Electron energy loss spectroscopy investigation through a nano ablated uranium dioxide sample

A lamella of uranium dioxide (similar to 10 x similar to 10 x similar to 0.02-0.20 mu m) was produced by focused ion beam for transmission electron and electron energy loss spectroscopy (EELS) examinations. This sample allows quantitative analysis of the EEL spectra recorded for UO2 as a function of the thickness. The M, N, O and P edges were recorded over zero loss to 4000 eV loss. The edges allow reconstruction of the electronic transitions, the lowest energy loss edges for P transitions corresponds to P3 electron transition (17.2 eV) from U6p3/2 level. The edge analysis allows also better interpretation of the loss spectrum with identification of the plasmon peak of the core electron transition edges. In addition, the energy lost was studied through a range of thicknesses going from similar to 20 to similar to 200 nm to derive the electron mean free path and cross section for inelastic scattering in the plasmon part of the spectrum. The mean free path of inelastic electron for uranium dioxide is compared with that reported earlier for other oxides from Be to Bi and for 200 keV incidents electrons. The present study emphasises the potential of combining FIB and EELS for the analysis of actinide compounds. (C) 2013 Elsevier B.V. All rights reserved

Quantification of platinum deposition in polymer electrolyte fuel cell membranes

Platinum catalyst dissolution with subsequent reduction and deposition of Pt particles in the membrane can lead to a significant loss of polymer electrolyte fuel cell (PEFC) performance. To quantify the amount of deposited platinum, a novel transmission electron microscopy (TEM) sectioning method was employed. This method was used to visualize, count and size Pt particles in a defined volume of the membrane, thus allowing the calculation of the deposited Pt mass. After potential cycling between 0.6 V and open circuit voltage, a Pt particle band was formed in the middle of the membrane containing 16% of the initial cathode Pt loading. Start/stop cycling was found to result in deposition of Pt particles both close to the cathode (3% cathode Pt loss) and the anode catalyst layer (1% anode Pt loss). TEM sectioning allowed for the separation of Pt surface area losses caused by deposition in the membrane and particle growth in the catalyst layers. Particle growth was the dominating surface area loss mechanism after potential cycling and start/stop cycling. Using TEM sectioning, the Pt surface area in the membrane was also accessible, which is a crucial parameter for membrane degradation. (C) 2011 Elsevier B.V. All rights reserved