Products > Field Emitters > Etched Carbides

Carbide research at Applied Physics Technologies is a continuation of efforts by Bill Mackie and co-workers at Linfield Research Institute dating back to the early 1980's. For the most part, early studies focused on transition metal carbides and their potential use as electron emission sources. A great deal of work was done with ZrC and HfC, two very high melting point refractory materials. Techniques were developed for zone refining these materials to obtain purified single-crystal stock of specific orientations that were used in plane-dependent work function and surface chemistry studies. This facilitated performance studies of single-crystal thermionic and single crystal etched field emitters made from these carbides.

The transition metal carbides are typified by high melting points, extreme hardness, low work functions and high vapor pressures in vacuum well below the melting point. Their hardness and durability make them useful as tribological coatings. Hafnium carbide has the highest melting point of any known binary substance, 3890 ºC. With low work functions in the 3.5 eV range, the carbides are good candidates for durable, high current density electron sources that perform well in poor vacuum environments. Our on-going research projects address the potiential uses for cold and moderately heated field emitters.

Emitter preparation:

Sintered transition metal carbides are crystallized in this laboratory through a process of floating zone, arc refinement. The carbon to metal ratios of the zone refined single crystal specimens are typically less than one. Applied Pable to adjust the C/M (carbon to metal) ratio by the number of zone melting passes or through the addition of extra free carbon to the sintered stock.

After the rods are zone refined, they are centerless ground to a diameter of 0.75 mm using 600 mesh diamond grit. Emitter blanks are then sandwiched between two 0.5 mm pyrolytic carbon blocks that are held in turn by the spring tension of the two Mo-Re posts of an emitter base. (see Fig. 1)

Field emission cathodes are then formed through an electrochemical polishing process. The emitter blank is suspended in a chemical solution and a DC voltage is applied. This causes the emitter blank to erode more at the surface of the solution, thus forming an hour-glass shape out of the remaining material. Eventually, the neck of the hour-glass will thin to the point of drop-off yielding a FE cathode.

The operating environment is extremely important to the successful operation of carbide sources. Applied Physics Technologies understands this; operating the source and controlling the environment go together to provide a superior gun and reliable operation. Our design, manufacture, and testing of the entire gun will increases the success and yield a positive outcome to any electron gun obtained. It is APTech’s policy to sell carbide cathodes only in Applied Physics Technologies designed and manufactured gun assemblies.