科研之友
微信
新浪微博
Facebook
分享链接
摘要
Secondary ion mass spectrometry, SIMS, is a method of choice for the characterization of nanoparticles, NPs. For NPs with large surface-to-volume ratios, heterogeneity is a concern. Assays should thus be on individual nano-objects rather than an ensemble of NPs; however, this may be difficult or impossible. This limitation can be side-stepped by probing a large number of dispersed NPs one-by-one and recording the emission from each NP separately. A large collection of NPs will likely contain subsets of like-NPs. The experimental approach is to disperse the NPs and hit an individual NP with a single massive cluster (e.g., C-60, Au-400). At impact energies of similar to 1 keV/atom, they generate notable secondary ion (SI) emission. Examination of small NPs (a parts per thousand currency sign20 nm in diameter) shows that the SI emission is size-dependent and impacts are not all equivalent. Accurate identification of the type of impact is key for qualitative assays of core or outer shell composition. For quantitative assays, the concept of effective impacts is introduced. Selection of co-emitted ejecta combined with rejection (anticoincidence) of substrate ions allows refining chemical information within the projectile interaction volume. Last, to maximize the SI signal, small NPs (a parts per thousand currency sign5 nm in diameter) can be examined in the transmission mode where the SI yields are enhanced similar to 10-fold over those in the (conventional) reflection direction. Future endeavors should focus on schemes acquiring SIs, electrons, and photons concurrently.
- 出版日期2015-8
