Abstract: In this paper convexity constraints are derived for a background model of electron energy loss spectra (EELS) that is linear in the fitting parameters. The model outperforms a power-law both on experimental and simulated backgrounds, especially for wide energy ranges, and thus improves elemental quantification results. Owing to the model’s linearity, the constraints can be imposed through fitting by quadratic programming. This has important advantages over conventional nonlinear power-law fitting such as high speed and a guaranteed unique solution without need for initial parameters. As such, the need for user input is significantly reduced, which is essential for unsupervised treatment of large datasets. This is demonstrated on a demanding spectrum image of a semiconductor device sample with a high number of elements over a wide energy range.

Abstract: We present an investigation of the microstructure changes in V2O3 as it goes through its inherent structural phase transition. Using V2O3 films with a well-defined crystal structure deposited by reactive magnetron sputtering on r-plane Al2O3 substrates, we study the phase coexistence region and its impact on the surface roughness of the films and the magnetic properties of overlying Ni magnetic layers in V2O3/Ni hybrid magnetic heterostructures. The simultaneous presence of two phases in V2O3 during its structural phase transition was identified with high resolution x-ray diffraction and led to an increase in surface roughness observed using x-ray reflectivity. The roughness reaches its maximum at the midpoint of the transition. In V2O3/Ni hybrid heterostructures, we find a concomitant increase in the coercivity of the magnetic layer correlated with the increased roughness of the V2O3 surface. The chemical homogeneity of the V2O3 is confirmed through transmission electron microscopy analysis. High-angle annular dark field imaging and electron energy loss spectroscopy reveal an atomically flat interface between Al2O3 and V2O3, as well as a sharp interface between V2O3 and Ni.

Abstract: Because of its low hysteresis, high dielectric constant, and strong piezoelectric response, Pb(Mg1/3Nb2/3)O-3-PbTiO3 (PMN-PT) thin films have attracted considerable attention for the application in PiezoMEMS, field-effect transistors, and energy harvesting and storage devices. However, it remains a great challenge to fabricate phase-pure, pyrochlore-free PMN-PT thin films. In this study, we demonstrate that a high deposition rate, combined with a tensile mismatched template layer can stabilize the perovskite phase of PMN-PT films and prevent the nucleation of passive pyrochlore phases. We observed that an accelerated deposition rate promoted mixing of the B-site cation and facilitated relaxation of the compressively strained PMN-PT on the SrTiO3 (STO) substrate in the initial growth layer, which apparently suppressed the initial formation of pyrochlore phases. By employing La-doped-BaSnO3 (LBSO) as the tensile mismatched buffer layer, 750 nm thick phase-pure perovskite PMN-PT films were synthesized. The resulting PMN-PT films exhibited excellent crystalline quality close to that of the STO substrate.

Abstract: Aberration-corrected transmission electron microscopy, electron energy-loss spectroscopy, and density functional theory (DFT) calculations are used to solve several key questions about the surface structure, the particle morphology, and the distribution and nature of nitrogen impurities in detonation nanodiamond (DND) cleaned by a recently developed ozone treatment. All microscopy and spectroscopy measurements are performed at a lowered acceleration voltage (80/120kV), allowing prolonged and detailed experiments to be carried out while minimizing the risk of knock-on damage or surface graphitization of the nanodiamond. High-resolution TEM (HRTEM) demonstrates the stability of even the smallest nanodiamonds under electron illumination at low voltage and is used to image the surface structure of pristine DND. High resolution electron energy-loss spectroscopy (EELS) measurements on the fine structure of the carbon K-edge of nanodiamond demonstrate that the typical * pre-peak in fact consists of three sub-peaks that arise from the presence of, amongst others, minimal fullerene-like reconstructions at the nanoparticle surfaces and deviations from perfect sp(3) coordination at defects in the nanodiamonds. Spatially resolved EELS experiments evidence the presence of nitrogen within the core of DND particles. The nitrogen is present throughout the whole diamond core, and can be enriched at defect regions. By comparing the fine structure of the experimental nitrogen K-edge with calculated energy-loss near-edge structure (ELNES) spectra from DFT, the embedded nitrogen is most likely related to small amounts of single substitutional and/or A-center nitrogen, combined with larger nitrogen clusters.

Abstract: Energy filtered TEM, EFTEM, provides three-dimensional data, two spatial and one spectral dimension. We propose to acquire these data by measuring a series of images with a defocused energy filter. It will be shown that each image is a projection of the data on the detector and that reconstruction of the data out of a sufficient number of such projections using a tomographic reconstruction algorithm is possible. This technique uses only a fraction of the electron dose an energy filtered series (EFS) needs for the same spectral and spatial resolution and the same mean signal-to-noise ratio. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden Popper structure La2Sr2Mn3O10 in epitaxial thin film form by sequentially layering La1-xSrxMnO3 and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr2+ predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature T-g approximate to 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.

