Soft Matter and electron sensitive materials
One of the research lines at the Advanced Microscopy Laboratory relies on the study and development of multiple approaches for the observation of porous solids. Nanoporous materials, commonly zeolites (pore size below 2 nm), mesoporous materials (pore size ranging from 2 to 50 nm) and metal organic framework (MOF) solids, which consist of metal ions or clusters coordinated to organic molecules have displayed countless applications in fields such as petroleum refining and petrochemistry, drug delivery systems, water/air treatment or gas storage materials. All these properties rely on the exploitation of the intracrystalline pore network and on the introduction and location of guest elements within the framework systems. In many cases, due to the complexity of the structures formed in addition to the high degree of information required (up to atomic level) electron microscopy is the only method powerful enough for the characterization of these nanostructures. The main drawback for the observation of these materials has been the extremely high beam sensitivity of these solids in the electron microscope. In our laboratory we have successfully controlled the microscope conditions in STEM mode which combined with the spherical aberration corrector and obtained truly atomic resolution images of several materials1.
STEM-HAADF images and the correspondent model of silver loaded zeolite A, LTA type. The brightest signal corresponds to the Ag atomic columns (in grey in the model).
a) and b) STEM-HAADF images of a mesoporous network where enzymes have been allocated inside the pores. c) Compositional map representing the different content between the pores and the walls corroborating the presence of the enzyme.
1 Mayoral, A., Carey, T., Anderson, P. A., Lubk, A. & Diaz, I.
Atomic Resolution Analysis of Silver Ion-Exchanged Zeolite A.
Angew. Chem. Int. Ed. 50, 11230-11233 (2011).
Owing to the great resolution achievable, especially with the aberration corrected microscopes, a research line has been devoted in to the atomic observation of metal nanoparticles. Studies on shape and structure have been a great topic of interest over the last 50 years. It is well-known that nanoparticles may adopt different structures from their bulk form and their applications are strongly related to their atomic distribution. By combining atomic resolution imaging with image analysis and spectroscopies techniques we analyze magnetic and noble metal nanoparticles as well as different alloys which display a combination of properties.
Aberration corrected STEM image recorded in the probe corrected Titan of a FeCoO, left, nanoparticle (inset the atomic distribution of atoms). Right: Thermal colored image of a decahedral gold nanoparticle, core, coated with a disordered layer of silver.