The in situ measurement technique for a metal/metal-oxide mixture at extra-high temperature above 2000 K has been desired in the field of nuclear safety engineering. In the present study, we succeeded in simultaneous XAFS-XRD measurements of the Zr oxidation [Zr + O → Zr(O) + ZrO2] up to 1952 K and ZrO2-Y2O3 reaction from 1952 to 2519 K. The chemical shift during Zr oxidation was observed in the absorption spectra around the Zr K-edge, and the interatomic cation-cation and cation-oxygen distances obtained by the fitting analysis of EXAFS during the Y2O3-ZrO2 reaction are explained. Also, the temperature dependency of the anharmonic effect was investigated by comparing the fitted second- and third-order cumulants with the theoretical ones in which the Morse potential was applied as an interatomic potential, giving a good explanation about the local structure dynamics. Finally, the applicability of the developed system to investigation of nuclear fuel materials, such as UO2-Zr, is discussed.

Due to the expression of “reduced activation”, the severe radioactivity of tantalum (Ta) after neutron irradiation in early decay years is easily neglected. In the presented study, after an irradiation of only 0.3 dpa by fission neutron and followed by a cooling stage of 305 days, the RAFM steel specimen with a weight of 0.8 g possessed drastic radioactivity of 4 mSv/hour at a measuring distance of 20 cm. It was ascertained that the high radioactivity was generated by 182Ta. The severe radioactivity seriously increased the danger of material experiments, even though the original Ta addition of the steel was only 0.13 wt%. Similar deteriorative radioactivity of Ta can be generated in both fission and fusion neutron irradiations. We appeal to seriously deliberate the radioactivity of Ta and control the Ta content in the RAFM steel.

Microstructural evolutions in two variants of the F82H 8 wt%Cr tempered martensitic steel under dual (He+ plus Fe3+) ion irradiations at 500 °C have been characterized by transmission electron microscopy. Emphasis is on understanding the combined effects of displacements per atom (dpa) and the helium/dpa ratio (He/dpa) on cavity evolution and void swelling (fv). The dual ion database includes 231 alloy-dpa-He/dpa conditions for irradiations up to ∼ 82 dpa and 3700 appm helium. We hypothesize that the large “scatter” observed in the fv data is primarily due to local microstructural variations, especially those that shield regions at shallower depths from the effects of injected interstitial atoms, which would otherwise reduce fv. More generally, our hypothesis is that the highest fv data, at a specified dpa and He/dpa, provides the most appropriate estimate of swelling for fusion neutron irradiation conditions. The dose dependence of fv can be described by an incubation dpai, marking the onset of significant void growth, and a post-incubation swelling rate, fv’ = Δfv/Δdpa. Both dpai and fv’ decrease with increasing He/dpa. The fv’ data are quantitatively consistent with a simple model for defect partitioning between evolving bubble, void, and dislocation sinks strengths and biases. Most notably, the model correctly predicts both the incubation dpai, and the subsequent fv’, in spite of the fact that they reflect somewhat different physics. Our analysis also suggests that defect recombination is modest at 500 °C. Along with other considerations, this supports the hypothesis that, even at high dpa rates, dual ion irradiations can be used to reasonably emulate void nucleation and growth for a range of fusion-relevant neutron irradiation service conditions. A companion paper incorporates the results of this study in a reduced-order, data-driven void swelling model.

The typical experimental conditions inside a transmission electron microscope (TEM), such as ultra-high vacuum, high-energy electron irradiation, and surface effects of ultrathin TEM specimens, can be the origin of unexpected microstructural changes compared with that of bulk material during in situ thermal-annealing experiments. In this paper, we report on the microstructural changes of a Fe-15%Si alloy during in situ TEM annealing, where, in its bulk form, it exhibits an ordering transformation from D03 to B2 at 650 °C. Using a heating-pot type double tilt holder with a proportional-integral-differential control system, we observed the precipitation of α-Fe both at the sample surface and inside the sample. Surface precipitates formed via surface diffusion are markedly large, several tens of nm, whereas precipitates inside the specimen, which are surrounded by Fe-poor regions, reach a maximum size of 20 nm. This unexpected microstructural evolution could be attributed to vacancies on Si sites, which are induced due to high-energy electron irradiation before heating, as well as enhanced thermal diffusion of Fe atoms.

The reactive behavior of zircon in three different solutions: 0.1 M HCl (aq), ultrapure water, and 0.1 M NaOH (aq) was examined under normal temperature and pressure conditions. Dissolved Si and Zr concentrations show that considerable Zr precipitated on the surface in all immersion cases. Bulk changes in the zircon were insignificant. However, the obvious surface change of the zircon immersed in 0.1 M NaOH (aq) was confirmed. Porous layer comprising an amorphous SiOx phase and needle crystals of ZrSiO4 around pores were detected on the near-surface area of the zircon immersed in 0.1 M NaOH (aq). Consequently, the reaction was limited when zircon was immersed in ultrapure water. Zr precipitated on the surface after the dissolution of ZrSiO4 in 0.1 M HCl (aq). Dissolved Zr and Si in 0.1 M NaOH (aq) precipitated on the surface, then the dissolution of ZrSiO4 formed a porous layer, and most dissolved Zr precipitated as zircon crystals.

In situ electron irradiation using high-resolution transmission electron microscopy (HRTEM) was performed to visualize the Frank loop evolution in aluminum-copper (Al-Cu) alloy with an atomic-scale spatial resolution of 0.12 nm. The in situ HRTEM observation along the [110] direction of the FCC-Al lattice, Frank partial dislocation bounding an intrinsic stacking fault exhibited an asymmetrical climb along the (112) direction opposed to those in the reference pure Al under an electron irradiation, with a corresponding displacement-per-atom rate of 0.055- 0.120 dpa/s in a high vacuum (1.2 (c) 1015 Pa). We performed theoretical calculations to simulate the asymmetrical climb of the dislocation with Burgers vector b of 1/3(111). The Cu-Cu bonding in Guinier-Preston zones was described as a possible pinning site of the dislocation climb by molecular dynamics simulation.

Samples of ultra-high-purity tungsten prepared using chemical vapour deposition (CVD) technique were irradiated with neutrons at temperatures Tirr = 373–483 K (stage II of defect recovery) and Tirr = 573–673 K (stage III) up to 0.15 displacements per atom (dpa) in the Belgian reactor (BR2). The study of the microstructure of neutron-damaged samples using transmission electron microscopy (TEM) revealed visible defects with a predominance of dislocation loops. With an increase in the neutron irradiation temperature, the spatial distribution of the loops acquired pronounced inhomogeneity, and their average size moderately increased. Cavities and voids were not observed. Irradiation-induced hardening was found and a linear correlation was obtained between Vickers microhardness and nanohardness for undamaged and neutron-irradiated CVD-W samples. Irradiation of tungsten with neutrons led to a significant increase in the retention of deuterium, which accumulated mainly in vacancy-type traps. Furthermore, the influence of the columnar grain structure in low-dose neutron-irradiated tungsten seemed to be non-trivial upon deuterium retention.

