CHARACTERIZATION OF NANOPARTICLES/NANOMATERIALS USING ELECTRON AND ION BEAMS

Nanoparticles are ubiquitous. The critical role of nanoparticles in our everyday lives makes increasing our knowledge of the properties and composition of these nanoparticles an important aspect of medical geology in addition to mineralogical, petrologic and geochemical research. Progressively decreasing particle sizes make characterization methodologies increasingly difficult and challenging. This paper presents advanced technology of nanoparticle characterization using electron and ion beams. Additionally, several examples utilizing such technologies in medical geology and related research will be discussed.

Among a variety of technology for materials characterization, electron microscopy is the most advanced, sophisticated and powerful technique used for the investigation of nanomaterials. The scanning transmission electron microscope (STEM), is a modern TEM with scanning capabilities that can reach a sub-angstrom spatial resolution below 0.05 nm when equipped with spherical and chromatic aberration correctors. At this resolution level, chemical bonds can be observed. The STEM may also be equipped with dispersive X-ray analyzer (EDS), electron energy loss spectroscopy (EELS) and energy image filter (EIF). The energy filter makes it possible to select electrons scattered by specific chemical elements and thus identify individual atoms of interest in the sample being studied. An example of using EELS and electron spectroscopic imaging (ESI) for a pathological study of the interaction of Gadolinium with affected tissue will be given.

Correct sample preparation for ultrahigh resolution EM poses an additional challenge. The focus ion beam (FIB) technique allows for localized preparation on a variety of materials. The latest FIB systems benefit from the combination SEM and FIB columns on the same chamber, enabling utilization of both. In suitably equipped instruments, cryogenically frozen samples can be prepared using FIB techniques, allowing for cross sectional analysis of samples containing liquids or fats, such as biological samples, pharmaceuticals, foams, inks, and food products. High resolution 3D image and elemental composition maps can be constructed using a series of thin sections cut by FIB and imaged by SEM and EDS. FIB can also be used for secondary ion mass spectrometry (SIMS).