Category Archives: General Optics and Vacuum

General information on repair, maintenance, and operation of both PHI (Physical Electronics) and other manufacturers’ systems and components

Scanning Auger Objective Coil Replacement Procedure

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This post describes the steps needed to successfully replace the objective coil on PHI 600 and 660 systems. Note: Use gloves, clean tools and place UHV aluminum foil on your workspace. For best results, dust off the assemblies with dry nitrogen or canned air as you reassemble the analyzer to remove any dust particles.

Tools required:

Latex gloves

Wrenches

Small screwdrivers

Tweezers and/or needle nose pliers

048-4 Bristol spline wrench

Disassembly Procedure

  1. Vent the system.
  2. Remove the filament housing (8″ flange on a hinge).
  3. Stand the analyzer on the back of the condenser nipple (8″ flange).
  4. Remove magnetic shield (4 screws).
  5. Remove conical ceramic (4 screws, aluminum ring).
  6. Remove the outer cylinder after first disconnecting the VM screw.
  7. Remove the upper inner cylinder assembly (4 screws). Be very careful not to touch the grids.
  8. Remove the 8 screws that hold the two aluminum rings in place and carefully lift up the Objective lens assembly. Scribe the objective lens assembly so that you can put it back with the exact same orientation.
  9. Turn the Objective lens housing upside down and remove the 8 screws that hold the nose cap in place.
  10. Hold the cap and point the lens assembly up and carefully lift the nose cap off.
  11. Carefully lift off the octopole ceramic and spacers. TIP: Position the spacers on the clean aluminum foil in the order in which you remove them so that you can replace them in the same order later.
  12. Remove the 3 flat spring couplers and ceramics from the objective coil wires. You will need a 0.048 4-spline wrench.
  13. Loosen and remove the 4 nuts which hold the objective coil to the base plate.
  14. Remove the objective coil. Note that there are 4 spacers on the studs.

Reassembly Procedure:

  1. Install the spacers on the objective coil studs and insert the objective coil into the base.
  2. Put the nuts on the studs and tighten the nuts finger tight.
  3. Using some 0.020 wire, slip it in and around the coil and the center tube so that the coil is evenly spaced around the center tube.
  4. Securely tighten the 4 nuts.
  5. Slide the ceramics over the objective wires and replace the 3 objective coil spring couplers.
  6. Stack up the octopole ceramic spacers and slide the octopole ceramic back on. It is keyed and can only go on one way.
  7. Carefully slide down the nose cap and replace the 8 screws finger tight.
  8. Slightly rotate the nose cap to make sure that the octopole ceramic is well seated and then tighten the 8 screws.
  9. Reinstall the objective lens assembly into the inner cylinder. It can only go in one way and still make the electrical connections.
  10. Install the two aluminum rings in place and tighten the 8 screws.
  11. Measure the resistance of the condenser and objective connectors and make sure that you have a good connection to the objective lens. The resistance on the two internal windings of the objective coil (Pins A, B and C) should be about 8 Ω each and 16 Ω across.
  12. Check for connectivity on pins A, B, C, D, E, F, G and H on the octopole deflection feedthrough to the octopole ceramic to ensure that you have a good contact on each plate. The best way to do this is to set your meter up so that it beeps with continuity and then insert a small (0.010) wire into the nose cap and move it around while having the other end of the meter connected to the octopole defection feedthrough. If the connections do not all check out then remove the objective lens assembly and look for a contact problem.
  13. Reinstall the upper inner cylinder assembly. (Do not touch the grids!)
  14. Install the outer cylinder and reattach the VM wire.
  15. Carefully place the conical ceramic on top of the outer cylinder and measure the resistance of the outer cylinder to ground. It should be 3 MΩ. If the conical ceramic is not making good contact, the resistance will be about 6 MΩ. It needs to be 3 MΩ. Shim with copper or gold foil if necessary. The resistance coating section (the dark sections between the rings) on the conical ceramic should be 180 degrees out from the resistance coating on the base.
  16. Replace the aluminum ring on top of the conical ceramic and tighten the 4 screws evenly and firmly (but not too tight!).
  17. Reinstall the magnetic shield.
  18. Degauss the analyzer.
  19. Ohm-out the objective connector one more time, and also ohm-out the VM to ground to ensure that the resistances are still correct.
  20. Use a new gasket and reinstall the CMA into the bell jar.
  21. Pump down the system and bake-out.

The pictures below will help you to understand this procedure.

RBD Instruments provides replacement objective coils for the PHI 600 and 660 scanning Auger systems. Contact us for more information. The coils are expensive but we occasionally have used coils that cost much less than a new one.

Additional information on the 25-120A CMA is posted below the pictures.

 

25-120A Analyzer Info

1. Resistance measurements:

  • Cond. coil, pins D & E, 10 ohms
  • Obj. coils, pins A, B, & C, 8 ohms, 16 ohms, open to ground

2. Steering – all pins open to ground

  • Cond. X: A & C, gnd at J
  • Cond. Y: B & D, gnd at M
  • Obj. X: E & G, gnd at L
  • Obj. Y: F & H, gnd at K

 20-622 System Test

It is possible for a 20-620 or 20-622 to work on the bench but not focus properly on a system. That is because on the bench the Objective and ISO Objective supplies are tested separately but on the system the objective coil is actually two coils which are tied together. It is possible for one of the objective supplies to cave in when connected to the objective coil. You can do a quick test by measuring the voltage across the current resistors behind the front panel of the 20-622 or 20-620.

