ToF-SIMS analyses of polystyrene and dibenzanthracene: Evidence for fragmentation and metastable decay processes in molecular secondary ion emission
ToF-SIMS analyses of polystyrene and dibenzanthracene: Evidence for fragmentation and metastable decay processes in molecular secondary ion emission
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DOI：
10.1016/s0039-6028(97)00070-8
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发表时间：
1997-06-01
期刊：
影响因子：
1.9
通讯作者：
Bertrand, P
中科院分区：
文献类型：
--
作者：
Delcorte, A;Segda, BG;Bertrand, P
为了了解不饱和聚合物的溅射过程，用 15 keV Ga+ 离子轰击二苯并蒽和聚苯乙烯样品，并通过飞行时间光谱仪对二次离子进行质量和能量分析。研究了各种现象的影响，这些现象可能在聚苯乙烯表面的二次离子发射中发挥重要作用：（1）“原始”碎片的发射，反映了聚合物结构； (2) 裂解、重排或氢损失的排放； (3)通过氢或质子捕获形成分子离子； (4)二次离子的单分子解离。选择二苯并蒽分子 (C22H14) 作为模型化合物，用于研究静态 SIMS 分析条件下多环芳烃 (PAH) 离子的发射和亚稳态衰变。从二苯并蒽溅射出的大多数二次离子的动能分布（KED）最多呈现三个峰。与负表观能量相对应的峰值是由于光谱仪加速部分中较大离子的亚稳态分解造成的。详细讨论了它们的起源，即延迟的 H 和 H-2 丢失反应。将二苯并蒽二次离子的动能分布与聚苯乙烯发射的 PAH 离子的动能分布进行比较，特别是在 PS 质谱的 m/z = 100-200 区域。事实证明，可以对聚苯乙烯提出类似的解释。为了确认聚苯乙烯的氢损失反应，还与从氘化 PS 溅射的类似但氘化 PAH 离子的 KED 进行了比较。根据这些氢损失反应，计算子离子的形成时间。 (C) 1997 Elsevier Science B.V.
To understand the sputtering processes in unsaturated polymers, dibenzanthracene and polystyrene samples were bombarded by 15 keV, Ga+ ions and the secondary ions were mass- and energy-analyzed by means of a time-of-flight spectrometer. The influence of various phenomena, which may play an important role in the secondary ion emission from polystyrene surfaces, is investigated: (1) emission of ''original'' fragments, reflecting the polymer structure; (2) emission with fragmentation, rearrangements or hydrogen losses; (3) formation of molecular ions by hydrogen or proton capture; and (4) unimolecular dissociation of the secondary ions. The dibenzanthracene molecule (C22H14) was chosen as a model compound for the study of the emission and metastable decay of polyaromatic hydrocarbon (PAH) ions under static SIMS analysis conditions. The kinetic energy distribution (KED) of most of the secondary ions sputtered from dibenzanthracene exhibits up to three peaks. The peaks corresponding to a negative apparent energy are due to the metastable decomposition of larger ions in the acceleration section of the spectrometer. Their origin, i.e. delayed H and H-2 loss reactions, is discussed in detail. The kinetic energy distributions of the dibenzanthracene secondary ions are compared with those of the PAH ions emitted from polystyrene, especially in the region m/z = 100-200 of the PS mass spectrum. It turns out that similar interpretations can be proposed for polystyrene. To confirm the hydrogen loss reaction in the case of polystyrene, the comparison is also made with the KED of similar but deuterated PAH ions sputtered from deuterated PS. On the basis of these hydrogen loss reactions, the formation times of the daughter ions are calculated. (C) 1997 Elsevier Science B.V.