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Gallium ion (Ga+) beam damage induced indium (In) precipitation in indium gallium arsenide (InGaAs)/indium aluminium arsenide (InAlAs) multiple quantum wells and its corresponding evolution under electron beam irradiation was investigated by valence electron energy loss spectroscopy (VEELS) and high‐angle annular dark‐field imaging (HAADF) in scanning transmission electron microscopy (STEM). Compared with argon ion milling for sample preparation, the heavier projectiles of Ga+ ions pose a risk to trigger In formation in the form of tiny metallic In clusters. These are shown to be sensitive to electron irradiation and can increase in number and size under the electron beam, deteriorating the structure. Our finding reveals the potential risk of formation of In clusters during focused ion beam (FIB) preparation of InGaAs/InAlAs quantum well samples and their subsequent growth under STEM‐HAADF imaging, where initially invisible In clusters of a few atoms can move and swell during electron beam exposure. LAY DESCRIPTION: In this paper, the evolution of Ga+ implantation induced In precipitation in InGaAs/InAlAs multiple quantum wells under electron beam irradiation was investigated by valence electron energy loss spectroscopy (VEELs), energy dispersive X‐ray spectroscopy (EDXs) and high‐angle annular dark‐field (HAADF) imaging technique based in a probe aberration corrected scanning transmission electron microscope. In contrast to Ar+ ion bombardment, the projectile of focused Ga+ ions is able to trigger the clustering of In interstitials in InGaAs/InAlAs multiple quantum wells, which allows the formation of metallic In precipitates. Afterwards, by exploiting an extensive electron beam rastering on the region of In precipitation, the increase of electron irradiation time could lead to a pronounced swelling of In cluster size. Especially for the region contains In precipitates of several atoms, where the morphology of In cluster is invisible in atomic image. The continuous electron irradiation could give rise to the promotion of In clustering, allowing the structure of In precipitates been resolved by HAADF image. Our finding reveals the potential risk of formation of In precipitates during focused Ga+ ion beam bombarded InGaAs/InAlAs semiconductors and the subsequent evolution of In clustering under electron beam rastering. These findings emphasise the need for caution when studying FIB prepared In‐based III–V quantum well specimens using TEM even in the In(Ga,Al)As system, as the initially formed In‐rich clusters are so small they can remain invisible for some time. [ABSTRACT FROM AUTHOR]

Three‐dimensional electron diffraction (3D ED) has become an effective technique to determine the structures of submicrometre‐ (nanometre‐)sized crystals. In this work, energy‐filtered 3D ED was implemented using a post‐column energy filter in both STEM mode and TEM mode [(S)TEM denoting (scanning) transmission electron microscope]. The setups for performing energy‐filtered 3D ED on a Gatan imaging filter are described. The technique and protocol improve the accessibility of energy‐filtered 3D ED post‐column energy filters, which are available in many TEM laboratories. In addition, a crystal tracking method in STEM mode using high‐angle annular dark‐field imaging is proposed. This method enables the user to monitor the crystal position while collecting 3D ED data at the same time, allowing a larger tilt range without foregoing any diffraction frames or imposing extra electron dose. In order to compare the differences between energy‐filtered and unfiltered 3D ED data sets, three well known crystallized inorganic samples have been studied in detail. For these samples, the final R1 values improved by 10–30% for the energy‐filtered data sets compared with the unfiltered data sets, and the structures became more chemically reasonable. Possible reasons for improvement are also discussed. [ABSTRACT FROM AUTHOR]

Quaternary alloys are essential for the development of high-performance optoelectronic devices. However, immiscibility of the constituent elements can make these materials vulnerable to phase segregation, which degrades the optical and electrical properties of the solid. High-efficiency III-V photovoltaic cells are particularly sensitive to this degradation. InAlAsSb lattice matched to InP is a promising candidate material for high-bandgap subcells of a multijunction photovoltaic device. However, previous studies of this material have identified characteristic signatures of compositional variation, including anomalous low-energy photoluminescence. In this work, atomic-scale clustering is observed in InAlAsSb via quantitative scanning transmission electron microscopy. Image quantification of atomic column intensity ratios enables the comparison with simulated images, confirming the presence of nonrandom compositional variation in this multispecies alloy.