Abstract: We report an atomic layer epitaxial growth of Ruddlesden-Popper (RP) thin films of SrO(SrTiO3)(n) (n = infinity, 2, 3, 4) by means of metalorganic aerosol deposition (MAD). The films are grown on SrTiO3(001) substrates by means of a sequential deposition of Sr-O/Ti-O-2 atomic monolayers, monitored in-situ by optical ellipsometry. X-ray diffraction and transmission electron microscopy (TEM) reveal the RP structure with n = 2-4 in accordance with the growth recipe. RP defects, observed by TEM in a good correlation with the in-situ ellipsometry, mainly result from the excess of SrO. Being maximal at the film/substrate interface, the SrO excess rapidly decreases and saturates after 5-6 repetitions of the SrO(SrTiO3)(4) block at the level of 2.4%. This identifies the SrTiO3 substrate surface as a source of RP defects under oxidizing conditions within MAD. Advantages and limitations of MAD as a solution-based and vacuum-free chemical deposition route were discussed in comparison with molecular beam epitaxy. (C) 2014 AIP Publishing LLC.

Abstract: Atomically resolved electron energy-loss spectroscopy experiments are commonplace in modern aberration-corrected transmission electron microscopes. Energy resolution has also been increasing steadily with the continuous improvement of electron monochromators. Electronic excitations however are known to be delocalized due to the long range interaction of the charged accelerated electrons with the electrons in a sample. This has made several scientists question the value of combined high spatial and energy resolution for mapping interband transitions and possibly phonon excitation in crystals. In this paper we demonstrate experimentally that atomic resolution information is indeed available at very low energy losses around 100 meV expressed as a modulation of the broadening of the zero loss peak. Careful data analysis allows us to get a glimpse of what are likely phonon excitations with both an energy loss and gain part. These experiments confirm recent theoretical predictions on the strong localization of phonon excitations as opposed to electronic excitations and show that a combination of atomic resolution and recent developments in increased energy resolution will offer great benefit for mapping phonon modes in real space.

Abstract: Electron vortex beams were only recently discovered and their potential as a probe for magnetism in materials was shown. Here we demonstrate a method to produce electron vortex beams with a diameter of less than 1.2 Å. This unique way to prepare free electrons to a state resembling atomic orbitals is fascinating from a fundamental physics point of view and opens the road for magnetic mapping with atomic resolution in an electron microscope.

Abstract: Solution derived La2Zr2O7 films have drawn much attention for potential applications as thermal barriers or low-cost buffer layers for coated conductor technology. Annealing and coating parameters strongly affect the microstructure of La2Zr2O7, but different film processing methods can yield similar microstructural features such as nanovoids and nanometer-sized La2Zr2O7 grains. Nanoporosity is a typical feature found in such films and the implications for the functionality of the films are investigated by a combination of scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) and quantitative electron tomography. Chemical solution based La2Zr2O7 films deposited on flexible Ni5 at.%W substrates with a {100}lang001rang biaxial texture were prepared for an in-depth characterization. A sponge-like structure composed of nanometer-sized voids is revealed by high-angle annular dark-field scanning transmission electron microscopy in combination with electron tomography. A three-dimensional quantification of nanovoids in the La2Zr2O7 film is obtained on a local scale. Mostly non-interconnected highly faceted nanovoids compromise more than one-fifth of the investigated sample volume. The diffusion barrier efficiency of a 170 nm thick La2Zr2O7 film is investigated by STEM-EELS, yielding a 1.8 ± 0.2 nm oxide layer beyond which no significant nickel diffusion can be detected and intermixing is observed. This is of particular significance for the functionality of YBa2Cu3O7 − δ coated conductor architectures based on solution derived La2Zr2O7 films as diffusion barriers.

Abstract: The degradation of colors in historical paintings affects our cultural heritage in both museums and archeological sites. Despite intensive experimental studies, the origin of darkening of one of the most ancient pigments known to humankind, vermilion (α-HgS), remains unexplained. Here, by combining many-body theoretical spectroscopy and high-resolution microscopic x-ray diffraction, we clarify the composition of the damaged paint work and demonstrate possible physicochemical processes, induced by illumination and exposure to humidity and air, that cause photoactivation of the original pigment and the degradation of the secondary minerals. The results suggest a new path for the darkening process which was never considered by previous studies and prompt a critical examination of their findings.