The unique properties of cerium hexaboride crystals provide stable electron emitting media with work functions less than 2.6 eV. The low work function yields higher currents at lower cathode temperatures, which means greater brightness, or current in the beam, and longer CeBix® cathode life.
We grow and fabricate our own high quality, single-crystal materials using a well-defined process called “Inert Gas Arc Float Zone Refining.” An electric arc melts a pressed-powder stick of CeBix® in a controlled atmosphere of inert gas, allowing the liquid-phase zone to freeze onto a selected-orientation seed crystal as the arc is moved along the stick. The finished crystal assumes the desired orientation of the seed with less than 30 parts per million by weight metal impurities. Correct melt zone temperature and process speed minimize
excessive boron evaporation to achieve the optimum ratio of metal to boron atoms in the grown crystal.
CeBix® cathodes have modest vacuum requirements and long shelf life. They only need only be brought up to operating temperature to provide emission, eliminating the activation procedure required of dispenser cathodes. Cebix® cathodes can provide long-term, stable operation at current densities up to 20 A/cm², and may be fabricated in a variety of shapes , with many different heating and mounting configurations as well. CeBix® cathodes are the materials of choice for high current cathodes in a variety of advanced and custom applications. APTech is the only producer of CeBix® cathodes worldwide.
Vacuum requirements are more stringent for CeBix® cathodes than others in order to minimize contamination. CeBix® cathodes are proven to be more resistant to the negative impact of carbon contamination, adding to the lifetime of the cathode. CeBix® cathodes have an evaporation rate lower than LaB6 cathodes when temperatures near 1800 K. As long as care is taken to operate the cathode below 1800 K, a CeBix® cathode should maintain an optimum tip shape longer, making it the longest lasting cathode available.
Coefficient of Thermal Expansion
Effective Work Function (100) at 1800 K
Absolute Work Function (100) at 300 K
Spectral Emissivity at 0.65 microns
Evaporation rate at 1800 K (UHV)
Orientation limit for specific orientation
Pyrolitic block mount resistance @ 1800 K
Clamping pressure of SMVM
Yield of finished cathodes
ppm by wt.
α x 10^6
1.6 x 10^-9
CeBix® cathodes (cerium hexaboride) can be used as a direct replacement for LaB6 in nearly every instrument currently using LaB6. CeBix® cathodes can have several advantages over LaB6 cathodes, including:
Lower Work Function
Lower Evaporation Rate
Capability to Recover from Contaminates
Reduced Effects of O2
Faster Stabilization after Air Exposure
Applied Physics Technologies exclusively offers CeBix® cathodes. CeBix® cathodes are ideal for many small spot size applications such as SEM, TEM, sterilization, surface analysis and metrology, and for high current applications such as microwave tubes, lithography, electron-beam welders, X-ray sources and free electron lasers.
In laboratory tests on-site at Applied Physics Technologies, CeBix® has proven to be more resistant to the negative impact of carbon contamination than LaB6, which gives it an edge in potential cathode lifetime. Additionally, the evaporation rate for CeBix® at normal temperatures near 1800 K is less than the rate for LaB6. As long as the cathode is being operated below 1800 K, CeBix® should maintain the tip shape longer and therefore last longer.
CeBix® has a significantly lower evaporation rate under certain conditions than LaB6. Studies have shown that the material loss rate for CeBix® is nearly 75% less than that of LaB6 at 1750 K in a vacuum of 2 x 10-8 torr. Thus, CeBix® can be expected to last 30-75% longer than a LaB6 cathode when operated under proper vacuum and temperature conditions.
In some applications, carbon contamination from pumping oils, solvents, or samples can effect the surface properties of LaB6 cathodes, resulting in severely decreased electron emission. In a case of mild contamination, the
operator is often unaware of the problem and only sees that it is necessary to increase the cathode heating current in order to maintain emission current. This increase in cathode temperature results in shortened lifetime. In the case of severe contamination, the emission current may be completely lost.
CeBix® cathodes are also affected by carbon contamination, but this contamination is removed by thermal desorption at normal operating temperatures. If there is a carbon bearing gas in the system, it will not adhere to the cathode surface at operating temperature; therefore it will not harm the CeBix® cathode.
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