The purpose of the present study is to clarify the instability behavior of M23C6 under irradiation, specifically the occurrence of radiation-induced amorphization (RIA). Ion irradiation of 10.5 MeV-Fe3+ at elevated temperatures from 573 to 623 K was conducted into the reduced activation ferritic/martensitic steels (F82H) and its model alloy (Fe-8Cr-0.1C). A bilayer contrast of the particle consisting of an amorphous-rim phase and inner crystalline core of M23C6 was observed in the irradiated F82H specimen, but not in the model alloy. From the high-resolution electron microscope observation, the preferential occupation site of W into M23C6 lattice was identified as 8c-site prior to irradiation in F82H specimen, which shifted to other sites due to chemical disordering upon irradiation. Evaluation of the intensity ratio between 8c and another site of M23C6, 8c/4a, then revealed that the extent of chemical disordering of W was mitigated at the amorphous-crystal interface region in comparison with the central of the particle. The hypothesis for the formation mechanism of an amorphous-rim in M23C6 was presumed as the deviation from the stoichiometric composition at the local interface due to the irradiation-enhanced diffusion and/or ballistic mixing under the current circumstances, although the efforts from experimental and/or simulation studies are still necessary to achieve a further understanding of the RIA behavior in M23C6.

Half-Heusler alloys, which possess the advantages of high thermal stability, a large power factor, and good mechanical property, have been attracting increasing interest in mid-temperature thermoelectric applications. In this work, extra Zr-doped TiZrxNiSn samples were successfully prepared by a modified solid-state reaction followed by spark plasma sintering. It demonstrates that extra Zr doping could not only improve the power factor on account of an increase in the Seebeck coefficient but also suppress the lattice thermal conductivity originated from the strengthened phonon scattering by the superlattice nanodomains and the secondary nanoparticles. As a consequence, an increased power factor of 3.29 mW m-1 K-2 and a decreased lattice thermal conductivity of 1.74 W m-1 K-1 are achieved in TiZr0.015NiSn, leading to a peak ZT as high as 0.88 at 773 K and an average ZT value up to 0.62 in the temperature range of 373-773 K. This work gives guidance for optimizing the thermoelectric performance of TiNiSn-based alloys by modulating the microstructures on the secondary nanophases and superlattice nanodomains.

Bimetallic plates of CuCrZr/316LN are important heat sink components in the ITER first wall. Their in-reactor performance was investigated with 6.4 MeV Fe3+ ion irradiation (500 °C/10.5 dpa), as an analogue for neutron damage. Detailed characterizations showed that the CuCrZr/316LN joints have maintained good structural integrity after irradiation. The as-irradiated interface consisted of a nanocrystalline interlayer, typically of <1 μm in width, mixed of CuCrZr and 316LN grains measuring 20–250 nm in size. Black-spots and loop/loop rafts dominated the damage microstructure on 316LN and CuCrZr sides of the interface, respectively. A series of 30 min long post-irradiation annealing experiments saw the onset of interlayer evolution in CuCrZr/316LN joints at 400 °C by grain boundary motion and Ostwald ripening, and further acceleration at ≥600 °C. Structural collapse of the interlayer is expected at extended time scales. Finally, a brief comparison between heavy-ion and neutron irradiation damage (Yi et al. 2021) in CuCrZr/316LN joints is made, with regard to defect production and interfacial transport behaviour of chemical elements.

Atom probe tomography (APT) and transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) have been used correlatively to explore atomic-scale local structure and chemistry of the exactly same area in the vicinity of growth front of a long-period stacking ordered (LPSO) phase in a ternary Mg-Al-Gd alloy. It is proved for the first time that enrichment of Gd atoms in four consecutive (0001) atomic layers precedes enrichment of Al atoms so that the formation of Al6Gd8 clusters occurs only after sufficient Al atoms to form Al6Gd8 clusters diffuse into the relevant portions. Lateral growth of the LPSO phase is found to occur by 'ledge' mechanism with the growth habit plane either {1[Formula: see text]00} or {11[Formula: see text]0} planes. The motion of ledges that give rise to lateral growth of the LPSO phase is considered to be controlled by diffusion of Al atoms.

Atom probe tomography (APT) and selected area electron diffraction (SAED) by transmission electron microscopy (TEM) were applied to nano-scale precipitates formed in a neutron-irradiated iron (99.99% pure) at high temperatures. In the conventional TEM, we discovered donut-type precipitates on the {100} planes that formed at the dilatational side of interstitial type dislocation loops with the Burgers vector of <100> on the habit planes of {100} in the bcc iron lattice. The precipitates were identified as nitride, bct α″-Fe N , by chemical composition and lattice structural analyses using APT and SAED. Image contrasts of the α″-Fe N in a weak beam dark-field electron microscopy study were carefully analysed with the diffraction vector and the sign of deviation parameter from the Bragg condition, and it was concluded to be a selective visualisation of α″-Fe N on one of the {100} planes. These results were in agreement with the crystallographic orientation between the α″-Fe N and matrix iron, thereby bridging a knowledge gap in α″-Fe N formation during neutron irradiation using a sodium-cooled experimental fast reactor, JOYO, or a 14 MeV D-T neutron source, RTNS-II. 16 2 16 2 16 2 16 2 16 2

To better understand the thermal stability of dislocation loops formed by long-term neutron irradiation in reactor pressure vessel (RPV) steels, in-situ scanning transmission electron microscopy (STEM) observation was performed for a surveillance test specimen of a European pressurized water reactor (PWR). The surveillance test specimen was neutron irradiated to a fluence of 8.2 × 10 neutrons•m . A membrane sample from the surveillance test specimen was annealed at 673 K and 723 K for 30 min using a heating holder, and the same area was in-situ observed under STEM. After annealing, dislocation loops with Burgers vectors of ½ 〈111〉 and 〈100〉 were quantitatively examined. When annealing temperature increased from 673 K to 723 K, the number of dislocation loops decreases, whereas the size of them becomes larger. Correspondingly, the proportion of 〈100〉 dislocation loops changes from 27% to 45%. The ratio of 〈100〉 to ½ 〈111〉 loops increases with annealing temperature rising. The evolution process of dislocation loops during annealing at 723 K was in-situ observed and analyzed to shed light on the transformation mechanism of dislocation loops going from ½ 〈111〉 to 〈100〉. It is the first time to directly observe that two ½ 〈111〉 dislocation loops collide with each other and coalesce to form a 〈100〉 dislocation loop. Moreover, small ½ 〈111〉 dislocation loops could be absorbed by large 〈100〉 dislocation loops, whereas the Burgers vector of 〈100〉 loops remained unchanged. Dislocation decoration occurs during annealing due to the interaction between dislocations and loops. The dislocations decorated by loops are pretty stable during the continuous annealing process, which is well explained by molecular dynamics simulation. 23 −2

