Spectroscopic Imaging of Soft Materials

This aspect of our research concentrates on the development and application of new methods to quantitatively measure the morphology of polymers and biological materials at nanoscale spatial resolution in the Transmission Electron Microscope. Instead of using heavy-element stains to induce differential image contrast based on the elastic scattering of high-energy electrons, a common method well suited to particular problems but accompanied by a number of constraints, we use spectroscopic imaging and exploit differences in the inelastic electron scattering associated with different chemical or compositional features within a specimen. We can, for example, differentiate between water and most polymers, and, we can consequently map the spatial distribution of water in tissue and in synthetic polymers. Some examples are provided at the links given to the right.

Polymer-Polymer Interfaces in Aqueous Nanocolloids Bioresorbable Polymeric Scaffolds for Tissue Engineering

The basic aspects of this work center on the fact that soft materials are quite sensitive to the energetic electrons used in a transmission electron microscope. The total amount of incident electron dose used to collect spectra and image data must therefore be minimized to avoid irrevocably changing the specimen during the imaging experiment. The spatial resolution is thus determined not by the quality of the electron optics as in TEM studies of hard, inorganic materials where much current work concentrates on spherical aberration correctors and the like. Instead, we face so-called Dose-Limited resolution where the challenge centers on optimizing collection efficiencies and on our ability to extract statistically significant information from inherently noisy datasets. Over the past five years, the group has improved the spatial resolution from approximately 70 nm to our current limit of about 5 nm. Importantly, this level of spatial resolution is sufficient to solve a number of important morphological problems associated with complex polymers and biological structures.