Mean free paths for inelastic electron scattering in silicon and poly(styrene) nanospheres

The mean free paths for inelastic electron scattering, λin, in silicon [Si] and poly(styrene) [PS] have been measured using off-axis electron holography in a field-emission transmission electron microscope (FEG TEM). The holographic imaging method determines both quantitative wave phase information as well as elastic energy-filtered wave amplitude information. Using the energy-filtered amplitude data, two-dimensional t/λin images are reconstructed. The present work uses spherical nanoparticles as samples, so the sample thickness at any point in a two-dimensional image can be calculated knowing the center and radius of the projected nanosphere. The thickness contribution to t/λin is removed to obtain quantitative λin values. This work finds values of λiSi=53.8±5.5 and 88.6±6.9 nm, and λiPS=78.1±3.4 and 113.0±5.9 nm for 120 and 200 keV incident electron energies, respectively.