A blog on the repair, operation and calibration of surface analysis systems and components including electron spectrometers, sputter ion guns and vacuum related hardware. Click on the Index tab below to see a list of all posts. Visit our website at http://www.rbdinstruments.com
Category Archives: Operation and Calibration Procedures
Operation and calibration procedures for PHI (Physical Electronics) components
Recently, I have seen the same problem on several 32-095 and 32-096 X-ray source controls which are used on older Physical Electronics PHI X-ray photo electron spectroscopy systems.
The issue is that C9, a 680 uF electrolytic capacitor blows out and the electrolytic material leaks out on the board. Left unattended, the electrolytic etches and oxidizes the traces on the board.
If you have an older PHI XPS system that uses a 32-095 or 32-095 X-ray source control you should pull if out of the rack, remove the cover and inspect the board immediately.
If corrosion is present, then remove the board and remove C9. Note the polarity of C9 as the + indicator on the board may be etched away. Then, carefully clean the corrosion from the board as best as you can. If in the shop I use some Alconox and let it sit on the board for a while, then rinse with DI water and let the board dry overnight. In the field I have used isopropanol or methanol and cotton swabs. Note that if the traces are corroded badly then they may come off the board as you clean it. If so, you will need to use some fine copper wire to rebuild the traces.
Once the board is clean and dry, replace C9 with a new one. I will dig into this issue some more and try to determine why this problem occurs so often and come up with a permanent solution. In the meantime, I would recommend that the C9 capacitor be replaced every 5 years.
The pictures below show where C9 is located on the control board and what the corrosion looks like.
The 80-360 and 80-365/366 analyzer controls provide all the voltages to the 10-360 spherical capacitor analyzer that is used on many PHI (Physical Electronics) XPS systems.
80-365 boards Retard board is third from left
The retard voltage is used to slow down electrons and is essentially the sweep voltage. In conjunction with the pass energy supply, the retard voltage controls the energy of the electrons that are being passed through the analyzer and into the electron multiplier and counting circuitry.
I recently had an interesting problem with a retard board on an 80-360 analyzer controller. The issue was that the retard board output voltage was not linear. Part of the calibration procedure for the retard board is to test the voltage at 11 specific voltages ranging from 253.6 volts to 1253.6 volts in increments of 100 volts. This is a convenient way to confirm that the retard supply is linear. The table below shows the hex commands that are used to set the voltages and the expected results.
In this particular case, the output voltages were close to correct at some points, but way off at other points as shown below. This non-linearity would present itself as inconsistent peak widths in the data as a function of kinetic energy.
These results at first glance look like a bit problem. That is, the digital to analog convertor (DAC) voltages are likely off. The DAC used in the retard board circuit is a 16 bit DAC and the output voltages should follow the voltages listed below.
DAC Voltages
However, the DAC voltages were fine. The retard voltage circuit comprises the DAC which drives a precision operational amplifier that in turn drives a high voltage switching supply. Some precision high voltage resistors are used to provide feedback. The next most likely component that might be non-linear was the OP07 ultra-low offset operational amplifier (op amp). The OP07 was replaced but did not solve the problem.
The next most likely cause of the non-linearity problem was the feedback resistors. There is a total of 5 of these SX3730 5 watt wire wound high precision axial resistors in series. To accurately measure those resistors, you need to lift one end off the circuit board. Using my Fluke multimeter, I tested the resistance of each resistor and they all checked out as OK. Ideally you will see very close to 1.0 megohms, but it might be off by .05 megohms. When a resistor is bad it will be open or be off by as much as .5 megohms. So, it seemed that the feedback resistors were OK as well.
That left not much in the circuit other than a few potentiometers. After spending some more time retesting all the components, I came to the conclusion that it had to be one of those feedback resistors.
To test that theory I removed all 5 of the SX3730 1 megohm feedback resistors and replaced them with a single 5 meg ohm resistor. And that worked! So now I knew for sure that one of those 5 feedback resistors was the problem. I measured the resistance of each resistor, and they looked OK. But then I realized that the non-linearity is a function of the voltage applied to the resistor. At some voltages the resistance was OK, but at other voltages the resistance was off.
I then decided to measure the resistance value again using a megohmmeter. The model that I used was a Protek DI-2000M. This megohmmeter (also called an insulation tester) puts 500 V across the resistor when measuring the resistance. I hoped that by putting 500V across the resistor that I would be able to see a greater difference in the resistance values. And that worked out as expected. One of the resistors showed only 965 Kohms with the megohmmeter and 995 Kohms with the Fluke. I replaced that resistor and the calibration was perfect. 😊
In hindsight, duh. Since the gain of the circuit was changing as a function of the non-linearity of one resistor, the lesson is that when checking the resistance of suspected non-linear resistors, always use a megohmmeter since that will put much more voltage across the resistor than what a normal DVM will put out. Better yet, if possible, use the highest voltage that the resistor is rated for.
