报告题目：Advances and Limitations of Composition Analysis by EDS in aberration corrected STEM and SEM
Abstract
The capabilities of energy dispersive X-ray spectrometry (EDS) using silicon drift detectors (SDDs) in STEM and SEM are explored. Examples of various materials studied on the nanoscale, will be given, e.g. silicon-based and III-V-based semiconductors, magnetic nanostructures [1], core-shell particles, coated multiwall carbon nanotubes [2] and life science samples.Although SDD-EDS is well established, the attainable high spatial resolution and accuracy of quantitative analysis continues to impress.
Optimal photon detection geometry in the microscope, including a large solid angle, a high take-off angle, good collimation and a suitable sample holder, is crucial for efficient EDS and will be explained. Multi-detector arrangements allow the realization of large solid angles at useful take-off angles in STEM [3, 4] and SEM [5]. Absorption and shadowing effects can be minimized at high take-off angle. Good collimation is necessary to ensure a high signal to background ratio and avoid system signals. This geometric optimization in combination with high beam current and aberration correction allows the identification of single atoms in graphene at 0.1sr [6] and on amorphous carbon meteorite material at 0.7sr in a few seconds [7]. Thus, not surprisingly, high solid angle in STEM offers quantitative analysis down to 0.02at% (for e.g. Rb in an Orthoclase mineral standard) in reasonable measurement time [8].
An annular detector design in SEM achieves a solid angle of more than 1sr at superb take-off angles of 50° to 70°. This enables element analysis of electron transparent samples in SEM on the nm scale and fast EDS of thin and bulk samples with high topography or/and high radiation sensitivity and large areas of interest [9]. For quantitative EDS of electron transparent samples the relative Cliff-Lorimer-method and the absolute Zeta-factor-method can be used [10] and combined with EELS [11]. To correctly interpret EDS element maps on the atomic scale though, simulations of relevant scattering and radiation effects are necessary [12], similarly to interpreting EELS data.
EDS of electron transparent samples in SEM (T-SEM) can be combined with other emerging complementary SEM-based techniques: micro-XRF allows trace analysis for higher Z elements at low spatial resolution and different penetration depth and Transmission Kikuchi Diffraction offers crystallographic analysis on the nm-scale [13].
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