This post will explain how to find the analyzer focal point on a PHI 5000 series XPS system and then align the system microscope to that point.
The general idea is that the lens on the SCA (spherical capacitive analyzer) has a very specific focal point where the highest counts, smallest analysis area, and best energy resolution can be obtained. By using a special slotted silver specimen that specific SCA focal point can be located and the system microscope and ion gun are then aligned to that same point. Once this procedure is performed then each time the sample is brought into focus on the microscope TV image the sample will be aligned to the analyzer focal point.
This procedure is written for the Physical Electronics 5000 series XPS instruments, but can be applied to other XPS instruments as well. In addition to this written procedure, there is also a video at this link: Finding the focal point of an XPS system.
Concept: The X-ray source illuminates the slotted silver sample and generates an XPS silver spectrum. The lens on the analyzer is set and the sample is moved while looking at the silver peak during a refresh alignment acquisition. By selecting progressively smaller lens areas and moving the sample, you can determine exactly where the focal point of the SCA is for the smallest analysis area.
If your system is equipped with a standard dual anode 15kV X-ray source, use it for the alignment and select it in the software hardware properties dialog box. If your system only has a mono source then you will need to use that as the source. It is more difficult to find the focal point with the mono source as the excitation area produced on the specimen is much smaller than the standard source.
- Load the slotted silver sample into the system. It should be mounted on a recessed sample mount. If you do not have a slotted sample mount then use washers to raise the slotted silver specimen up from the sample mount. The slits in the silver specimen should line up with the Y axis of the chamber (parallel with the analyzer lens).
- Position the silver sample so that it is about 0.65 inches from the end of the analyzer lens. This is approximately the correct Z height and is a good starting point.
- Lightly sputter clean the slotted silver sample with the largest possible raster size (10 mm X 10 mm on most systems).
- Set up an alignment acquisition on the silver peak: 375eV upper limit, 365eV lower limit, a high pass energy such as 187.75, eV per step of 1 and a time per step of 30 to 50mS. The pass energy for your system may be different, just use a large one that is about 150 to 200 eV.
- Select aperture 3 minimum area in the XPS hardware properties dialog box and also set the analyzer lens knob to 3. That will set the analysis area to 400 µM. Note: This part of the procedure is written for a 5500, 5600 or 5700 XPS system. If you have a 5400 then set the analyzer lens to 2 and select aperture 2 small area. For more information on the lenses for the different PHI analyzers refer to this link: phi-xps-lens-area-information
- If using the standard –x-ray source, turn the screw CCW on the X Y Z aligner until the nose of the X-ray source is as close as you can get without blocking the microscope TV image. If using a mono source do not move the source. If necessary, refer to the PHI user manual or contact RBD Instruments for information on how to align the monochromator if you are not sure it is properly aligned.
- Start the alignment acquisition and adjust the X and Y on the x-ray source for maximum counts on the 367.8 eV silver peak (standard dual anode source only, do not change any settings on the mono source).
- Move the silver specimen until you can determine that you are in the largest slit. When the analyzer lens is looking in the slit the silver peak counts will drop. Move to where you are in the corner of the slit. Since the analysis area on the lens is set to 400 µm and the largest slit is 1000 µm, the counts will drop to essentially zero when you are in the slit, and will come up to some maximum when out of the slit.
- Once you are certain that you have determined where the analysis area is on the largest slit, place an erasable mark on the TV monitor at that spot. This is your initial alignment location. You may need to adjust the microscope X and Y to get the image to match where you think you are looking at on the specimen.
- Next, move over to the 800 µm slit and confirm that the analysis area is where you think it is. Adjust the spot on the TV monitor if needed.
- Move into the 400 µm slit and adjust the Z height for the lowest counts when in the slit. For the 400 µm analysis area setting, the counts will drop by two thirds when in the slit – they will not go to zero. Once you have found the minimum count rate in the 400 µm slit Z height, then move over to the 400 µm hole and fine tune the X, Y and Z positions on the specimen stage for the lowest count rate when inside the hole. That should be about 30% of the maximum signal.
- Using the highest zoom on the microscope, adjust the camera focus ring and X Y positions so that the 400 µm hole is centered and in focus on the TV monitor.
- Now, we will repeat the procedure using the smallest aperture. In the XPS hardware properties dialog box select lens 1 minimum area. On the analyzer set the lens knob to position 1.
- For the 5500, 5600 and 5700 XPS systems, repeat this procedure using the 150 µm slit and hole. For the 5400 XPS systems, repeat this procedure using the 200 µm slit and hole.
- Once the focal point as been determined using the 150 µm hole, adjust the microscope focus ring (at the highest zoom), X and Y position so that the hole is centered and in focus. Only the center of the image will be in focus, the edges will be slightly blurred. TIP: Once the camera is in focus and tightened down, gently whack it a few times and see if the image comes back to the exact same place. If not, readjust and re-tighten until it stays in the same place when whacked. If it is not really tight then it may move when the system gets bumped and you will no longer be at the correct focal point. Also, by having it really tight then if you need to remove the microscope for a bake out the X and Y should stay pretty close, this will make the post bake-out alignment check easier.
The key to this alignment is to have a known good silver slotted specimen. Over time the silver coating on the specimen will wear away (from sputter cleaning) and although still coated, the silver may be very thin in some areas. That can give you a false minimum when adjusting the position of the slotted silver sample. RBD Instruments now provides these slotted silver samples for a fraction of what they cost elsewhere. At our low price, you can replace your old slotted silver sample with a known good one. You can get more information on our slotted silver sample at this link: slotted-silver-specimen-alignment-standard or by phoning us at 541 330 0723 X 310. For a limited time, mention this blog post and receive a 25% discount off the purchase price of any slotted silver specimen alignment standard.