Abstract
We examine laser-induced ion and neutral emissions from single-crystal CaHPO4·2 H2O (brushite), a wide-band-gap, hydrated inorganic single crystal, with 248-nm excimer laser radiation. Both laser-induced ion and neutral emissions are several orders of magnitude higher following exposure to 2 keV electrons at current densities of 200 μA/cm2 and doses of 1 C/cm2. In addition to intense Ca+ signals, electron-irradiated surfaces yield substantial CaO+, PO+, and P+ signals. As-grown and as-cleaved brushite show only weak neutral O2 and Ca emissions, whereas electron-irradiated surfaces yield enhanced O2, Ca, PO, PO2, and P emissions. Electron irradiation (i) significantly heats the sample, leading to thermal dehydration (CaHPO4 formation) and pyrolysis (Ca2P2O7 formation) and (ii) chemically reduces the surface via electron stimulated desorption. The thermal effects are accompanied by morphological changes, including recrystallization. Although complex, these changes lead to high defect densities, which are responsible for the dramatic enhancements in the observed laser desorption.
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