A blog on the repair, operation and calibration of surface analysis systems and components including electron spectrometers, sputter ion guns and vacuum related hardware. Click on the Index tab below to see a list of all posts. Visit our website at http://www.rbdinstruments.com
Category Archives: General Optics and Vacuum
General information on repair, maintenance, and operation of both PHI (Physical Electronics) and other manufacturers’ systems and components
This blog will describe the symptoms and solution for lens elements that charge up due to an oxidized graphite coating.
Overview – The Physical Electronics SCA (Spherical Capaitive Analyzer) has a series of 2 or 4 lenses that focus electrons into the energy analyzer section of the SCA. The first two lenses determine the analysis area and the second two lenses focus the electrons into the SCA for optimal counts and energy resolution. The voltages applied to the lenses change as a function of the kinetic energy of the electrons being detected. The sketch below shows the general concept on an SCA that uses a Position Sensitive Detector. Most SCAs today have a MCD multi-channel detector but the lenses work the same way.
SCA Lens Concept
The 5600 XPS system lenses are constructed out of stainless steel. In order to reduce the secondary electron yield (a lower secondary electron yeild improves energy resolution), Aquadag is sprayed on the inside of the lens surfaces. Aquadag is basically pure carbon, and carbon has a low secondary electron yield.
Problem – unstable data at higher pass energies, larger analysis areas, or higher x-ray source power.
Normally charging presents itself as unstable data with very high spikes in the counts followed by rapid discharges. In this case, the problem presented itself more like a digital step problem with very repeatable steps in the data at particular eVs. Another interesting effect was the ratio of peak heights would also change as a function of the pass energy, analysis area or x-ray source power.
Initially the symptoms pointed to the MCD multi channel detector or the chevron plates. The MCD was pulled and inspected an no problems were seen. The chevron (channel) plates were replaced and that did not change the symptoms.
Another clue was that if the lens cables were removed from the SCA and the lens elements shorted to ground, the data looked correct. In addition, one lens could be grounded and the other lens could have voltage applied to it and the data would also look correct. However, if the area of one of the the lenses were changed (by selecting large area mode) the problem would return, even with the other lens still grounded.
The conclusion was that the surfaces of the lenses must be charging, but only at large areas where more electrons would fill the lenses.
The SCA lens was removed and the resistivity of the lens elements were measured. The resistance of the lens coating would vary from tens of ohms to thousands of ohms depending on where the measurements were made. These resistance measurements matched the symptoms as a high resistance surface would not conduct the electrons that hit the inside of the lens cylinders.
Aquadag works well to reduce secondary electrons. But if exposed to air for extended periods of time it (evidently) can form an oxide layer which increases the resistance of the coating substantially.
A clean stainless steel scouring pad with a very light touch was used to break the oxide layer without removing too much of the Aquadag coating.
The technique used was to lightly rotate the scouring pad inside the lens elements and then check the resistance of the lens coating. The resistance would gradually drop with each rotation of the scouring pad. When the resistance dropped close to a few ohms, no further scouring was done.
Lens element
When this process was completed, the inside of the lens elements were conductive but still black, so most of the Aquadag coating was still intact.
After reinstalling the lens, pumping down and baking the vacuum chamber, the SCA performed correctly.
The first step is to remove the bolts on the flange that hold the lens to the chamber. Then, tilt the SCA back so that it rests on the arm stop. Remove the aperture size knob and the two lens feedthroughs. Next remove the nipple. Then, remove the magnetic shield (4 long screws) and finally the lens assembly (2 screws).Once the lens assembly is out you need to separate all of the sections in order to be able to use the scouring pad. The lens sections are held in place with screws and ceramics.Close up of lens electrical contacts. The top one has been removed by unscrewing the rod CCW.
If you are experiencing this problem please contact RBD Instruments for more details.
Laboratory gases are readily available in large cylinders from companies such as Airgas, Norco and local welding supply companies.
Large gas cylinders
But for small quantities of gases or specialty gases used in vacuum optics such as UV sources and Ion guns, it may make more fiscal sense to use lecture bottles instead of the larger size gas cylinders which are commonly found in laboratories.
Lecture bottles are small compressed gas cylinders that are typically 12-18 inches long and 2 to 3 inches in diameter.
