Tag Archives: X-ray photoelectron spectroscopy

CasaXPS – Data processing software for XPS

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X-ray Photoelectron Spectroscopy or XPS (also known as ESCA, an abbreviation for Electron Spectroscopy for Chemical Analysis), has become one of the most prevalent surface analysis techniques for the characterization of solid surfaces in vacuum.

XPS systems come with software. Frequently, however, the functionality isn’t sufficient to meet the needs of research scientists who routinely work with XPS spectra. CasaXPS (Computer Aided Surface Analysis for X-ray Photoelectron Spectroscopy) was created to provide the additional functionality that these scientists required.

The surface analysis system companies that currently sell CasaXPS include:

FOCUS – XPS

Hiden – SIMS

Kore Technology – SIMS

KRATOS -XPS

OMICRON -XPS

PREVAC -XPS

RBD Instruments –AES, refurbished XPS

SPECS – XPS

VG Scienta/GammaData Scienta – XPS

PHI, Thermo, and JEOL(XPS) do not sell CasaXPS directly. However, many surface scientists who run PHI, Thermo, and JEOL XPS systems use CasaXPS for their XPS data processing. In fact, CasaXPS is so prevalent that Google Scholar identified about 900 papers that cited CasaXPS last year alone! For large companies that have surface analysis systems from multiple manufacturers, CasaXPS is a great way to compare data sets from different instruments. A site license for CasaXPS (whether for a company or a university) is very reasonably priced.

CasaXPS is also a data browser for VAMAS (ISO 14976) Surface Chemical Analysis Standard Data Transfer Format. Spectra presented in this ISO standard can be viewed, processed, and printed or exported as ASCII in products such as Word or Excel. CasaXPS also provides data processing for AES, SIMS, and image files.

For CasaXPS training and support, instruction manuals are available as printed or by this link: http://www.casaxps.com/help_manual/

Polymer fitting information is available at this link: http://www.casaxps.com/help_manual/curve_fitting_polymers.htm

In the U.S. an annual training course on CasaXPS is provided by John Grant’s Surfaceanalysis.org. The 2013 Surface Analysis short course program in Dayton, Ohio, USA will be held at the Crowne Plaza Hotel, 8-12 April 2013.

The first 3 days of the course will be on X-ray Photoelectron Spectroscopy (XPS/ESCA) including Data Processing. It will cover these topics in detail (see the course description http://www.surfaceanalysis.org/xps_and_data_processing.html). Examples of Data Processing will be given throughout the course and will illustrate processing with many different software programs, including PHI Multipak, Thermo Avantage, Service Physics ESCA 2007, QUASES Tougaard, and CasaXPS. This 3-day course is not designed to teach users how to use these software programs, but to illustrate their applications to various aspects of processing XPS/ESCA data. A comprehensive set of notes on XPS/ESCA will be provided for each course participant. Early-bird registrants may also order an optional copy of the 900-page book “Surface Analysis by Auger and X-ray Photoelectron Spectroscopy,” edited by D. Briggs and J.T. Grant, 2003.

The last 2 days of the course will be hands-on training with CasaXPS for the processing of XPS/ESCA data (see the course description http://www.surfaceanalysis.org/casa.html). A complete 30-day trial copy of CasaXPS and appropriate XPS/ESCA data will be provided to attendees so they can follow the examples on their own laptops. Electronic copies of “An Introduction to XPS and AES” by Neal Fairley and a user manual will be provided as well. Attendees are encouraged to bring their laptops to the course. The software runs in a Microsoft Windows™ environment.

For more information on CasaXPS (and to view a video demonstration) please visit the RBD Instruments website at https://www.rbdinstruments.com/Products/CasaXPS.html

CasaXPS dialog box

Titanium sublimation pump operation

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The TSP (titanium sublimation pump) is used in conjunction with an ion pump to improve pumping efficiency.  It works by evaporating a titanium film onto the cryopanel or TSP shield. The titanium film is very reactive and so the gas molecules in the chamber that collide with the cryopanel wall will react with the titanium and stick. The titanium film also helps to replenish the ion pump elements.

On Physical Electronics surface analysis instruments such as X-ray photoelectron and Auger spectrometers, there are 4 filaments on the titanium sublimation pump flange. Since the lifetime of each filament is limited, having 4 filaments extends the time before needing to vent and replace the filaments.

When using a Boostivac or TSP control, I always recommend that you use the Cycle mode. The reason is that if you happen to get distracted while operating the TSP in the Continuous mode you may forget to turn the control off and could put much more titanium into the system than you planned on, and also burn up the filament.

To operate the TSP:

  1. Set to Mode switch to Cycle
  2. Press the Reset button (located under the Cycle Length Minutes knob).
  3. Turn up the filament current to just above 50 amps.  Note that the filament current will drop as the filament warms up. You want it to be at 50 amps after it warms up.
  4. Observe the chamber vacuum on the ion gauge control. The pressure in the chamber will come up as the filament heats up initially. Then, the pressure will drop as the TSP filament sublimates.
  5. After about 2 minutes the pressure will stop falling and start to rise again. At that point, turn the TSP control to OFF.  In the cycle mode, the filament will automatically shut off after about 2 minutes. But if left in the cycle mode it will turn on again once every 30 to 45 minutes (depending on what the cycle length time is set to).  It is better to turn the TSPs off when not in use in order to extend the filament lifetime.