Rapid solidification of the intermetallic Ni 3 Sn compound from an undercooled liquid was investigated using time-resolved synchrotron X-ray diffraction. Primary growth of an ordered and a disordered cubic solid was observed in situ at a low and a high undercooling, respectively. The disordered cubic solid was reordered after rapid solidification and experienced a solid-state transformation in cooling. A HRTEM study revealed high density of crystal defects and nanodomains in the transformed matrix. A HAADF-STEM study determined that the nanodomains are antiphase domains with chemical disorder. These observations indicated a possibility of online control of mechanical properties in additively manufactured intermetallics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Sequential Au and Ag ion implantation of 260 nm thick TiN films was performed. • The implantation was done using high ion fluences of Ag (200 keV) and Au (150 keV). • The TiN surface undergoes topographic and chemical changes after ion implantation. • Spherical and crystalline particles with the diameter below 15 nm were formed. • STEM showed that the obtained nanoparticles are Au-Ag alloys. Formation of Au-Ag alloy nanoparticles in TiN thin films is demonstrated through sequential implantation of Au and Ag ions. The irradiations were done with 200 keV Au ions at fluence of 1.0 × 1016 ions/cm2 and 150 keV Ag ions to the fluences in the range of 0.7–1.3 × 1017 ions/cm2. It was found that irradiations introduce around 1.5 at.% of gold and up to ~20 at.% of silver species causing also the significant sputtering of the surface. TiN surface besides the topographic undergoes chemical changes. The presence of silver and gold is confirmed by photoemission spectroscopy showing that the implanted ions did not form any kind of compound with the surrounding matrix. Electron microscopy evidenced the formation of crystalline and quasi-spherical particles with dimensions below 10 nm. Elemental analysis revealed that the obtained nanoparticles present Au-Ag alloys, with two elements mixed over the whole volume of the particles in different Au:Ag ratios. [ABSTRACT FROM AUTHOR]

The interfacial atomic structure of epitaxial Fe films grown by molecular beam epitaxy on c(4x4) reconstructed (001) GaAs was investigated using high-angle annular dark-field imaging in scanning transmission electron microscopy. No extended interfacial reaction phase is observed and the image contrast is discussed in terms of the interface atomic configuration. The images show an As-terminated semiconductor. The interface consists of a single partially occupied plane inserted between the Fe film and the GaAs, which most likely is occupied by Fe. This interface structure provides strong evidence for preferential Fe–As bonding across the interface.

To provide mechanistic insight into the phase stability of M 23 C 6 under irradiation, bulk M 23 C 6 (Cr-W-C system) specimens with a W concentration range of 0–12 at.% were first subjected to helium ion irradiation and then investigated by systematic TEM/STEM observation. The atomic resolution electron microscopy analysis revealed that the preferential occupation site of the W atom is the 8c site, and the 48 h site is also occupied when the W concentration is >7 at.%. The atomic arrangement of the M 23 C 6 particle in F82H steel is similar to that of the specimen of 1 W (3 at.% W), and the chemical formula of the M 23 C 6 particle in F82H steel is described as Cr 13 Fe 9 W 1 C 6. Radiation-induced amorphization was strongly related to the W concentration in the bulk M 23 C 6 , and amorphization was observed only at W concentrations of ∼12 at.% under the present irradiation condition. Line analysis of HAADF and its FFT images confirmed the chemical disordering associated with W atoms, which appears to increase with increasing W concentration. Based on these results, the mechanism of radiation-induced amorphization appears to be different between bulk M 23 C 6 and the M 23 C 6 particles. Specifically, the amorphization of bulk M 23 C 6 is mainly influenced by the addition of a high concentration of W, while the synergistic effects of elements including Cr, Fe, and W are attributed to RIA in fine M 23 C 6 particles. Moreover, the energetic change associated with the W/Fe atom exchange in the M 23 C 6 system is estimated to explain the occurrence of chemical disordering and its resultant amorphization behavior, which provides a new viewpoint to achieve a deeper understanding of the mechanisms behind radiation-induced amorphization. The chemical composition of M 23 C 6 particles in F82H steel and the hypothesis of its radiation-induced amorphization mechanism was proposed by HREM observation of He-irradiated M 23 C 6 ingots. [ABSTRACT FROM AUTHOR]

High-angle annular dark-field imaging in scanning transmission electron microscopy and x-ray photoelectron spectroscopy were used to investigate thermal SiO2 layers doped with Hf by ion-implantation. Hf was mobile under the focused electron beam in the asimplanted samples. After annealing for 5 min at 1200 °C, clusters of crystalline HfO2 were observed that were a few nm in size and surrounded by residual Hf that had remained trapped in the SiO2. Hf was not mobile under the electron beam in the annealed samples. Further annealing caused an expansion of the SiO2 that was damaged by ionimplantation. Hf rearrangement was confined to the ion beam damaged regions of the SiO2 layer. No diffusion of Hf into the undamaged SiO2 was observed. The implications of the results for complementary metal-oxide-semiconductor transistors with HfO2 gate dielectrics are discussed.

The influence of thick (~10 nm) AlN overlayers on the interface structure and reactions in Si gate stacks with HfO2 dielectrics was investigated. Annealing caused a reduction of the interfacial SiO2 at the Si interface. At high temperatures (~1000 °C) a silicide reaction was observed at the HfO2/Si interface. No reactions were observed for stacks processed similarly but with WN or TiN overlayers instead of AlN. The reaction mechanisms, in particular, the role of oxygen deficiency of the HfO2, and the consequences for the electrical properties are discussed.

