691 research outputs found
Physical electrostatics of small field emitter arrays/clusters
This paper improves understanding of electrostatic influences on apex field
enhancement factors (AFEFs) for small field emitter arrays. Using the "floating
sphere at emitter-plate potential" (FSEPP) model, it re-examines the
electrostatics and mathematics of three simple systems of identical post-like
emitters. For the isolated emitter, various approaches are noted. On need
consider only the effects of sphere charges and (for separated emitters) image
charges. For the 2-emitter system, formulas are found for "charge-blunting" and
"neighbour-field" effects, for widely spaced and "sufficiently closely spaced"
emitters. Mutual charge-blunting is always dominant, with a related (negative)
fractional AFEF-change {\delta}_two. For sufficiently small emitter spacing c,
|{\delta}_two| varies as 1/c; for large spacing, |{\delta}_two| decreases as
1/c^3. In a 3-emitter linear array, differential charge-blunting and
differential neighbor-field effects occur, but the former are dominant, and
cause the "exposed" outer emitters to have higher AFEF ({\gamma}_0) than the
central emitter ({\gamma}_1). Formulas are found for the exposure ratio
{\Xi}={\gamma}_0/{\gamma}_1, for large and for sufficiently small separations.
The FSEPP model for an isolated emitter has accuracy around 30%. Line-charge
models (LCMs) are an alternative, but an apparent difficulty with recent LCM
models is identified. Better descriptions of array electrostatics may involve
developing good fitting equations for AFEFs derived from accurate numerical
solution of Laplace's equation, perhaps with equation form(s) guided
qualitatively by FSEPP-model results. In existing fitting formulas, the
AFEF-reduction decreases exponentially as c increases, which differs from
FSEPP-model formulas. FSEPP models might provide a useful guide to the
qualitative behaviour of small field emitter clusters larger than those
investigated.Comment: 34 pages, including 3 figures, with an extra 7 pages of Supplementary
Material (giving details of algebraic analysis); v3 is slightly revised
version, submitted after reviewin
The Murphy-Good plot: a better method of analysing field emission data
Measured field electron emission (FE) current-voltage Im(Vm) data are
traditionally analysed via Fowler-Nordheim (FN) plots, as ln{Im/(Vm)**2} vs
1/Vm. These have been used since 1929, because in 1928 FN predicted they would
be linear. In the 1950s, a mistake in FN's thinking was found. Corrected theory
by Murphy and Good (MG) made theoretical FN plots slightly curved. This causes
difficulties when attempting to extract precise values of emission
characterization parameters from straight lines fitted to experimental FN
plots. Improved mathematical understanding, from 2006 onwards, has now enabled
a new FE data-plot form, the "Murphy-Good plot". This plots
ln{Im/(Vm)**(2-({\eta}/6)} vs 1/Vm, where {\eta} depends only on local work
function. Modern ("21st century") MG theory predicts that a theoretical MG plot
should be "almost exactly" straight. This makes precise extraction of
well-defined characterization parameters from ideal I_m(V_m) data much easier.
