Low loss EELS and EFTEM study of Bi_2Te_3 based bulk and nanomaterials

摘要

Energy-filtered transmission electron microscopy (EFTEM) yields new possibilities for the investigation of Bi_2Te_3 based nanomaterials. Combined low-loss electron energy-loss spectroscopy (EELS) and energy-dispersive x-ray microanalysis (EDS) and energy-filtered TEM were applied on a Zeiss 912Ω TEM to investigate nanowires, thin films, and bulk materials. Multilayered Bi-Sb-Te nanowires with a diameter of 65 nm and a period of 200 nm and stoichiometric Bi_2Te_3 nanowires were grown by potential-pulsed electrochemical deposition. Tellurium elemental maps of the multilayered nanowires were obtained by two-window edgejump ratio images (EJI). EDS chemical analysis showed that small Te fluctuations of 3 at.% yielded significant contrast in EJI. Energy-filtered TEM applied on nano-alloyed Bi_2Te_3 thin films grown by molecular beam epitaxy (MBE) revealed 10-20 nm thick Bi-rich blocking layers at grain boundaries. Plasmon spectroscopy by EELS was applied on Bi_2(Te_(0.91)Se_(0.09))_3 bulk and yielded a plasmon energy of 16.9 eV. Finally, plasmon dispersion was measured for Bi_2(Te_(0.91)Se_(0.09))_3 bulk by angle-resolved EELS, which yields a fingerprint of the anisotropy and the dimensionality of the electronic structure of the materials.