At present, copper sulfide materials have been predicted as promising thermoelectric materials due to their inexpensiveness and nontoxicity property. Most researches on copper sulfide are focused on Cu2S and Cu1.8S because they are more easily synthesized into a single phase; however, the improper electrical conductivity greatly hindered their thermoelectric properties. In this work, a series of high-performance Cu1.9-xNi x S (x = 0, 0.01, 0.015, and 0.02) bulk samples were fabricated by accurately manipulating the ratio of Cu/S with appropriate Ni-doping. The thermoelectric properties of Ni-doped Cu1.9S were explored in detail for the first time. It can be found that carrier thermal conductivity and lattice thermal conductivity of Cu1.9-xNi x S were effectively reduced via Ni-doping, simultaneously, without the great influence on the power factor. Here, the carrier thermal conductivity (κe) was reduced due to the extreme reduction of Hall carrier concentration. In addition, amounts of nanopores introduced by Ni-doping and complex crystal structure from the phase transition of the second phase strengthen the phonon scattering and reduce lattice thermal conductivity (κl) remarkably. As a consequence, the lowest carrier thermal conductivity and lattice thermal conductivity reach 0.006 and 1.08 W m-1 K-1 for Cu1.88Ni0.02S at 773 K, and the average ZT is about 0.39 from 323 to 773 K (the ZTmax is about 0.9 at 773 K). This work demonstrates that low-cost and easily fabricated Ni-doped Cu1.9S is a pleasurable candidate for thermoelectric application despite it usually being treated as an ion conductor.

To study the effects of helium (He) produced by the nuclear transmutation of 14 MeV neutron irradiation on the stability of grain microstructure of tungsten (W)-fabricated through a powder metallurgically (PM) process-high energy He and post implantation experiments were conducted. The recovery of worked structure and recrystallization behavior were examined using hardness measurement and microstructural observation. He with a concentration of 20 appm was implanted homogeneously though the specimen thickness below 100 °C. Post-implantation annealing was then conducted from 1100 °C to 1500 °C in vacuum. The hardness of the PM-W specimen increased after the He implantation, and the decrease of the hardening through the annealing was suppressed in the He-implanted specimens. Metallographic observations demonstrated that the dislocation cell structure in the grain of He-implanted PM-W was retained even after the 10 h annealing at 1500 °C. In conclusion, the 20 appm He suppressed the recovery of cell structure and recrystallization of the PM-W up to 1500 °C.

© 2019 Elsevier Ltd Ultra-high purity (> 99.9999 wt%) chemical vapour deposited tungsten (CVD–W) samples were neutron irradiated in the BR2 reactor (Belgium) at Tirr < 210 °C to ~ 0.15 dpa, followed by isochronal annealing at 500, 800 and 1100 °C. Defect characterization showed that dislocation loops dominated the as-irradiated damage microstructure and were mostly ≤5 nm. Void formation was observed after post-irradiation annealing at 1100 °C. The mechanical and thermal properties of CVD-W were evaluated based on tensile tests, Vickers hardness and temperature wave analysis. Fractography study suggested that a transition from intergranular fracture to cleavage fracture took place in the material after neutron irradiation. Hardening was found ~ 23% after irradiation. Subsequent annealing below 800 °C saw further increase in hardness, featuring a maximum value of about Hv = 487. Softening occurred at 1100 °C. Thermal diffusivity dropped by ~ 65% after irradiation and ~ 40% of this degradation recovered at 1100 °C.

Atomic-scale relaxations of platinum nanoparticles (Pt NPs) for fuel-cell catalysts are evaluated by spherical-aberration corrected environmental transmission electron microscopy (ETEM) under reference high-vacuum and N2 atmospheres, and then under reactive H2, CO and O2 atmospheres, combined with ex situ durability test using an electrochemical half-cell. In high-vacuum, increasing roughness due to continuous relaxation of surface-adsorbed Pt atoms is quantified in real-space. Under H2 and N2 atmospheres at a critical partial pressure of 1 × 10-2 Pa the stability of the surface facets is for the first time found to be improved. The adsorption behaviour of CO molecules is investigated using experimentally measured Pt-Pt bond lengths on the topmost surface layer of Pt NPs. The deactivation of Pt NPs in the anode environment of a proton-exchange-membrane fuel-cell is demonstrated at the atomic-scale in the ETEM, and the transformation of NPs into disordered nanoclusters is systematically quantified using the partial size distribution of Pt atomic clusters under controlled heating experiments at 423, 573 and 723 K.

© 2019 Elsevier B.V. Two kinds of 9Cr–2W steels with and without the addition of 0.1 wt% Si were irradiated with neutrons up to a fluence of 4.8 × 10 23 n/m 2 at 563 K. Precipitates, dislocation loops, radiation-enhanced nano-clusters and radiation-hardening were studied using advanced electron microscopy and micro-hardness test. Si reduced the number density of dislocation loops, and therefore the extent of radiation-hardening decreased. It also favored the formation of silicide-like nano-clusters. In this study, the role of Si in neutron irradiated 9Cr–2W steels is discussed, and then extended to nano-clusters and irradiation-hardening.

We investigated the fluence dependence of irradiation-induced solute cluster, dislocation loop, and very small defect to reveal the hardening mechanism in surveillance test specimens from a reactor pressure vessel steel with low-Cu content (0.04 wt%) using atom probe tomography (APT), weak-beam scanning transmission electron microscopy (WB-STEM), and positron annihilation spectroscopy. A high number density (>10(23) m(-3)) of solute clusters mainly composed of Ni, Mn, and Si atoms were found in highly neutron irradiated specimens (similar to 10(24) neutrons m(-2) (E>1 MeV)) by APT. These solute clusters were one of the main sources of hardening as reported previously. On the other hand, it was also revealed that dislocation loops were formed with a number density of similar to 10(22) m(-3) in the high-fluence specimens by WB-STEM. The estimated hardening due to dislocation loops was more than half of the actual hardening, showing that dislocation loops are also main source of irradiation hardening at high neutron fluence with the solid experimental evidences. Regarding specimens subjected to a low neutron fluence (similar to 10(23) neutrons m(-2)), very small defects, not detected by either WB-STEM or APT, were formed by positron annihilation spectroscopy. This result suggested that, at a low neutron fluence, the defects were the initial hardening source and they may grow the dislocation loops observed by WB-STEM at high fluence range. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

To evaluate dislocations induced by neutron irradiation, we developed a weak-beam scanning transmission electron microscopy (WB-STEM) system by installing a novel beam selector, an annular detector, a high-speed CCD camera and an imaging filter in the camera chamber of a spherical aberration-corrected transmission electron microscope. The capabilities of the WB-STEM with respect to wide-view imaging, real-time diffraction monitoring and multi-contrast imaging are demonstrated using typical reactor pressure vessel steel that had been used in an European nuclear reactor for 30 years as a surveillance test piece with a fluence of 1.09 × 1020 neutrons cm-2. The quantitatively measured size distribution (average loop size = 3.6 ± 2.1 nm), number density of the dislocation loops (3.6 × 1022 m-3) and dislocation density (7.8 × 1013 m m-3) were carefully compared with the values obtained via conventional weak-beam transmission electron microscopy studies. In addition, cluster analysis using atom probe tomography (APT) further demonstrated the potential of the WB-STEM for correlative electron tomography/APT experiments.

