Cylindrical mirror analyzer fringe field termination ceramics

Posted on March 14, 2021 by Randy

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.

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.

Low-Cost High-Potter

Posted on December 18, 2020 by Randy

Occasionally Ion Pumps can short out from the flakes that accumulate over the years because of using titanium sublimation pumps (TSP). An old trick is to use a high potter (high voltage potential generator) to create an arc which can sometimes (if you are lucky) burn off the short. High potting can work well for ion pumps, ion guns and practically any electrical feedthrough on a vacuum chamber where flakes or deposition build up is an issue.

High potting will only work on small flakes as the current generated is low (100uA max). But the voltage generated is extremely high at 20,000 to 50,000 volts. Think of this as a small Van der Graaf generator where you can direct the arc towards the electrical feedthrough on the vacuum chamber. The voltage from the arc is applied to the shorted electrical feed though and will work it’s way to the short inside the vacuum chamber and if you are lucky, will melt the short.

High potting does not always work but when it does it buys you some time before you need to vent the chamber and perform the necessary maintenance to fix the underlying shorting issue.

Back in the 80s it was common to see high potters in labs that had vacuum chambers for analytical instruments or deposition systems. These days you do not see high potters as often due to more stringent electrical safety standards. Used properly a high potter is perfectly safe. Although it is a little bit exhilarating to be pointing a device that has a 50,000-volt arc coming out of the end. 😊

Electro-Technic Products, Inc. provides an assortment of high frequency generator testers that work well as high-potters (high voltage potential) to melt away small particles and flakes that can cause shorts in high and ultrahigh vacuum applications. In particular, these are useful for high-potting shorted ion pumps and ion guns.

We prefer the BD-10AS as it has an ON-OFF switch. As with all high voltage, only qualified personnel should use this device. Check with your organizations’ electrical safety officer to make sure that your organization allows high potter use before purchasing a high potter.

For more information or to place an order, contact Electro-Technic by phone at 773-561-2349.

Surface Analysis Systems and Unstable Line Voltage

Posted on November 12, 2020 by Randy

We all tend to take the stability of our electric power for granted. Some parts of the US and the rest of the world can have very unstable power, and experience frequent power outages or brownouts that cause loss of productivity and sometimes damage to the system. This is especially true in warmer months, when there can be frequent and severe thunderstorms.

This blog post will explore some UPS (uninterruptible power supply) options that are suitable for surface analysis instruments as well as SEMs and other vacuum-related systems.

Uninterruptible power supplies are rated in kilovolt-amps (kVA) so the first thing you need to do is to calculate the kVA for your system. For example, let’s say that my system draws a maximum of 30 amps at 208 VAC. Using this kVA calculator, I come up with 6.24 kVA, which means I would need a UPS with a rating of at least 6.24 kVA. The higher the kVA rating, the higher the cost of the UPS.

There are three other things to consider for the kVA rating.

The first consideration: What is the main breaker on the system rated at? On older Physical Electronics XPS and AES systems, the main breaker ranges from 30 amps up to 60 amps depending on the type of system. A 60-amp 208V kVA calculation comes out to 12.48 kVA.

The second consideration: What is the actual current draw of the system? Usually, this is much lower than the main breaker current rating. For example, a PHI 5600 XPS system may have a 50-amp main breaker and a kVA of 10.4, but the actual maximum current draw might be only 20 amps (during a bake-out), which comes out to only 4.16 kVA. So, technically, a 4 kVA UPS would be adequate for a 5600 system, except that most electrical codes require that the power connection to the system is rated higher than the main breaker. This means that a 50-amp main breaker system would need a 60-amp 12.48 kVA connection to the system.

Before installing a UPS, refer to your local electrical codes because you may need to get a permit or have the UPS installed by a licensed electrician.

The third consideration: Do you need a battery backup or just a line conditioner? A line conditioner costs much less than a UPS with batteries, and batteries also require maintenance and occasional replacement. Batteries in the UPS provide backup power to the system. Longer backup times require more batteries, which drives up the cost and the maintenance of the UPS.

If you have only brownouts rather than a complete loss of power, then a line conditioner may be all that you need.

https://www.powervar.com/produ cts/power-conditioners

This paper has a lot of useful information about things to consider when researching a UPS: https://www.falconups.com/cleanpowerpaper.htm

The links below show UPS providers that are recommended by some of the surface analysis system manufacturers. The key things to look for in a UPS are its kVA rating and that the input voltage is single phase, 208-to-240 VAC (this depends on what system you have and what your local line voltage is).

https://www.powervar.com/products/single-phase-ups