Lecture Bottle
They hold approximately 2 cubic feet of gas and are pressurized to as much as 1800 PSI. High pressure gas cylinders require a regulator to step the pressure down. The pressure required for the application will determine which regulator is needed. For example, the Varian variable leak valve used on many 04-303 ion sources can take a maximum pressure of 500 PSI. However, it is recommended that the argon gas pressure be set to 15 to 25 PSI for best results.
Since lecture bottles are small, it costs less to ship them. But most importantly, when you buy a lecture bottle you are buying the bottle as well as the gas. Full sized cylinders are generally rented for a monthly fee in addition to the cost of the gas and delivery. Factoring in the monthly rental fee for the cylinder, a lecture bottle could be much less expensive over time. Especially for optics like UV sources where you may only use it a few times a year.
In the US, Matheson provides a wide assortment of specialty gases in lecture bottles. Matheson also has a worldwide distribution network.
Gas regulators are available from these companies as well as from Grainger. Be sure to specify the type of connection on the gas bottle when you order it and also to order the correct connection on the regulator. For best results, insert a valve between the regular and the outlet line. Finally, you also will need to pump out the line and regulator before opening the gas bottle as otherwise your gas will become contaminated with air.
This procedure will explain how to replace the channel plates (technically, they are Chevron plates) in the MCD detector used on Physical Electronics (PHI) 5600, 5700 and 5800 X-ray Photoelectron spectrometers. You may also want to check out our blog post on checking the MCD pins continuity.
Set up a work area with some aluminum foil and lint free cloths.
Vent the system.
Mark the MCD feedthrough flange to confirm the orientation of the flange when you replace it later.
Mark flange
Remove most of the bolts and nuts that secure the MCD feedthrough flange to the analyzer. The MCD feedthrough flange has some springs on the inside so there will be some tension when you remove the flange. There are 3 studs that are used to guide the MCD feedthrough flange when it is removed or installed.
Remove the last few nuts or bolts and carefully lower the MCD feedthrough flange and place it on the aluminum foil. Incidentally, most food grade aluminum foil has oil on it. If possible, use UHV compatible foil when working with electron optics.
Remove MCD feedthrough flange
The MCD assembly is located inside the 6″ CF flange where you just removed the MCD feedthrough flange from. You can remove one of the analyzer braces in order to gain better access to the MCD assembly.
MCD assembly
At this point put on a pair of gloves as you will be working inside the analyzer and want to prevent oil contaminator from your hands. Use tools that have been cleaned with Isopropanol or Methanol.
Remove the screw that holds the capacitor in place.
Remove capacitor screw
Remove the capacitor by pulling on the pin that is connected to the MCD assembly. Do not pull on the capacitor. The pin wire is silver soldered to the capacitor and it can come off easily, so be very careful with the capacitor.
Remove capacitor by pulling on the pin connector
Remove the POS and NEG pins from the MCD assembly. Just pull up on the pins, keep the wires attached to the SHV feedthrough pins.
Remove POS and NEG pin connectors
The MCD assembly is held in place with 2 slotted screws. Remove one of the screws completely. Be careful as it is easy to drop.
Loosen the second screw and then reach up and hold the MCD assembly as you remove the screw. Ease the MCD assembly down and out of the 6″ CF flange.
Remove MCD assembly
Set the MCD assembly on a clean working surface.
Pull up on the pins and insert a small Allen wrench or rod to hold the pins in place. The pins are spring loaded and by inserting a small Allen wrench or rod into the holes in the pins, that will prevent the pins from contacting the plates or 16 channel ceramic when replacing the plates.
Insert Allen wrenches or rods
Remove the two inner slotted screws.
Remove inner two screws
Hold the MCD assembly as you rotate it 180 degrees so that the grid screen is facing up.
Hold together and rotate so that grid is facing up
Remove the grid screen. Set it to the side.
Remove the grid screen
Remove the ceramic. Set it next to the grid screen. As you remove parts, set them down next to each other in sequence. That will make it easier to reassembly the parts in the correct order.
Ceramic with grid screen removed
Remove the gold spacer. Sometimes that part will stick to the bottom of the ceramic.
