Paper AS-TuM1
Important Variables in Polymer Analysis with Cluster Beams

Tuesday, October 21, 2008, 8:00 am, Room 207

Metrology to monitor the surface and in-depth compositions in polymeric materials is important for several applications spanning drug delivery and tissue engineering to microelectronics applications (e.g. photoresists, conducting polymers and dielectric materials). With the advent of cluster Secondary Ion Mass Spectrometry (SIMS), we have shown that one can obtain spatially resolved surface and in-depth molecular information from several polymer systems with depth resolutions on the order of 8-10 nm. However, this technology still has several limitations for polymeric depth profiling. For example, some polymers are more amenable to depth profiling with cluster SIMS than others, while still others experience extensive beam-induced degradation (e.g. polystyrene and polyethylene) resulting in total loss of signal. Described here are our recent efforts at NIST to better understand and define the parameters for successful polymeric depth profiling. For example, temperature has been repeatedly demonstrated to play a crucial role in polymeric depth profiling for both C₆₀⁺ and SF₅⁺ sources.^1-3 We also have discovered that different beam chemistries yield different results (e.g. SF₅⁺ sources has a limited erosion depth as compared to C₆₀⁺). Other important parameters include oxygen flooding, beam energy and angle, and the stereochemistry of the polymer. Much of what we observe stems from basic radiation chemistry of polymers.

¹ Mahoney, C.M.; Fahey, A.J.; Gillen, G. Anal. Chem. 2007, 79(3), 828-836.
² Mahoney, C.M.; Fahey, A.J.; Gillen, G.; Xu, C.; Batteas, J.D. Anal. Chem. 2007, 79(3), 837-845.
³ Mollers, R.; Tuccitto, N.; Torrisi, V.; Niehuis, E.; Licciardello, A. Applied Surface Science 2006, 252, 6509-6512.