This article gives the theory needed to extract characterization parameters
from MG plots, setting it within the framework of wider difficulties in
interpreting FE Im(Vm) data (among them, use of the "planar emission
approximation"). Careful use of MG plots could also help remedy other problems
in FE technological literature. It is argued MG plots should now supersede FN
plots.Comment: Intended articl
Improved approach to Fowler-Nordheim plot analysis
This article introduces an improved approach to Fowler-Nordheim (FN) plot
analysis, based on a new type of intercept correction factor. This factor is
more cleanly defined than the factor previously used. General enabling theory
is given that applies to any type of FN plot of data that can be fitted using a
FN-type equation. Practical use is limited to emission situations where slope
correction factors can be reliably predicted. By making a series of
well-defined assumptions and approximations, it is shown how the general
formulas reduce to provide an improved theory of orthodox FN-plot data
analysis. This applies to situations where the circuit current is fully
controlled by the emitter characteristics, and tunneling can be treated as
taking place through a Schottky-Nordheim (SN) barrier. For orthodox emission,
good working formulas make numerical evaluation of the slope correction factor
and the new intercept correction factor quick and straightforward. A numerical
illustration, using simulated emission data, shows how to use this improved
approach to derive values for parameters in the full FN-type equation for the
SN barrier. Good self-consistency is demonstrated. The general enabling
formulas also pave the way for research aimed at developing analogous
data-analysis procedures for non-orthodox emission situations.Comment: Paper is extended version of poster presented at the 25th
International Vacuum Nanoelectronics Conference, Jeju island, South Korea,
July 2012. Third version includes small changes made at proof correction
stag
Comment on "Advanced field emission measurement techniques for research on modern cold cathode materials and their applications for transmission-type x-ray sources" [Rev. Sci. Instrum. 91, 083906 (2020)]
This Comment suggests that technological field electron emission (FE) papers,
such as the paper under discussion [P. Serbun et al.,, Rev. Sci. Instrum. 91,
083906 (2020)], should use FE theory based on the 1956 work of Murphy and Good
(MG), rather than a simplified version of FE theory based on the original 1928
work of Fowler and Nordheim (FN). Use of the 1928 theory is common practice in
technological FE literature, but the MG treatment is known to be better physics
than the FN treatment, which contains identifiable errors. The MG treatment
predicts significantly higher emission current densities and currents for
emitters than does the FN treatment. From the viewpoint of the research and
development of electron sources, it is counterproductive (and unhelpful for
non-experts) for the technological FE literature to use theory that undervalues
the performance of field electron emitters.Comment: 2 published page
21st Century Planar Field Emission Theory and its Role in Vacuum Breakdown Science
For explaining electrical breakdown, field electron emission (FE) is a
mechanism of interest. In the period 2006 to 2010 there were significant
developments in basic FE theory, but these have not yet fully entered general
thinking in technological FE areas, which are often still based on 1960s
thinking or (in some contexts) 1920s thinking about FE theory. This paper
outlines the history of FE theory and provides an overview of modern
developments and of some related topics, in so far as these affect the
interpretation of experiments and the explanation of physical phenomena. The
paper concentrates on principles, with references given where details can be
found. Some suggestions are made about moving to the use of "21st-Century" FE
theory. In addition, an error in Feynman's treatment of the electrostatics of
pointed conductors is displayed, and it is found that Zener tunneling is
implausible as a primary cause of vacuum breakdown from a CuO overlayer.Comment: 8 pages, 1 figure. Originally presented at the 29th International
Symposium on Discharges and Electrical Insulation in Vacuum (hosted virtually
from Padova, September 2021). This version (v2) corrects typographic errors
(including two in an equation) in the original arXiv verwion and the
published versio
Field emission: applying the "magic emitter" validity test to a recent paper, and related research-literature integrity issues
This work concerns studies of field electron emission (FE) from large area
emitters. It discusses--and where possible corrects--several literature
weaknesses related to the analysis of experimental current-voltage data and
related emitter characterization, using a recent paper in Applied Surface
Science to exemplify these weaknesses. One weakness, not detected in the
published paper, is that current-density experiments and related theoretical
predictions there differ by a large factor, in this case of order 10^(16). The
work also shows that a recently introduced validity test--the "magic emitter"
test--can be used, at the immediate-pre-submission or review stages, to help
uncover scientific problems. More generally, in the literature of FE from large
area emitters over the last 15 years or so, there appear to be many papers
(perhaps hundreds of papers) with some or all of the weaknesses discussed. The
scientific integrity of this research area, and of the related peer review
processes, appear to be significantly broken, and attempts to correct the
situation by the normal processes of science have had limited effect. There
seems a growing case for independent wider investigation into research
integrity issues of this general kind, and possibly for later action by
Governments.Comment: 15 pages, 0 figures. Submitted for publication. v2 has typos
corrected and conclusions section slightly extende
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