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Final Report 95-ERP-015
Hard Carbon Field Emitters for Flat Panel Displays*
D. R. Kania, A. Fernandez, J. P. Spallas
Lawrence Livermore National Laboratory
Livermore, CA 94551-0808
The goal of this project was to investigate the field emission properties of laser-ablated hard
carbon coatings. The Fowler-Nordheim description of field emission clearly demonstrates
an exponential relationship between the field-emitted current and the geometry and work
function of the emitter. Previous studies on the field emission measurements of hard
carbons have been performed on nominally flat surfaces. Typically, a nominally flat
surface is not smooth on the atomic scale, especially laser-ablated coatings that are prone to
particulate contamination. This severely compromises the measurements resulting in
inconsistent or incorrect measurements of the field emission characteristics which may be
dominated by geometry of the surface rather than the material under test. We have taken
an innovative approach to the measurement of the field emission by using micromachined
substrates, tip arrays. The use of an array of 1000 (100 x 100), 1 micron molybdenum tips
were fabricated using a Spindt-type process. The large number of tips statistically averages
out the variations in the detailed morphology of the surface while the electric field
enhancement of the tip permits testing at low voltages. An additional advantage is that the
tip arrays use only a small fraction of the area for emission; the probability of a particulate
from the deposition overlapping with an emission tip is very unlikely.
Carbon coatings were deposited on the molybdenum tip arrays using laser ablation. The
thickness of the coating varied from 5 to 20 nm. The deposition rate was 2.5 nm/s. The
deposition pressure was 106 Torr. Electron energy loss spectroscopy (EELS) showed
significant sp3 bonding which is diamond-like relative to sp2 or graphite-like bonding.
The field emission characteristics were measured with an ion field emission microscope.
All of the samples had excellent Fowler-Nordheim behavior, plots of the logarithm of the
emission current divided by the square of the voltage versus the inverse of the voltage are
linear. This indicates the tips are operating as field emitters.
The field emission characteristics of the uncoated tips were measured before being coated
with the laser-ablated carbon. The field emission current of the as-coated tip arrays was
found to be lower than the uncoated tips. This factor was as large as 50% and occurred for
all coating thicknesses. This observation is in disagreement with many other reported
observations in the literature.
The carbon coated tips were cleaned in a hydrogen plasma. This resulted in two significant
effects. One, the emission current increased beyond the levels of the uncoated tips. This
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Kania, D.R. Hard carbon field emitters for flat panel displays, report, March 20, 1996; California. (https://digital.library.unt.edu/ark:/67531/metadc675547/m1/3/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.