Atomic resolution high-angle annular dark-field imaging (HAADF) in scanning transmission electron microscopy was used to investigate the interface atomic structure of epitaxial, (111) oriented SrTiO3 films on epitaxial Pt electrodes grown on (0001) sapphire. The cube-on-cube orientation relationship of SrTiO3 on Pt was promoted by the use of a Ti adhesion layer underneath the Pt electrode. While a Ti-rich Pt surface was observed before SrTiO3 growth, HAADF images showed an atomically abrupt SrTiO3/Pt interface with no interfacial layers. The SrTiO3 films contained two twin variants that were related by a 180° rotation about the surface normal. HAADF images showed two different interface atomic arrangements for the two twins. The role of Ti in promoting (111) epitaxy and the implications for the dielectric properties are discussed.

High-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy was used to determine the atomic structure of interfaces between epitaxial ErAs layers with the cubic rock salt structure and In0.53Ga0.47As and GaAs, respectively. All layers were grown by molecular beam epitaxy. We show that the interfacial atomic arrangement corresponds to the so-called chain model, in which the zinc blende semiconductor is terminated with a Ga layer. Image analysis was used to quantify the expansion between the first ErAs plane and the terminating Ga plane. In the HAADF images, a high intensity transfer from the heavy Er columns into the background was observed in the ErAs layer, whereas the background in In0.53Ga0.47As was of much lower intensity.

In this study, we demonstrated the formation of a new type of AuAg@Ag nanostructure in titanium nitride (TiN) thin films using sequential implantation of Au and Ag ions. The TiN films deposited by DC reactive sputtering were sequentially implanted with 200 keV gold ions at fluences of 0.5 × 1016 and 1 × 1016 ions/cm2 and 150 keV silver ions at fluences of 1 × 1016, 2 × 1016, 3 × 1016, and 4 × 1016 ions/cm2. Formation of spherical-like particles with dimensions below 10 nm, homogeneously distributed along the ion track of implanted ions is verified by high resolution transmission electron microscopy. Specific nanostructure containing Au Ag alloy in the center of the particle and only silver on the periphery was found in the TiN sample sequentially implanted with 1.0 × 1016 ions/cm2 of Au and 4 × 1016 ions/cm2 of Ag using high angle annular dark field scanning electron microscopy together with elemental mapping analysis. On the other hand, for the sample implanted with 0.5 × 1016 ions/cm2 of Au and 4 × 1016 ions/cm2 of Ag only formation of Au Ag alloy was observed. A mechanism for the formation of a new type core/shell nanostructure in ion implanted TiN thin films is proposed. By varying the implantation fluence of the gold and silver ions properly, the optimized experimental parameters for creation of a specific AuAg@Ag core/shell nanoparticles were achieved. • TiN films were implanted sequentially with Au and Ag ions at different fluences. • Formed nanostructures are influenced by gold ion fluence. • The formation of spherical like nanoparticles below 10 nm is identified. • Au Ag alloy nanoparticles were obtained using lower concentration of gold ions. • A new AuAg@Ag core/shell nanostructures were formed with higher Au concentration. [ABSTRACT FROM AUTHOR]

The bonding interface of pure Al – galvanized steel spot magnetic pulse welds was characterized at the atomic scale. The Al-Zn interface microstructure is worthy of attention as it contains a few micrometers thick biphased layer. This singular layer consists of an aggregate of grains with a 200 to 400 nm size containing islands of either Al or Zn solid solutions oversaturated in Zn or Al, respectively. Inside a grain, some mottled contrasts with a size in-between 5 and 10 nm correspond to fluctuant solute contents. Besides, some native oxides have been dissolved at the interface suggesting the incorporation of oxygen atoms in the biphased layer. Large and elongated (Al,Fe,Si) particles primitively contained in the base Al were also dissolved which gives rise to some round shaped Si particles in the biphased layer. All these microstructural features and changes are consistent with a ballistic origin. Due to both the absence of solidification defects and the rather planar morphology of the bonding interface, the process is expected to occur at the solid state. • The dissimilar magnetic pulse joint interface is formed via a ballistic mechanism. • The large (Al + Zn) bonding interface is expected to form at the solid state. • The randomly distributed grains at the interface present various crystal orientations. • Oversaturated Al and Zn based solid solutions with local enrichments are detected. • Precipitates dissolution and formation occurred during welding at the interface. [ABSTRACT FROM AUTHOR]

