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.