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Dislocation mediated alignment processes during gold nanoparticle coalescence were studied at low and high temperatures using molecular dynamics simulations and transmission electron microscopy. Particles underwent rigid body rotations immediately following attachment in both low temperature (500 K) simulated coalescence events and low temperature (∼315 K) transmission electron microscopy beam heating experiments. In many low temperature simulations, some degree of misorientation between particles remained after rigid body rotations, which was accommodated by grain boundary dislocation nodes. These dislocations were either sessile and remained at the interface for the duration of the simulation or dissociated and cross-slipped through the adjacent particles, leading to improved co-alignment. Minimal rigid body rotations were observed during or immediately following attachment in high temperature (1100 K) simulations, which is attributed to enhanced diffusion at the particles' interface. However, rotation was eventually induced by {111} slip on planes parallel to the neck groove. These deformation modes led to the formation of single and multi-fold twins whose structures depended on the initial orientation of the particles. The driving force for {111} slip is attributed to high surface stresses near the intersection of low energy {111} facets in the neck region. The details of this twinning process were examined in detail using simulated trajectories, and the results reveal possible mechanisms for the nucleation and propagation of Shockley partials on consecutive planes. Deformation twinning was also observed in-situ using transmission electron microscopy, which resulted in the co-alignment of a set of the particles' {111} planes across their grain boundary and an increase in their dihedral angle. This constitutes the first detailed experimental observation of deformation twinning during nanoparticle coalescence, validating simulation results presented here and elsewhere.

In this study, strontium titanate bicrystals with a twist grain boundary were successfully formed using a spark plasma sintering apparatus. Diffusion bonding was accomplished at high pressure and fast heating, and provides a novel method to form bicrystals at lower temperatures and accelerated time scales compared to more established techniques. Scanning electron microscopy was used to quantitatively evaluate the degree of successful interfacial bonding. Atomic resolution imaging using transmission election microscopy techniques combined with spatially resolved electron energy-loss spectroscopy measurements confirm a clean and atomically abrupt interface free of secondary phases.

▪ Abstract In the nanoscience era, the properties of many exciting new materials and devices will depend on the details of their composition down to the level of single atoms. Thus the characterization of the structure and electronic properties of matter at the atomic scale is becoming ever more vital for economic and technological as well as for scientific reasons. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) represents a powerful method to link the atomic and electronic structure to macroscopic properties, allowing materials, nanoscale systems, and interfaces to be probed in unprecedented detail. Z-contrast STEM uses electrons that have been scattered to large angles for imaging. The relative intensity of each atomic column is roughly proportional to Z2, where Z is the atomic number. Recent developments in correcting the aberrations of the lenses in the electron microscope have pushed the achievable spatial resolution and the sensitivity for imaging and spectroscopy in the STEM into the sub-Ångstrom (sub-Å) regime, providing a new level of insight into the structure/property relations of complex materials. Images acquired with an aberration-corrected instrument show greatly improved contrast. The signal-to-noise ratio is sufficiently high to allow sensitivity even to single atoms in both imaging and spectroscopy. This is a key achievement because the detection and measurement of the response of individual atoms has become a challenging issue to provide new insight into many fields, such as catalysis, ceramic materials, complex oxide interfaces, or grain boundaries. In this article, the state-of-the-art for the characterization of all of these different types of materials by means of aberration-corrected STEM and EELS are reviewed.