Titanium sublimation pump

 

 

 

 

 

Common Questions

How often should I operate the TSP?

In general, unless you are pumping a high gas load you only need to use the titanium sublimation pump occasionally.  Many people will use them just once a week, on Friday afternoon so that the system can recover over the weekend for example.  If you are using them to help pump the chamber back down after being up to air, then they are used once every hour or so for the first few hours of the pump down process.  They should also be used after a bake out.

What vacuum do I need to be at before I use the TSPs?

You can use them starting in the mid 10-4 Torr range. In fact, they are very helpful at this vacuum level in helping start the ion pumps (which need to be in the low 10-5 or better vacuum to start). Typically the TSPs are operated after loading gassy samples to help the vacuum recover more quickly from the 10-8 Torr into the 10-9 Torr range.

How long do the TSP filaments last?

That depends on how often you use them, but on most vacuum chambers they will last for a year or more before all 4 filaments are burnt up. They should be replaced as part of any preventive maintenance program. Note that the filaments may not actually burn out before the titanium becomes depleted.  As the filaments are used up the maximum current that they will come up to is reduced. When they can no longer be driven up past 45 amps they are no longer effective and should be replaced.

Should I use the TSP filaments one at a time or rotate them?

My preference is to use them one at a time until that filament is shot and then move onto the next one. The exception is that I outgas all 4 filaments into the turbo pump for 2 to 3 cycles anytime that new filaments have been installed. Out-gassing the new TSP filaments into the turbo pump will significantly reduce the outgas load on the ion pumps.  Each time you vent the chamber you need to outgas the filaments into the turbo pump as part of the pump down procedure.

How to replace the filaments:

Replacing the filaments is very simple; there are only 2 things that you need to know:

  1. Make sure that the filaments face out from the center post on the TSP assembly. The reason is that the filaments should warp out of position away from the filament shaft. If you face them towards the shaft then the filaments will short out and melt when they warp. See the pictures below.
  2. Use pliers to hold the copper coupler when tightening the filament to the shaft to prevent the shaft from bending. You need to tighten the couple quite a bit to make sure that the filament does not loosen up as the filament heats up. Note that the copper couplers get soft from use and so you may need to replace them when you change the filaments.  If the coupler strips out it needs to be replaced.

TSP Filament orientation

 

 

 

 

 

 

 

 

 

Warped TSP filament

Warped TSP filament

 

 

 

 

 

 

 

RBD Instruments provides replacement titanium sublimation pump filaments, TSP flange assemblies and offers repair services for the Boostivac and TSP controllers.

Preventive maintenance

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While performing preventive maintenance on an X-ray photoelectron spectrometer recently I was reminded of how important the simple tasks are in preventing problems. On this particular system the card rack air filters were relatively clean and as a result of that, all of the boards in the card rack were dust free and clean. When we inspect the boards as part of a PM visit we often find that some of the components have attracted dust and dirt which in turn can cause arcing and damage on high voltage boards.

Here are some easy preventive maintenance tasks that you can perform yourself which will help to keep your X-ray photo electron, Auger electron spectroscopy or Secondary Ion Mass spectroscopy system running smoothly:

  1. Clean the air filters on a regular basis. Depending on how dusty your lab is, that could mean once a month or once every 6 months.  Be sure to turn the card rack power OFF and the fans OFF before you remove the air filters.
  2. Keep the temperature in the room that your system is located cool at all times. For older surface analysis systems, 68 degrees F (20C) or lower is ideal.  If the room temperature gets up to the mid to upper 70s F you can expect to have more component failures.
  3. Vacuum out the back of the electronics console and the inside of the electronic units the same time that you clean the air filters.
  4. Check the cooling fans in the electronics rack and inside any electronic power supply or control. If the fans are spinning slowly or not at all, replace them. Keeping air moving is very important for older electronics and can help to extend the lifetime of the electronic components inside.

These 4 simple tasks can prevent more serious problems from occurring. Then  hopefully the only maintenance that your system may need will be the occasional replacement of consumable parts such as ionizers, filaments and electron multipliers.

RBD Instruments always performs these simple tasks as part of a PM visit.  If you service your system yourself or have it serviced by another company, always insist that these tasks are performed during the preventative maintenance visit.  The pictures below filters that were removed from a system that had been on service contract with another company. Obviously they had not been cleaned in a long time!

dirty air filters

As the old Fram oil filter commercial in the 80’s said, you can pay me now or you can pay me later. The idea being that if you don’t change your automotive oil filter on a regular basis that it will end up costing you a lot more to fix your engine later. The same thing applies with any piece of expensive equipment. Do the simple preventive maintenance tasks on a regular basis and you will avoid most of the severe time consuming problems.

air filter locations