72-030 Neutralizer Current limit procedure

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After you replace the filament in the 04-085 or 04-090 neutralizer you may need to readjust the current limit on the 72-030 neutralizer board. The 72-030 provides the filament current and bias voltage to the neutralizer. This procedure shows you how to set the current limit on the 72-030 so that you generate enough electrons to neutralize the sample and also maximize the filament lifetime.

Tools Needed:

HV card rack extender board

Voltmeter with 2 clip leads

Potentiometer adjustment tool

72-030 Calibration procedure

  1. Turn off the card rack power
  2. Extend the 72-030 neutralizer card (located in the card rack)
  3. Connect the DVM across R59 / E6
  4. Make sure that the filament cable is connected to the neutralizer on the system
  5. Turn on the card rack power
  6. Turn on the 147 PC Interface unit
  7. Open AugerScan software
  8. Turn on the neutralizer in AugerScan
  9. Monitor the target current with a picoammeter and a +90V bias
  10. Turn up the Emission in the Augerscan Neutralizer dialog box to 20 to 23 mA while monitoring the DC voltage in millivolts across R59 / E6.
  11. There should be approximately 34 mV across R59 / E6 and you should also be able to see the end of the neutralizer glowing orange to white in the vacuum chamber.
  12. Set the Emission to 25 mA and if necessary adjust R48 / B6 so that you have 2 to 3 uA of target current.   Do not adjust R48 / B6 to exceed 36mV across R59 / E6. 36mV corresponds to 3.6 amps of filament current. The lower the filament current, the longer the filament lifetime.
  13. Turn off the card rack power and reinstall the 72-030 neutralizer card in the card rack.

Ideally, adjusting R48 for a value that provides a few uA of target current and with less than 36mV across R59 / E6 will result in the longest filament lifetime.

72-030 board extended
R59 current sense resistor
Measure voltage across R59 34mV corresponds to 3.4 amps of filament current

72-030 Neutralizer bias voltage notes

There are two revisions of 72-030 neutralizer boards.  The older original 72-030 has a bias voltage range of 0 to -12V.   The newer 72-030s have a bias voltage range of 0 to -24V.

You can tell the difference by two things.  First of all, U6 is a OP07 op amp on the older 72-030s, and it is a LM344H high voltage op amp on the newer 72-030s.  Secondly, there is a 5V to 15V power convertor on the newer boards, the older 72-030s do not have that power converter.

12V bias 72-030
24V bias 72-030

72-100 Electron Multiplier Supply Notes

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The 72-100 electron multiplier supply is used on older Physical Electronics (PHI) Auger electron spectroscopy systems to provide voltage to the cylindrical mirror analyzer (CMA) and secondary electron detector (SED) electron multipliers.

The 72-100 comprises a digitally controlled 0 to +4000V variable switching supply, a 0 to 300V fixed supply, and a voltage to frequency monitoring circuit. The digital control from the PC software is converted to an analog output which drives a switching supply.  

The AES and SED 72-100 board addresses are set by changing the segments on SW2 as follows;

72-100 switch settings
Switches set up for AES SW2 segment 3 closed

Changing the switch settings allows you to swap the 72-100 boards to confirm whether or not there is a problem. For example, if you think that your SED 72-100 board has a problem, you can swap it out with the CMA 72-100 after first changing the CMA 72-100 address to SED (SW2 segment 4 closed). If the SED image works after swapping the boards, then you know that your SED 72-100 board does have a problem.

Once you confirm that your 72-100 is not functioning properly there are a some simple things that you can try.   ***CAUTION – high voltages (up to 6kV) are present on this board, refer servicing to qualified personnel who have been trained to work safely with high voltage.***

Note that the CMA 72-100 is controlled by AugerScan software and the SED 72-100 is controlled by AugerMap software.   You can also use the AugerScan diagnostic menu to send commands to the board per the 72-100 manual calibration procedure. 

Make sure that the card rack power is OFF and then extend the 72-100 board.   Use the high voltage extender (the one with red wires on the bottom section).

72-100 board mounted on extender card

For testing the AES 72-100 board, you can first check the analog output from the DAC to see if you are getting the proper control voltage. Note that the card rack power needs to be ON when measuring voltages.  For the high voltage supply, measure from the left side of R 32 with respect to the left side of CR 3.   

Meter ground left side of CR 3
Meter POS left side of R 32

With the electron gun supply off, set up and acquire a survey in AugerScan. The DAC output voltage should ramp up from 0 to about 5 volts as the multiplier voltage is being set by AugerScan.  Since there is no electron beam current, the AES electron multiplier voltage will default to the PC (pulse count) voltage which is typically 1800 to 2200V. 5 volts on the DAC output corresponds to 2000V on the multiplier supply POS output.

If the DAC voltage output is correct, then the problem is probably related to the switching supply transistors.  With the 72-100 board on the bench (card rack power OFF when removing or inserting the 72-100), test the diodes and transistors for shorts.   Note that two legs on all of the power transistors will show as shorted because those points are connected to the switching transformers.