If quantitative scanning transmission electron microscopy is used for very precise thickness measurements with atomic resolution, it is commonly referred to as »atom counting«. Due to scattering and the finite probe extent the signal recorded in one atomic column is dependent not only on its own height but also on the height of its neighbours. Especially for thicker specimens this crosstalk effect can have significant impact on the measured intensity. If it is not appropriately accounted for in the evaluation, it can result in a deterioration of accuracy that impedes the possibility of actual atom counting. However, as the number of possible neighbour configurations can be excessively large, a comprehensive consideration of all in the evaluation reference is neigh impossible. This work proposes a method that allows for the a-posteriori reduction of crosstalk during the evaluation by algebraic means. Based on a parametric model, which is described in detail in the article, the crosstalk is expressed by an invertible matrix. Applying the inverted matrix to the measurement yields crosstalk corrected intensity values with very little computational effort. These can subsequently be evaluated by direct comparison to simple reference data. The working principle of the method is presented on the example of crystalline gold. The crosstalk parametrisation is found by fitting a model to sets of specifically created multislice simulations. The parameters are given for both aberration corrected and uncorrected STEM. Subsequently the abilities and potential of the technique are assessed in simulative studies on multiple model systems including gold nanoparticles. Overall a significant and robust improvement of the attainable precision can be demonstrated making the proposed method a promising tool for reference-based atom counting. • A scheme for the correction of column crosstalk in STEM is proposed. • Crosstalk is modelled by a parametrised, linear matrix expression. • Using this parametrisation, crosstalk can be reversed a-posteriori. • Parameters for crystalline gold were determined using multislice simulations. • A clear improvement of the accuracy of atomic column height determination (atom counting) is demonstrated. [ABSTRACT FROM AUTHOR]

The structure of defects and their elemental distributions is the decisive factor to metal’s mechanical properties. The γ/γ′ structure Co-Al-W-based superalloy is a potential replicable alloy to Ni-based superalloys that have been used for a long time. Revealing the microstructure of a defect induced by high-temperature crept provides direct clues for the alloy development. Our work revealed the high-resolution, high-angle annular dark field images and corresponding elemental distributions on crept defects. Defects in the γ phase mainly contain dislocation networks, while the γ′ phase contains lots of stacking faults and anti-phase boundaries. The results indicate that dislocation networks and stacking faults contain more weight elements than the base γ′ phase, while anti-phase boundaries contain more light elements. Disclosing atomic structure and its elemental distributions gives direct evidence for alloy design and further high-temperature mechanical improvement.

Abstract Annealing-induced microstructural changes in yttria partially stabilized zirconia (YSZ) have been investigated by scanning transmission electron microscopy combined with computer simulation. It is shown that the high-temperature annealing results in the formation of voids in YSZ and structural ordering in the surrounding area of the voids. Atomic-scale Z -contrast imaging shows one-dimensional distortion of the cation sub-lattice by alternate arrangement of narrow and wide (100) planes of the cation sub-lattice along the [100] direction of the cubic ZrO2 structure. Such distortion of the cation sub-lattice is attributed to the 1/4[001] displacement of the oxygen atoms in the (100) plane, which is confirmed experimentally by annual bright field imaging along with the density-functional theory and computer simulations of the atomic-scale Z -contrast imaging and electron diffraction. Highlights • Annealing at 1200 °C leads to the formation of a high density of nanometer sized voids inside the YSZ. • The crystal structure of YSZ becomes ordered in the surrounding area of the voids. • The cation sub-lattice shows one-dimensional distortion with alternative arrangement of narrow and wide (100) planes. • The distortion of the cation sub-lattice is attributed to the 1/4[001] displacement of oxygen atoms in the (001) plane. [ABSTRACT FROM AUTHOR]

Highlights • Interface evolution of Co/Mo 2 C/Y and Co/Y/Mo 2 C periodic multilayer systems upon annealing by STEM were studied. • Both kinds of samples show significant amount of intermixing even in the as-deposited state. • Sharpening interface for samples annealed at 600°C is observed. • Most of the mixing occurs between the Co and the Mo elements, the Y layers staying comparatively preserved. [ABSTRACT FROM AUTHOR]

MoW catalysts supported on Al 2 O 3 with equal surface content of metals (Mo + W = 3.9 at/nm 2 ) were synthesized by using mixed Keggin type heteropolyacids ( HPAs ) H 4 [SiMo 1 W 11 O 40 ] and H 4 [SiMo 3 W 9 O 40 ] and corresponding mixture of monometallic H 4 [SiMo 12 O 40 ] and H 4 [SiW 12 O 40 ] HPAs. After liquid phase sulfidation, catalysts were characterized by high-resolution transmission electron microscopy ( HRTEM ) and X-ray photoelectron spectroscopy ( XPS ). For the first time, High Angle Annular Dark Field microscopy ( HAADF ) was used to evidence the morphology and composition of the active sulfide phase. The catalysts were tested in hydrotreating of model feed that contained dibenzothiophene ( DBT ) and naphthalene. Using mixed SiMo n W 12-n HPAs as starting precursors had a beneficial effect on the catalytic activity. Incorporation of molybdenum in the structure of SiW Keggin-type HPA led to a decrease of the size of active phase crystallites, to an increase of the metal sulfidation degree and of the number of active sites. Substitution of a quarter of tungsten atoms by molybdenum allowed to achieve DBT conversion comparable to value obtained on pure SiMo 12 HPA based catalyst and higher conversion of naphthalene. Both SiMo n W 12-n HPAs based catalysts had higher rate constants in studied reactions compared to their corresponding references prepared from two separate monometallic HPAs. Moreover, Mo n W 12-n /Al 2 O 3 catalysts had the highest selectivity in respect of hydrogenation ( HYD ) pathway of DBT hydrodesulfurization ( HDS ). The presence of mixed Mo x W 1-x S 2 slabs was evidenced by HAADF analysis. On Mo 3 W 9 /Al 2 O 3 , small randomly distributed islands of Mo were present in the WS 2 slabs, while on Mo 3 + W 9 /Al 2 O 3 , Mo islands appeared larger and in the core of the WS 2 slabs. Moreover, on this last sample, some monometallic slabs were also present. It was concluded that using mixed HPA precursors resulted in the formation of mixed Mo x W 1-x S 2 active phase possessing higher synergetic effect between the two metals and consequently higher catalytic activity. [ABSTRACT FROM AUTHOR]