We study HAADF-STEM analysis of Ag/Al2O3 samples (as-calcined and reduced at 25, 300, 500 and 900 degrees C). Ag atoms are classified into subnanoclusters (0.3-1 nm), nanoclusters (1-3 nm), nanoparticles (3-10 nm) and polycrystals ([10 nm). The size of Ag increases with the reduction temperature, which is supported by EXAFS analysis. The effect of Ag size on the activity for borrowing-hydrogen and acceptorless dehydrogenative couplings of alcohols is discussed.

Using a method that combines experimental and simulated Aberration-Corrected High Resolution Electron Microscopy images with digital image processing and structure modeling, strain distribution maps within gold nanoparticles relevant to real powder type catalysts, i.e., smaller than 3 nm, and supported on a ceria-based mixed oxide have been determined. The influence of the reduction state of the support and particle size has been examined. In this respect, it has been proven that reduction even at low temperatures induces a much larger Compressive strain on the first {111} planes at the; interface. This increase in compression fully explains, in accordance with previous DFT calculations, the loss of CO adsorption capacity of the interface area previously reported for Au supported on ceria-based oxides.

The water gas shift (WGS) reaction, CO + H2O -&gt; CO2 + H-2, is the basis of heterogeneous catalysis important in the generation of clean hydrogen energy for fuel cells, transportation fuels and in ammonia manufacture. Ceria supported gold and related nanoparticles are potentially viable catalysts for the low temperature WGS reaction. The WGS catalytic reaction is a dynamic process and takes place on the solid catalyst surface at the atomic level. The current understanding of the reaction is inferred from studies of static catalysts and from indirect chemical studies without single atom sensitivity. Therefore the nature of dynamic atomic processes in the WGS reaction has remained inaccessible. Since the catalyst reaction site and atomic processes by which it activates and deactivates, change both in magnitude and mechanism with the reaction environment it is of fundamental importance to visualise the dynamic catalyst at the atomic level in WGS (CO + water mixture) environments, in real time. Novel environmental (scanning) transmission electron microscope with singe atom resolution is used herein to directly visualise and characterise, in real time, evolving atomic structures and processes in practical gold/ceria catalysts in controlled WGS environments. The in situ observations in WGS have revealed the formation of clusters of only a few gold atoms resulting from single atom dynamics and the catalytic effect of low coordination surface sites. The new insights have important implications for applications of nanoparticles in chemical process technologies including for transportation fuels and emission control.

The gas injection line of the latest spherical aberration-corrected environmental transmission electron microscope has been modified for achieving real-time/atomic-scale observations in moisturised gas atmospheres for the first time. The newly developed Wet-TEM system is applied to platinum carbon electrode catalysts to investigate the effect of water molecules on the platinum/carbon interface during deactivation processes such as sintering and corrosion. Dynamic in situ movies obtained in dry and 24% moisturised nitrogen environments visualize the rapid rotation, migration and agglomeration of platinum nanoparticles due to the physical adsorption of water and the hydroxylation of the carbon surface. The origin of the long-interconnected aggregation of platinum nanoparticles was discovered to be a major deactivation process in addition to conventional carbon corrosion.

In situ transmission electron microscopy (TEM) was performed to observe the hydrogenation of Mg-Ni films in a hydrogen atmosphere of 80-100 Pa. An aberration-corrected environmental TEM with a differential pumping system allows us to reveal the Angstrom-scale structure of the films in the initial stage of hydrogenation: first, nucleation and growth of Mg2NiH4 crystals with a lattice spacing of 0.22 nm in an Mg-rich amorphous matrix of the film occurs within 20 s after the start of the high-resolution observation, then crystallization of MgH2 with a smaller spacing of 0.15 nm happens after approximately 1 min. Our in situ TEM method is also applicable to the analysis of other hydrogen-related materials. (C) 2014 AIP Publishing LLC.

We show that the magnetoresistance of Co2FexMn1-x Si-based spin valves, over 70% at low temperature, is directly related to the structural ordering in the electrodes and at the electrodes/spacer (Co2FexMn1-x Si/Ag) interfaces. Aberration-corrected atomic resolution Z-contrast scanning transmission electron microscopy of device structures reveals that annealing at 350 degrees C and 500 degrees C creates partial B-2/L(2)1 and fully L2(1) ordering of electrodes, respectively. Interface structural studies show that the Ag/Co2FexMn1-x Si interface is more ordered compared to the Co2FexMn1-x Si/Ag interface. The release of interface strain is mediated by misfit dislocations that localize the strain around the dislocation cores, and the effect of this strain is assessed by first principles electronic structure calculations. This study suggests that by improving the atomic ordering and strain at the interfaces, further enhancement of the magnetoresistance of CFMS-based current-perpendicular-to-plane spin valves is possible.

In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1-xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co-Si disorder has higher energies of formation in CFMS compared to Co2MnSi and Co2FeSi, with maximum values occurring for x in the range 0.5-0.75. Cross-sectional structural studies of reference Co2MnSi, Co2Fe0.5Mn0.5Si, and Co2FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures.

We present further modifications to aberration-corrected environmental transmission electron microscopy (AC-ETEM) for the dynamic HRTEM observation of single atoms. Additional pumping levels that include three additional turbomolecular pumps (TMPs) enable a base pressure of 3.5 × 10 -5 Pa in the sample chamber. The effect of these additional TMPs on image resolution was measured in reciprocal space using information limit (Young's fringes) on a standard cross grating sample and also with platinum (Pt) single atoms on an amorphous carbon film (Pt/a-carbon). The Pt/a-carbon was used for measuring the effect of gas pressure on single-atom imaging in addition to the evaluation of vibrations of TMPs, samples, magnetic lenses and a microscope column of the AC-ETEM. TMPs did not affect the ETEM imaging performance when an anti-vibration table was used, and 0.10-nm resolution was achieved. Dynamic ETEM observation of Pt single atoms was achieved in 4.0 × 10-2 Pa of air, using a modified AC-ETEM system and a high-speed CCD camera with a time resolution of 0.05 s. © 2013 The Author.

We present further modifications to aberration-corrected environmental transmission electron microscopy (AC-ETEM) for the dynamic HRTEM observation of single atoms. Additional pumping levels that include three additional turbomolecular pumps (TMPs) enable a base pressure of 3.5 x 10(-5) Pa in the sample chamber. The effect of these additional TMPs on image resolution was measured in reciprocal space using information limit (Young's fringes) on a standard cross grating sample and also with platinum (Pt) single atoms on an amorphous carbon film (Pt/a-carbon). The Pt/a-carbon was used for measuring the effect of gas pressure on single-atom imaging in addition to the evaluation of vibrations of TMPs, samples, magnetic lenses and a microscope column of the AC-ETEM. TMPs did not affect the ETEM imaging performance when an anti-vibration table was used, and 0.10-nm resolution was achieved. Dynamic ETEM observation of Pt single atoms was achieved in 4.0 x 10(-2) Pa of air, using a modified AC-ETEM system and a high-speed CCD camera with a time resolution of 0.05 s.

