thermionics laboratory, inc
3kW Rod fed e-gun manual Page 6
Note:
Oxide formation can prevent an evaporant charge from melting in some cases.
Some metals (aluminum and copper are examples) will form an oxide that prevents
melting and causes the beam to appear unfocused. When this occurs you can invert the
melted slug and re-melt it to remove the oxide -or- replace the charge with fresh material.
DEPOSITING MATERIALS THAT DO NOT MELT (SUBLIME OR SEMI-SUBLIME)
Subliming materials may require that you defocus the beam to make it broader so that
you cover the tip of the rod. This will require removal of the dipoles. Try with the
standard configuration and if it does not work well, contact the factory for information on
the dipole removal.
Note:
some subliming materials will not support electrical current until heated. This
causes surface charging on the material that results in arcing. The surface charging
effects can also cause the beam to be “scattered” behind the crucible and onto the top
plate of the e-gun. This is normal with some materials. The e-gun top plate is designed to
dissipate this energy. To evaporate materials that have surface charging effects you must
increase the “soak” times of the electron beam as you increase power. If you allow the
source to set at a power level of
~50 to ~75 milliamperes for an extended time (make
sure arcing is not severe) the material will eventually be heated sufficiently to “fire” and
the beam will stop scattering beyond the crucible. You will in many cases still see some
hazing on the e-gun source (this is normal) during evaporation. As the e-gun becomes
coated with these materials hazing may increase.
e-GUN SHUT DOWN
Once the desired rate is achieve; close shutter (if so equipped) or reduce emission
current to zero. Turn off high voltage. Allow adequate cooling time prior to venting the
system. The e-Gun must be allowed to cool of for at least 5 minutes unless venting to an
inert gas to protect the filament. Most metals will cool down quickly ~5 minutes unless
they are used in a crucible liner. Subliming and dielectric materials or metals used in
insulating liners require additional cool down time. Normally 20 minutes will be adequate
although conditions can vary.
CHANGING THE FILAMENT
Filament life is greatly affected by the vacuum level and the types of gas present in the
vacuum system (example: Oxygen partial pressures will reduce filament life). Normally
filaments will last between 200 and 800 hours. To change a filament follow the procedure
listed below (also see Appendix C):
1. Remove screws around the circumference of the shield then lower the shield.
2. Remove the emitter assembly by disconnecting the high voltage leads from the
cathode blocks (#8, #9) and then removing the set screws (#4). (See figure below)
3. Loosen both leg attachment screws (#10) and remove the anode (#15) exposing
the filament
4. Remove the filament clamp screws (#6)
5. Remove the old filament and clean the surface where the filament contacted the
cathode blocks (use a clean abrasive pad)
6. Install a new filament and replace the filament clamp screws. Snug the filament
clamp screws (#15) to allow the filament to be located but still move. Adjust the