If your 80-360 or 80-365/366 analyzer control is not functioning properly and you need some help, please contact RBD Instruments for assistance as needed.
The AugerScan software that is used on older Physical Electronics (PHI) AES and XPS surface analysis systems provides for control of data acquisition electronics such as analyzer controllers and electron multiplier supplies. This blog post will explain how AugerScan automatically sets the electron multiplier voltage when acquiring data.
On Auger Electron Spectrometer (AES) systems there are two modes of signal collection. V/F (voltage to frequency) is the analog detection mode and is used for electron beam currents of 100 nA or more. The model 96A (or 96B) V/F preamplifier converts the current that flows through the electron multiplier into a voltage which is then converted to a frequency so that the computer interface can read in the signal. Zero to 500 nA of current through the electron multiplier corresponds to zero to 1 M cps of signal. V/F preamps were developed back in the early 80s when high resolution A/Ds (analog to digital) converters were very expensive and V/F preamps were a lower cost alternative. V/F preamps also replaced lock-in recorder preamplifiers which were used on the very early AES spectrometers.
The other AES detection mode is pulse count (PC). In pulse count mode an amplifier discriminator is used to count low currents (think of it as counting individual electrons). Pulse count mode is used with electron beam currents of 100 nA or less.
XPS systems are always operated in some type of pulse count mode – single channel, position sensitive detector or multi-channel detector. The detector currents are much lower in XPS than in AES.
Auto EMS is the AugerScan software feature that controls the electron multiplier voltage. The first step in setting up the Auto EMS is to determine the electron multiplier plateau voltage. The plateau voltage sets the upper limit that the electron multiplier will be set to.
For a given current electron current, as voltage is applied to an electron multiplier more electrons are generated and counted by the detector. More electron multiplier voltage translates into more counts until the multiplier gets into a mode where more electron multiplier voltage does not generate more electrons, it flat-lines. That region is called the electron multiplier plateau. The plateau region can span several hundred volts and only when the multiplier voltage is increased further do the counts start coming up again. The higher count rate at very high multiplier voltages is saturation and you do not want to operate the multiplier in this range as the electron enriched material in the multiplier can become depleted very quickly. The correct setting for pulse count mode would be about 50 to 100V past the knee where the signal has plateaued.
The figure below shows an AES multiplier plateau voltage of 1700V.
Before you acquire an AES gain curve you must first set the target current to 10nA.
Also make sure that your V/F preamp model (96, 96A/B, VF4) is selected in the AES Hardware Properties dialog box and then press the Preamp Defaults button in the AES Multiplier Properties dialog box. The V/F set points values are different depending on your systems V/F preamp. The very old 96 V/F preamp has a maximum count rate of 100 k cps, the 96A/B has a maximum count rate of 1 M cps and the V/F4 has a maximum count rate of 4 M cps.
Next, open the AES Multiplier Properties dialog box and check the Auto EMS box and the Pulse Count Input box.
Press the Acquire Gain Curve button and a message will pop up to confirm that you have the beam current set to 10nA –
Press the Yes button and then the EMS gain curve will acquire and display the counts vs. voltage. The cursor will display what it thinks is the correct multiplier plateau (Pulse Count) voltage value. You can change it a little bit if desired, but it should be about 50 to 100V past the knee where the counts plateau.
Press the OK button and the Pulse Count Settings voltage will be set. The Pulse Count Settings voltage will be the upper limit of the electron multiplier voltage.
Let’s look at the logic for how AugerScan sets the AES electron multiplier voltage in a Survey. The V/F setpoint for surveys is typically set to 800 K cps which is also 80% of the maximum 1 M cps for a 96A/B V/F preamp.
AES surveys are typically acquired starting at 30 eV and ending at 1030 or 2030 eV depending on where the Auger peaks of interest are. For this example, we will use a 30 to 1030eV survey.
The background in AES rises as a function of the kinetic energy as shown by the red line. The higher the eV, the higher the counts. This means that the highest kinetic energy is typically also the highest count in the survey. However, in some cases (as in the survey below) there can be an auger peak that is near the end of the survey which has a higher count rate than the very end of the survey. For this reason, the survey V/F setpoint is set to 80% of the maximum counts in the V/F mode. Otherwise, the electron multiplier would saturate if there is a large peak near the end of the survey. Saturation presents itself as a straight line at the top of the survey.
The logic for setting the multiplier voltage for a survey is as follows –
Set the analyzer auger energy to the end of the range (1030 eV in this case).
Start ramping up the electron multiplier voltage while monitoring the count rate. The starting voltage, volts per step and time per step are the values in the Multiplier Properties dialog box. In this case the starting voltage is 500, the volts per step is 5 and the time per step is 25ms.
If the count rate gets to 80% of the maximum V/F value (800 K cps for the 96A/B V/F preamp) then that multiplier voltage is set and used for the survey and the input is set to VF1.
