Putting Together a Compact UHV (Ultra-high Vacuum) Chamber for Spectroscopy

Small, inexpensive UHV chambers have been the backbone of many commercial labs and universities for decades. The cost of larger, feature-rich systems has gone up dramatically in recent years, making compact, DIY chambers even more cost-effective for specialized applications and education.

RBD has a range of products available to add value to your compact chamber, and in fact built our own recently to develop and test our microCMA compact Auger analyzer.

RBD Kimball Chamber
Kimball Physics chamber with RBD miniZ, IG2, and microCMA compact Auger analyzer

The Chamber

We started with an 8 inch spherical octagon chamber from Kimball Physics. This chamber has two 8.00″ CF and eight 2.75″ CF mounts, with an internal volume of  106.6 cu. in. (1,747 cc):

Kimball Physics Chamber
Kimball Physics 8.0″ Spherical Octagon – Vacuum Chamber

The vacuum chamber was fitted with an ion pump from Gamma Vacuum, and valves and windows from MDC. Affordable turbo pumps can be sourced from Pfeiffer (HiCube 80 Eco) and Edwards (nEXT85).

Rough vacuum gauges are available from a number of companies including Digivac.

Rough Vacuum Gauge
Rough vacuum gauge

Ion gauges and ion gauge controllers are available from a number of companies including Stanford Research Systems

Ion Gauge Controller
Ion gauge controller

Accessories

To assist with water vapor desorption, the chamber is fitted with RBD’s miniZ. The mini-Z uses UVC radiation to desorb water from the chamber walls, resulting in faster pump-down times and lower ultimate vacuum.

RBD miniZ
RBD miniZ water vapor desorption system

This chamber is also fitted with RBD’s IG2 2 kV low cost sputter ion gun for specimen cleaning:

Instrumentation

The ultimate purpose of this system was to house RBD’s microCMA compact Auger analyzer (shown below with the Z translator attached):

RBD microCMA
RBD’s microCMA compact Auger Analyzer

For applications that require elemental analysis, this chamber, with the addition of a PC and CMapp AES acquisition and data massage software, is now a complete system providing quantitative, surface-sensitive Auger electron spectroscopy. At around $50,000 for all the components listed here, this is one example of a budget-sensitive spectroscopy system that can be assembled, repaired and upgraded without costly field service visits.

microCMA Software Update – New Features for Auger Multiplexes

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

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.