Tag Archives: lab6

25-110 Analyzer Filament

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This is an old tech tip that I wrote back in 2002. The 25-110 analyzer was the first CMA that Physical Electronics used a Lab6 filament in. These days there are not a lot of 590 systems still in operation, but the ones that are still work well especially as depth profile instruments. RBD provides Lab6 filaments and repair services for the venerable 590 scanning auger systems and the 25-110 analyzer.

General tips:

Use gloves.

Clean and demagnetize all of your tools.

Place all removed parts on a clean work area covered with aluminum foil.

If possible, dust off all parts with nitrogen as you re-assemble them.

Never force any part that doesn’t want to go.

Use methanol as a lubricant if screws don’t move easily.

 

To replace the filament in the 25-110 analyzer:

  1. Remove the magnetic shield (4 screws).
  2. Carefully remove the conical ceramic ring (4 flat-head screws) and remove the conical ceramic.
  3. Remove the outer cylinder (1 screw), being careful not to force it. If necessary, use a heat gun to loosen it up.
  4. Separate all of the wires in the bottom of the analyzer using 2 needle-nose pliers or tweezers. Be careful not to stress the wires.
  5. Position the wires so that you can easily remember where they belong. In the case of the F1 and F2 wires, this is easy. For the DELF/STIG wires, position the wires as upper right and upper left, lower right and lower left.
  6. Loosen the 4 spline set screws on the top of the inner cylinder by 1 turn CCW.
  7. Remove all but one of the 8 screws around the middle of the inner cylinder.
  8. Remove the upper inner cylinder grid cap (4 set screws).
  9. Holding on to the nose of the electron gun, remove the final screw at the middle of the inner cylinder.
  10. Carefully pull the electron gun up and out of the inner cylinder. Be careful not to stress any of the wire connectors.
  11. Place the electron gun on a sheet of aluminum foil.
  12. Loosen the bottom cap of the electron gun (4 screws and 4 set screws).
  13. Carefully slide the bottom cap down the ceramics for about 2 inches, enough room to get at the filament.
  14. Remove the filament assembly (4 cap screws, 2 splines connecting the filament wires).
  15. Install the new filament assembly and reverse all of the above steps.
  16. When you slide the electron gun ceramic tubes back down inside the analyzer be careful not to crimp the copper foil on the ceramics.  Also make sure that you tighten the set screws to hold the copper foil in place. If the copper foils slides up the ceramic it may cause arcing in the electron gun.

 

 

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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