Spherical-aberration-corrected environmental transmission electron microscopy (AC-ETEM) was applied to study the catalytic activity of platinum/amorphous carbon electrode catalysts in proton-exchange-membrane fuel cells (PEMFCs). These electrode catalysts were characterized in different atmospheres, such as hydrogen and air, and a conventional high vacuum of 10 -5 Pa. A high-speed charge coupled device camera was used to capture real-time movies to dynamically study the diffusion and reconstruction of nanoparticles with an information transfer down to 0.1 nm, a time resolution below 0.2 s and an acceleration voltage of 300 kV. With such high spatial and time resolution, AC-ETEM permits the visualization of surface-atom behaviour that dominates the coalescence and surface-reconstruction processes of the nanoparticles. To contribute to the development of robust PEMFC platinum/amorphous carbon electrode catalysts, the change in the specific surface area of platinum particles was evaluated in hydrogen and air atmospheres. The deactivation of such catalysts during cycle operation is a serious problem that must be resolved for the practical use of PEMFCs in real vehicles. In this paper, the mechanism for the deactivation of platinum/amorphous carbon electrode catalysts is discussed using the decay rate of the specific surface area of platinum particles, measured first in a vacuum and then in hydrogen and air atmospheres for comparison. © 2013 IOP Publishing Ltd.

Understanding the effect of the interface on electrical spin injection is of great importance for the development of semiconductor spintronics. Fe/GaAs(001) is one of the leading systems for exploring these effects due to the small lattice mismatch. We report on the correlation between the experimentally observed Fe/GaAs(001) interface with the spin-transport properties. Using high-angle annular dark-field scanning transmission electron microscopy, we observe a predominantly abrupt interface with some regions of partial mixing also observed in the same film. We report that reproducible behavior with no bias-dependent polarization inversion was achieved for three-terminal devices. Using ab initio calculations of the experimentally observed interfaces, we show that the contribution to the transport from minority carriers is strongly dependent on the interface structure. © 2013 American Physical Society.

Environmental transmission electron microscopy (ETEM) enables the study of catalytic and other reaction processes as they occur with Angstrom-level resolution. The microscope used is a dedicated ETEM (Titan ETEM, FEI Company) with a differential pumping vacuum system and apertures, allowing aberration corrected high-resolution transmission electron microscopy (HRTEM) imaging to be performed with gas pressures up to 20 mbar in the sample area and with significant advantages over membrane-type E-cell holders. The effect on image resolution of varying the nitrogen gas pressure, electron beam current density and total beam current were measured using information limit (Young's fringes) on a standard cross grating sample and from silicon crystal lattice imaging. As expected, increasing gas pressure causes a decrease in HRTEM image resolution. However, the total electron beam current also causes big changes in the image resolution (lower beam current giving better resolution), whereas varying the beam current density has almost no effect on resolution, a result that has not been reported previously. This behavior is seen even with zero-loss filtered imaging, which we believe shows that the drop in resolution is caused by elastic scattering at gas ions created by the incident electron beam. Suitable conditions for acquiring high resolution images in a gas environment are discussed. Lattice images at nitrogen pressures up to 16 mbar are shown, with 0.12 nm information transfer at 4 mbar. (C) 2012 Elsevier B.V. All rights reserved.

Understanding the effect of the interface on electrical spin injection is of great importance for the development of semiconductor spintronics. Fe/GaAs(001) is one of the leading systems for exploring these effects due to the small lattice mismatch. We report on the correlation between the experimentally observed Fe/GaAs(001) interface with the spin-transport properties. Using high-angle annular dark-field scanning transmission electron microscopy, we observe a predominantly abrupt interface with some regions of partial mixing also observed in the same film. We report that reproducible behavior with no bias-dependent polarization inversion was achieved for three-terminal devices. Using ab initio calculations of the experimentally observed interfaces, we show that the contribution to the transport from minority carriers is strongly dependent on the interface structure. DOI: 10.1103/PhysRevB.87.024401

We present studies of the structure and stability of catalytic gold nanoparticles through in situ aberration-corrected electron microscopy to investigate the effect of heating on the nature of the identified atomic active sites. Low coordination surface atoms are replaced by atomically clean surface facets through local rearrangements to minimise surface energy. The associated movement of surface atoms is proposed to directly precede Ostwald ripening. Expansive surface strain resulting from inherently strained structures, such as the decahedra, is shown to diminish with increasing particle size and the associated elastic energy is reduced through a shifting of the disclination axis towards the particle surface. At elevated temperatures a reduction in surface energy anisotropy may lead to energetically favourable morphologies with minimal intrinsic strain. Such processes will act as structural deactivation mechanisms, resulting in a loss of active sites without any necessary associated loss of surface area or change in particle size through traditional sintering mechanisms. Considerations of the active site stability and the particle size according to the reaction conditions are described.

Here, we reveal origins of the planar electrical transport of closely-packed carbon nanotubes (CNTs) and silicon-doped CNTs (Si-CNTs) films. Their electrical resistivities increased with decreasing temperature, but exhibit a plateau below 60 K. This phenomenon can be well described using the simple-two-band model, which is often used to understand the electronic properties of graphite. Cryogenic energy-filtered transmission electron microscopy visualizes Si atoms dispersed finely in CNTs, preserving the structural features of CNTs. These Si atoms induced effective carriers above 150 K, while three-dimensional variable range hopping and weak localization are dominant in their transport below 50 and 10 K, respectively. (C) 2012 The Japan Society of Applied Physics

A variety of advanced (scanning) transmission electron microscopy experiments, carried out in aberration-corrected equipment, provide direct evidence about subtle structural changes taking place at nanometer-sized Aullceria oxide interfaces, which agrees with the occurrence of charge transfer effects between the reduced support and supported gold nanoparticles suggested by macroscopic techniques. Tighter binding of the gold nanoparticles onto the ceria oxide support when this is reduced is revealed by the structural analysis. This structural modification is accompanied by parallel deactivation of the CO chemisorption capacity of the gold nanoparticles, which is interpreted in exact quantitative terms as due to deactivation of the gold atoms at the perimeter of the Aullcerium oxide interface.

A new mechanism for reactivity of multiply twinned gold nanoparticles resulting from their inherently strained structure provides a further explanation of the surprising catalytic activity of small gold nanoparticles. Atomic defect structural studies of surface strains and quantitative analysis of atomic column displacements in the decahedral structure observed by aberration corrected transmission electron microscopy reveal an average expansion of surface nearest neighbor distances of 5.6%, with many strained by more than 10%. Density functional theory calculations of the resulting modified gold d-band states predict significantly enhanced activity for carbon monoxide oxidation. The new insights have important implications for the applications of nanoparticles in chemical process technology, including for heterogeneous catalysis.

