Tag Archives: lab6 filament

Lab6 filament replacement procedure

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This procedure shows the steps to replace the Lab6 filament in the 25-120A CMA used in the Physical Electronics 600 and 660 scanning auger systems.

First, vent the system. Here is a link to a procedure on how to do that: 600_System_Up-to-air_Procedure

  1. Remove the filament cap on the top of the analyzer. Do not unscrew the cable! Remove the 3 screws as shown in the picture below and then lift the cap up and off of the analyzer filament ceramic.
  2. Remove the twenty 5/16″ bolts that hold the filament flange to the CMA. Those may be 1/2 ” hex head or 12 point cap head bolts.
  3. Tilt the filament flange back on the hinge.
  4. Use gloves and a clean straight blade screwdriver to loosen the 4 filament screws as shown in the picture below.
  5. Remove the 4 filament screws and carefully lift up and remove the whenelt cap. The filament is mounted inside the whenelt cap.
  6. Install the new filament making sure that the filament legs line up with the filament contact tabs.
  7. Hold the filament down while you install and tighten the 4 filament screws.
  8. Install a new 8″ copper gasket and gently tilt the filament housing back onto the analyzer.
  9. Tighten the bolts (use anti seize compound if the bolts are dry) and then
  10. Pump the system down.

Although it is recommended that the system is baked out where ever it is up to air, baking may not be necessary if the system is back filled with dry nitrogen and given a few days for the vacuum to recover. If you install the new filament on a Friday and let the system pump over the weekend, then the vacuum will likely recover into the low 10-9 Torr range without a bake out.

To condition the new filament, slowly (over a period of an hour or more)  bring up the filament current to a starting value of 1.3 amps at 3 kV beam voltage and see if you can get sufficient emission current and target current. If so, then you can operate the filament with 1.3 amps of filament current. You may need to use oxygen to rejuvenate the filament if the emission does not come right up. Here is a link to a tech tip on how to thoroughly characterize the new filament if you want to really dial it in: imaging procedure for 600 and 660

RBD Instruments provides the Lab6 filaments used in the Physical Electronics 600 and 660 scanning auger analyzers.

LaB6 filament Rejuvenation

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Lanthanum hexaboride (LaB6 ) filaments provide a very stable emission of electron current in the hot cathode electron sources used in many scanning Auger electron spectrometers. However, this type of filament is susceptible to deactivation from vacuum contaminants such as fluorine.

If your LaB6 filament becomes contaminated it may exhibit symptoms such as unstable emission current or no emission current at all.  The Auger data below shows instability in the background that was caused by unstable emission current from the cathode.

Unstable Auger data

Usually it is possible to rejuvenate a LaB6 filament by backfilling the chamber with Oxygen while monitoring the emission current as outlined in the procedure below.

LaB6 filament: rejuvenation procedure:

  1. Set the beam voltage to 1kV and the emission voltage to 100% (or the maximum for that beam voltage).
  2. Increase the filament current up to the normal operating value. 1.3 to 1.5 amps is typical for a PHI 600 or 660 scanning auger spectrometer.
  3. Bleed O2 into the system to about 5 X 10 -7 Torr.
  4. Slowly reduce the emission voltage until you get about 50uA of emission current.  Keep an eye on it, as the O2 cleans the filament the emission will rise and you will need to increase the emission voltage in order to keep the emission current from going up too much. The maximum recommended emission current is 100uA.

Once the emission current is stable then you can turn off the O2. This process typically takes 5 to 20 minutes. In some cases the vacuum chamber may have some low level contamination where the emission current of the filament will drop once the O2 is turned off. In those cases, you may want to leave the O2 on for an extended period of time at a higher vacuum such as 2 X10-8 Torr.

If rejuvenating the filament does not work then the filament may need to be replaced. RBD Instruments Inc. provides LaB6 filaments for the Physical Electronics PHI 590 through 660 series scanning auger spectrometers.  Visit  us at rbdinstruments dot com