Compositional Analysis with Atomic Column Spatial Resolution by 5th-Order Aberration-Corrected Scanning Transmission Electron Microscopy

ArticleinMicroscopy and Microanalysis 17(4):578-81 · May 2011with33 Reads
DOI: 10.1017/S1431927611000213 · Source: PubMed
We show in this article that it is possible to obtain elemental compositional maps and profiles with atomic-column resolution across an InxGa1-xAs multilayer structure from 5th-order aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. The compositional profiles obtained from the analysis of HAADF-STEM images describe accurately the distribution of In in the studied multilayer in good agreement with Muraki's segregation model [Muraki, K., Fukatsu, S., Shiraki, Y. & Ito, R. (1992). Surface segregation of In atoms during molecular beam epitaxy and its influence on the energy levels in InGaAs/GaAs quantums wells. Appl Phys Lett 61, 557-559].
    • "The composition of semiconductor heterostructures has been widely studied by transmission electron microscopy (TEM) techniques , where the development of aberration corrected microscopes has allowed a revolutionary improvement in spatial resolution [18,19]. Thus, important information has been obtained at atomic scale about common phenomena such as diffusion [20,21], segregation [22] or clustering [23,24]. However, the main drawback of these techniques is that they normally provide only 2D information from the projection of the 3D features of the specimen thin foil. "
    [Show abstract] [Hide abstract] ABSTRACT: In this work, we analyse by Atom Probe Tomography (APT) the composition distribution of InAs/GaAs stacked quantum dots (QDs) with InAlGaAs capping layers. Two different GaAs barrier layer thicknesses have been considered, 20 nm and 30 nm. Our results have shown the vertical alignment of QDs in the structure with reduced barrier layer and the unexpected formation of InGaAs quantum rings (QRings) surrounded by an Al-rich area in this sample. The APT data show that the QRings contain an amount of In atoms that is double the In composition in the QDs. The reduced strain measured in the QRings with regard to the QDs suggests that this change in morphology is promoted by the reduction in the strain of the nanostructure. The behaviour of Al during the process of formation of the QRings is also discussed.
    Full-text · Article · Jan 2016
    • "Transmission electron microscopy (TEM) plays an important role in charactering structure and chemistry information of cat- alysts [15] at the atomic scale. The recent development of the spherical aberration corrector has dramatically improved the spatial resolution for a scanning TEM (STEM), offering a capability of imaging the atomic structure of the nanostructured materials at sub-angstrom resolution using a high angle annular dark field (HAADF) detector16171819. Combining aberration corrected STEM-HAADF imaging with simultaneous energy disperse X-ray spectroscopy (EDS) and/or electron energy loss spectroscopy (EELS) provides unique atomic column-by-column structural and correlated chemical information, which has become a powerful tool of characterizing nanomaterials [20]. "
    [Show abstract] [Hide abstract] ABSTRACT: NixZn1-xGa2O4 has already been demonstrated as a noteworthy example of potentially useful catalytic properties such as NOx reduction. In our previous work, it was interesting to find out that the operating temperature of NiGa2O4 catalyst in NOx reduction can be tuned by simple chemical substitution of Ni2+ by Zn2+. It is believed that the mechanism behind such stoichiometry-dependence on operating temperature should be strongly correlated with microstructure, surface morphology as well as the local composition of the nanocatalysts. In the present investigation, NixZn1-xGa2O4 solid solution was synthesized via a hydrothermal ion-exchange reaction, using NaGaO2 and the corresponding acetic salts as the starting materials. By means of a state-of-the-art aberration corrected STEM and high resolution TEM, the structural and chemical characterization at the atomic scale on the NixZn1-xGa2O4 nanocatalyst was carried out, including the crystal structure, size, morphology, surface structure and local composition. It is found that the catalyst was solid solution and most possible exposed facets may be (111).
    Full-text · Article · Jun 2015
    • "In order to being able to compare these experimental results to the simulated images, it is necessary to average the intensity over a significant number of atomic columns. For this, we have used a method for measuring the integrated intensities around each atomic column [29] that has been successfully used previously for the calculation of the composition of different semiconductor materials from experimental HAADF-STEM image303132. In the case of more than one MoS 2 layers, the crystal can4. "
    [Show abstract] [Hide abstract] ABSTRACT: In this work we examined MoS2 sheets by aberration-corrected scanning transmission electron microscopy (STEM) at three different energies: 80, 120 and 200kV. Structural damage of the MoS2 sheets has been controlled at 80kV according a theoretical calculation based on the inelastic scattering of the electrons involved in the interaction electron-matter. The threshold energy for the MoS2 material has been found and experimentally verified in the microscope. At energies higher than the energy threshold we show surface and edge defects produced by the electron beam irradiation. Quantitative analysis at atomic level in the images obtained at 80kV has been performed using the experimental images and via STEM simulations using SICSTEM software to determine the exact number of MoS2 layers.
    Full-text · Article · Jun 2014
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