For the purpose of checking the performance of a surface analysis spectrometer such as a cylindrical mirror analyzer (CMA) or spherical capacitive analyzer (SCA), looking at an ion induced low energy electron peak can be extremely helpful. The peak typically occurs at about 20 to 50 eV and the size if the peak is directly related to both the alignment of the ion beam to the analyzer as well as the amount of ion current.

Checking XPS Performance

Set up an alignment for a range of zero to 100 eV kinetic. The eV range in binding energy depends on which anode energy you have selected in the software. See the table below.  Most systems use an Al anode, so the energy would be 1480 to 1380 eV (which is about 0 to 100 eV kinetic).

1. Using a blank sample mount, position a sample to the focal point of the analyzer.
2. Look under the Hardware Properties Menu for XPS and note the X-ray Anode type.
3. Set up an alignment with the following parameters:

• Upper Limit 1480 eV if Al is the anode, 1250 eV if Mg is the anode.
• Lower limit 1380 eV if Al is the anode, 1150 eV if Mg is the anode
• EV per step .5 (or the closest selection .5)
• Time per step 20 ms

4. Start the alignment and turn on the ion gun (no raster). You should have a low energy peak at around 20 to 50 eV kinetic.
5. If necessary, reduce the ion gun beam current to prevent the detector from saturating. (You can increase the ion gun condenser lens setting or reduce the emission current in order to reduce the ion beam  current).

If you do not get the peak, then you have a problem with the analyzer or analyzer electronics. If you do, then the analyzer and  electronics are probably OK.

This is a very useful technique for isolating a low signal XPS problem between the analyzer and the X-ray source. You can also use the low energy peak to rough in the alignment of the ion gun to the XPS analyzer focal point.

Checking AES Noise Level

Analyzer noise (noisy data) can be caused by these things:

• Poor contact between the inner and outer cylinder terminating ceramics
• Analyzer control
• Electron Multiplier supply
• Electron gun control or Electron gun high voltage supply

This technique will help isolate analyzer noise by determining if it is related to the electron gun, which in tern would be caused by the electron gun control or electron gun high voltage supply.

Overview

This procedure uses both the electron gun and ion gun as a source to generate low energy electrons. By comparing the relative noise levels, you can determine if the problem is related to the electron beam only, or both beams.  If it is related only to the electron beam, then the problem is in the electron gun control or electron gun high voltage supply.

If both the electron and ion beams are noisy, then the problem is either the analyzer control, multiplier supply or poor contact in the analyzer.  The analyzer control and electron multiplier supplies can be tested for noise using the appropriate calibration procedure.

 Procedure

This procedure was written specifically for a Physical Electronics 600 scanning auger system, but the principles can be applied to other systems as well.

Set up an alignment with these parameters:

Lower Limit 0, Upper Limit 100, EV per step 1, Time per step 20 ms

In AugerScan, go to the Multiplier Properties dialog box and uncheck the Auto EMS box. This will keep the computer from trying to automatically set up the electron multiplier voltage.

1. In AugerScan, go to the Hardware Properties dialog box and make sure the input is VF1.
2. With the electron beam on and set up for a normal elastic peak, start the acquisition and manually adjust the 32-100 CMA electron multiplier until you have a maximum count rate of approximately 100Kcps.  You will see a low energy peak around 20 to 50 eV depending on your sample.
3. Use the yellow cycle stop button to end the alignment and then save the file.
4. Blank the electron beam and turn on the ion gun. Do not use any raster.
5. Start the acquisition and manually adjust the 32-100 CMA electron multiplier until you have a maximum count rate of approximately 100Kcps.
6. Use the yellow cycle stop button to end the alignment and then save the file.

Compare the two files to determine whether or not they have similar amounts of noise.  In the examples shown below, then electron gun as a source exhibits more noise than the ion gun as a source.  In this instance the problem was isolated to a noisy emission supply in the 20-610 High Voltage supply on a 600 system.

Ion Gun Alignment

On systems that do not have scanning electronic guns for TV imaging, you can use the low energy peak to center the ion beam with respect to the analyzer focal point. If you have scanning then you can simply look at the ion beam in real time on a SiO2 sample.

 AES Ion Gun Alignment Procedure (for non-scanning AES):

Using a blank sample mount, position a sample to the focal point of the analyzer (Elastic peak).

1. Set up an alignment with the following parameters:

• Lower limit 0 eV
• Upper Limit 100 eV
• Time per step 20 ms

3. In the Multiplier Properties dialog box, un-check the Auto EMS Box.
4. In the Hardware Properties dialog box, make sure the input is V/F1.
5. On the 32-100, set the CMA multiplier switch to Analog and make sure the potentiometer is fully CCW.
6. Start the alignment and turn on the ion gun (no raster).
7. Slowly turn up the 32-100 CMA multiplier supply (or the 20-075 multiplier supply if you have an older system) until you have about a 100K cps low energy electron peak at 20 to 50eV.  This should occur at no more than 2000 volts on the multiplier (5.0 on the 32-100 potentiometer).
8. Finally, adjust the X and Y position of the ion gun for maximum signal. The ion gun is now aligned to the focal point of the analyzer.

XPS Ion Gun Alignment Procedure:

Using a blank sample mount, position a sample to the focal point of the analyzer.

1. Look under the Hardware Properties Menu for XPS and note the X-ray Anode type.
2. Set up an alignment with the following parameters:

• Upper Limit 1480 eV if Al is the anode, 1250 eV if Mg is the anode.
• Lower limit 1380 eV if Al is the anode, 1150 eV if Mg is the anode
• EV per step .5 (or the closest selection to .5)
• Time per step 20 ms
• Pass Energy 100 (or the closest selection to 100)

4. Start the alignment and turn on the ion gun (no raster). You should have a low energy electron peak at around 20 to 50 eV kinetic.
5. If necessary, reduce the ion gun beam current to prevent the detector from saturating. (You can increase the condenser lens setting or reduce the emission current in order to reduce the ion beam  current).
6. Finally, adjust the X and Y position of the ion gun for maximum signal. The ion gun is now aligned to the focal point of the analyzer.  Once roughed in you can use a piece of TaO5 to check the alignment of the ion gun with respect to the system microscope because when you burn through the oxide layer you will see a blue ring on the TaO5 sample. RBD Instruments provides TaO5 samples for this purpose.