However, if the multiplier voltage reaches the Pulse Count Settings voltage (1700) before the count rate reaches 800 K cps, then the pulse count input is selected, and the electron multiplier voltage is set to 1700 volts.
To summarize the logic – If there is a lot of signal the multiplier voltage will be lower, and the detection mode will be V/F. If the amount of signal is lower, then the multiplier voltage will be higher. But when the multiplier voltage reaches the Pulse Count Settings voltage value, then the multiplier voltage will be set to the Pulse Count Settings value and the detection mode will be PC1 (amplifier discriminator).
For AES multiplexes and depth profiles, the center of the highest kinetic element being acquired is used for the V/F setpoint. The V/F setpoint values for multiplexes and depth profiles are lower than in surveys. For depth profiles there needs to be more room for the counts to come up without saturating the electron multiplier because counts for some elements will increase as the sample is sputtered.
For an elastic peak alignment, the beginning of the sweep is used for the analyzer energy since there are essentially no counts after the elastic peak. The elastic peak (alignment) setpoint value is typically 30% (300 K cps for the 96A/B) of the max V/F counts. If your elastic peak clips, lower the alignment setpoint to 20%.
The electron multiplier logic is only applied to AES. For XPS, the multiplier is always set to the pulse count (plateau) value.
To run an XPS gain curve, turn on the X-ray source to the power that you normally run at (typically 300 watts) and select an analyzer energy of 500. The pass energy can be set from 50 to 100eV. The input is set in the Hardware Properties dialog box. Double pass CMAs are set to PC1, 5100 XPS systems are set to PC1, 5400 XPS systems are set to PSD, and 5600 to 5800 XPS systems are set to MCD.
Acquire the gain curve and AugerScan will automatically set the multiplier voltage to the plateau voltage to about 100V past the knee. Sometimes if the counts are too high or too low AugerScan may not pick the correct voltage in which case you can move the cursor to the correct value and then set the Multiplier voltage by pressing the OK button.
For all XPS acquisitions the electron multiplier is set to the plateau voltage which is entered in the Multiplier section of the XPS Multiplier Properties Dialog box as shown above. There is no input selection logic for XPS acquisitions, the input is always set to pulse count (single channel), PSD (position sensitive detector) or MCD (multichannel detector) input depending on the specific XPS detector that your XPS analyzer has.
AES input tips –
In the older PHI 10-150 AES analyzers there is no PC (pulse count) output, only a V/F output. When there is no PC output on a CMA then the Pulse Count Settings voltage needs to be set higher than the Max V voltage in the AES Multiplier Properties dialog box. Since the multiplier voltage will not be set higher than the Pulse Count Settings voltage, the input will always be V/F.
In the Multiplier Dialog box below the max voltage (Max V) is set to 2000, and the Pulse Count Settings voltage is set to 2100. So, the multiplier voltage will not go past 2000 V and never reach the Pulse Count Settings value. Since the input is set to V/F1 in the AES Hardware Properties dialog box, the input will stay in V/F mode. The electron multiplier voltage will still be set to the V/F setpoint value automatically for any acquisition type.
For the Auto EMS to work, the AES Hardware Properties Input must be set to V/F (typically V/F1). Then the electron multiplier voltage logic will select the input based on the amount of signal. If the input is set to PC (typically PC1) in the AES Hardware Properties dialog box, then the input will be set to PC and the electron multiplier voltage is set to the Pulse Count Settings value. In that case the electron multiplier voltage is not ramped up to the V/F Setpoints value, it is set to the Pulse Count Settings voltage. You normally would not want to force the input to PC on an AES analyzer as if the target current is high the electron multiplier could be damaged.
If the Auto EMS box is not checked, then the input is set to whatever is specified in the AES Hardware Properties dialog box and the voltage is set to the Pulse Count Settings value in the AES Multiplier Properties dialog box. On some of the oldest AES systems the electron multiplier supply is the model 20-075 and the multiplier voltage is set manually. If you have a 20-075 electron multiplier supply, then the Auto EMS must not be checked.
Auto EMS vs. manual setting of the electron multiplier voltage –
If you have a 32-100 electron multiplier supply, for the Auto EMS logic to work the mode switch must be set to Digital. You can also control the electron multiplier voltage manually by setting the mode to Analog. Uncheck the Auto EMS box in the AES Multiplier Properties dialog box and set the input to V/F1 or PC1 in the AES Hardware Properties dialog box depending on whether you are acquiring AES or XPS data.
0 to 10 turns CW on the Analog multiplier knob translates into 0 to 4,000V of electron multiplier voltage, or 400 volts per turn. Elastic peaks usually need about 1000 volts or 2.5 turns on the CMA analog multiplier potentiometer, and surveys typically need 1200 to 1600 volts or 3 to 4 turns. When operating the 32-100 in the manual mode, make sure to turn the Mode switch to OFF when not acquiring data.
