XPS: PHI VersaProbe 3
XPS provides elemental and chemical information about the surface region (first 1- 30 monolayers) of nearly any solid material. XPS is useful for determining the elemental composition on the surface of all non-volatile materials semiquantitatively. It is sensitive to all elements except H and He and also provides some chemical information about the valence state of elements. XPS is sensitive to the top 5 nm of a sample, but it can be used to provide elemental composition as a function of depth by analyzing a sample while removing surface layers by ion etching. XPS is useful for chemically sensitive materials since damage from the x-ray beam is minimal. It is particularly useful for insulating materials such as polymers, oxides, and powders were charging effects limit other surface techniques.
Basic theory of operation: In XPS, soft x-rays (1486 eV for our instrument) illuminate a region of the sample being analyzed, and photolelectrons emanating from it are energy analyzed. From the energies detected, the elements present and sometimes their chemical state (valence) can be determined. Because only atoms near the surface of the sample emit electrons that escape without losing energy, the technique is very surface sensitive.
- Compositional Analysis: Atomic abundance of all elements (except H and He) on insulators, powders, metals, etc.
- Chemical Analysis: Identifies bonds between specific atoms in the surface region. Polymers, oxides, etc. characterized.
- Depth Profiles: Characterizes buried regions as they are exposed by ion etching.
The PHI VersaProbe 3 XPS offers improved sensitivity over the VersaProbe 1 through greater signal collection for elemental surface composition measurements and high-resolution binding energy chemical shift measurements of solid samples under high vacuum. It uses Al(Ka) radiation (1486 eV) and is equipped with the following advanced features:
- Heating/Cooling Stage
- For controlled heating experiments from room temperature to 600C.
- For controlled cooling experiments (-140C) using liquid nitrogen.
- Some sample restrictions apply.
- Focused Ion Gun (FIG)
- Bombards sample with a focused beam of energized Ar ions.
- Provides surface cleaning and depth profile capabilities at various beam energies and raster sizes.
- Ar 2500+ Gas Cluster Ion Beam Gun (GCIB)
- Bombards sample with clusters of Ar ions at various beam energies.
- Provides surface cleaning and depth profiling with minimal sample damage and disruption to stoichiometry.
- Ideal for polymer samples and other samples easily damaged by traditional ion beam etching.
- Improved Angle Resolved XPS (ARXPS) with collection angle-limiting aperture.
- Intro Chamber Camera
- Records top-down image of sample before entry for sample registration and easy navigation.
- SmartSoft-VersaProbeTM Software
- For improved sample throughput and data collection efficiency.
- Spot sizes: 10um - 200um or 1400um x 100um with High Power setting.
- Sample size: 0.1mm to ~5cm dia. x 5mm thick
- Spectrometer: Monochromatized Al(Ka) Source; Vacuum ~ 1.2x10E(-7) Pa
Restrictions on samples: Samples must be solid and vacuum compatible. A sample can range in size from 0.1 mm in diameter and very thin to 5cm in diameter and 5mm thick. Powdered and other rough surfaced samples can also be analyzed. Samples are generally mounted using clips onto standard fixtures. It is useful to know in advance if the sample is conducting. Samples requiring air-free transfer will be directed to the VersaProbe 1 XPS instrument.
In order to become a qualified user on the PHI VeraProbe 3, you need to follow each of these steps in the order as listed here:
- Complete the process to become a lab member of SNSF and follow the instructions to activate a Badger account.
- Complete Axess STARS EHS-2470-WEB: COVID-19 Hygiene Best Practices.
- Join EdX and take all 9 parts of the PHI XPS VersaProbe III online training module, including all 9 quizzes.
- Click on this link and navigate to the XPS section, under Surface Characterization & Analysis
- Send an email to Juliet Jamtgaard to request training.
- One or more 1-on-1 trainings may be necessary for full qualification.
Training modules for the VersaProbe 3 XPS are now available on EdX. Anyone interested in general XPS information is welcome to take the first two modules in the XPS VersaProbe 3 series, which are entitled “Introduction to XPS” and “XPS: Background and Theory.”
To complete VersaProbe 3 training and qualification, there are 7 more modules and quizzes in the series. Please start with the link above and take the two introductory modules. Then, proceed to the remaining 7 modules and 7 quizzes listed under the “PHI VersaProbe III Remote Training at Stanford” heading. This 9-part series replaces the “group training” experience that was previously required as the first training step.
Once you have completed the 9-part series, the next step is one or more 1-on-1 sessions on the instrument with your own samples. These sessions will be competed using social distancing and media-based interaction.
XPS Background Info: There are numerous texts discussing the use of XPS. Some useful examples are:
- Electron Spectroscopy: Theory, Techniques and Applications. C. R. Brundle and A. D. Baker, eds. (a 5 volume series)
- Practical Surface Analysis, D. Briggs and M. P. Seah eds.
- Handbook of XPS, C. D. Wagner (published by Physical Electronics, Inc.)
- Or try http://www.york.ac.uk/org/esca/tech/xps.html