In this work, we investigate the influence of the molecular weight of poly(methyl methacrylate) (PMMA) thin films coated on silicon wafer on the time-of-flight secondary ion mass spectrometry (ToF-SIMS) sputtering mechanisms and kinetics during depth profiling using low-energy monoatomic caesium ions. The sputtering yield volumes are determined as function of molecular weight, film thickness and beam energy. The results show that the sputtering yield volume decreases with increasing molecular weight M_w down to a threshold value below which it becomes nearly constant, as previously observed with argon cluster ions. The relevance of physical parameters such as the glass transition temperature T_g—determined here from ellipsometry measurements—and the entanglement of the polymer chains to account for this behaviour is discussed. The variation of the sputtering yield was also found to vary logarithmically with the primary beam energy. In addition, preliminary experiments carried out using a low molecular weight PMMA (4 kg/mol) evidenced a nanoconfinement effect similar to that observed with argon cluster sputtering but of lower magnitude.

中文翻译：

---

分子量对使用低能 Cs+ 溅射的 PMMA 薄膜深度轮廓的影响

在这项工作中，我们研究了涂覆在硅片上的聚甲基丙烯酸甲酯 (PMMA) 薄膜的分子量对深度剖析过程中飞行时间二次离子质谱 (ToF-SIMS) 溅射机制和动力学的影响使用低能单原子铯离子。溅射产量体积被确定为分子量、薄膜厚度和束能量的函数。结果表明，溅射产额体积随着分子量M _{w 的}增加而降低至阈值，低于该阈值它变得几乎恒定，如先前用氩簇离子观察到的。玻璃化转变温度T _g等物理参数的相关性——此处由椭圆光度法测量确定——并讨论了聚合物链的纠缠以解释这种行为。还发现溅射产额的变化与初级束能量呈对数变化。此外，使用低分子量 PMMA (4 kg/mol) 进行的初步实验表明，纳米限制效应类似于使用氩簇溅射观察到的效应，但幅度较低。