Trace element analysis in pre-solar stardust grains via full-field imaging XPS (Nano-ESCA)

An acid-resistant, SiC-rich, residue from the Murchison meteorite was investigated by means of a novel imaging XPS instrument. The micrometer-sized grains were deposited on a Si wafer from an aqueous suspension. Energy filtered ESCA images have been taken in the kinetic energy range from the threshold up to about 400eV for various photon energies. A lateral resolution of the order of 120nm along with a high energy resolution in the range of 100meV provides the basis for chemical trace element analysis with maximum sensitivity. Apart from major (Si, C) and minor (N, Mg, Al, Fe) elements, the energy filtered images and local microspectra revealed the presence of a variety of heavy trace elements: Sr, Y, Zr, Nb, Mo, Ba and, interestingly the rare earth elements Dy, Er and possibly Tm. Nano-ESCA thus provides a powerful non-destructive screening method for a later analysis of isotopic abundance anomalies using, e.g. Nano-SIMS.