Cylindrical mirror analyzer fringe field termination ceramics

Posted on by
Reply
Print Friendly, PDF & Email

Physical electronics (PHI) cylindrical mirror analyzers ( CMA) use fringe field termination ceramics to reduce the fringe fields from the end of the cylinders.

Abstract an early patent:

Field termination plates for cylindrical electron analyzers are provided wherein the plates are constructed of an insulative material coated on the interior surface with a high resistance, electrically conducting coating. Spaced concentric rings of relatively high conductivity material in electrical contact with said coating are provided; the rings providing equi-potential regions on the plates, thereby minimizing field fringing near the ends of the cylindrical tube electron analyzer.

The PHI CMA (cylindrical mirror analyzer) utilizes conical and flat termination ceramics to eliminate electrostatic edge effects between the inner and outer cylinders. These ceramics are essentially gold rings with resistors in between that divide the outer cylinder sweep voltage down in even steps. The result is a very high throughput and even energy distribution of the Auger electrons. If a CMA has a poor contact on a termination ceramic, the results are noisy data and poor energy linearity.

Single pass AES CMAs have just 2 terminating ceramics, a conical at the front of the CMA and a flat at the base. Double Pass AES/XPS CMAs have 3 terminating ceramics, a conical at the front, a center and a base.

The conical and flat ceramics are essentially resistors and so the total resistance between the inner and outer cylinders add up like this:

The table below lists the values on the combined resistances of the older PHI CMAs.

Values are in Meg ohms

If the VM or IC to OC (inner to outer cylinder) resistances are off significantly in your CMA then you probably have a contact issue between a conical or flat (base) ceramic between the outer cylinder or the inner cylinder. Sometimes the resistances of the conical ceramic can be off due coating caused by years of sputter depth profiling.

A poor electrical contact can result in high background counts or extremely high noise levels in the data due to arcing. If you suspect that your CMA has a contact issue with a terminating ceramic then you will need to tear down your CMA to where you can add improve the electrical contact by adding some thin copper or gold shim foil between the suspect ceramic and cylinder. If you need some guidance on how to do that, please contact RBD Instruments.

The pictures below show the conical and flat ceramics from a 25-120A CMA. You can see the gold rings and also the thin film resistors.

5 kV floating Picoammeter Video

Posted on by
Reply
Print Friendly, PDF & Email

This post has been updated to include a video that shows how the High Voltage 9103  (PN 91035K) picoammeter can float up to +/- 5 kV.

RBD Instruments has released a new version of its 9103 USB Picoammeter which incorporates faster reads per second as well as 5000 DC volts of isolation to chassis ground.

9103 HV

9103 HV

Increasing the DC voltage isolation from chassis ground to 5000 volts (5kV) opens up new possibilities for researchers such as direct DC current measurement of very small electron and photo multiplier signals. Electron and ion beam measurements can be biased to reduce secondary electrons or to retard the beam as needed for experiments.

Designed to provide accurate bipolar DC current measurements in noisy environments such as synchrotron beam lines, the 9103 can measure bi-polar DC currents from low picoamps to milliamps.

The drawing below shows how the 9103 is floated on your HV power supply. The high voltage is referenced to chassis ground, and the signal ground is referenced to the high voltage. To help keep the supply and signal connections clear, the HV connection is a MHV connector and the signal input is a SHV connector.

Floating picoammeter

Floating picoammeter

There are a number of manufacturers of programmable DC power supplies that can be used to float the 9103 up to whatever voltage is needed (as long as you do not exceed +/- 5 kV).

For example, TDK-Lambda provides a programmable 0 to 6.5kV supply that can be voltage limited to 5 kV and can drive up to 2 mA of current.

The model number for a 120 VAC line input is PHV6.5P2-USB-1P115.  The base model has a ripple of 700mV which is somewhat high, but TDK-Lambda does offer a low ripple option that gets the ripple down to 75mV.  You can also easily make a simple RC filter to do the same thing. A number of interface options are available including USB, Ethernet, Serial and analog.

TDK Lambda supply

TDK Lambda supply

PHV series

PHV series

The new high speed option for the 9103 increases the reads per second from 40 to over 500, which is fast enough to perform optical chopper experiments. And, by taking more reads in the same amount of time as the first generation 9103 could, the accuracy is improved.

The Actuel software included with the 9103 provides new features for high speed acquisitions and display, but you can also write your own software to control the 9103 using the simple ASCII commands or in LabVIEW.

Since 9103s can be synced, it is now possible to configure a multichannel DC Picoammeter with up to 256 channels that has high speed, high voltage, or both options.

And if you do not need the high speed or high voltage options, the standard 9103 USB Picoammeter is still available as well.

For more information visit the RBD Instruments website at http://www.rbdinstruments.com

CMapp New Features

Posted on by
Reply
Print Friendly, PDF & Email

We have added a few new features to CMapp, our microCMA acquisition and data massage software.

For example, when you first open the electron gun dialog box, a filament warm-up reminder pops up:

It is recommended that you warm up the filament at the beginning of each session so that the microCMA can thermally stabilize. The filament warm-up routine brings the filament current up over a 5-minute period and then keeps the filament on.  What is nice about this feature is that you can just click “Yes” and then walk away and come back later when you want to use the microCMA.

Another new feature is the “Auto Set the Beam Voltage to 2 kV ” for alignments:

The alignment acquisition is typically used to acquire a 2 kV elastic peak that sets the analyzer to the sample distance. Surveys and multiplexes are typically acquired with the beam voltage set to 3 kV.  Then, if you move to a new sample, or if you move the same sample to a new location, you would need to re-acquire a 2 kV elastic peak. With the “Auto Set beam to 2 kV” feature, you can just acquire the elastic peak alignment and the beam voltage will automatically change from 3 kV to 2 kV.

The new Diff/Smooth feature combines the differentiate and smooth commands into one click:

Related to the Diff/Smooth command is the ability to automatically Diff/Smooth at the end of an acquisition:

By checking the “Auto Diff/Smooth After Acquisition” box, the data will automatically differentiate and then smooth when the acquisition is complete. The “Auto Diff/Smooth” feature works for surveys, multiplexes, and alignments. Since you need to differentiate the data for quantification anyway, you might as well have it happen automatically.

Finally, we have added a feature that provides estimated target current. This is helpful if your target is grounded internally on your sample manipulator and you have no way to measure the actual electron beam current. Rather than using the emission current to set the relative target current, you can use the estimated target current to set the electron beam current to the recommend 300 nA.

First, select Estimate Target (Beam) Current in the Hardware Properties dialog box:

The estimated target current will be displayed in the Electron Gun dialog box as shown below:

Each electron gun filament behaves a little bit differently so the user-settable Emission Current-to-Target Current ratio can be adjusted in the Hardware Properties dialog box. We will have a video soon that will show you how to set this ratio.

If you have our 9103 USB picoammeter or some other picoammeter, you can measure the target current and enter the value into an acquisition manually (or, in the case of the 9103, automatically). You define this setting in the Hardware Properties dialog box.

If Estimate Target Current is selected, then the estimated target current will be entered into the acquisition before the acquisition starts. Whether entered manually, automatically, or estimated, the target current is displayed on the left-hand side of the alignment, survey, or multiplex acquisition.

For more information on our microCMA compact Auger Electron Spectrometer visit our website:

RBD Instruments microCMA