| AVS 61st International Symposium & Exhibition | |
| Applied Surface Science | Monday Sessions |
| Session AS+MC-MoM |
| Session: | Quantitative Surface Analysis |
| Presenter: | Peter Cumpson, Newcastle University, UK |
| Authors: | P.J. Cumpson, Newcastle University, UK A.J. Barlow, Newcastle University, UK J.F. Portoles, Newcastle University, UK N. Sano, Newcastle University, UK |
| Correspondent: | Click to Email |
Nondestructive depth-profiling by inversion of Angle Resolved XPS spectra[1] has been a desire in the XPS community for a long time. The lack of reference specimens with known structures has been a severe handicap in the development of the technique. Until now, reference materials with known depth-profiles have largely been confined to thin oxide layers on aluminium or silicon, and even these have uncertain carbon contamination layers. Progress has been made, though, with depth-profiling numerical methods[2] that need comparison with real known structures. It is difficult to fabricate structures with nanometre-scale variation in concentration with depth, and even more difficult to transport them without contamination (and the potentially damaging removal of such contamination).
We have developed protocols for the fabrication of two different samples, one organic and the other inorganic, with known depth-profiles in situ in XPS instruments;
Indium arsenide and PEDOT:PSS are both widely-available, almost atomically flat and sufficiently electrically conductive to ensure no sample charging occurs. Glancing angle monatomic sputtering of PEDOT:PSS leaves a PEDOT enhanced region at the surface, the spatial parameters of which depend only on sputter ion conditions under direct experimental control. Recently we have demonstrated the unexpected result that argon gas-cluster sputtering of InAs results in a thin, coherent metallic indium layer at the surface[3], the basis for InAs reference material structure.
The ill-posed nature of the inversion of ARXPS data means it is sensitive to small experimental uncertainties. We apply three different ARXPS algorithms, including regularization, to the data from these in situ reference structures. This gives a set of reference data that will allow comparison with results from any XPS work following the same preparation protocol. This should greatly improve confidence in the results of ARXPS depth-profiling.
[1] P J Cumpson, Angle-resolved XPS and AES: depth-resolution limits and a general comparison of properties of depth-profile reconstruction methods, J Electron Spectrosc. and Rel. Phenom. 73 (1995) 25-52.
[2] R W Paynter, Regularization methods for the extraction of depth profiles from simulated ARXPS data derived from overlayer/substrate models, J Electron Spectrosc. and Rel. Phenom. 184 (2012) 569–582.
[3] A J Barlow and P J Cumpson, Observed damage during Argon gas cluster depth profiles of compound semiconductors, submitted to J Appl. Phys.