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We outline a simple routine to correct for non-uniformities in the energy dispersion of a post-column electron energy-loss spectrometer for use in scanning transmission electron microscopy. We directly measure the dispersion and its variations by sweeping a spectral feature across the full camera to produce a calibration that can be used to linearize datasets post-acquisition, without the need for reference materials. The improvements are illustrated using core excitation electron energy-loss spectroscopy (EELS) spectra collected from NiO and diamond samples. The calibration is rapid and will be of use in all EELS analysis, particularly in assessments of the chemical states of materials via the chemical shift of core-loss excitations.

With advancements in aberration-corrected electron optics, the resolution in scanning transmission electron microscopy (STEM) has been significantly improved. More importantly, the reduction of the probe size and the increase of the probe current density enable the acquisition of elemental maps at the atomic scale in a fast manner using both EELS and EDS. With the latest generations of EELS spectrometers, atomic resolution compositional and chemical maps allow interfaces, oxidation state, and even single atoms to be examined with increasing detail. These improvements have also enabled elemental and chemical maps to be acquired rapidly using both low- and high-energy edges from elements across the periodic table, including heavy atoms such Au or Pt. On the EDS side, the introduction of large-area silicon drift detectors (SDD) has allowed these high-beam-current sources to be fully utilized. Improved detector area and support for higher count rates, compared to the previous generation of EDS detectors, allows the acquisition of EDS intensity maps from most types of material in the STEM, even for moderately thin samples. For the case of light elements, the reduced detector dead layer of SDD-based systems partially overcomes the very low florescence yield typical of low-energy X-ray lines. Also as reported in, atomic-level X-ray maps using fast detectors and bright sources can now be collected under some conditions. Because EDS and EELS provide complementary information about the sample, and are both generated with the electron beam, it would be wasteful to not acquire both datasets with every sample run.

Positive temperature coefficient of resistivity (PTCR) ceramics of 0.912(Ba1+xTiO3)–0.088(Bi0.5Na0.5TiO3) (BT–BNT) (x = −0.03 to 0.03) were prepared using the mixed oxide route and sintered at 1340°C for 4 h. Products were predominantly single phase with a tetragonal structure and grains in 2–6 μm size containing 90° ferroelectric domains. Samples with Ti/Ba > 1 contained second-phase Ba6Ti17O40. HRTEM and aberration-corrected Z-contrast high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) suggested that the dopants, Bi and Na, occupy the Ba site of the perovskite lattice, and revealed the presence of dissociated dislocations in x = −0.03 and x = 0.00 materials. The interval between two partial dislocations was 1.9–3.4 nm, yielding stacking fault energies of 363–649 mJ/m2. The PTCR behavior of the ceramics increased with Ti/Ba content, reaching a maximum of six decades change in resistivity for x = −0.03. The anomalous increase in resistivity depends critically on stoichiometry, increasing with the Ti/Ba ratio; this in turn is directly correlated with an increase in the amount of second-phase Ba6Ti17O40, an increase in the stacking fault energy, and an increase in the tilt angle of the grain boundaries.

The discovery of unusual nanorod precipitates in bismuth ferrite doped with Nd and Ti is reported. The atomic structure and chemistry of the nanorods are determined using a combination of high angle annular dark field imaging, electron energy loss spectroscopy, and density functional calculations. It is found that the structure of the BiFeO3 matrix is strongly modified adjacent to the precipitates; the readiness of BiFeO3 to adopt different structural allotropes in turn explains why such a large axial ratio, uncommon in precipitates, is stabilized. In addition, a correlation is found between the alignment of the rods and the orientation of ferroelastic domains in the matrix, which is consistent with the system's attempt to minimize its internal strain. Density functional calculations indicate a finite density of electronic states at the Fermi energy within the rods, suggesting enhanced electrical conductivity along the rod axes, and motivating future investigations of nanorod functionalities.

We present and compare two different imaging techniques for plasmonic excitations in metallic nanoparticles based on high energy-resolution electron energy-loss spectroscopy in a monochromated transmission electron microscope. We demonstrate that a recently developed monochromated energy-filtering (EFTEM) approach can be used in addition to the well established scanning technique to directly obtain plasmon images in the energy range below 1 eV. The EFTEM technique is described in detail, and a double experiment performed on the same, triangular gold nanoparticle compares equivalent data acquired by both techniques, respectively.

Energy-filtering TEM (EFTEM) has turned out to be a very efficient and rapid tool for the chemical characterization of a specimen on a nanometer and even subnanometer length scale. Especially, the detection and measurement of very thin layers has become a great application of this technique in many materials science fields, e.g. semiconductors and hard disk technology. There, the reliability of compositional profiles is an important issue. However, the experimentally obtainable spatial resolution strongly influences the appearance of a thin layer in an EFTEM image, when dimensions reach subnanometer levels, which mainly leads to a broadening of the layer in the image. This fact has to be taken into account, when measuring the thickness of such a thin layer. Additionally, the convolution decreases contrast which makes the layer less visible in the image and finally determines the detection limit. In this work we present a systematic study on specifically designed Mn/PdMn multilayer test specimens to explore the practical aspects of spatial resolution and detection limits in EFTEM. Although specific to the ionization edges used, we will present general conclusions about the practical limitations in terms of EFTEM spatial resolution. Additionally, work will be shown about low energy-loss imaging of thin oxide layers, where delocalization is the main factor responsible for broadening.

