The analytical spatial resolution and surface sensitivity of EDS analysis in the SEM is fundamentally limited by the interaction volume of the electron beam with the sample. We discuss applications enabled by large solid angle EDS detectors operated at low-kV and a new windowless detector that uses low noise electronics and a high resolution 100mm2 SDD sensor together with a new detector geometry to achieve sub 10-nm analytical resolution in the SEM with previously unmatched sensitivity.
The significantly improved sensitivity of this new detector enables the analysis of nanoparticles in the SEM. Using automated particle analysis we can correlate the electron image with an EDS map of the area. This way, the particle size distribution can be measured from the less noisy, higher resolution electron image. As every pixel in the electron image is correlated to a full X-ray spectrum in the EDS map, the software can reconstruct the X-ray spectrum for each particle in order to confirm the particle composition and particles below 5nm are clearly resolved.
Excellent results can also be achieved with very thin layers. As an example we show mapping of a heterostructure comprising a WSe2 layer and a MoS2 layer. Despite monolayer thicknesses, both the WSe2 layer and the MoS2 layer can be mapped and their thickness accurately determined using AZtec LayerProbe.
Analysis of TEM lamellae in the FIB-SEM using this new detector allows the identification of defects at high resolution on the surface and also enables high resolution analysis of the lifted-out lamella. The lamella thickness as well as the amount of ions implanted during the milling process can be measured using EDS; this allows in-situ monitoring of the lamella quality before going to TEM.
These applications demonstrate how SEM-EDS can contribute to nano-characterisation studies previously limited to TEM and Auger/XPS.