Electron Microscopy Investigation of a-C and ta-C Coated Mo Field Emitters
A. F. Myers and E. B. Steel
- Surface and Microanalysis Science Division (837)
- Chemical Science and Technology Laboratory,
- NIST, Gaithersburg, MD 20899;
- M. Q. Ding, J. J. Cuomo, and J. J. Hren
- Materials Science and Engineering Department,
- North Carolina State University, Raleigh, NC 27695.
- Amorphous carbon coatings, including diamond-like carbon (DLC) and
highly sp3-bonded tetrahedral amorphous carbon (ta-C), also
referred to as amorphous diamond, have recently been explored for field
emission applications. These coatings can be deposited uniformly at low
temperatures, and possess chemical and mechanical properties similar to
those of diamond. They also can be doped with nitrogen to form n-type semiconductors.
Diamond coatings, on the other hand, are microscopically nonuniform, usually
require deposition temperatures greater than 600° C, and cannot be
doped to produce shallow donor levels. Diamond, a-D, and DLC coated emitters
all show enhanced electron emission properties.
In the present study, the microstructure of highly sp2 bonded
amorphous carbon and partially tetrahedrally bonded amorphous carbon deposited
on needle-shaped molybdenum field emitters by pulsed laser ablation was
investigated using transmission electron microscopy and electron energy
loss spectroscopy. Both undoped and nitrogen-doped films were included in
this study. The films were continuous and relatively uniform, exhibiting
an isotropic microstructure at the emitter tip and a columnar microstructure
along the shank. The undoped films contained approximately 50% sp2
bonded carbon at the emitter tip and 65% sp2 along the shank,
while the N-doped films were highly sp2 bonded both at the tip
and along the shank.