INTERACTIVE IMAGE-SPECTRUM EELS - APPLICATION TO ELEMENTAL MAPPING OF LUBRICANT COLLOIDS

Image-spectrum EELS consists of acquiring series of energy-filtered images of a specimen with an energy-selecting TEM (or an imaging filter in general). Special software was developed for this application. It allows the immediate display of an energy-filtered image or an EELS spectrum to be obtained interactively. The main advantage of the method, compared to the spectrum-image EELS mode, is in the parallel detection of the image instead of that of the spectrum leading to a drastic decrease of the acquisition time (typically several hundred times faster). The total acquisition time for an experiment does not exceed five minutes for 256 images. To illustrate the capabilities of the method, the image-spectrum EELS method was applied to fast high resolution chemical mapping of elements (calcium, boron an oxygen) in the core of nanometer-scale colloidal particles. Results show that the composition of the micellar core could be studied in much greater detail than expected and a two-phase internal structure is proposed. Some limitations are due to the equipment at hand (low accelerating voltage of the electron gun, non-corrected filter for second-order aberrations, low dynamic range of the camera due to 8-bit digitization of the images). Despite these limitations, the performance in terms os spatial and chemical resolutions generally approached the theoretical predictions based on inelastic scattering theories for the TEM.