Chemical Phase Analysis of a Layered Structure

It can be advantageous to check hyperspectral images for the existence of chemical phases without applying prior knowledge. Bruker’s ESPRIT AutoPhase automatically finds specimen regions of similar composition by analyzing a HyperMap based on Principle Component Analysis of the spectra. The sensitivity of this procedure can be adjusted. The approach is demonstrated using a multi-layer structure in cross-section as an example.

The first image shows the quantitative mixed element map of the specimen, the second image shows some of the existing distinct chemical phases. Those can be found automatically by the AutoPhase procedure or by assigning particular specimen regions, which are to be treated as one chemical phase during further analysis of the complete map by the procedure. The composition of the phases found either way can be revealed and attributed to an existing specific substance, if a latter is known. The definition or “assigning” of the specimen regions to be used for phase analysis of the whole map can be based on prior knowledge about the specimen or based on information obtained by a first assumption less AutoPhase run.

For demonstration three interesting representative areas of the element map were assigned here after a first AutoPhase run. These areas are marked by two large rectangles and a smaller circular area. The result of the next AutoPhase run for the whole Map is shown in the second image. Two phases differing in Zn and Cd content, the actual interest of the study, defined from area 1 and area 3 were correctly located throughout the whole map. The carbon contamination on the sample surface caused by e-beam exposure was found and located correctly as another specific phase also in other places than previously assigned by area 2. The grey region on the left is apparently differently composed than the three pre-assigned phases and therefore could not be assigned. The layer on the right seems to contain similar species as the contamination spot assigned in region 2. Further refinement of the procedure by increasing the sensitivity could reveal more about possible differences between the spot marked as phase 2 and the layer on the right.

Combined element maps of a layered system in cross-section
Chemical phase map of a layered system in cross-section obtained by AutoPhase using pre-assigned regions of interest