Quantitative EDX microanalysis of Bi2Te3 in the TEM



Quantitative chemical analysis by energy dispersive X-ray spectrometry (EDX) in a transmission electron microscope (TEM) Zeiss912Ω was applied to p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 thermoelectric materials. Preliminary results yielded artifacts due to Bi spurious X-rays and hole-counts significantly beyond zero. A stray aperture was inserted in the TEM to absorb the stray radiation. With this aperture inserted a high-accuracy quantitative chemical analysis was established. The hole-counts decreased by a factor of 5 and the scatter of data decreased by a factor of 4 with respect to no aperture inserted. The mole fractions of Te and Se were 54.4 at% and 5.5 at% and varied by 0.5 at% for n-type material. A similar behaviour was found for Sb and Bi in p-type material. The variation in stoichiometry is smaller on the sub-micrometer scale and increases with increasing length scale for both, n-type and p-type Bi2Te3. Measurements in the TEM confirmed the inhomogeneous chemical composition found by wavelength dispersive X-ray spectrometry. The improved accuracy of the quantitative EDX analysis is also important for other compounds with unique physical properties. This was demonstrated on thin foils containing heavy elements and on powders of light elements dispersed on Cu-grids, i.e., the high-TC superconductor Bi2Sr2CaCu2O8 and the mineral salt hydroxyapatite Ca10(PO4)6OH2. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)