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.