One common problem that causes the HV output to be zero is that Q7 and Q8 are defective, even though they may check out OK with the diode test.  If the DAC voltage is correct but you do not have any high voltage output, then try replacing Q7 and Q8 with the correct 2N5337 transistor.  Some 72-100 boards have 2N3725 transistors instead of 2N5337 transistors installed. The 2N5337 can dissipate 6 watts of power but the 2N3725 can only dissipate 3 watts. The lower power rating of the 2N3725 can result in poor switching characteristics.

Q7 and Q8 are located under the black high voltage cover. It is held in place with 3 screws. Remove the cover and you will see Q7 and Q8.

Remove the high voltage cover
Q7 and Q8

Assuming that replacing the transistors solved the issue, you can adjust the high voltage by adjusting R7 to match the software.  For example, if the AES PC voltage is 2000 V then adjust R7 for 2000V between the POS and NEG cables. Note that you need to use a high voltage probe when measuring the POS output voltage as most DVMs are limited to 1000 V or less.

R2 is the 300V adjustment and you measure that voltage from the NEG cable center pin to the outer cable or vacuum chamber.

The easiest place to connect your high voltage probe to measure the AES high voltage is between the center pin of the J6 HV POS IN cable to the 96A/B / VF4 preamp and the center pin of the NEG cable on the CMA electron multiplier.

When testing the SED 72-100 then you need to control the SED voltage in the Auger Map TV dialog box.  As you change the SED voltage in AugerMap you should see the DAC output voltage change.  2000V would correspond to about 5V on the DAC output. For the SED high voltage, measure between the center pins on the 97 SED preamp POS and NEG cables. Set the SED voltage in Auger Map to 2000V and then adjust R7 on the SED 72-100 board for 2000V. Remember that you need to use a high voltage probe when measuring the SED and CMA POS output voltages.

Regarding the V/F circuitry on the 72-100 board, those components are not used and so can be removed if your board has them installed in sockets. Some 72-100 boards do not have those ICs installed at all, but others do and they may be soldered in.  If they are soldered in just leave them as is; it is not worth the effort to pull them off the board if they are soldered in place.  The ICs which can be removed are:

U1, U2, U3, U4, U5, U6 and U9.

72-100 board with no V/F ICs installed
72-100 with V/F ICs removed from sockets

Finally, the 1K ohm filter resistors on the 72-100 mother board can fail (burn and become open).  In that case the 72-100 board may be working properly, but the voltage will not get out to the cables.  You can ohm out the resistors on the motherboard to see if that is an issue.

72-100 R1 R2
72-100 R1 R2

72-100 R1 R2

And here is the schematic that shows both resistors:

72-100 mother board schematic
72-100 mother board schematic

If you can’t repair the 72-100 board yourself, RBD Instruments provides a 72-100 repair service and loaner 72-100 boards. 

Cylindrical mirror analyzer fringe field termination ceramics

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Physical electronics (PHI) cylindrical mirror analyzers ( CMA) use fringe field termination ceramics to reduce the fringe fields from the end of the cylinders.

Abstract an early patent:

Field termination plates for cylindrical electron analyzers are provided wherein the plates are constructed of an insulative material coated on the interior surface with a high resistance, electrically conducting coating. Spaced concentric rings of relatively high conductivity material in electrical contact with said coating are provided; the rings providing equi-potential regions on the plates, thereby minimizing field fringing near the ends of the cylindrical tube electron analyzer.

The PHI CMA (cylindrical mirror analyzer) utilizes conical and flat termination ceramics to eliminate electrostatic edge effects between the inner and outer cylinders. These ceramics are essentially gold rings with resistors in between that divide the outer cylinder sweep voltage down in even steps. The result is a very high throughput and even energy distribution of the Auger electrons. If a CMA has a poor contact on a termination ceramic, the results are noisy data and poor energy linearity.

Single pass AES CMAs have just 2 terminating ceramics, a conical at the front of the CMA and a flat at the base. Double Pass AES/XPS CMAs have 3 terminating ceramics, a conical at the front, a center and a base.

The conical and flat ceramics are essentially resistors and so the total resistance between the inner and outer cylinders add up like this:

The table below lists the values on the combined resistances of the older PHI CMAs.

Values are in Meg ohms

If the VM or IC to OC (inner to outer cylinder) resistances are off significantly in your CMA then you probably have a contact issue between a conical or flat (base) ceramic between the outer cylinder or the inner cylinder. Sometimes the resistances of the conical ceramic can be off due coating caused by years of sputter depth profiling.

A poor electrical contact can result in high background counts or extremely high noise levels in the data due to arcing. If you suspect that your CMA has a contact issue with a terminating ceramic then you will need to tear down your CMA to where you can add improve the electrical contact by adding some thin copper or gold shim foil between the suspect ceramic and cylinder. If you need some guidance on how to do that, please contact RBD Instruments.

The pictures below show the conical and flat ceramics from a 25-120A CMA. You can see the gold rings and also the thin film resistors.