We show that individual Hf atoms may get incorporated into the SiO2 interlayer which is formed between the HfO2 dielectric film and the Si substrate during rapid thermal annealing. We report atomically-resolved Z-contrast images of a Si/SiO2/HfO2 structure together with first-principles calculations which demonstrate that single Hf atoms are in fact present in the interlayer. The location of individual Hf atoms within the interlayer oxide is closely related to the structure of the amorphous oxide near the Si/SiO2 interface. The Hf defects may affect channel mobility and leakage currents in the HfO2/Si electronic devices.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

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

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Temperature dependent current-voltage measurements show that the addition of only 10% Pt to NiSi causes an increase of Schottky barrier height (SBH) from 0.65 eV for NiSi to 0.78 eV for the 10% Pt alloy. Internal photoemission measurements resolve two SBHs in all alloyed samples with ≥5% Pt incorporation corresponding to NiSi and PtSi (∼0.68 eV and ∼0.80 eV), proving that each contributes independently to junction current. High angle annular dark field imaging with scanning transmission electron microscopy confirms Pt segregation to the Ni(Pt)Si/Si interface. The resulting increased SBH may therefore be detrimental to contact resistivity in future technology nodes.

The VG Microscopes 100 kV and 300 kV scanning transmission electron microscopes at Oak Ridge National Laboratory were equipped with Nion aberration correctors several years ago. This chapter reviews our experience with these correctors, specifically, the reduction in probe size by more than a factor of two and the associated benefits for materials research, which extend far beyond improved resolution. A smaller, brighter probe brings enhanced image contrast and signal to noise ratio, making it possible to image light atom columns in materials such as oxide perovskites. It vastly increases the sensitivity to single atoms, both for imaging and electron energy loss spectroscopy. In addition, aberration correction greatly improves the collection efficiency for bright field phase contrast imaging, allowing simultaneous, aberration-corrected, Zcontrast and phase contrast imaging. Finally, the larger probe-forming aperture gives a reduced depth of field, giving a depth resolution less than the thickness of a typical specimen. It becomes possible to focus directly on features at different depths in the specimen, and three-dimensional information can be extracted with single atom sensitivity. In conjunction with density functional and elasticity theory, these advances provide a new level of insight into the atomistic origins of materials properties. Several examples are discussedmore » that illustrate the potential for applications including the detection of orbital occupation stripes and interface stacking in complex oxides, the mechanism for improved critical currents in Ca-doped grain boundaries in high-Tc superconductors, the segregation of rare earth dopants in Si3N4 grain boundaries, the quantitative analysis of strain-induced growth phenomena in semiconductor quantum wells, the determination of the three-dimensional distribution of stray Hf atoms in a high dielectric constant device structure, and the origin of the remarkable catalytic activity of Au nanoparticles« less

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

The recent successful correction of lens aberrations in the electron microscope has improved resolution by more than a factor of two in just a few years, bringing many benefits for the study of materials. These benefits extend significantly beyond enhanced resolution alone. Aberration correction gives higher resolution by allowing the objective lens to have a wider aperture, which also results in a reduced depth of field. This effect can be used to only focus specific sections inside materials for the first time. In this contribution we describe recent results exploiting this capability. Additionally, we show how combining the microscopy data with first–principles theory gives new insights into materials properties. We cover two applications, both involving heavy atoms in a lighter host. The first shows how single Hf atoms can be mapped in three dimensions inside the 1 nm–wide SiO2 region of a high dielectric constant device structure, and how a link to macroscopic device properties results through theoretical calculations. The second example is from the field of nanoscience, where individual Au atoms are imaged inside Si nanowires grown by a vapour–liquid–solid mechanism. The majority of Au atoms are probably injected by the highly energetic electron beam. However, their observed sites and atomic configurations represent at least meta–stable configurations and match well to results from density functional calculations.

The influence of Hf-based dielectrics on the underlying SiO2 interfacial layer (IL) in high-k gate stacks is investigated. An increase in the IL dielectric constant, which correlates to an increase of the positive fixed charge density in the IL, is found to depend on the starting, pre-high-k deposition thickness of the IL. Electron energy-loss spectroscopy and electron spin resonance spectra exhibit signatures of the high-k-induced oxygen deficiency in the IL consistent with the electrical data. It is concluded that high temperature processing generates oxygen vacancies in the IL responsible for the observed trend in transistor performance.