Combination of HAADF‐STEM and ADF‐STEM Tomography for Core–Shell Hybrid Materials

Abstract

1wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Characterization of core-shell type nanoparticles in 3D by transmission electron microscopy (TEM) can be very challenging. Especially when both heavy and light elements coexist within the same nanostructure, artifacts in the 3D reconstruction are often present. A representative example would be a particle comprising an anisotropic metallic (Au) nanoparticle coated with a (mesoporous) silica shell. To obtain a reliable 3D characterization of such an object, a dose-effi cient strategy is proposed to simultaneously acquire high-angle annular dark-fi eld scanning TEM and annular dark-fi eld tilt series for tomography. The 3D reconstruction is further improved by applying an advanced masking and interpolation approach to the acquired data. This new methodology enables us to obtain high-quality reconstructions from which also quantitative information can be extracted. This approach is broadly applicable to investigate hybrid core-shell materials.of an object from its 2D projections, a monotonic relationship between image intensity and mass thickness is required. [ 1 ] When applying electron tomography to crystalline solids, diffraction contrast must therefore be avoided. [ 7 ] Indeed, diffraction contrast depends on the orientation of the object with respect to the electron beam and therefore the projection requirement for electron tomography is not fulfi lled. [ 1 ] As a consequence, artifacts will occur in the fi nal 3D reconstruction. [ 8,9 ] This is one of the main reasons why electron tomography in materials science is mostly based on high angle annular dark fi eld scanning transmission electron microscopy (HAADF-STEM). [ 1,10 ] For each composition, the intensity of the HAADF-STEM images changes monotonically with specimen thickness thus fulfi lling the projection requirement. To obtain 3D reconstructions from HAADF-STEM tilt series, reconstruction algorithms such as the simultaneously iterative reconstruction technique (SIRT), [ 11 ] total variation minimization, [ 12,13 ] and the discrete algebraic reconstruction technique [ 14 ] are currently used. Also for samples that consist of more than one type of element, HAADF-STEM tomography is very valuable since not only morphological but also chemical information can be extracted. [ 10 ] However, for samples in which elements with a high and low atomic number ( Z ) are simultaneously present, data acquisition becomes even more challenging. Since the intensity is strongly dependent on the atomic number, [ 10 ] a high difference in Z in the material leads to a large difference in the collected signal that is not always possible to cover with detector's dynamic range. Therefore, some areas of the image can be either overor undersaturated. This situation is often encountered when investigating core-shell hybrid materials such as nanoparticles encapsulated by a lighter matrix. In this paper, we propose an improved approach to obtain reliable 3D reconstructions for these systems, which requires optim...

Encapsulation of Single Plasmonic Nanoparticles within ZIF‐8 and SERS Analysis of the MOF Flexibility

“…In this manner, heavy and light elements in the same sample are both visualized. Furthermore, this technique can be considered as dose efficient, which is of great importance to image electron beam sensitive materials in 3D . Visualizations along different directions of the 3D reconstruction obtained in this manner are presented in Figure and a video is available as Supporting Information (SV1).…”

“…Furthermore, this technique can be considered as dose effi cient, which is of great importance to image electron beam sensitive materials in 3D. [ 27 ] Visualizations along different directions of the 3D reconstruction obtained in this manner are presented in Figure 4 and a video is available as Supporting Information (SV1). The MOF shell is highlighted in green, whereas Ag and Au in the NR are labeled with gray and yellow colors, respectively.…”

Electron Tomography: A Unique Tool Solving Intricate Hollow Nanostructures

“…ET technique has been well applied to distinguish nanostructures in core-shell nanoparticles. [101][102][103][104] A representative example would be the hybrid particle of Au@mesoSiO 2 , in which the core can be clearly distinguished due to their obvious contrast compared to amorphous silica. [101] Upon the growth of short nanowires on gold cores, these detailed nanostructures are precisely determined by 3D analysis, favorably using HAADF-STEM tomography.…”

Artifact Reduction Based on Sinogram Interpolation for the 3D Reconstruction of Nanoparticles Using Electron Tomography

“…[1][2][3] The method has already been applied to a large variety of materials such as (supported) nanoparticles, [3] assemblies of nanoparticles, [8] and porous materials. [9] Recently, electron tomography was furthermore combined with analytical techniques such as X-ray energy-dispersive spectroscopy [10,11] and electron energy loss spectroscopy [12,13] yielding both structural and chemical information.…”

“…In materials science, projection images are mostly acquired using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) . The method has already been applied to a large variety of materials such as (supported) nanoparticles, assemblies of nanoparticles, and porous materials . Recently, electron tomography was furthermore combined with analytical techniques such as X‐ray energy‐dispersive spectroscopy and electron energy loss spectroscopy yielding both structural and chemical information.…”