AVS 56th International Symposium & Exhibition
    Applied Surface Science Wednesday Sessions
       Session AS-WeA

Paper AS-WeA8
A Case Study of Depth Profile Reconstruction from Parallel ARXPS Data by Application of a Genetic Algorithm : Characterization of a Novel, Low-Energy Plasma Treatment

Wednesday, November 11, 2009, 4:20 pm, Room C2

Session: Angle-resolved X-ray Photoelectron Spectroscopy
Presenter: R.G. White, Thermo Fisher Scientific, UK
Authors: P. Mack, Thermo Fisher Scientific, UK
R.G. White, Thermo Fisher Scientific, UK
J. Wolstenholme, Thermo Fisher Scientific, UK
E.H. Lock, Naval Research Laboratory
S.G. Walton, Naval Research Laboratory
D.Y. Petrovykh, Naval Research Laboratory and University of Maryland, College Park
Correspondent: Click to Email
Maximum entropy methods are often used to reconstruct depth profiles from angle resolved XPS data. Such methods typically rely on searching a vast parameter space for potential solutions, but in the past, it has been left to the analyst to decide when the optimum solution has been identified. An undesirable side-effect of this approach is that different analysts are likely to reconstruct different depth profiles from the same ARXPS data set. By contrast, depth profile reconstruction software based on a genetic algorithm rapidly samples many thousand potential solutions in the maximum entropy parameter space, but only reports the optimum result without input from the analyst,

This approach has been applied to characterize the surfaces generated by a new, low-energy plasma treatment. Polystyrene films, modified by a variety of plasmas, were analysed using parallel angle resolved XPS (PARXPS). An evaluation of different methods of ARXPS depth profile reconstruction was performed, comparing “boxcar” and “Cumpson” models with maximum entropy method results. The maximum entropy calculations employed the genetic algorithm to search for the optimum solutions. The non-destructively measured PARXPS profiles were compared with low-energy argon sputter profiles of the polymer surfaces.

Additionally, angle resolved reflection electron energy loss spectroscopy (AREELS) measurements were performed, giving depth-dependent information on the level of carbon unsaturation in the plasma-modified regions of the surface.

This work was supported by the Office of Naval Research.

E. H. Lock is NRL/NRC Postdoctoral Research Associate.