordheim paper, by explicitly calculating the size of the
resulting error, and by showing in detail why most FE theoreticians regard the
1950s modifications as better physics. Suggestions are made, about nomenclature
and about citation practice, that may help to diminish misunderstandings.Comment: Submitted for publication; in v2 a correction to historical
information (with no numerical consequences) has been made in Appendix