In the present work, direct and detailed investigation was carried out with respect to the precipitation in the grit-blasted single-crystal superalloy of DD6 after thermal exposure at 1100°C for 8 h. The precipitation was confirmed to be an orthorhombic topologically close-packed phase of P. In the phase, abundant atomic stacking faults were clearly revealed by bright field transmission electron microscope imaging and high-resolution HAADF imaging. Furthermore, statistical analysis for the 42 P phase particles observed by electron backscattered diffraction revealed that they had a mean size of 0.21 µm and volume percentage of 0.172% in the recrystallised region. The orientation distribution was essentially random besides very weak textures of {511}<0-32> and {921}<0-15>. [ABSTRACT FROM AUTHOR]

The development of reliable interconnects in thermoelectric (TE) modules is essential for the durability and serviceability of these solid-state devices. PbTe-based devices are used in mid-temperature range applications, with Ni being the most preferred interconnect. Ni reacts with PbTe to form a binary intermetallic, Ni 3 Te 2 (β 2). The sustained growth of this phase at higher service temperatures is adversarial to the long-term reliability of interconnects. This paper reports and discusses the beneficiary role of minor Fe-addition in the Ni contact alloy to arrest such unwarranted chemical interaction while ensuring proper bonding. PbTe and Ni-Fe (Fe = 1 at.%, 5 at.%) discs are diffusion bonded at 700 °C for various holding times. The current investigation leads to three noteworthy observations: 1) the formation of Fe-enriched Ni-Fe phase islands at the interface at microscale (1 - 10 µm), (2) Fe-segregation at the local interfaces (∼ 10 nm), and (3) the growth of a Ni-rich metastable Ni 3-x Te phase, not present in Ni-Te binary phase diagram. Detailed examinations of these phenomena and crystallographic relations (β 2 and Ni 3-x Te) are conducted through advanced analytical TEM/STEM techniques. Furthermore, the PbTe-Ni reaction formulation is modified to accommodate such a Fe-enrichment phenomenon and is validated through free energy calculations. [Display omitted] [ABSTRACT FROM AUTHOR]

Analytical electron microscopy was used to examine the grain boundary chemistry in boron carbide containing Al-O-rich phases at triple junctions. In this study, SiO 2 , Al 2 O 3 , and B 2 O 3 additives were used to synthesize an aluminoborosilicate glass on the grain boundaries with the long-term goal to enhance fracture resistance. Nanolayer films were not observed using high-angle annular dark field imaging; however, energy-dispersive spectroscopy quantification revealed grain boundaries with varying excess of Si and Al. Overall, it was concluded variations in grain boundary chemistry depend upon the intrinsic grain boundary character and spatial heterogeneity of the oxide additives. [ABSTRACT FROM AUTHOR]

The adaptation of quantitative STEM techniques to enable atom-counting in supported metal nanoparticles with a modern, conventional (non-aberration-corrected) TEM/STEM (a JEOL JEM2100F) without the need for any modifications or special hardware is presented. No image simulation is required, either. This technique enables the practical analysis of the size, mass, and basic shape information of statistically robust populations of hundreds to thousands of nanoparticles. The methods for performing the necessary calibrations of the microscope and images are detailed. A user-friendly semi-automated analysis program was also written to facilitate high throughput. The program optimizes the analysis parameters, applying the procedure consistently across the entire dataset, enhancing the meaningfulness of the statistics as well as the reproducibility and transferability of the results. A series of atomically precise Au nanoparticles were used to validate the technique, which was determined to be accurate within a (nearly uniform) scaling factor of around two for the given instrument, and could be brought into better agreement with a calibration standard. The magnitude of the disparity was found to significantly and unexpectedly rely on the chosen magnification and spot size, the underlying reasons for which are unclear and likely instrument-dependent. The possible sources of error from the calibration and acquisition were examined and their impact on the accuracy and precision of quantification were estimated. The scattering cross-sections measured using this technique are relatively insensitive to moderate errors in the various detector calibrations but particularly sensitive to pixel size error. [ABSTRACT FROM AUTHOR]

The effect of the tilt of the crystallographic orientation with respect to an incident electron probe on high-angle annular dark field (HAADF) imaging in aberration-corrected scanning transmission electron microscopy (STEM) is investigated in experiment and simulation. A small specimen tilt can lead to unequal deviations of different atom species in the HAADF image and result in further relative displacement between anion and cation. Simulated HAADF images also confirm that the crystal tilt causes an artifact in atom polarization. The effect is derived from the scattering abilities of different atoms. [ABSTRACT FROM AUTHOR]