Nanometric inclusions filled with nitrogen, located adjacent to FenN (n ¼ 3 or 4) nanocrystals within (Ga,Fe)N layers, are identified and characterized using scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). High-resolution STEM images reveal a truncation of the Fe-N nanocrystals at their boundaries with the nitrogen-containing inclusions. A controlled electron beam hole drilling experiment is used to release nitrogen gas from an inclusion in situ in the electron microscope. The density of nitrogen in an individual inclusion is measured to be 1.4 6 0.3 g/cm3 . These observations provide an explanation for the location of surplus nitrogen in the (Ga,Fe)N layers, which is liberated by the nucleation of FenN (n > 1) nanocrystals during growth. Fil: Kovács, A.. Peter Grunberg Institute; Alemania Fil: Schaffer, B.. University of Glasgow; Reino Unido Fil: Moreno, Mario Sergio Jesus. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Jinschek, J. R.. FEI Company; Países Bajos Fil: Craven, A. J.. University of Glasgow; Reino Unido Fil: Dietl, T.. Polish Academy of Sciences; Argentina Fil: Bonanni, A.. Johannes Kepler University; Austria Fil: Dunin Borkowski, R. E.. Peter Grunberg Institute; Alemania

This work presents results from high-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy on twin boundaries (TBs) and nontwin grain boundaries (GBs) in CuðIn; GaÞSe2 thin films. It is shown that the atomic reconstruction is different for different symmetries of the grain boundaries. We are able to confirm the model proposed by Persson and Zunger [Phys. Rev. Lett. 91, 266401 (2003)] for Se-Se-terminated �3 f112g TBs, showing Cu depletion and In enrichment in the two atomic planes closest to the TB. On the contrary, Cu depletion without In enrichment is detected for a cation-Se-terminated TB. At nontwin GBs, always a strong anticorrelation of Cu and In signals is detected suggesting that the formation of InCu or CuIn antisites within a very confined region of smaller than 1 nm is an essential element in the reconstruction of these GBs.

The coupling of angstrom-sized electron probes with spin-polarized electronic transitions shows that the inelastically scattered probe electron is in a mixed state containing electron vortices with nonzero orbital angular momentum. These electrons create an asymmetric intensity distribution in energy filtered diffraction patterns, giving access to maps of the magnetic moments with atomic resolution. A feasibility experiment shows evidence of the predicted effect. Potential applications are column-by-column maps of magnetic ordering, and the creation of angstrom-sized free electrons with orbital angular momentum by inelastic scattering in a thin ferromagnetic foil.

Reactions at the interfaces can occur in metal inserted high-k gate stacks and are likely to evolve during device processing. Such reactions may affect the electrical properties of the stack and hence these could change during processing. The key interfaces are often not atomically flat and characterising the reaction layers on the near atomic scale required is a challenge. Aberration corrected scanning transmission electron microscopy (STEM) and spectrum imaging (SI) using electron energy loss spectroscopy (EELS) is used to characterise an HfN or Hf(O,N) reaction layer, ∼0.25 nm wide, between HfO2 and TiN. This demonstrates the very significant advances in high spatial resolution characterisation made in recent years.

Electronic defects at interfaces between different materials or at extended structural defects such as grain boundaries (GB) or dislocations can deteriorate the performance of a semiconductor device considerably. Cu(In,Ga)Se2 (CIGS) thin-film solar cells consist of several interfaces between individual layers of different materials. In addition, the main light-absorbing layer, the CIGS absorber, exhibits a high density of GBs (i.e., the average grain size is typically smaller than the layer thickness) as well as of dislocations (up to 10 10 cm -2 in high-efficiency solar cells [1]). Still, CIGS solar cells exhibit highest power-conversion efficiencies of up to 20.8 % [2]. Today, the roles of interfaces and extended structural defects in the solar-cell device are not yet fully understood, although extensive research efforts have been made. We applied various methods in transmission electron microscopy (TEM), such as inline electron holography, electron energy-loss spectroscopy (EELS), as well as energy-dispersive X-ray spectroscopy (EDS) in order to obtain more information about these features.