Voltages for the 20-622 are listed below. The 20-620 should show a similar trend.

20-622 3kV Beam voltage, COND set to 35%, OBJ set to 74.49%, and Objective fine pot set to midrange. COND .856 V DC
OBJ 3.68  V DC
ISO OBJ 3.69  V DC

Protect the CF flange knife edge

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The CF flange (also commonly referred to as the Varian trade-marked Conflat) uses a knife edge that cuts into a soft metal gasket (usually copper) to provide a leak-tight metal-to-metal seal. “Protect the knife edge at all costs” is a common catchphrase at RBD Instruments that we like to drill into anyone who works on a UHV vacuum chamber. Simply put, it means to use care when removing used copper gaskets from Conflat (CF) flanges, and to protect the flange edge with aluminum foil when it is being stored on a shelf. Even a small scratch on the knife edge can result in a leaky seal on the flange.

Specialized tools are available for removing copper gaskets, but most labs do not have them. So, what is the best way to remove a copper gasket from a CF flange if you do not have a special tool? IMO you should use a clean regular channel lock or vice grip type of pliers whenever possible to remove used copper gaskets instead of a flat blade screwdriver. You need to use pliers that have teeth, not the smooth ones. In some cases you will not be able to use pliers as there is not enough room to get the pliers onto the gasket without risking damage to a ceramic or some other optic part. In those cases, you will need to use a straight blade screwdriver.

To use pliers, you simply position the jaws of the pliers on the inner and outer diameters of the gasket and tilt the pliers back. The applied leverage will pop the gasket out of the groove. Be sure to get a good grip on the edge of the gasket as quite often the gasket is pressed in very tightly and will be somewhat difficult to remove. Other times the gaskets will practically fall out by themselves. It just depends on the fit of the flanges and whether or not the system has been baked out (the copper expands during bake-out).

When using a screwdriver, extreme care must be taken to ensure that the screwdriver does not slip off the side of the gasket and damage the knife edge once the gasket pops out of the flange recess. You can reduce the chances of damage by using a screwdriver that has a tip that is flat with sharp edges and slightly thinner than the height of the exposed gasket edge. Apply downward pressure on the tip of the screwdriver as you try to pry the gasket up. Sometimes the gaskets can be wedged in very tightly after compression and be difficult to remove. Use the tip of the screwdriver to leverage the gasket out; do not push the screwdriver. This is when one is most likely to damage a knife edge: if the screwdriver slips as the gasket comes loose, it may scrape across the knife edge and cause a large scratch or gouge. Once that happens, the flange may no longer seal properly.

If you do gouge a knife edge you might be able to still get it to seal by using a small piece of a soft vacuum-compatible metal such as gold or platinum to fill in the void on the gouge. Small scratches can be polished out with some ultra-fine emery cloth. If the gouge is too big then the flange may need to have the knife edge touched-up with a metal lathe. That is not always practical or even possible. So, the best thing to do is to… protect the knife edge at all costs.

When flanges are being stored for long periods of time or are being stacked up on a shelf, the best way to protect them is to wrap them in UHV aluminum foil. You can purchase UHV compatible aluminum foil from All-Foils Inc. http://www.allfoils.com/single-product/uhv-foil/

Below are some pictures of the correct and incorrect techniques to remove copper gaskets from CF flanges. If you need to purchase some copper gaskets for your UHV vacuum chamber and also want to pay the lowest possible price, RBD Instruments Inc. now provides copper gaskets for CF flanges in small or large quantities at low prices.  Click on this link for more information // Copper gaskets for CF flanges // or visit us at our website by going to RBD Instruments dot com.

Ion Plasma to clean ion pumps

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If you try to start an ion pump when the vacuum in the chamber is in the mid 10-4 range, the gas load will be high enough to produce a visible ion plasma.  Normally you don’t start the ion pumps until the vacuum is pulled down to the low 10-5 range by the turbo pump.  But, sometimes you want to deliberately generate an ion plasma to help clean the ion pump elements.

http://youtu.be/vqTTybwSDl0

There are two ways to do this.

  1. Just start the ion pumps when the vacuum reaches the mid to low 10-4 Torr range.  You may see that the pressure in the chamber rises to the 10-3 Torr range when the ion pump high voltage is turned on. That is OK; keep the ion pumps on while pumping the chamber with the turbo pump.  You can leave them on for 5 minutes or so, then shut off the ion pump supply and let them cool down for 5 minutes. Then repeat the process. After a number of cycles, vacuum will be in the low 10-5 range and the ion pumps will start. You know when the ion pumps start because the vacuum goes into the 10-6 range and keeps improving slowly. By forcing the ion pumps to start in the high 10-4 range the resultant ion plasma helps to clean the ion pump elements.
  2. If the pumps are loaded with argon or contaminated with hydrocarbons, you want to use oxygen to produce the ion plasma because oxygen will react with the contaminants.  Assuming the ion pumps are started, back fill oxygen into the vacuum chamber to 5 X 10-5 Torr.  Turn off the ion gauge and monitor the current on the ion pump control.  Increase the oxygen until you get about 50mA of current on the ion pump control.  Adjust the oxygen leak valve as needed to maintain 50mA or so of current.  Maintain this condition for about 30 minutes, and then turn the oxygen off.  As the pumps cool down the vacuum will recover and typically by the next day the ion pumps are happy once again.

For more info on ion pumps type Ion Pump Element rebuild procedure in the RBD TechSpot search box