microCMA Length, the Long and Short of It

RBD Instruments’ microCMA compact Auger electron energy analyzer is designed to fit on a standard 2.75″ / 70 mm CF flange. This makes it possible to add surface sensitive AES (Auger Electron Spectroscopy) to an existing vacuum chamber, as long as there is an available port.

The standard length of the microCMA analyzer is 11.1″ / 283 mm which works well for most 8″ / 200 mm diameter vacuum chambers. This standard length factors in a Z translator that is used to move the microCMA to the sample for analysis and to retract the microCMA when it is not in use. 

However, what if your flange-to-chamber distance is much longer or much shorter than the standard length? There is a 4.5″ / 114 mm limit on how short the microCMA can be due to the geometry of the analyzer section. For longer flange-to-target distances, the analyzer section can be extended as needed. The photo below shows a short 5″ microCMA and a long 21″ / 533.4 mm microCMA.

microCMA Auger Electron Spectrometer

No matter what your flange-to-target distance is, if you have a 2.75″ / 70 mm flange available, it is possible to add the surface-sensitive analytical AES technique to your chamber. The microCMA and Auger Electron Spectroscopy are especially useful for MBE chambers and other research experiments that deposit thin films and where surface-sensitive elemental analysis is required.

For more information on the microCMA visit RBD Instruments’ website here – microCMA

Monochromator upgrade for PHI 5600 XPS system

Installing a monochromator

This blog post shows the steps required to install a monochromator upgrade on a PHI 5600 XPS system.

The components of a monochromator upgrade include the monochromator housing, the crystal substrate and aligner, the mono X-ray source, and the X-ray source aligner.    If your X-ray source is a 32-095 then you will need to replace that with a 32-096 that can drive two x-ray sources (standard dual anode and mono source). An additional water line is included to complete the cooling circuit between the standard and mono X-ray sources.

monochromator schematic

Step by step procedure:

First, vent the vacuum chamber.

Use a new 4 5/8” copper gasket and install X-ray source X Y Z aligner to the monochromator housing.  It is much easier to install the X Y Z aligner onto the mono housing before the mono housing is mounted to the chamber.

X Y Z aligner

Use a new 6” copper gasket and Install the monochromator housing to the chamber on the flange that is opposite of the hemispherical analyzer.  It is heavy and so you will need at least two people to mount the monochromator housing to the flange on the chamber. 

Once mounted tighten the nuts on the flange.  In my experience, going in a circular pattern is the best way to tighten flanges on UHV chambers.   The trick is to not over-tighten the nuts or bolts as you go around.  Start out with just a little bit of torque and gradually increase it as you go around.   One or two of the nuts on the back of the monochromator housing are exceedingly difficult to get to.  A ½” U-shaped or half-moon wrench makes getting to those nuts easier. 

Or you can simply cut a standard ½” wrench in half. 

Once the nuts are tight and there is no gap between the flanges it is sealed.

Install the mono crystal substrate into the top mono flange assembly:  Use gloves and very carefully remove the crystal substrate from its box and unwrap it, being careful not to touch the crystals.  There are 3 recesses in the crystal block that line up with flat spaces on the mono flange assembly. 

The crystal substrate is held in place with 3 clamps.  The clamps mount on a guide screw and then there are two spring loaded set screws that provide tension to hold the crystal substrate in place.  

Tighten the set screws to where they just start to tighten up, and then about 1/16” more.   Do not over-tighten the set screws.  They should be tight enough to hold the crystal substrate in place firmly, but not so tight that the springs inside the set screws are fully compressed.

Next, install a new rectangular Helicoflex type monochromator gasket into the top of the monochromator housing. It will sit into a recess and should be centered in the recess.

Put the mono housing shutter in the bakeout position.  The chamber will be baked out and so the shutter will need to be set prior to the bake out.  Also, you can see how the shutter works before the top mono flange is installed.

Install the top mono flange assembly onto the top of the mono housing.  This can be done by one person.  Make sure that the crystal substrate does not touch the sides of the mono housing as you lower the mono flange assembly.   There are two guide pins to hold the mono flange assembly in place.   The serial number on the mono flange assembly should line up with the serial number on the mono housing.

Install the bolts into the holes in the mono flange assembly and tighten them.   For this flange, use little torque as you tighten the flange in a circular (rectangular) pattern.  The bolts are coarse threads and you want to tighten the flange evenly. 

Once the bolts are tight and there is no gap between the two flanges then it should be sealed.

Use a new 6” copper gasket and mount the 10-610 mono X-ray source to the 6” flange on the X Y Z aligner and tighten the nuts until there is no gap between the flanges or until the nuts are very tight, which ever comes first. 

At this point the chamber can be pumped down and baked out.   Make sure that all the housing parts and O-ring seals are removed from the 10-610 mono source prior to bake out.

The pictures below show the components of the 10-610 X-ray source as they are reassembled after the bake out.

After the chamber has been baked out, refer to the 10-610 mono X-ray source and 10-420 monochromator manuals for outgas, operation, and alignment information.

Removing and Installing Copper Gaskets On Vacuum Chambers

If you are new to UHV vacuum chambers and how to create a seal using copper gaskets when mounting optics, this blog post has some useful tips.