Ceramics of 0.9La2/3TiO3–0.1LaAlO3 prepared by the mixed oxide route were sintered at 1400°C in air for 4 h and cooled at rates 180°–1°C/h. The products were at least 97% dense with grain sizes of 7–10 μm and relative permittivities 66.9±0.7 at 4 GHz. Rapidly cooled samples (180°C/h) were single phase and exhibited the highest dielectric Q×f values of 16 300±900 GHz. High-resolution transmission electron microscopy revealed microtwins and domains in all the ceramics, with the highest density of both features in the rapidly cooled samples. A-site vacancies in rapidly cooled 0.9La2/3TiO3–0.1LaAlO3 ceramics were imaged by aberration-corrected scanning transmission electron microscopy. It is shown that vacancies and La1 atoms occupy the 4(h) sites and the 4(g) site is fully occupied by La2 atoms in the orthorhombic Cmmm structure of lanthum titanate. The microtwin boundaries in the microstructure of La2/3TiO3 stabilized by LaAlO3 lie on the La2 atomic planes. On twinning, La2 and La1 atoms share the same site. The sharing of the 4(h) and 4(g) atomic sites at the twin boundaries is a mechanism to reduce lattice strain upon the continuous transformation from a high-temperature simple cubic Fm3m form to a low-temperature orthorhombic Cmmm form, which involves vacancy/cation ordering and anti-phase tilting of the oxygen octahedra.

We demonstrate the imaging capabilities of energy-filtered transmission electron microscopy at high-energy resolution in the low-energy-loss region, reporting the direct image of a surface plasmon of an elongated gold nanoparticle at energies around 1 eV. Using complimentary model calculations performed within the boundary element method approach we can assign the observed results to the plasmon eigenmodes of the metallic nanoparticle.

In this work we show how energy-filtered imaging can be used to obtain spectrum images of electron energy-loss spectrometric data. Focus is placed on improved energy resolution within these data sets. Using two multilayer samples (GaN/AlN and InP/InAs), we demonstrate the advantages of spectrum-imaging and its extended mapping capabilities. Plasmon-ratio maps are used to quickly create high-contrast material maps with high signal-to-noise ratio, ratio-contrast plots are used to gain optimum settings for the ratio maps, and plasmon-position maps are used to map small shifts of the energy position of bulk plasmon peaks.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

BiFeO3 has been the subject of intense interest in recent years on account of possible multiferroic properties. Recently, Reaney and co-workers demonstrated that rare-earth doping can induce the formation of antipolar order with similarities to the PbZrO3 structure. This study reports for the first time studies of the atomic structure and chemistry of nanoscale defects in such materials.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Observation of an unusual, negatively-charged antiphase boundary in (Bi0.85Nd0.15)(Ti0.1Fe0.9)O3 is reported. Aberration corrected scanning transmission electron microscopy is used to establish the full three dimensional structure of this boundary including O-ion positions to ~ ± 10 pm. The charged antiphase boundary stabilises tetragonally distorted regions with a strong polar ordering to either side of the boundary, with a characteristic length scale determined by the excess charge trapped at the boundary. Far away from the boundary the crystal relaxes into the well-known Nd-stabilised antiferroelectric phase.

High resolution scanning transmission electron microscope (HRSTEM) and electron energy loss spectroscopy spectrum imaging (EELS SI) methods have been successfully applied to the analysis of planar antiphase boundaries in (Bi0.85Nd0.15)(Fe0.9Ti0.1)O3 (BNFT) ceramics. Two distinct structures for these boundaries have been identified, one of which has never previously been reported for perovskites. This latter form has a characteristic ladder structure in the core, and comes in stepped and unstepped forms. Atomic resolution spectrum imaging reveals that excess Ti is key to the formation of these ladder-structured antiphase boundaries.

Using EELS spectrum imaging, an HfN or Hf(O,N) reaction layer has been identified at the TiN/HfO2 interface in a metal inserted high-k gate stack. The reaction layer has a mean thickness of 0.45nm over an 18nm length of the interface. This reaction layer formed in the original HfO2. By binning the data ×4 along the interface, a variation of the width from 0.35nm to 0.65nm along the interface can be seen. The 10%-90% widths of the elemental profiles can also be found but the binning required is greater (×10). The profile widths are approximately constant along the interface but the values differ from element to element. Thus the reaction has not formed a conformal layer of uniform thickness. An efficient way of processing the data at different levels of binning is described.

High resolution scanning transmission electron microscope (HRSTEM) imaging and electron energy loss spectroscopy spectrum imaging (EELS SI) methods have been successfully applied to the analysis of (Bi0.85Nd0.15)(Fe0.9Ti0.1)O3 (BNFT) ceramics. The atomic scale structural and chemistry of defects in these ceramics have been determined, leading to the discovery of a new class of Nd-rich nanoprecipitates in these ceramics.

Electron energy loss (EEL) spectroscopy and high angle annular dark field (HAADF) imaging in aberration-corrected electron microscopes are powerful techniques to determine the chemical composition and structure of materials at atomic resolution. Aberration correction enables the formation of angstrom sized electron probes that contain enough current for both low loss and near-edge core excitation spectroscopy to be performed. Therefore, spatially distributed EEL spectra can be collected and correlated with atomic resolution HAADF images.

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