Surface Science Western, Room G-1, WSC, The University of Western Ontario, London, Ontario N6A 5B7, Canada.
Anal Chem. 2010 Apr 15;82(8):3371-6. doi: 10.1021/ac100671q.
Condensed octadecylphosphonic acid (OPA) dimers, i.e., two OPA molecules combined with the loss of a water molecule, were detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) on OPA self-assembled monolayers (SAMs) that are only weakly bonded on the native oxide layer of a silicon wafer. In contrast, these condensed dimers were absent on OPA SAMs formed on the oxide layer of an aluminum film, where the OPA molecules are chemically bonded on the substrate through a P-O-Al linkage. These observations lead us to conclude that the OPA molecules in their SAMs have to be free from chemical bonding with the substrate in order for the primary ion beam to generate ion fragments of the condensed dimer. We demonstrate that the detection of condensed OPA dimers serves as an analytical criterion for TOF-SIMS to reveal the bonding mode of OPA molecules in their SAMs on different oxides.
凝聚十八烷基膦酸（OPA）二聚体，即两个 OPA 分子结合失去一个水分子，通过在硅片的自然氧化层上仅弱键合的 OPA 自组装单层（SAM）的飞行时间二次离子质谱（TOF-SIMS）检测到。相比之下，在通过 P-O-Al 键合与基底化学结合的铝膜的氧化层上形成的 OPA SAM 上则不存在这些凝聚二聚体。这些观察结果使我们得出结论，SAM 中的 OPA 分子必须与基底没有化学结合，以便初级离子束产生凝聚二聚体的离子碎片。我们证明，凝聚 OPA 二聚体的检测可作为 TOF-SIMS 的分析标准，以揭示其 SAM 中 OPA 分子在不同氧化物上的键合模式。