We study in situ behavior of platinum single atoms on amorphous carbon (a-carbon) using a spherical aberration-corrected transmission electron microscope (AC-TEM). Diffusion of single atoms, bi-atoms, clusters (&lt; 1 nm) and nanoparticles (&lt; 3 nm) was recorded in the same image with a time resolution of 1 s, and such diffusion matches the expected mechanism of Ostwald ripening, which was seen on these samples. In situ AC-TEM shows promise for dynamical observation of single atom diffusion, which is important for understanding nanosized catalysts and ceramic sintering processes. We apply in situ AC-TEM to image platinum (Pt) nanoparticles on a-carbon, which is a model catalyst system for the real Pt electrode catalysts using alloys and core-shell structures supported on carbon/oxide composite materials in the proton exchange membrane fuel cell.

We present a study on the effect of an interlayer of thin MgO(111) film on SiC(0001) on the interface phase stability and structure of the BaFe12O19 (BaM). The 10 nm MgO(111) interlayer followed by the BaM film were grown by molecular beam epitaxy on 6H-SiC. Cross-sectional transmission electron microscopy shows the formation of a magnesium ferrite spinel phase at the interface, and after 25 nm, a well structured BaM film was observed. In addition to the two main phases (Mg-ferrite and BaM), a thin layer of SiOx (2-3 nm) is formed at the SiC interface. In spite of the formation of this amorphous layer, the diffraction studies show that the BaM film is epitaxially grown and it has a single crystal structure. The energy dispersive x-ray analysis from the interface region shows that the MgO layer prevents significant outdiffusion of the Si into the film. Total energy calculations by density functional theory were used to investigate the stability of the various phases and to explain the observed interfacial phases in the studied system. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676614]

We perform transmission electron microscopy (TEM) at different accelerating voltages for analysis of complex nano-structures of platinum (Pt) nanoparticle catalysts synthesized on titanium dioxide. TEM images obtained at 80, 200, 300, and 1000kV are carefully compared. The particle size, density and volume of the Pt nanoparticles deposited under different conditions are evaluated using electron tomography. The atomic structures of Pt nanoparticles on the TiO 2 and amorphous carbon a surfaces are also investigated using spherical aberration corrected TEM in order to study the diffusion of these Pt nanoparticles and atoms.

Titanium dioxide (TiO2) with metal nanoparticles exhibits a high photocatalytic activity by a charge separation. Recently the size of the nanoparticles has been reduced to less than 1 nm. In contrast, the size of TiO2 support particles has been kept at sub-micron sizes to ensure stability for practical use at high temperatures. For visualizing and analyzing the metal nanoparticles which are supported on different positions of those complex substrates, a high voltage transmission electron microscope(HVEM) shows a strong performance because of its high transmission capability to view whole areas of the catalysts. Electron tomography is also important to quantify the three-dimensional morphology such as size, density, surface area and nearest particle distance. Here we report the data obtained by using He-cooled 3D TEM/STEM, a newly developed 1MV high voltage environmental TEM/STEM and a 200kV aberration corrected TEM/STEM. Nanostructures of catalytic samples are characterized using these EMs as well as measurement of their chemical activity.

A detailed investigation on the microwave-assisted preparation of iron oxide nanoparticles on mesoporous Si-SBA-15 support is described, employing a dedicated single-mode microwave reactor with internal reaction temperature control. Using iron(II) chloride as iron precursor and ethanol as solvent, extensive optimization studies demonstrate that after 3-5 min at 150-200 degrees C well-defined 3-5 nm iron oxide nanoparticles (Fe2O3, hematite phase) are obtained. In contrast to the chosen reaction temperature, reaction time and stirring efficiency are of critical importance in the preparation of these supported nanoparticles. Extended reaction times (&gt;10 min) lead to a significant proportion of larger aggregates while inefficient stirring also produces low quality nanoparticles as a result of poor dispersion and delivery of the iron precursor to the mesoporous support. Carefully executed control studies between microwave and conventionally heated experiments applying otherwise identical reaction conditions demonstrate that the quality of the obtained supported iron oxide nanoparticles is largely independent on the heating mode, as long as a the exact same temperature profile can be maintained.

Grain-size evolution with increasing annealing time has been investigated in polycrystalline Co2FeSi films. The samples were prepared by sputtering giving differing grain sizes. Large grains were formed after annealing at 500 degrees C, with grains over 200 nm forming in the L2(1) phase in a layer-by-layer mode. Further annealing causes a decrease in the average grain size, agreeing well with previously reported results for Co2MnSi. Magnetic measurements showed moments with values of up to 75% of those predicted from the Slater-Pauling curve providing further evidence for the formation of the L2(1) phase.

Broadband near ultraviolet (NUV) random laser was achieved by Au nanoparticle loaded ZnO 3-D nanowalls. Au nanoparticle was loaded on ZnO 3-D nanowalls by photo-chemical deposition method using ionic liquid. The optical confinement by the 3-D nanowalls and enhancement of incident light scattering by Au nanoparticle increase the number of resonant modes, and thus leading to a broadband multiple spectrum random lasing. The results demonstrate an important step towards to expand the application scope of NUV laser on medical imaging of cells, solid-state lighting and optical sensor.

By using MgO(111) as a model system for polar oxide film growth, we show by first-principles calculations that H acts as a surfactant, i.e., the H changes its position and bonding during the growth process, remaining in the surface region. Continuous presence of H during the growth of MgO(111) film efficiently removes the microscopic dipole moment, thus enabling the growth of perfect fcc-ordered MgO(111) films. These theoretical predictions are confirmed experimentally by molecular beam epitaxy single crystal growth of MgO(111) on SiC(0001).

Structural and compositional studies of nanomaterials of technological importance have been carried out using advanced electron microscopy methods, including aberration-corrected transmission electron microscopy (AC-TEM), AC-high angle annular dark field scanning TEM (AC-HAADF-STEM), AC-energy filtered TEM, electron-stimulated energy dispersive spectroscopy in the AC-(S) TEM and high-resolution TEM (HRTEM) with scanning tunneling microscopy (STM) holder. The AC-EM data reveal improvements in resolution and minimization in image delocalization. A JEOL 2200FS double-AC field emission gun TEM/STEM operating at 200 kV in the Nano-centre at the University of York has been used to image single metal atoms on crystalline supports in catalysts, grain boundaries in nanotwinned metals, and nanostructures of tetrapods. Joule heating studies using HRTEM integrated with an STM holder reveal in situ crystallization and edge reconstruction in graphene. Real-time in situ AC-HAADF-STEM studies at elevated temperatures are described. Dynamic in-column energy filtering in an AC environment provides an integral new approach to perform dynamic in situ studies with aberration correction. The new results presented here open up striking new opportunities for atomic scale studies of nanomaterials and indicate future development directions. Microsc. Res. Tech. 74: 664-670, 2011. (C) 2010 Wiley-Liss, Inc.