The success of aberration correction techniques at the end of the 20th century came at a time of increasing need for atomic resolution imaging to better understand known structural defects that influence semiconductor device operation, and to advance the search for new structures and behavior that will form the basis for devices in the future. With this in mind, it is a pleasure to recognize the contributions of Ondrej Krivanek to the success of aberration correction techniques, and his extension of aberration techniques to EELS equipment that further promises to unite structural studies with characterization of behavior from meV to keV energies in the STEM. [ABSTRACT FROM AUTHOR]

Tomographic reconstruction algorithms offer a means by which a tilt-series of transmission images can be combined to yield a three dimensional model of the specimen. Conventional reconstruction algorithms assume that the measured signal is a linear projection of some property, typically the density, of the material. Here we report the use of multislice simulations to investigate the extent to which this assumption is met in HAADF-STEM imaging. The use of simulations allows for a systematic survey of a range of materials and microscope parameters to inform optimal experimental design. Using this approach it is demonstrated that the imaging of amorphous materials is in good agreement with the projection assumption in most cases. Images of crystalline specimens taken along zone-axes are found to be poorly suited for conventional linear reconstruction algorithms due to channelling effects which produce enhanced intensities compared with off-axis images, and poor compliance with the projection requirement. Off-axis images are found to be suitable for reconstruction, though they do not strictly meet the linearity requirement in most cases. It is demonstrated that microscope parameters can be selected to yield improved compliance with the projection requirement. [ABSTRACT FROM AUTHOR]

Abstract 1 1 Abbreviations: LED: light-emitting diode; HAADF-STEM: High-angle annular dark-field scanning transmission electron microscopy; TDS: thermal diffuse scattering; FWHM: full width at half maximum. Three-dimensional (3D) distributional analysis of individual dopant atoms in materials is important to development of optical, electronic, and magnetic materials. In this study, we adopted through-focus high-angle annular dark-field (HAADF) imaging for 3D distributional analysis of Eu dopant atoms in Ca-α-SiAlON phosphors. In this context, the effects of convergence semi-angle and Eu z-position on the HAADF image contrast were investigated. Multi-slice image simulation revealed that the contrast of the dopant site was sensitive to change of the defocus level. When the defocus level matched the depth position of a Eu atom, the contrast intensity was significantly increased. The large convergence semi-angle greatly increased the depth resolution because the electron beam tends spread instead of channeling along the atomic columns. Through-focus HAADF-STEM imaging was used to analyze the Eu atom distribution surrounding 10 nm cubes with defocus steps of 0.68 nm each. The contrast depth profile recorded with a narrow step width clearly analyzed the possible depth positions of Eu atoms. The radial distribution function obtained for the Eu dopants was analyzed using an atomic distribution model that was based on the assumption of random distribution. The result suggested that the Ca concentration did not affect the Eu distribution. The decreased fraction of neighboring Eu atoms along z-direction might be caused by the enhanced short-range Coulomb-like repulsive forces along the z-direction. [ABSTRACT FROM AUTHOR]

In this study, the substitution behavior of Ag atoms in the Ti2AlC ceramic was investigated using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The TEM sample of the Ag/Ti2AlC interaction area was prepared following the wetting experiment, which was carried out at 1030°C for 5 minute using the sessile drop method. The Ag 'single atoms' or 'nanoclusters' were found in the crystal lattice of Ti2AlC substrate. The characterizations along two typical crystallographic orientations suggest that both the Ti and Al atoms could be substituted by Ag atoms during the wetting process. In addition, the substitution behavior would contribute to the lattice expansion, which was coordinated by elastic distortion in the Ag nanoclusters with small size. However, when the Ag nanoclusters exceeded the critical size, the intact Ti2AlC structure could no more sustain and defects like stacking faults formed, based on which the Ag nanotwins or polycrystals nucleated. [ABSTRACT FROM AUTHOR]

In this paper, we propose an algorithm to obtain a three-dimensional reconstruction of a single nanoparticle based on the method of atom counting. The location of atoms in three dimensions has been successfully performed using simulations of high-angle-annular-dark-field images from only three zone-axis projections, [110], [310] and [211], for a face-centred cubic particle. These three orientations are typically accessible by low-tilt holders often used in high-performance scanning transmission electron microscopes. [ABSTRACT FROM AUTHOR]

The detection and quantification of fabrication defects is vital to the ongoing miniaturization of integrated circuits. The atomic resolution of HAADF-STEM combined with the chemical sensitivity of EDS could provide the means by which this is achieved for the next generation of semiconductor devices. To realize this, however, a streamlined acquisition and analysis procedure must first be developed. Here, we report the simulation of a HAADF-STEM and EDS tilt-series dataset of a PMOS finFET device which will be used as a testbed for such a development. The methods used to calculate the data and the details of the specimen model are fully described here. The dataset consists of 179 projections in 2 ° increments with HAADF images and characteristic X-ray maps for each projection. This unusually large calculation has been made possible through the use of a national supercomputer and will be made available for the development and assessment of reconstruction and analysis procedures for this highly significant industrial application. [ABSTRACT FROM AUTHOR]

