| AVS 60th International Symposium and Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS-WeA |
| Session: | Developments in Electron Spectroscopies for Non-Ideal Samples 2 |
| Presenter: | S.J. Coultas, Kratos Analytical Limited, UK |
| Authors: | S.J. Coultas, Kratos Analytical Limited, UK J.D.P. Counsell, Kratos Analytical Limited, UK S.J. Hutton, Kratos Analytical Limited, UK A.J. Roberts, Kratos Analytical Limited, UK C.J. Blomfield, Kratos Analytical Limited, UK C. Moffitt, Kratos Analytical Limited, UK D. Surman, Kratos Analytical Limited, UK |
| Correspondent: | Click to Email |
The concept of high energy X-ray sources for laboratory based XPS analysis has been around for a long time. The often cited work by Yates and West was published thirty years ago [1]. However, it is still rare to find data in the literature recorded using X-ray sources other than Al Kα or Mg Kα. In this paper we attempt to illustrate the usefulness of the Ag Lα source for a variety of sample types.
After Al Kα, Ag Lα is probably the most practical monochromatic source for standard laboratory based XPS instrumentation as it utilises the second order diffraction of the same quartz crystals as used for Al Kα. This allows it to be easily accommodated on a modern spectrometer.
The photon energy of Ag Lα is 2984.2 eV, approximately twice that of Al Kα (1486.6 e). This greater energy leads not only to the excitation of additional, higher binding energy, core lines for some elements (Table 1) but also the possibility of analysis of deeper layers due to the decrease in attenuation length with increasing photoelectron energy [2]. For example, the ineleastic mean free path (IMFP) of C 1s, binding energy 285 eV, using Al Kα X-rays is 3.14 nm at a kinetic energy (KE) 1201 eV, but for Ag Lα this is increased to 5.89 eV at KE 2699 eV [3].
In this work we present examples of sample analysis where the consequences of using a higher energy excitation source have been exploited. Examples of using higher binding energy core lines, such as Si 1s and Hf 3d, are presented together with applications utilising the greater information depth available from the source. We have studied samples using both spectroscopy and imaging and explored the depth dimension by ARXPS and depth profiling.
Table 1: Elements with core line binding energies in the range of Ag Lα X-rays but not Al Kα (*at least one half of doublet)[4]
| Core Line | Element |
| 1s | Al Si P S Cl |
| 2s | As - Mo |
| 2p | Br - Ru |
| 3s | Pr - Re |
| 3p* | Sm - Tl |
| 3d* | Tm - Rn |
References
[1] K Yates & RH West, Surf. Interface Anal., 1983, 4, 5
[2] MP Seah & WA Dench, Surf. Interface Anal., 1979, 1, 2
[3] www.nist.gov/srd/nist71.cfm
[4] X-Ray Data Booklet LBNL/PUB-490 Rev.2 Jan 2001