Ceramic and gold spacer removed
Remove the Teflon tubes
Remove the Teflon tubes
Remove the top plate.
Remove the top plate
Remove the second plate. Note that the plates have a little dot on them. Those dots need to face each other. So, the bottom plate has the dot facing up, and the top plate has the dot facing down.
Dot on plate, near the holeRemove the bottom plate
Use some clean air or nitrogen to blow off the 16 channel ceramic. Feel free to dust off the MCD assembly and plates frequently. Dust is to be avoided as much as possible.
16 channel ceramic
Install the new bottom plate. It sits on the gold spacer which is on top of the 16-pin ceramic. The hole in the plate needs to line up with the pin. The pin is centered in the hole in the plate. The little dot on the plate needs to face up.
Install bottom plate. Dot up.
Install the new top plate. The dot needs to face down and the pin should be centered in the hole in the plate.
Install top plate, dot facing down
Install the gold spacer. The tab on the spacer should be above the pin.
Install gold spacer. Tab over pin.
Install the Teflon tubes.
Install Teflon tubes
Install the ceramic over the Teflon tubes. The top of the tubes should be flush with the ceramic.
Install ceramic
Set the grid screen on top of the ceramic.
Position grid screen
While holding the grid screen and ceramic in place, rotate the MCD assembly 180 degrees so that the pins face up. Since the screw are not get installed, the only thing holding the grin screen and ceramic in place is you.
Rotate MCD assembly so that pins face up
Install the two screws to secure the grid screen. You may need to rotate things just a little bit. Tighten the screws firmly but not too tightly or you may crack the ceramic.
Install screws
Remove the Allen wrench or rods from the pins. Rotate the pins a little bit to make sure that they are seated.
Remove Allen wrenches or rods from pins
Measure the resistance between the POS and NEG pins. You should have 15 to 24 meg ohms. From the other pin to POS or NEG should be about 1 Meg ohm.
Measure resistance between POS and NEG
The MCD assembly is now ready to install back into the analyzer.
Before you insert the MCD assembly, prepare one of the screws for mounting. A pronged grabber works well as does a starter screw driver. In a pinch you can use a regular screw driver with a little bit of tape to hold the screw on. The tape needs to stick to the screwdriver so that it all comes out when you remove the screwdriver.
Insert the MCD assembly (it can only go in one way or else the screw will not line up) and rotate it slightly to make sure that it is seated properly. Tighten the one screw to where it is just snug.
Install the second screw and tighten it to where it is just snug.
Slightly rotate the MCD assembly to make sure that it is seated properly and then tighten both screws firmly.
Reconnect the POS and NEG pins. Refer to the drawing to make sure that you do not insert the pins backwards. Also make sure that the POS and NEG wires are centered as the MCD feedthrough flange will need to clear the POS and NEG pins.
POS and NEG pin to SHV connectors
Insert the capacitor pin. Be careful not to stress the capacitor.
Reattach the capacitor wire screw and tighten the screw. The capacitor should be perpendicular (not tilted) as the MCD feedthrough flange will need to clear it.
POS, NEG and capacitor reconnected
Remove the used 6″ copper gasket.
Install a new 6″ copper gasket on the MCD feedthrough flange.
Carefully line up the MCD feedthrough flange and slide it onto the 3 guide studs. Install the 3 nuts to hold the MCD feedthrough flange in place and then slightly rotate the flange to make sure it is seated. The springs on the MCD feedthrough flange fit into the 16 holes in the MCD ceramic and press against the metal discs which in turn make contact with small capacitors inside the MCD assembly.
Install the bolts and lightly tighten the MCD feedthrough flange.
Measure the capacitance of all of the pins on the MCD feedthrough with respect to the vacuum chamber. The four center pins should read approximately 100 pf (open). All of the other pins should read 250 to 300 pf. If not, you need to drop the MCD feedthrough flange down and inspect to see where it is hanging up. Sometimes the spring pins do make contact with the MCD assembly and need to be adjusted slightly.
Once you have the correct capacitance on all of the pins, tighten all of the nuts and bolts.
The vacuum chamber is ready to pump down and baked.
Installation complete.
Note: Set the MCD multiplier voltage to 1800V in the software so that after the bake out you start outgassing the new plates at a lower operating voltage.
