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Pulsed infrared laser irradiation was used to modify the optical and physical properties of gold nanoparticles in a SiO2 substrate. The primary laser wavelength used for annealing was 8 μm, where the primary absorption was in the substrate. The optical absorption spectra exhibit a typical surface plasmon peak at 520 nm, which increases with laser fluence. This implies growth of the gold nanoparticles during laser annealing but the size distribution remains narrow, unlike some thermal annealing procedures that produce bimodal size distributions. The results were confirmed by scanning transmission electron microscopy and were consistent with the calculations of expected extinction spectra. [ABSTRACT FROM AUTHOR]

We find signatures of superconductivity at Tc = 12 K in a molybdenum arsenide sample containing ∼4% of MoO2-δ impurity by weight. Below is a report on the electronic structure calculations, structures analyses, and thermodynamic and transport properties on MO2AS3, MO5As4, and MoO2, in order to uncover the reasons for superconductivity for the sample that contains a mixture of these phases. The experimental and theoretical evidence suggest that superconductivity in the MoO2-δ phase is likely and may be caused by nesting-type fluctuations. [ABSTRACT FROM AUTHOR]

This paper covers the optimization of methane volumetric storage capacity by controlling the sub-nanometre (<1 nm) and supra-nanometre (1-5 nm) pore volumes. Nanospace engineering of KOH activated carbon generates an ideal structure for methane storage in which gas molecules are adsorbed as a high-density fluid by strong van der Waals forces into pores that are a few molecules in diameter. High specific surface areas, porosities, sub-nanometre (<1 nm) and supra-nanometre (1-5 nm) pore volumes are quantitatively selected by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. The formation of tuneable sub-nanometre and supra-nanometre pores is validated by sub-critical nitrogen adsorption. Aberration-corrected scanning transmission electron microscopy data show the atomic structure of high-surface-area activated carbon (2600 m2/g). While high surface area and high porosity are optimal for gravimetric methane storage, the results indicate that an exclusive sub-nanometre region, a low porosity and an acceptable surface area (approximately 2000 m2/g) are ideal for methane volumetric storage, storing 120 g CH4/l (184 vol/vol) at 35 bar and room temperature (22 °C). High-pressure methane isotherms up to 150 bar at 30, -25 and -50 °C on optimal activated carbons are presented. Methane volumetric storage capacity at 35 bar reaches 176 g/l (269 vol/vol) and 202 g/l (309 vol/vol) at -25 and -50 °C, respectively. [ABSTRACT FROM AUTHOR]

The successful development of third-order aberration correctors in transmission electron microscopy has seen aberration-corrected electron microscopes evolve from specialist projects, custom built at a small number of sites to common instruments in many modern laboratories. Here we describe some initial results illustrating the two- and three-dimensional (3D) performance of an aberration-corrected scanning transmission electron microscope with a prototype improved aberration corrector designed to also minimize fifth-order aberrations and a new, higher brightness gun. We show that atomic columns separated by 0.63 Å can be resolved and demonstrate detection of single dopant atoms with 3D sensitivity. [ABSTRACT FROM AUTHOR]

Thin films of the metastable and elusive [variant_greek_epsilon]-Fe2O3 have been epitaxially stabilized on SrTiO3 (111) substrates. The [variant_greek_epsilon]-Fe2O3 films present a (001) orientation perpendicular to the substrate and three in-plane domains measuring a few nanometers and showing atomically sharp interfaces. We argue that this domain structure, rather than the epitaxial-strain, plays an essential role in stabilizing the [variant_greek_epsilon]-Fe2O3 by minimizing the energy of (100) surfaces. The [variant_greek_epsilon]-Fe2O3 films show a large in-plane coercivity ∼8 kOe which combined with the magnetoelectric character claimed for this oxide may lead to novel applications in spintronics. [ABSTRACT FROM AUTHOR]

For over 40 years impurities have been believed to stabilize the ceramic α-Si3N4 but there is no direct evidence for their identity or lattice location. In bulk materials electron microscopy can generally image heavy impurities. Here we report direct imaging of N columns in α-Si3N4 that suggests the presence of excess light elements in specific N columns. First-principles calculations rule out Si or N interstitials and suggest O impurities, which are then confirmed by atomically resolved electron-energy-loss spectroscopy. The result provides a possible explanation for the stability of α-Si3N4 with implications for the design of next-generation structural ceramics. [ABSTRACT FROM AUTHOR]

For over 40 years impurities have been believed to stabilize the ceramic α-Si3N4 but there is no direct evidence for their identity or lattice location. In bulk materials electron microscopy can generally image heavy impurities. Here we report direct imaging of N columns in α-Si3N4 that suggests the presence of excess light elements in specific N columns. First-principles calculations rule out Si or N interstitials and suggest O impurities, which are then confirmed by atomically resolved electron-energy-loss spectroscopy. The result provides a possible explanation for the stability of α-Si3N4 with implications for the design of next-generation structural ceramics. [ABSTRACT FROM AUTHOR]

Using a combination of atomic-resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope, we examine the atomic and electronic structures at the interface between Si3N4 (1010) and CeO2-d intergranular film (IGF). Ce atoms are observed to segregate to the interface in a two-layer periodic arrangement, which is significantly different from the structure observed in a previous study. Our EELS experiments show (i) oxygen in direct contact with the terminating Si3N4 open-ring structures, (ii) a change in the Ce valence from a nominal oxidation state of +3 to almost +4 moving from the interface into the IGF, and (iii) a uniform concentration of Si in the film. [ABSTRACT FROM AUTHOR]

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

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

Ca3Co409 has a unique structure that leads to exceptionally high thermoelectric transport. Here we report the achievement of a 27% increase in the room-temperature in-plane Seebeck coefficient of Ca3Co409 thin films. We combine aberration-corrected Z-contrast imaging, atomic-column resolved electron energy-loss spectroscopy, and density-functional calculations to show that the increase is caused by stacking faults with Co4+-ions in a higher spin state compared to that of bulk Ca3Co409. The higher Seebeck coefficient makes the Ca3Co409 system suitable for many high temperature waste-heat-recovery applications. [ABSTRACT FROM AUTHOR]

We have examined the atomic and electronic structures of epitaxially grown, ultrathin SrTiO3 (100) films on GaAs (001) using 80-kV aberration-corrected atomic-resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) to develop a fundamental understanding of the interfacial structure-property relationships. We find that the interface is atomically abrupt and no surface reconstruction of the GaAs (001) surface is observed. Using atomic-column resolved EELS, we examine the oxygen vacancy and Ti concentrations in the SrTiO3 film and across the heterointerface. We show that Ti diffuses into the first few monolayers of GaAs. Using a combination of EELS and first-principles calculations, we present evidence for the formation of As oxides at the interface depending on the thin-film growth conditions. These findings are used to explain the differences in the transport behavior of the films. [ABSTRACT FROM AUTHOR]