We present direct link between the transport properties of Co2MnSi and Co2FeMnSi Heusler based current-perpendicular-to-plane spin valves (CPP-SVs) and interface atomic structures resolved by aberration-corrected electron microscopy. The structure of the Co2FeMnSi electrodes is L2(1) but their interface with the CoSi spacer is disordered. In contrast to the Co2FeMnSi-electrodes, the Co2MnSi-electrodes have abrupt interfaces with the Ag spacer though their ordering is not fully L2(1). The magnetoresistance of the Co2MnSi-SV is over two orders of magnitude better than those of Co2FeMnSi-SV, demonstrating that the atomic interface ordering is crucial for the enhancement of the magnetoresistance in the Heusler CPP-SVs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3600792]

We have studied interface phase stability of the BaFe(12)O(19) (BaM) thin films grown by molecular beam epitaxy on SiC(0001). The films were epitaxially grown with the following crystallographic relation: BaM(0001)parallel to SiC(0001) and BaM(11-20)parallel to SiC(11-20). High resolution TEM reveals the existence of two interfacial bands with different structure than BaM. The first band close to SiC is SiO(x) while the second has spinel structure and chemically corresponds to Fe(3)O(4). These findings suggest that at initial growth stages Fe(3)O(4) is more favorable than BaM. Density functional theory modeling of the phase stability of BaM compared to Fe(3)O(4) shows that BaM is only stable at high oxygen partial pressures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3559496]

Various porous titania photocatalysts are analyzed three-dimensionally in real space by electron tomography. Shapes and three-dimensional (3D) distributions of fine pores and silver (Ag) particles (2 nm in diameter) within the pores are successfully reconstructed from the 3D data. Electron tomography is applied for measuring the specific surface area of the porous structures including open and closed porosity. Calculated specific surface areas of 22.8 m(2)/g for a conventional sol-gel TiO2 sample and 366 m(2)/g for a highly porous TiO2 sample prepared using the Pluronic P-123 self-assembly process are compared with those measured by the general BET method. The real-space surface measurement indicates that the highly porous TiO2 produced by the present method using block copolymers has a greater number of effective reaction sites for the degradation of methylene blue. Electron tomography shows a great potential to contribute considerably to the nanostructural analysis and design of such catalyst materials for photocatalysis.

Using HAADF-STEM electron tomography and aberration-corrected TEM/STEM electron microscopy, 3D reconstructions and high resolution images have been recorded of heterogeneous catalysts consisting of gold nanoparticles supported on titanium dioxide (anatase); these catalysts have gained attention recently because of their potential for use in many reactions with both industrial and environmental importance. We will illustrate how through the combination of high resolution images and segmented 3D tomographic data, structural features of the supported phase can be revealed which are normally not accessible through conventional imaging. The location of the nanoparticles preferentially at the grain boundaries, confirmed by these studies, is likely to influence the stability of the nanoparticles and is a key step in understanding and facilitating the development of better catalysts. (C) 2010 Elsevier B.V. All rights reserved.

In heterogeneous catalysis the identification of the active site and crucially its location to prevent unwanted sintering and deactivation during the transformation of the precursor to active catalyst require the integration of dynamic in situ imaging at the atomic level and reactivity studies. We report nanostructural and physico-chemical studies towards an efficient low temperature heterogeneous catalytic process for nonsteroidal anti-inflammatory drugs (NSAIDS) such as N-acetyl-p-aminophenol (paracetamol or acetaminophen) on tungstated zirconia nanocatalysts of only a few nanometres in size. We directly visualised, in real-time, the dynamic precursor transformation to the active catalyst, which is of great significance in heterogeneous catalysis, using double aberration-corrected in situ electron microscopy at the atomic level under controlled conditions. We quantified the observations with catalytic activity studies for the NSAIDS. The observations using negative defocus imaging in AC-TEM combined with HAADF-STEM have provided the direct evidence for the presence of surface WO(x) species with dimensions of &lt;= 0.35 nm, nanoclusters and nanoparticles of WO(x) from up to 0.6 to 1 nm, located at grain boundaries on the surface of the zirconia nanoparticles. The observations illustrate that the nanoparticles (NPs) are disordered (distorted) tungsten trioxide. The correlation between the nanostructure and activity of catalysts with different W loadings indicate that surface WO(x) species, nanoclusters and distorted WO(3) nanoparticles create Bronsted acid sites highly active for the low temperature N-acetyl-p-aminophenol reaction, with distorted WO(3) NPs contributing to the activity. The results further elucidate that the anchoring of active sites at grain boundaries of the zirconia nanoparticles prevents undesirable coalescence of the active species and improves the catalyst stability and performance to make more product.

Electron tomography is applied to photocatalytic gold/titanium oxide and gold/silver/titanium oxide samples. In order to obtain a tilt series for the electron tomography measurement, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is used under cryogenic conditions. Dedicated programs have been developed for measuring volume, surface area, thickness distribution and nearest-neighbour distance of metallic nanoparticles on samples. Using these quantification programs, the 3D morphology of gold and silver nanoparticles is accurately characterized. We paid particular attention to the quantitative measurement of surface area. The measurement error of the method and appropriate magnification are defined using spherical nanoparticle models. We measured the 3D morphology of gold nanoparticles supported on titanium oxide (total volume=6.5 x 10(5) [nm(3)j, surface area=1.4 x 10(5) [nm(2)], and average nearest-neighbour distance=40 [nm]). (C) 2010 Elsevier B.V. All rights reserved.

We discuss the effect of annealing on the interfacial structure of Fe/GaAs films, with 2 x 4 surface reconstructions, and the subsequent effect on the Schottky barrier height. Images of the interfaces indicate that the annealing process can greatly reduce the level of atomic mixing. A study of the I-V characteristics of Fe/GaAs Schottky barrier diodes, in a wide temperature range of 10-300 K, reveals a strong temperature dependence for the unannealed case, arising from the presence of mixed surface states. The annealing process reduces the existence of the interfacial states, leading to more ideal behavior, with a reduced temperature dependence of the Schottky behavior.

Highly active and dispersed copper (Cu) nanoparticles on mesoporous silicas have been prepared via microwave irradiation of a solution of copper precursors with a previously synthesized mesoporous hexagonal silica (HMS) support. The protocol allowed differently low-loaded (typically 0.5 wt%) Cu materials containing Cu metal and small quantities of metal oxides. Materials were then tested as catalysts in the hydrogenation of carbonyl compounds under microwave irradiation. Cu materials were found to be highly active, selective and reusable in the reduction of substituted aromatic ketones and aldehydes, providing quantitative conversion of starting material within 5-10 min reaction at mild reaction conditions with complete selectivity to the alcohols. (C) 2010 Elsevier B.V. All rights reserved.

We applied the cryo-HAADF-STEM tomography (cryogenic Tecnai G2 Plara) for analysing three-dimensional nano-structures of platinum (Pt) and gold (Au) nanodots synthesised on titanium dioxide. The structural parameters such as particle size, density and volume were successfully evaluated and compared between macroscopic properties (inethylene blue dissolution and CO oxidation). The atomic structures of metallic clusters on the TiO2 surface were also carefully investigated by using double aberration corrected TEM/STEM (double AC JEOL JEM-2200FS) in order to study the quantum size effect of these noble metals.

