Time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy protocol for the analysis of organic multilayers

Abstract

With the development in the early 2000s of new cluster ion sputtering sources, a reliable analysis of organic multilayers and interfaces has become possible. Nowadays, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) depth profiling are routinely used to investigate organic stacks. However, analysis beams can cause bond scission or beam-induced degradations that accumulate in buried layers. We developed a correlative protocol that minimises damages related to analysis beams. It uses a shallow angle bevel crater fabricated inside the ToF-SIMS analysis chamber. With this preparation method, the in-depth information is displayed over the surface of the bevel crater. XPS profiles and high-resolution spectra paired with ToF-SIMS images enable an easy identification of the organic layers and complete understanding of their chemistry. The reduction of beam-induced degradation is achieved by minimising the acquisition times, therefore beam exposure on materials. Finally, an important advantage of this preparation method is that the analysis can be performed on exactly the same spot by multiple techniques. Several ToF-SIMS and XPS acquisitions can be carried out with various parameters (investigation of backscattered Ar_n⁺ cluster ion fragments, tandem MS imaging…) as well as analysis with other techniques that possess limitations in spatial resolution and/or inaptitude to probe buried layers such as Raman or AFM.