Cluster secondary ion mass spectrometry imaging of interfacial reactions of TiO₂ microspheres embedded in ionic liquids

Rationale Our goal is to develop protocols for the elucidation of the identity and structure of reaction products embedded in a reaction medium. Results should find significance in a variety of disciplines ranging from the study of biological cells and tissues, to the steps associated with the functionalization of nanoparticles. Methods We utilize cluster secondary ion mass spectrometry (cluster-SIMS) to acquire three-dimensional (3D) information about 5-30 μm TiO₂ microspheres imbedded into an ionic liquid. The method allows molecular depth profiling with submicron spatial resolution and depth profiling with a resolution of several tens of nanometers. The ionic liquid matrix enshrouds the spheres, allowing them to be introduced into the vacuum environment of the mass spectrometer. Results The results provide 3D chemical information about these microspheres as they are synthesized by interfacial sol-gel reactions. We show that with 40 keV C₆₀⁺, it is possible to Erode through the reaction medium and map the distribution of those embedded TiO₂ microspheres. Moreover, we demonstrate that it is possible to monitor surface modification of the particles and, via ion beam drilling, elucidate their internal structure. Conclusions Using cluster-SIMS imaging, we are able to elucidate the identity and structure of reaction products embedded in a reaction medium, a problem of long-standing interest for materials characterization. With this strategy, we have provided a new approach that may be especially useful for the characterization of biological tissue and cells within the vacuum confines of the mass spectrometer.