Low Energy Loss Structure of Small Aluminum Particles

Abstract

Usually, configuration effects are ignored in microanalytical work. That is, the energy loss mechanisms in small volumes are expected to be similar to those in large volumes. However, it is shown elsewhere in these proceedings1 that this assumption is not valid for bulk plasmons in small Al spheres. In fact, ‘configurational’ energy loss effects can dominate the low energy loss region when probing small volumes. These effects include: surface plasmons, bulk plasmon spatial quantization, Schottky barriers, and any other mechanisms that rely on the close proximity of surfaces or interfaces. We have examined the energy loss structure for ˜200Å Al particles (formed as explained in Ref. 1) with the VG Microscopes, Ltd. HB5 scanning transmission electron microscope at 100KeV. The particles consist of single crystal Al cores covered by ˜40Å of Al2O3, and possibly further covered by 5-15Å of carbon contamination. We obtained electron energy loss spectra (EELS), and inelastic scattering images of the particles to correlate the observed EELS structure with the spatial structure and to make a tentative identification of the losses. The spectra were recorded with a probe angular diameter of 8mR (1.4Å−1) and an energy loss resolution of 0.7eV. The images were recorded with an energy loss resolution of 2eV.