PARALLEL EELS ELEMENTAL MAPPING IN SCANNING-TRANSMISSION ELECTRON-MICROSCOPY - USE OF THE DIFFERENCE-METHODS

The feasibility to obtain semi-quantitative elemental maps with a STEM microscope from first or second difference recorded PEELS spectra is demonstrated. These methods called "FD or SD methods" have been already used for the local quantitative analysis of trace elements. It has been shown that it can be a powerful technique to overcome the problems related to the background subtraction and inhomogeneous responses of adjacent diodes in PEELS spectra and also to greatly improve the detectability of the elements. We extended this technique to create semi-quantitative multi-element maps on biological material. The experiments are done with a 300 kV STEM (C.M. 30 Philips) coupled with a GATAN PEELS and an EDAX computer. A software developed on a host computer allows the control of the STEM probe position and the acquisition of energy shifted EELS spectra for each pixel. By comparing elemental maps obtained, with the conventional method (power law background generation and subtraction above the edge), and with the difference methods we demonstrate both the validity and the advantages offered by FD and SD methods to create multi-elements semi-quantitative maps.