In many cases, installing the copper gaskets that are used to seal flanges on UHV vacuum chambers is as simple as placing the copper gasket in the knife edge recess. If the flange is facing down, then the gasket can be placed on the optics part being installed and the gasket will stay in place.

But in cases where the flange is perpendicular to the floor, the gasket will not stay in place on its own because the gravitational constant will prevent the gasket from staying in place. In other words, the gasket will fall.

There are a few ways to install a gasket onto the flange. But first, you need to make sure you’ve removed the old gasket properly.

Removing Gaskets

When you remove the old gaskets, you want to be very careful not to nick the knife edge on the flange when removing the old copper gasket because a nicked knife edge often results in a vacuum leak. And, nicked knife edges are difficult and sometimes very expensive to repair.

Usually the gaskets will come off easily with a minimum amount of force. For those gaskets that are pressed in tightly and very hard to remove, I have found that using a long-nosed vice grips locking pliers works quite well.

6" long nose Vice Grip needle nose pliers

You can adjust the gap on the pliers so that it firmly clamps down on the gasket, then simply bend the pliers so that the leverage will pop the gasket off the flange. It works every time and most importantly, it follows the number one rule of flanges – protect the knife edge. You can use a screwdriver to pry up the edge of the gasket, but if the screwdriver slips, you risk damaging the knife edge.

Pry up gasket

Two resources for removing gaskets:

Removal of metal UHV gaskets; Journal of Vacuum Science and Technology 12, 654 (1975) https://doi.org/10.1116/1.568642 https://avs.scitation.org/doi/abs/10.1116/1.568642?journalCode=jvs

A UHV-Gasket Removal Tool; Published March 1, 1983 https://www.nist.gov/publications/uhv-gasket-removal-tool

Installing New Gaskets

Method 1: Gasket Clips

The first method is to use a gasket clip. Gasket clips hold the copper gasket to the flange via a spring action. They line up with the flange’s leak check groove and hold the gasket in an area that is just past the knife edge of the flange.

Gasket Clip

Here is a link to the gasket clips that Ideal Vac provides:

https://www.idealvac.com/Agilent-GC0275S-Conflat-Gasket-Clip-Set-Package-of-10/pp/P105418

Gasket clips work well most of the time. Sometimes they will not work due to geometry limitations with other nearby flanges or optics.

If you do not have gasket clips, there are some other ways to mount a copper gasket to a horizontal flange.

Method 2: Elongate the Gasket

The second method is to elongate the gasket. This works well for larger copper gaskets, such as those for 10-inch and 8-inch flanges. It works with smaller gaskets as well, but you will need to drop them from a higher distance from the floor.

For an 8-inch gasket, hold the gasket about 1 foot above the floor. Hard concrete floors work best. This technique will not work on carpet.

Hold the gasket

Drop the gasket on its edge and it will hit the floor and bounce back up. You need to catch it when it bounces back up. If you don’t catch it and it falls to the floor, that is OK. You will just need to clean the gasket off with some isopropanol or methanol.

It takes a little bit of practice to get the correct height from which you are dropping the gasket. But the general rule is that the smaller the gasket, the higher the height. I have used this technique on 10-inch to 4.5-inch gaskets with good results. 10-inch flange gaskets should be dropped from about 6 inches. 4.5-inch gaskets should be dropped from about 18 inches. 2.75-inch gaskets are more difficult as they are harder to deform than the larger gaskets.

When you insert the gasket into the flange, you need to press it into the knife edge recess. The slight elongation will act like a spring and the gasket will stay in place.

Method 3: Cellophane (Scotch) Tape

Which brings us to the third method for mounting copper gaskets – cellophane (Scotch) tape.

Scotch Tape

You can use Scotch tape to mount the gasket as long as the tape is just barely on the gasket. Since the tape is mounted outside the knife edge, then it is OK if any of the tape stays on the gasket because it will be on the air side of the knife edge.

The pictures below show the knife edge cuts on common gasket sizes. For most copper gaskets (2.75- to 10-inch flange sizes) the knife edge is approximately .100 inches from the outside edge of the gasket. For the very small 1.33” flange, it is .050 inches from the gasket’s outside edge.

Knife edges

The procedure is to place the tape to where it is barely on the gasket (outside the knife edge region) and then very lightly touch the flange. You can use 2 or 3 sections of tape as needed.

Tape on copper gasket
6 inch CF flange
Gasket with tape

Once you get the optics part mounted to the flange with just a few nuts or bolts to hold it in place, pull the tape straight up and away from the flange. Usually all of the tape will come out. But if any small piece of tape is left behind, it will not matter since it is on the air side of the knife edge and will not have an effect on the vacuum.

Rotate the flange slightly to make sure that the copper gasket is properly seated before you tighten the bolts.

And don’t forget that if you are up to air for awhile and need to cover a flange or optics component with aluminum foil, you should use a UHV foil such as All Foils. UHV foil does not have an oil coating on it like foil from the super market does.

https://www.allfoils.com/single-product/uhv-foil/

UHV aluminum foil

RBD Instruments provides copper gaskets for less than what most other vacuum supply companies charge. – https://rbdinstruments.com/phi/uhv-parts.html