In order to obtain comprehensive performance, heavy elements were added into superalloys for solid-solution hardening. It is found that, rather than adopting random distributions, the heavy atoms prefer to form short-range ordered columns with heavy-element stripes 1–2 nm in length. This is supported by ourab initiocalculations. Owing to the strong bonding strength between the refractory elements and nickel atoms, this short-range ordering may be beneficial to the mechanical performances of superalloys. [ABSTRACT FROM AUTHOR]

ABSTRACT With the development of spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM), high angle annular dark filed (HAADF) imaging technique has been widely applied in the microstructure characterization of various advanced materials with atomic resolution. However, current qualitative interpretation of the HAADF image is not enough to extract all the useful information. Here a modified peaks finding method was proposed to quantify the HAADF-STEM image to extract structural and chemical information. Firstly, an automatic segmentation technique including numerical filters and watershed algorithm was used to define the sub-areas for each atomic column. Then a 2D Gaussian fitting was carried out to determine the atomic column positions precisely, which provides the geometric information at the unit-cell scale. Furthermore, a self-adaptive integration based on the column position and the covariance of statistical Gaussian distribution were performed. The integrated intensities show very high sensitivity on the mean atomic number with improved signal-to-noise ( S/N) ratio. Consequently, the polarization map and strain distributions were rebuilt from a HAADF-STEM image of the rhombohedral and tetragonal BiFeO3 interface and a MnO2 monolayer in LaAlO3/SrMnO3/SrTiO3 heterostructure was discerned from its neighbor TiO2 layers. Microsc. Res. Tech. 79:820-826, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This work presents recent advances in transmission scanning electron microscopy (t-SEM) imaging control capabilities. A modular aperture system and a cantilever-style sample holder that enable comprehensive angular selectivity of forward-scattered electrons are described. When combined with a commercially available solid-state transmission detector having only basic bright-field and dark-field imaging capabilities, the advances described here enable numerous transmission imaging modes. Several examples are provided that demonstrate how contrast arising from diffraction to mass-thickness can be obtained. Unanticipated image contrast at some imaging conditions is also observed and addressed. [ABSTRACT FROM AUTHOR]

We have evaluated atomic resolution high-angle annular dark field images with ordinary beams and electron vortex beams for thin crystals of bcc iron, explicitly considering the atomic vibrations using molecular dynamics. The shape of the image representing an atomic column depends on the orbital angular momentum, sample thickness and temperature. For electron vortex beams we observe characteristic doughnut-shaped images of atomic columns. It is shown how the thermal diffuse scattering reduces the depth of their central minima, which get further smeared by finite source size effects. In addition, it is shown that in calculations of HAADF-STEM images at low temperatures one has to explicitly consider the nuclear quantum effects (zero point vibrations), otherwise the effect of atomic vibrations is strongly underestimated. [ABSTRACT FROM AUTHOR]

The introduction of preparation artifacts is almost inevitable when producing samples for (scanning) transmission electron microscopy ((S)TEM). These artifacts can be divided in extrinsic artifacts like damage processes and intrinsic artifacts caused by the deviations from the volume strain state in thin elastically strained material systems. The reduction and estimation of those effects is of great importance for the quantitative analysis of (S)TEM images. Thus, optimized ion beam preparation conditions are investigated for high quality samples. Therefore, the surface topology is investigated directly with atomic force microscopy (AFM) on the actual TEM samples. Additionally, the sectioning of those samples by a focused ion beam (FIB) is used to investigate the damage depth profile directly in the TEM. The AFM measurements show good quantitative agreement of sample height modulation due to strain relaxation to finite elements simulations. Strong indications of (sub-) surface damage by ion beams are observed. Their influence on high angle annular dark field (HAADF) imaging is estimated with focus on thickness determination by absolute intensity methods. Data consolidation of AFM and TEM measurements reveals a 3.5 nm surface amorphization, negligible surface roughness on the scale of angstroms and a sub-surface damage profile in the range of up to 8.0 nm in crystalline gallium arsenide (GaAs) and GaAs-based ternary alloys. A correction scheme for thickness evaluation of absolute HAADF intensities is proposed and applied for GaAs based materials. [ABSTRACT FROM AUTHOR]

The growth of III-III-V axial heterostructures in nanowires via the vapor-liquid-solid method is deemed to be unfavorable because of the high solubility of group III elements in the catalyst droplet. In this work, we study the formation by molecular beam epitaxy of self-catalyzed GaAs nanowires with AlxGa1-xAs insertions. The composition profiles are extracted and analyzed with monolayer resolution using high-angle annular dark-field scanning transmission electron microscopy. We test successfully several growth procedures to sharpen the heterointerfaces. For a given nanowire geometry, prefilling the droplet with Al atoms is shown to be the most efficient way to reduce the width of the GaAs/AlxGa1-xAs interface. Using the thermodynamic data available in the literature, we develop numerical and analytical models of the composition profiles, showing very good agreement with experiments. These models suggest that atomically sharp interfaces are attainable for catalyst droplets of small volumes. [ABSTRACT FROM AUTHOR]

