Abstract

The principle for determining the optical properties of materials from the low-loss electron energy-loss spectrum in the TEM has been known for many years. This technique promises the ability to identify the optical properties of particles and structures with a spatial resolution on the nano-scale. Moreover, the advent of monochromated electron sources and improved spectrometers have created the instrumental capabilities required for studying the energy-loss spectrum in the 1.8-3.1 eV energy-loss range corresponding to visible light. However, factors such as Cherenkov radiation and surface plasmon resonances create significant challenges for the application of this technique. Here, these challenges will be discussed with respect to the aim of determining the optical properties of sub-micrometre atmospheric light-absorbing carbon species, as will the reasons for the successful identification and optical property determination of atmospheric brown carbon spheres. Recognition of this aerosol species will be consistent with the aim of improving the assumptions and accuracy of aerosol data for climate models.