microCMA Software Update – New Features for Auger Multiplexes

Posted on by
Reply
Print Friendly, PDF & Email

This past year there have been a number of new features added to CMapp – the application software for the microCMA. Most of these provide you with improved (and safer) control of your microCMA hardware. For example, there’s is now a “Dynamic Mode” feature that assists in automatically conditioning the multiplier.

The most significant addition to the CMapp software is the Multiplex Survey Region View.

Earlier versions of CMapp – like its AugerScan cousin – displayed Multiplex data in two ways – either individual survey region windows, or a bar graph representing the peak-to-peak or atomic concentration (a.c.) data.

The most recent version of CMapp (0.4) has an additional view, which displays the survey region data in one graph of kinetic energy vs. counts or concentration. It’s now much easier to visualize all of the survey data in one window. Additionally, the graph updates in real-time while acquiring, much like a single survey.

CMapp Mutiplex By Energy
Multiplex Region View (legend ordered by energy)

This latest feature was actually added to CMapp in a recent previous version, but we’ve updated it to provide the option to order data legend and atomic concentration table by energy, alphabetically, by descending atomic concentration, or by the order the regions were added to the acquisition.

CMapp Mutiplex By Energy
Multiplex Region View (legend ordered by atomic concentration)

You can change the order of regions in the legend (and in the optional atomic concentration annotation) in the View menu – choose the Options command, Graph tab:

CMapp View Options - Graph
CMapp View Options Dialog – Multiplex Legend Options

You can find more information about RBD’s microCMA and download the latest version of CMapp here.

We’ll be soon be updating our YouTube channel with more microCMA tutorial videos to help you get the most out of your compact Auger analyzer and CMapp software.

9103 USB Picoammeter Filter Settings – Part 1

Posted on by
Reply
Print Friendly, PDF & Email

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

Posted on by
Reply
Print Friendly, PDF & Email

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.