Piezoelectric and spontaneous polarization play an essential role in GaN-based devices. InGaN quantum wells (QWs) in GaN host material, especially grown along the polar c-direction, exhibit strong internal fields in the QW region due to the indium-induced strain. An exact knowledge of the electric fields is essential, since they are one of the factors limiting the performance of green LDs and LEDs. Differential phase contrast in a scanning transmission electron microscope enables direct, local, and quantitative measurements of these electric fields. For a multi-QW sample, it was possible to determine the piezoelectric field in the range of 43-67 MV m−1 with a resolution of 10 MV m−1 ( [ABSTRACT FROM AUTHOR]

The geometry of atom probe tomography tips strongly differs from standard scanning transmission electron microscopy foils. Whereas the later are rather flat and thin (<20 nm), tips display a curved surface and a significantly larger thickness. As far as a correlative approach aims at analysing the same specimen by both techniques, it is mandatory to explore the limits and advantages imposed by the particular geometry of atom probe tomography specimens. Based on simulations (electron probe propagation and image simulations), the possibility to apply quantitative high angle annular dark field scanning transmission electron microscopy to of atom probe tomography specimens has been tested. The influence of electron probe convergence and the benefice of deconvolution of electron probe point spread function electron have been established. Atom counting in atom probe tomography specimens is for the first time reported in this present work. It is demonstrated that, based on single projections of high angle annular dark field imaging, significant quantitative information can be used as additional input for refining the data obtained by correlative analysis of the specimen in APT, therefore opening new perspectives in the field of atomic scale tomography. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes using phosphorescent dyes (PHOLEDs) have excellent performance, with internal quantum efficiencies approaching 100%. To maximize their performance, PHOLED devices use a conductive organic host material with a sufficiently dispersed phosphorescent guest to avoid concentration quenching. Fac-tris(2-phenylpyridine) iridium, [Ir(ppy) 3 ] is one of the most widely used green phosphorescent organic compounds. In this work, we used scanning transmission electron microscopy (STEM) equipped with HAADF (high-angle annular dark-field) and EDS (energy dispersive X-ray spectroscopy) detectors to analyze the distribution of the [Ir(ppy) 3 ] concentration in the host material. This analysis technique, employed for the first time in co-deposited organic thin films, can simultaneously obtain an image and its respective chemical information, allowing for definitive characterization of the distribution and morphology of [Ir(ppy) 3 ]. The technique was also used to analyze the effect of the vibration of the substrate during thermal co-deposition of the [Ir(ppy) 3 ] molecules into an organic matrix. [ABSTRACT FROM AUTHOR]

In this paper, the local compositional and structural changes occurring in association with stacking faults in a Ni-base superalloy are characterized and related to the possible rate-controlling processes during creep deformation at intermediate temperatures. These rate-controlling processes are not presently understood. In order to promote stacking fault shearing, compression creep tests on specially prepared single crystals of an exploratory Ni-base superalloy were conducted at 760 °C in the [0 0 1] orientation. Scanning transmission electron microscopy (STEM) imaging was coupled with state-of-the-art energy dispersive X-ray (EDX) spectroscopy to reveal for the first time an ordered compositional variation along the extrinsic faults inside the γ′ precipitates, and a distinct solute atmosphere surrounding the leading partial dislocations. The local structure and chemistry at the extrinsic fault is consistent with the η phase, a D0 24 hexagonal structure. Density Functional Theory (DFT) and high angle annular dark field (HAADF)-STEM image simulations are consistent with local η phase formation and indicate that a displacive–diffusive transformation occurs dynamically during deformation. [ABSTRACT FROM AUTHOR]

Ni x Zn 1− x Ga 2 O 4 has already been demonstrated as a noteworthy example of potentially useful catalytic properties such as NO x reduction. In our previous work, it was interesting to find out that the operating temperature of NiGa 2 O 4 catalyst in NO x reduction can be tuned by simple chemical substitution of Ni 2+ by Zn 2+ . It is believed that the mechanism behind such stoichiometry-dependence on operating temperature should be strongly correlated with microstructure, surface morphology as well as the local composition of the nanocatalysts. In the present investigation, Ni x Zn 1− x Ga 2 O 4 solid solution was synthesized via a hydrothermal ion-exchange reaction, using NaGaO 2 and the corresponding acetic salts as the starting materials. By means of a state-of-the-art aberration corrected STEM and high resolution TEM, the structural and chemical characterization at the atomic scale on the Ni x Zn 1− x Ga 2 O 4 nanocatalyst was carried out, including the crystal structure, size, morphology, surface structure and local composition. It is found that the catalyst was solid solution and most possible exposed facets may be (1 1 1). [ABSTRACT FROM AUTHOR]