Tag Archives: 9103 USB picoammeter

High-speed Support Improved in Latest Actuel Release (1.7) for the 9103 Picoammeter

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RBD has released Actuel version 1.7 for the 9103 Picoammeter, with improvements for high-speed data acquisition and (especially) data logging and graphing.

The latest version can be found here.

If you do not have a high-speed 9103 Picoammeter and are already running Actuel version 1.6, there no reason to download the latest version. However, high-speed users will find a number of improvements.


Oscilloscope emulation


Although Actuel was not designed to have an oscilloscope emulation (with features such as triggering), at higher speeds you can come close to emulating scope current monitoring.

In the Data Window, click the Show Options button and select “Last” from the Graph Options. You can scroll in increments as low as 0.1 second, but you can type in a smaller increment, such as “0.05” in order to display at higher resolution.

Last time option in Actuel
Using the “Last” time option in Actuel


(Note: The graph display options can get out of sync with data collection if you change and option when recording or after stopping and clearing data – it may be necessary to re-enter the value or reset recording. We’re working to make this smoother in the next version.)

For smoother real-time graphing, use standard-speed at 25 mS unless faster rates are needed

The 9103 can run as fast as 25 mS per sample in standard-speed mode, and 2 mS per sample in high-speed. In order to optimize faster data acquisition in high-speed mode, the 9103 collects 10 samples per message, as opposed to 1.

However, note that if you are collecting data at 25 mS in Standard-speed, your PC will be updated with new data every 25 mS. In High-speed, you’ll be updated every 250 mS.

For that reason, the Acutel software always collects data in standard-speed mode at 25 mS and above, regardless of the high-speed mode settings. It is recommended you do the same if you are writing your own software to control the 9103.

That also means that for real-time graphing, you may not want to sample at a rate of, for example, 24 mS, if you can achieve the same results at 25 mS. At faster rates, the delay in caused by receiving 10 samples per message is less noticeable, but it’s visible at rates of 20 mS- 25 mS if you are graphing only the latest points in relatively high resolution:

Actuel 25 mS Standard Speed

Actuel – 25 mS Standard Speed

Actuel 25 mS High Speed

Actuel – 24 mS High Speed

9103 USB Picoammeter Filter Settings – Part 1

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The 9103 Picoammeter uses a continuously sampling A/D when measuring current. These samples are then averaged using an low-pass infinite impulse response (IIR) filter.

Filter Settings

When using the 9103 to sample current, you have control over the filter response and the degree of smoothing (both in Actuel in when programming the unit). The filter setting will make little difference for most constant signals, but for dynamic and periodic signals, the filter can be set to attenuate noise, or to provide detail and catch peaks.

A filter coefficient that is user-programmable determines the amount of smoothing the filter will apply. The higher the value, the more smoothing of the signal.

The filter can be set to 0, 2, 4, 8, 16, 32, and 64. A value of 0 is essentially the same as bypassing the filter. A value of 64 is the greatest amount of filtering. For most cases, values of 4, 8, and 16 will work best. Higher values may produce more accurate results for stable signals, but it will take longer for measurements to stabilize.

Example

In the examples below, a 1 Hz sine wave is sampled at a 25 mS rate, yielding 40 discrete data points per cycle. Each data point is comprised of multiple filtered A/D readings.

The filter settings used in the examples are 2, 4, 8, 16, and 32.

filter setting 2
Filter Setting 2
filter setting 4
Filter Setting 4
filter setting 8
Filter Setting 8
filter setting 16
Filter Setting 16
filter setting 32
Filter Setting 32

There’s quite a bit of noise present when using low filter values of 2 and 4, while values of 16 and 32 reduce the noise but also attenuate the signal somewhat. For this application, a value of 8 produces the most accurate result.

Conclusion

In general, any low-pass filter will of course mask high-frequency data. While the 9103 is not typically used to measure periodic signals, the filter’s effect on your application may be significant. When in doubt, start with the filter set to 8 for some noise reduction without significant smoothing or signal attenuation.

In Part 2 we’ll discuss use of the additional first-level filter implemented in the high-speed model of the 9103.

Stability testing of surface analysis optics

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There are two easy ways to check the stability of the electron or photon source on an X-ray photoelectron spectrometer, Auger electron spectrometer or Scanning Electron microscope:

  1. Measure the target current and plot the results vs. time using a data logging picoammeter such as RBD’s 9103.
  2. Acquire a depth profile region over a wide energy range but do not turn on the sputter ion gun.

Method 1 – Plot the target current vs. time.

As shown in the pictures below, plotting the target current versus time shows the stability of the electron beam as well as trends in the current.  In this case the current being measured is an electron beam in the range of approximately 300nA.

Electron Current vs time
current measurement display

By changing the scale of the plot, you can see finer details of the current stability and any trend. In this measurement the current drifted up by about 30 nA over a 2 hour period and started to stabilize after the first hour. Room temperature changes can effect the stability of electron optics as can thermal mass of the electron source.

close up of current measurement

Measuring target current vs. time works well for electron beams on Auger spectrometers and SEMs, as well as secondary electrons generated by X-ray sources on XPS systems.  The secondary electron current generated by X-ray sources is directly proportional to the X-ray flux.

Method 2 – Wide energy range depth profile.

For this method you want to set up a region for a depth profile that is at least 1000 eV wide.  In the example below we acquired from 1000 to 0 eV on a silver sample, 2 sweeps per cycle. Normally the ion gun is turned on for a depth profile but for this test the ion gun is not turned on.

In the picture below you can see the Profile vs. time display where the highest count in each cycle is displayed.   

Depth profile vs time

This picture of all 95 Ag cycles super imposed shows that the stability is pretty good.   A depth profile test like this tests not only the X-ray source stability, but also the analyzer voltages, electron multiplier and detector electronics. You can do the same test with an AES system which would test the electron gun as well as the analyzer,electron multiplier and detector electronics.

This picture below shows the first cycle and the next picture shows the last cycle.  If you look very closely you will see a small increase in the carbon peak that coincides with the over all slight drop in the intensity of the Ag profile vs. time display.  Carbon will typically increase over time in UHV systems due to adsorption and desorption effects.

If you have some extra time you may want to run one of these test methods on your XPS, AES or SEM.   The results can be interesting and if nothing else will let you know that your system is stable.