XPS: PHI VersaProbe 1
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.
We have a PHI VersaProbe 1 Scanning XPS Microprobe. This system allows for high sensitivity elemental surface composition measurements and high-resolution binding energy chemical shift measurements of solid samples under high vacuum. It uses Al(Kα) radiation (1486 eV) and is equipped with an argon ion sputter gun to clean the sample surface or do depth profile analysis. In addition to argon ion sputtering, the PHI VersaProbe 1 is equipped with a C60 cluster ion sputtering gun for depth profiling of polymer and organic films with minimum ion impact modification to the surface.
- Detection limits (all elements except H and He): ~ 0.01 monolayer, or ~ 0.1% bulk
- Measurement depth: 10 - 50 Å;
- Spot sizes: 10um - 100 um or 1400 um x 300 um with High Power setting.
- Sample size: 0.1 mm to ~5 cm dia. x 5 mm thick
- Spectrometer: Monochromatized Al(Kα) 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 or adhesives onto standard fixtures. It is useful to know in advance if the sample is conducting.
The VersaProbe 1 is in the process of being replaced with a new instrument. Only legacy users may use this tool. All XPS needs, including samples requiring vacuum transfer capability, can be satisfied with the VersaProbe 3 XPS.
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.