AVS 60th International Symposium and Exhibition
    Applied Surface Science Monday Sessions
       Session AS+BI-MoM

Paper AS+BI-MoM1
Combining Gas Cluster Ion Beam (GCIB) and Angle-Resolved XPS (ARXPS) Depth-Profiling

Monday, October 28, 2013, 8:20 am, Room 204

Session: Organic Depth Profiling
Presenter: P. Cumpson, Newcastle University, UK
Authors: P. Cumpson, Newcastle University, UK
A. Barlow, Newcastle University, UK
N. Sano, Newcastle University, UK
J. Portoles, Newcastle University, UK
Correspondent: Click to Email

Over the last decade there have been progressive developments in analytical sputter sources within the surface analysis community[1]. These sources (moving from monoatomic ions, to polyatomic ions, to large gas cluster ions) have progressively reduced damage, but importantly gradually reduced the thickness of the damaged layer. With argon GCIB sources at low-to-medium energy-per-atom this depth should now be smaller than the inelastic mean free path (IMFP) for analysis by XPS for normal monochromated lab x-ray sources. This offers the prospect of seeing through the damage to produce XPS depth-profiles of polymer and other organic materials that are damage-free for the first time. Angle-Resolved XPS[2] has the potential to give information at each step in the sputter-depth profile so that the undamaged profile can be faithfully reconstructed.

We have a new XPS instrument that combines an argon GCIB source with a parallel-acquisition Angle-Resolved XPS analyser, meaning that we can acquire Angle-Resolved XPS spectra simultaneously from analytical points without tilting the specimen. This combination of GCIB and parallel-acquisition ARXPS is unique as yet, so far as we know. This instrument allows us to take angle-resolved spectra at each step of a GCIB sputter-depth profile, and reconstruct the surface concentration as a function of depth. Instrument performance has been reliable and very effective since the instrument was installed in January 2013.

We have developed numerical algorithms to “unfold” damage from GCIB/ARXPS depth-profiles. These are stable and virtually automatic. X-ray damage can be an important limiting factor[3] in the case of some specific polymer types, but we present some strategies to overcome this. Otherwise the almost automatic nature of GCIB/ARXPS depth-profiling (i.e. involving no time from an expert in interpretation of damage artefacts) suggests this combination of GCIB and ARXPS is a powerful technique for the surface analysis community, especially where (such as in organic electronics) electronic information is sought as function of depth, or cases where we start with very little a priori certainty about the structure of samples (as is often the case in analysing biological materials).

[1] S. Rabbani, A. M. Barber, J. S. Fletcher, N. P. Lockyer, and J. C. Vickerman, Anal. Chem. 83, 3793 (2011).

[2] PJ Cumpson, J Elec spectrosc 73 (1), 25-52 (1995)

[3] X-ray enhanced sputter rates in argon cluster ion sputter-depth profiling of polymers. P. J. Cumpson, J. F. Portoles, N. Sano and A. J. Barlow, J. Vac. Sci. Technol. B 31, 021208 (2013)