[en] The three-dimensional (3D) faceting morphology of ceria nanoparticles is analysed using transmission electron microscopy (TEM)-based computed tomography on the nanometre scale. A novel tomography mode of electron energy loss spectroscopic imaging using a single energy window for inelastically scattered electrons is introduced and found to be reliable and fast for freestanding nanoparticles. To compare the new tomographic method with other methods, we provide the first comprehensive application of three complementary TEM-based imaging techniques, including bright field TEM and annular dark field specific TEM (STEM). Traditional bright-field TEM tomography is found to be applicable, in spite of obvious artefacts, for crystalline particles of constant composition. However, the safest interpretation is achieved by a combined recording of bright field and spectroscopic images

[en] Electron tomography is a valuable three-dimensional characterization method, but the technique has so far been limited to a nanometer scale resolution, and therefore complementary two-dimensional structural analysis is generally performed using other techniques. In this paper, computer simulations of the latest transmission electron microscope technologies are performed on a CeO₂ supercell to investigate the extension of electron tomography to the atomic scale resolution, from a tilt series of high resolution electron microscopy (HREM) images. We showed that high-voltage and aberration-corrected microscopes were both capable of retrieving adjacent oxygen and Ce atoms for a thickness up to 2.5 nm. In the case where only a few tilt angle projections are in zone-axis orientations, we introduced a hybrid tomography method, whereby a lattice-resolved tomogram obtained from a few zone-axis projections is combined with the external shape reconstruction of the crystal from binary projections. Finally, we discussed some experimental challenges related to the proposed HREM tomography technique.

[en] Electron energy loss spectroscopy (EELS) fine structure is a powerful technique for analyzing oxidation levels of rare-earth oxides and coordination numbers in glasses and ceramics, especially for boron. To exploit the unique advantage of EELS over x-ray absorption spectroscopy (XAS)/x-ray absorption near edge structure (XANES), namely nm-scale spatial resolution, EELS spectrum imaging across precipitates in glasses has been employed to detect lateral changes of EELS fine structure. Alkali borosilicate (ABS) glasses doped with Cr₂O₃, CeO₂ and ZrO₂ or Fe₂O₃ were melted to simulate high level radionuclide immobilization glasses. Precipitates with diameter in the range of ∼20 nm to ∼500 nm were found homogeneously distributed in the glasses. Ce valence was found to be mainly +3 in the glass matrix, and +4 in crystalline precipitates, while some amorphous particles show +3 as well. Another powerful TEM technique for the analysis of glass-nano-composites is electron tomography, as it is up to now the only technique for the three-dimensional reconstruction of nano-particles. A 3D reconstructed nuclear waste glass is presented in this paper by using a tilt series of ADF STEM images covering a glass fragment of ∼3μm field of view containing several tens of nano-particles distributed throughout its volume. (authors)

[en] The γ′ strengthening phase in an advanced nickel-based superalloy, ATI 718Plus, was characterized using a blind source separation applied to a four dimensional X-ray microanalysis dataset obtained by scanning transmission electron microscopy. Selected patterns in the X-ray spectra identified by independent component analysis were found to be spatially and chemically representative of the matrix (γ) and precipitate phases (γ′) present in the superalloy, enabling their size, shape and distribution to be determined. The three dimensional chemical reconstruction of the microstructure may provide insight into the role of the various alloying elements in the evolution of the microstructure at the nano-scale.

[en] 3D analysis of an arsenic-doped silicon fin sample is performed in a transmission electron microscope (TEM). High angle annular dark-field scanning TEM (STEM-HAADF) and energy-dispersive x-ray spectroscopy (STEM-EDX) modes are used simultaneously to extract 3D complementary multi-resolution information about the sample. The small pixel size and angular step chosen for the STEM-HAADF acquisition yield reliable information about the sidewall roughness and the arsenic clusters’ average volume. The chemical sensitivity of STEM-EDX tomography gives insights into the 3D conformality of the arsenic implantation and its depth distribution. Non-negative matrix factorization method is employed to identify the chemical phases present in the sample automatically. A total variation minimization algorithm, implemented in 3D, produces high-quality volumes from heavily undersampled datasets. The extension of this correlative approach to electron energy-loss spectroscopy STEM tomography and atom probe tomography is also discussed. (paper)

