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SIMS21, Poland 2017 - Heng-Yong Nie abstract

Heng-Yong Nie oral presentation (FN2-Tue1-1-2)

The Selection of C4H¯ for Intensity Normalization for CnH¯: a Principal Component Analysis

Heng-Yong Nie1,2

1 Surface Science Western, The University of Western Ontario, 999 Collip Circle, N6G 0J3 London, Canada
2 Department of Physics and Astronomy, The University of Western Ontario, , N6A 3K7 London, Ontario, Canada

Negative hydrocarbon ions CnH¯ are ubiquitous in time-of-flight secondary ion mass spectrometry (ToF-SIMS), but their utility might have been overlooked. Recently, however, it has been demonstrated that the ion intensity ratio between C6H¯ and C4H¯ is capable of differentiating the chemical structures of polyethylene, polypropylene, polyisoprene and polystyrene [1], as well as depth profiling the cross-linking degree of poly(methyl methacrylate) [2]. This intensity ratio increases with increased “carbon density” of the polymers. In order to understand why C4H¯ can be used as the reference ion, we applied principal component analysis (PCA) to analyze the relationships among the CnH¯ intensities for the four polymers. Our PCA results revealed that higher and lower "carbon density" polymers favor the formation of larger and smaller CnH¯, respectively. PCA also verified that the variation of C4H¯ intensity is relatively small in comparison with those of the other CnH¯ intensities. Assisted with the PCA results, we demonstrate that CnH¯ are useful in differentiating chemical structure of polymers.

[1] H.-Y. Nie, J. Vac. Sci. Technol. B 34, 2016, 030603.

[2] S. Naderi-Gohar, K. M. H. Huang, Y. L. Wu, W. M. Lau and H.-Y. Nie, Rapid Commun. Mass Spectrom. 31, 2017, 381-388