Aberration-Corrected STEM-EELS Research Articles

Influence of Frozen Curation on Volatile Retention in Pristine Apollo 17 Samples: Initial Results Using Aberration-Corrected STEM-EELS and EDS

Influence of Frozen Curation on Volatile Retention in Pristine Apollo 17 Samples: Initial Results Using Aberration-Corrected STEM-EELS and EDS

Measuring Electronic and Structural Transformations in Solar Thermochemical Water Splitting Materials with Aberration-Corrected STEM-EELS

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Atomistic origin of high-concentration Ce3+ in {100}-faceted Cr-substituted CeO2 nanocrystals

Improving the potential of promising CeO2-based nanocatalysts in practical applications requires an atomic-scale analysis of the effects of active dopants on the distribution of Ce valence states and the formation of oxygen vacancies (VOs). In this study, a Cr dopant is introduced into the cubic {100}-faceted CeO2 nanocrystals (NCs) with an average size of 7.8 nm via supercritical water. The Cr dopants substitute Ce sites in the amount of approximately 3 mol%. Based on the aberration-corrected STEM-EELS, the effects of Cr dopant on the distribution of cerium valence states are investigated layer by layer across the ultrafine Cr-substituted CeO2 NC perpendicular to the {100} exposed facet. It is found that an increased amount of Ce3+ cations is present in Cr-substituted CeO2 NCs, particularly in the internal atomic layers, compared to the pristine CeO2 NCs. The atomic-scale analysis of the local structure combined with theoretical calculations demonstrates that Cr dopant reduces the formation energy of VOs and increases the mobility of oxygen atoms for the nano-sized CeO2. These effects, in principle, result in an improved oxygen storage capacity and provide a fundamental understanding of role of the dopant in the formation and distribution of VOs in the doped CeO2 NCs.

Atomistic Origin of High-Concentration Ce <sup>3</sup>+ in {100}-Faceted Cr-Doped CeO <sub>2</sub> Nanocrystals

Improving the potential of promising CeO2-based nanocatalysts in practical applications requires an atomic-scale analysis of the effects of active dopants on the distribution of Ce valence states and the formation of oxygen vacancies (Vos). In this study, a Cr dopant is introduced into the cubic {100}-faceted CeO2 nanocrystals (NCs) with an average size of 7.8 nm via supercritical water. The Cr dopants substitute Ce sites in the amount of approximately 3 mol%. Based on the aberration-corrected STEM-EELS, the effects of Cr dopant on the distribution of cation valence states in the Cr-doped CeO2 NCs are investigated layer by layer across the ultrafine Cr-doped CeO2 NC perpendicular to the {100} exposed facet. It is found that an increased amount of Ce3+ cations is present in Cr-doped CeO2 NCs, particularly in the internal atomic layers, compared to the non-doped CeO2 NCs. The atomic-scale analysis of the local structure combined with theoretical calculations demonstrates that Cr dopant reduces the formation energy of Vos and increases mobility of oxygen atoms for the nano-sized CeO2. These effects, in principle, result in an improved oxygen storage capacity and provide a fundamental understanding of role of the dopant in the formation and distribution of VOs in the doped CeO2 NCs.

Impurity Segregation via Extended Defects in Oxide Thin Films Probed by Aberration-Corrected STEM-EELS

Impurity Segregation via Extended Defects in Oxide Thin Films Probed by Aberration-Corrected STEM-EELS

Nanophase Fe-Oxide, Fe-Sulfide, and Ilmenite in High-Ti Lunar Soil using Aberration-Corrected STEM-EELS and EDS

Nanophase Fe-Oxide, Fe-Sulfide, and Ilmenite in High-Ti Lunar Soil using Aberration-Corrected STEM-EELS and EDS

Strain Control at Two-Dimensional Oxide Interfaces Probed by Aberration-Corrected STEM-EELS

Strain Control at Two-Dimensional Oxide Interfaces Probed by Aberration-Corrected STEM-EELS

Grain Boundary Segregation Behavior of Boron in Low-Alloy Steel

The boron concentration profiles around prior austenite grain boundaries in Fe-0.05C-0.5Mo-0.001B (mass pct) are examined using aberration-corrected STEM-EELS. In order to obtain the precise distribution of boron around the boundaries, tilt series measurements with thin specimens (<30 nm) are performed and the EEL spectra are analyzed by principal component analysis (PCA) and multivariate curve resolution (MCR). The boron concentration profile changes with the cooling rate from the solid solution temperature. The concentration at grain boundaries is maximized at a medium rate (30 °C/s), where the concentration reaches 8 at. pct, and it decreases at a larger (250 °C/s) or smaller (5 °C/s) rate. On the other hand, the boron distribution becomes wider as the cooling rate becomes smaller. The current results suggest that the boron segregation in the alloy is formed by the “non-equilibrium segregation mechanism.”

The nature of electrostatic potential fluctuations in Cu2ZnSnS4 and their role on photovoltaic device performance

Aberration corrected STEM EELS is used to investigate point defects in Cu2ZnSnS4 (CZTS). Nano-scale clusters of ZnCu anti-site donors are observed with the donor concentration being sufficiently high to degenerately dope the semiconductor. Uncompensated donors and acceptors result in electrostatic potential fluctuations within the material. The effect of these potential fluctuations on the photovoltaic device properties is discussed.

Boron segregation to austenite grain boundary in low alloy steel measured by aberration corrected STEM–EELS

Boron concentration profile around prior austenite grain boundaries in Fe-0.05C–0.5Mo–0.001B (mass%) is examined by using aberration corrected STEM–EELS. Tilt series measurements of line analysis with a thin specimen (<30nm) and the principal component analysis (PCA) are performed to obtain the precise distribution of boron around the boundary. The concentration on the grain boundary reaches beyond 8at% and the distribution width is about 1.2nm. The effects of the boundary inclination and the specimen thickness are also examined by calculation based on the Gaussian broadening model. The obtained concentration profile implies that the boron segregation in the present material is formed by ‘non-equilibrium segregation mechanism’.

Nanoscale Chemical and Structural Characterization of Transient Metallic Nanowires using Aberration-Corrected STEM-EELS

Direct chemical and structural characterization of transient iron-nickel alloy nanowires was performed at subnanometer spatial resolution using probe spherical aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy. Nanowires with diameter less than 2 nm retaining their nominal bulk alloy composition were observed. In some cases, the nanowires were oxidized. Before rupture, a nanojunction as thin as three atoms in width could be imaged. The time-dependent structural analyses revealed the nanowire rupture mechanisms. It is found that the atoms on the {111} planes were the easiest to be removed by electron irradiation and fluctuations between low-energy and high-energy facets were observed. The hitherto unknown rich variety of structural and chemical behavior in alloyed magnetic nanojunctions should be considered for understanding their physical properties.

Correlating Nanoscale Defects with Electronic Properties in MgO Magnetic Tunnel Junctions by Aberration-Corrected STEM-EELS

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.