Abstract: Copper chalcogenides find applications in different domains including photonics, photothermal therapy and photovoltaics. CuTe nanocrystals have been proposed as an alternative to noble metal particles for plasmonics. Although it is known that deviations from stoichiometry are a prerequisite for plasmonic activity in the near-infrared, an accurate description of the material and its (optical) properties is hindered by an insufficient understanding of the atomic structure and the influence of defects, especially for materials in their nanocrystalline form. We demonstrate that the structure of Cu1.5±xTe nanocrystals canbe determined using electron diffraction tomography. Real-space high-resolution electron tomography directly reveals the three-dimensional distribution of vacancies in the structure. Through first-principles density functional theory, we furthermore demonstrate that the influence of these vacancies on the optical properties of the nanocrystals is determined. Since our methodology is applicable to a variety of crystalline nanostructured materials, it is expected to provide unique insights concerning structure–property correlations.

Abstract: We present a study of the relation between the surface chemistry and nanocrystal shape of PbSe nanocrystals with a variable Pb-to-Se stoichiometry and density of oleate ligands. The oleate ligand density and binding configuration are monitored by nuclear magnetic resonance and Fourier transform infrared absorbance spectroscopy, allowing us to quantify the number of surface-attached ligands per NC and the nature of the surface−Pb−oleate configuration. The three-dimensional shape of the PbSe nanocrystals is obtained from high-angle annular dark field scanning transmission electron microscopy combined with an atom counting method. We show that the enhanced oleate capping results in a stabilization and extension of the {111} facets, and a crystal shape transformation from a truncated nanocube to a truncated octahedron.

Abstract: Very uniform and well shaped Mn3O4 nano-octahedra are synthesized using a simple hydrothermal method under the help of polyethylene glycol (PEG200) as a reductant and shape-directing agent. The nano-octahedra formation mechanism is monitored. The shape and crystal orientation of the nanoparticles is reconstructed by scanning electron microscopy and electron tomography, which reveals that the nano-octahedra only selectively expose {101} facets at the external surfaces. The magnetic testing demonstrates that the Mn3O4 nano-octahedra exhibit anomalous magnetic properties: the Mn3O4 nano-octahedra around 150 nm show a similar Curie temperature and blocking temperature to Mn3O4 nanoparticles with 10 nm size because of the vertical axis of [001] plane and the exposed {101} facets. With these Mn3O4 nano-octahedra as a catalyst, the photodecomposition of rhodamine B is evaluated and it is found that the photodecomposition activity of Mn3O4 nano-octahedra is much superior to that of commercial Mn3O4 powders. The anomalous magnetic properties and high superior photodecomposition activity of well shaped Mn3O4 nano-octahedra should be related to the special shape of the nanoparticles and the abundantly exposed {101} facets at the external surfaces. Therefore, the shape preference can largely broaden the application of the Mn3O4 nano-octahedra.

Abstract: The 3D reconstruction of a tilt series for electron tomography is mostly carried out using the weighted backprojection (WBP) algorithm or using one of the iterative algorithms such as the simultaneous iterative reconstruction technique (SIRT). However, it is known that these reconstruction algorithms cannot compensate for the missing wedge. Here, we apply a new reconstruction algorithm for electron tomography, which is based on compressive sensing. This is a field in image processing specialized in finding a sparse solution or a solution with a sparse gradient to a set of ill-posed linear equations. Therefore, it can be applied to electron tomography where the reconstructed objects often have a sparse gradient at the nanoscale. Using a combination of different simulated and experimental datasets, it is shown that missing wedge artefacts are reduced in the final reconstruction. Moreover, it seems that the reconstructed datasets have a higher fidelity and are easier to segment in comparison to reconstructions obtained by more conventional iterative algorithms.

Abstract: In materials science, high angle annular dark field scanning transmission electron microscopy is often used for tomography at the nanometer scale. In this work, it is shown that a thickness dependent, non-linear damping of the recorded intensities occurs. This results in an underestimated intensity in the interior of reconstructions of homogeneous particles, which is known as the cupping artifact. In this paper, this non-linear effect is demonstrated in experimental images taken under common conditions and is reproduced with a numerical simulation. Furthermore, an analytical derivation shows that these non-linearities can be inverted if the imaging is done quantitatively, thus preventing cupping in the reconstruction.

Abstract: The plasmonic properties of metal nanoparticles have acquired great importance because of their potential applications in very diverse fields. Metal nanoparticles with localized surface plasmon resonances (LSPR) in the near-infrared (NIR, 7501300 nm) are of particular interest because tissues, blood, and water display low absorption in this spectral range, thus facilitating biomedical applications. Cetyltrimethylammonium chloride (CTAC) was used to induce the seedless formation of highly anisotropic, twisted single crystalline Au nanoparticles in a single step. The LSPR of the obtained particles can be tuned from 600 nm up to 1400 nm by simply changing the reaction temperature or the reagents concentrations. The tunability of the LSPR is closely associated with significant changes in the final particle morphology, which was studied by advanced electron microscopy techniques (3D Tomography and HAADF-STEM). Kinetic experiments were carried out to establish the growth mechanism, suggesting that slow kinetics together with the complexation of the gold salt precursor to CTAC are key factors favoring the formation of these anisotropic particles.