Journal of Synchrotron Radiation

Volume 19, Part 6 (November 2012)

research papers

J. Synchrotron Rad. (2012). 19, 976-987    [ doi:10.1107/S0909049512034486 ]

Accurate dosimetry in scanning transmission X-ray microscopes via the cross-linking threshold dose of poly(methyl methacrylate)

A. F. G. Leontowich, A. P. Hitchcock, T. Tyliszczak, M. Weigand, J. Wang and C. Karunakaran

Abstract: The sensitivity of various polymers to radiation damage by soft X-rays has been measured previously with scanning transmission X-ray microscopes. However, the critical dose values reported by different groups for the same material differ by more than 100%. Possible sources of this variability are investigated here for poly(methyl methacrylate) (PMMA) using controlled exposure to monochromatic soft X-rays at 300 eV. Radiation sensitivity, judged by several different criteria, was evaluated as a function of dose rate, pre-exposure thermal treatments and X-ray polarization. Both the measured critical dose and the dose required to initiate negative mode (cross-linking) were observed to depend only on dose, not the other factors explored. A method of determining detector efficiency from the dose required to initiate negative mode in PMMA is outlined. This method was applied to many of the soft X-ray STXMs presently operating to derive the efficiencies of their transmitted X-ray detectors in the C 1s absorption-edge region.

Keywords: poly(methyl methacrylate); STXM; radiation damage; dosimetry; detector efficiency.

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