[en] Supported ZnO nanorods have been prepared at 405 K by plasma-enhanced chemical vapour deposition (PECVD) using diethylzinc as precursor, oxygen plasma and silver as the promotion layer. The nanorods are characterized by a hollow and porous microstructure where partially percolated silver nanoparticles are located. By changing different deposition parameters like the thickness of the silver layer, the type of oxidation pretreatment or the geometry of the deposition set-up, the length, the width and the tilting angle of the nanorods with respect to the substrate can be modified. Other nanostructures like nanobushes, zigzag linear structures and stacked bilayers with nanocolumns of TiO₂ can also be prepared by adjusting the deposition conditions. A phenomenological model relying on the assessment of the diverse nanostructure morphologies and the evidence provided by an in situ x-ray photoelectron spectroscopy (XPS) experiment has been proposed to describe their formation mechanism. From this analysis it is deduced that the effect of the electrical field of the plasma sheath, the high mobility of silver and silver oxide, and the diffusion of the precursor molecules are some of the critical factors that must converge by the formation of the nanorods. (paper)

[en] Thin films based on layers of Fe₅₂Co₂₈B₂₀ (at%), Fe₆₅Co₃₅ (at%), and Ni₈₀Fe₂₀ (at%) were deposited by sputtering on 8″ bare Si and Si/200 nm-thermal-SiO₂ wafers by simultaneous use of two or more cathodes. Due to the continuous rotation of the substrate cage, such that the substrates faced different targets alternately, the multilayers consisted of stacks of alternating, nanometer-thick regular layers. The composition of the films was determined by Rutherford Backscattering Spectrometry (RBS) and Nuclear Reactive Analysis (NRA), whereas Plasma Profiling Time of Flight Mass Spectrometry (PP-TOFMS) analysis gave depth profile information about the chemical elements. The structural and magnetic properties of the films were investigated by X-ray Diffraction and by TEM analysis, B-H loop tracer and high frequency single coil technique permeametry, respectively. The linear dependence of the coercivity of these thin films versus the grain size can be explained by the random anisotropy model. These novel, composite soft magnetic multilayers, with tunable in-plane anisotropy, allow operation at tunable frequencies, as shown by broadband (between 100 MHz and 10 GHz) RF measurements that exhibit a classical Landau-Lifschitz-Gilbert (LLG) behavior and, combine the magnetic properties of the individual materials in an advantageous way. This article presents a method to produce nanostructured soft magnetic multilayers, the properties of which can easily be tuned by choosing the ratio of the individual nanolayers. In this way it’s possible to combine soft magnetic materials with complementary properties, e.g. high saturation magnetization, low coercivity, high specific resistivity and low magnetostriction

[en] The recent mathematical concept of compressed sensing (CS) asserts that a small number of well-chosen measurements can suffice to reconstruct signals that are amenable to sparse or compressible representation. In addition to powerful theoretical results, the principles of CS are being exploited increasingly across a range of experiments to yield substantial performance gains relative to conventional approaches. In this work we describe the application of CS to electron tomography (ET) reconstruction and demonstrate the efficacy of CS–ET with several example studies. Artefacts present in conventional ET reconstructions such as streaking, blurring of object boundaries and elongation are markedly reduced, and robust reconstruction is shown to be possible from far fewer projections than are normally used. The CS–ET approach enables more reliable quantitative analysis of the reconstructions as well as novel 3D studies from extremely limited data. - Highlights: • Compressed sensing (CS) theory and its application to electron tomography (ET) is described. • The practical implementation of CS–ET is outlined and its efficacy demonstrated with examples. • High fidelity tomographic reconstruction is possible from a small number of images. • The CS–ET reconstructions can be more reliably segmented and analysed quantitatively. • CS–ET is applicable to different image content by choice of an appropriate sparsifying transform

[en] HAADF-STEM tomography has been used for characterisation of novel unsupported intermetallic Ga-Pd catalysts, with accompanying analysis by HRTEM and EDXS. Image processing techniques applied to the tomogram have facilitated segmentation and the subsequent extraction of size and shape parameters. The fidelity of the analysis has been critically examined, enabling identification of reconstruction artefacts and thereby more reliable determination of catalytically relevant properties. Further steps towards robust and accurate metrology by electron tomography are discussed.

[en] Graphical abstract: Precipitate formation during the in situ annealing experiment at 650 ^oC. -- Formation of M₂₃C₆ carbides and chromium-depleted zones in commercially available type 304L stainless steel were investigated by in situ transmission electron microscopy and analytical transmission electron microscopy. It was found that each individual small M₂₃C₆ carbide starts to grow with a clear orientation relationship with the matrix, and film-like carbide was subsequently observed at the interfaces with asymmetric Cr-depleted zones. From these experimental results, a model describing the precipitation of M₂₃C₆ and the formation of the Cr-depleted zone was proposed.