Analysis of the electron energy loss spectra of core-level electronic transitions, O K- and Ca L 2,3 -edges, combined with composition-sensitive annular dark field imaging shows that under electron-beam irradiation portlandite can easily be transformed into calcium oxide. The low-loss region of the energy loss spectra measured before and after transformation also supports the observations. Two possible mechanisms of the electron beam-induced modification of the specimen, radiolysis and knock-on damage, are discussed, and it was found that radiolysis is likely to be the primary mechanism for this transformation of Ca(OH) 2 into CaO, while some knock-on damage is also expected.
Bibliographical noteFunding Information:
This work is supported primarily by the Nanoscale Science and Engineering Initiative of the NSF EEC-0117770 and NYSTAR C020071. The sample preparation facilities and STEM are supported by NSF through the Cornell Center of Materials Research DMR 9632275. We would also like to acknowledge M. Thomas and E. Kirkland for technical support and S. Maccagnano for critical reading of the manuscript.