A New Method for Quantitative XEDS Tomography of Complex Heteronanostructures

Abstract

396 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Reliable quantifi cation of 3D results obtained by X-ray energy-dispersive spectroscopy (XEDS) tomography is currently hampered by the presence of shadowing effects and poor spatial resolution. Here, a method is presented which overcomes these problems by synergistically combining quantifi ed XEDS data and high angle annular dark fi eld-scanning transmission electron microscopy tomography. As a proof of principle, the approach is applied to characterize a complex Au/Ag nanorattle obtained through a galvanic replacement reaction. However, the technique that is proposed here is widely applicable to a broad range of nanostructures.very challenging to use HAADF-STEM tomography for samples in which mixing of elements is expected. Also for samples that contain unknown elements or elements with atomic number Z close to each other, HAADF-STEM tomography may no longer be informative. However, it is well known that the properties and applications of nanostructures are strongly dependent on their morphology as well as their chemical composition. [ 4 ] Traditional electron microscopy techniques do not provide quantitative information on the composition of single nanoparticles. In an increasing number of recent studies, X-ray energy-dispersive spectroscopy (XEDS) is combined with tomography to understand complex nanostructure morphology and composition in 3D. These studies rely on newly developed XEDS detectors, [ 5,6 ] such as the Super-X detection system, which consists of four individual detectors, symmetrically arranged around the Transmission Electron Microscope (TEM) sample. Although qualitative results obtained by XEDS tomography have been reported, [7][8][9][10] it remains challenging to obtain quantitative information by 3D XEDS and therefore further progress is required. By using the Super-X detector, one is able to overcome problems that were previously related to extreme shadowing of the XEDS signal caused by the sampledetector confi guration. Although this problem can be largely overcome, some shadowing effects remain, [ 11,12 ] as illustrated in Figure 1 . Since such shadowing effects vary for different tilt angles, the XEDS signal integrated over the four detectors will also depend on the tilt angle [11][12][13] and the projection principle for electron tomography is no longer fulfi lled. [ 12 ] Different methodologies have been proposed to overcome this challenge. For example, signals from individual detectors can be combined, [ 11,14 ] the acquisition time can be adjusted as a function of the tilt angle [ 12 ] or the total signal for every map can be normalized to the same value. [ 13,15 ] However, in order to maximize the signal-to-noise ratio, it is of great importance to collect as many counts as possible. Selectively switching off detectors is therefore disadvantageous, while changing the acquisition time improves the quality of the tilt series, but a calibration of the holder is required and the fi nal result is still hampered by ...

Electron Tomography: A Unique Tool Solving Intricate Hollow Nanostructures

“…For example, Bals and co-workers [134] recently combined the tomographic information from both EDS and HAADF-STEM, presenting more accurate and intensive elemental signals. As an emerging powerful tool kit, great efforts have been devoted to an improved tomographic technology with quality and reliable imaging.…”

Numerical methods for low-dose EDS tomography

“…The purpose of this simulation is to study the reconstruction methods on inhomogeneous structures liked alloyed materials, as opposed to the homogeneous structures used in the first simulation. The phantom was created resembling the nano-rattle sample investigated in [29]. The alloyed nanoparticle consists of Au and Ag components, which have inhomogeneous concentrations.…”

Total generalized variation regularization for multi-modal electron tomography

“…[26][27][28][29] It has been shown that TV minimization can be especially favorable for analytical electron tomography experiments, where usually only limited and noisy data are available. 14,30 Two major limitations can be identified with current TV minimization approaches and their application in analytical tomography. First, the underlying model of TV minimization assumes that the sample only contains sharp interfaces between different phases, severely restricting the range of materials that can be analyzed using TV minimization.…”