A synergetic Fe-Al effect in Fe2O3 nanoparticles supported on mesoporous aluminosilicates compared to pure siliceous silicates has been demonstrated, for the first time, by a remarkably superior catalytic activity of the former in the microwave-assisted selective oxidation of benzyl alcohol to benzaldehyde. This significant finding, that also deeply influences the acidity of the materials (increasing total and particularly Lewis acidity), can have important consequences in the improved efficiency of these systems in related oxidations as well as in acid catalysed processes.

Highly active and stable supported iron oxide nanoparticles show excellent activities and switchable selectivities to target products in the microwave-assisted N-alkylation of amines with alcohols.

The nanostructure of titanate nanotubes known as a one-dimensional catalytic/electric subject is combinatorially characterized using x-ray diffraction (XRD), micro-Raman, photoluminescence (PL) and advanced electron microscopy. The micro-Raman and PL spectra prove the successful synthesis of TiO6 octahedron units in macroscopic scale. Cryo-high-angle annular dark-field (HAADF)-STEM and aberration-corrected (AC) TEM visualize in real-space the TiO6 octahedron unit formed as a TiO2-based tubular structure prepared by the alkaline hydrothermal methods. The chirality and scrolling-up mechanism of the TiO6 octahedron nanosheets in relation to an asymmetrical chemical environment and mechanical tensions are discussed.

We report the development of technologically important nickel (Ni) nanodots (nanoparticles) dispersed in amorphous silica (SiO(2)) for high-temperature permselectivity for hydrogen separation membranes, crucial in hydrocarbon reactions and H(2) production, and present the systematic reconstruction of the three-dimensional (3D) structures of the nanodots using electron nano-tomography. 3D structures using cryogenic high-angle annular dark field scanning transmission electron microscopy (Cryo-HAADF-STEM), which is a more accurate method for nanoparticle morphology than conventional chemisorption, are correlated with experimental reversible hydrogen adsorption properties. The correlations provide the first direct evidence of very high activity on the nanoparticle surface and the nature of adsorption sites. The results have important implications in general for the use of electron nano-tomography in the design of supported metallic nanoparticles for hydrogen separation membranes.

Multi-wall titanate nanotubes (MW-TNNTs) with high aspect ratio, large surface area and good uniformity were produced by alkaline hydrothermal treatment of grounded TiO(2) aerogels and further by applying freeze-drying. Not only the crystal phase and diameter, but also morphology of the starting materials impact on the aspect ratio and transformation efficiency of the obtained nanotubes. Other parameters, such as pH value during neutralization process and drying method for the final products, are important to control length and dispersion of MW-TNNTs. By spherical aberration corrected high-resolution transmission-electron-microscopy (Cs-corrected HRTEM) with lateral space resolution of 0.14 nm at 200 W accelerating voltage and electron energy loss spectrum (EELS), the detailed structural analysis of MW-TNNTs reveals that (1) diameters of inner and outer tubes are about 4-7 nm and 10 nm, respectively, (2) numbers of layers are different from part to part along the longitudinal tube axis, (3) the walls of the tubes have interlayer spacing of 0.70-0.80 nm and the lateral fringes which are vertical to the walls have spacing of 0.32 nm, (4) each layer of MW-TNNT is the nanosheet composed by the arrayed TiO(6) octahedrons, and respective octahedron being slightly strained, and (5) no chirality of MW-TNNT tubular structure is observed. (C) 2009 Published by Elsevier Ltd

An efficient protocol for the hydrogenation of platform molecules (e.g. succinic acid) in aqueous environments using supported metal nanoparticles on polysaccharide derived mesoporous carbonaceous materials is reported for the first time.

Two dimensional (2D) and three dimensional (3D) microstructures of metal nanoparticledispersed amorphous silica (Si-O) prepared by chemical solution process were observed using high angle annular dark field STEM (HAADF-STEM). In this study, the nickel nanoparticles in Si-O matrix were precisely studied on the relationship between microstructure and hydrogen affinity of the particles at high temperature. Total surface area of the Ni nanoparticles in Si-O was evaluated from average particle size derived from the particle size distribution of 2D HAADF-STEM images of powders with different metal contents. Amount of reversively adsorbed hydrogen on the interface of the nanoparticles and Si-O matrix for the samples were calculated using these data. Evaluated amount of adsorbed hydrogen was linearly increased and corresponds with the experimentally obtained result when the nanoparticles ideally dispersed in Si-O matrix with lower Ni contents. From 3D HAADF-STEM images, agglomerated particles were located on the surface of the composites, which results in decreasing the amount of reversible adsorbed hydrogen. Thus, it is thought that the reversible adsorption site was located at the interface of the Si-O and Ni nanoparticles. Copyright © 2008 MS&amp T'08®.

A transmission electron microscope (TEM) sample for observing photocatalysis in a liquid was prepared by using N,N,N-trimetyl-N-propylammonium-bis(trifluoromethanesulfonyl)imide. The ionic liquid (IL) was used as a reaction solvent. Tetrachloroauric acid was dissolved in the IL as gold ion species. Rutile particles were added in the solution as a photocatalyst. The low vapor pressure of the IL enables a diffusing system in high vacuum of TEM. Rutile particles were UV irradiated in that liquid phase. After 3 h UV irradiation, a gold particle of 8 nm diameter was grown on the TiO2 surface. Photonucleation of Au/TiO2 system was discussed from the high-resolution TEM images.

Rutile type titanium dioxide (TiO2) thin films are prepared by pulse laser deposition (PLD) with controlled oxygen pressure. Transmission electron microscopy (TEM) analysis clarified that crystalline structures, surface structures and electric states of the TiO2 films almost correspond to those of the bulk rutile. We observed crystalline domain including strain in the PLD film. The strain of the TiO2 film was measured by nano-beam diffraction. The strain-included domains affected properties of the film as optical absorption. The obtained optical band gap energy value was 3.30 eV, which was larger than that of bulk. TEM results such as crystalline grain sizes and distribution were used to consider quantum size effect in order to explain the larger band gap value. Moreover the influence of strain in rutile crystalline grains upon optical properties was suggested in the present study. The difference of band gap energy between experimental and theoretically calculated ones was considered to come from the strain effects. (c) 2006 Elsevier B.V. All rights reserved.

We have developed a spherical aberration corrected transmission electron microscopy (C-s-corrected TEM) technique that allows us to obtain clearer images in real space than ever before. We applied this technique to titanium oxide, in which light elements such as oxygen are difficult to observe using TEM because of its small cross section and electronic damage. In the present study, we successfully observed oxygen atoms in rutile TiO2. In addition, this direct observation of oxygen atoms enabled us to study the Magneli structure (TinO2n-1), which is caused by oxygen vacancies. These vacancies caused an atomic relaxation of the titanium and oxygen atoms. The relaxed atoms formed a characteristic shear structure of rutile titanium dioxide phase. This shear structure of the Magneli structure (TinO2n-1) was visualized with a spatial resolution of 0.119 nm. At the same time, the selected area diffraction ( SAD) pattern of the defect structure was obtained. Additional spots were shown inside the rutile [110] spot. We made structural models of the shear structure and simulated the diffraction pattern and images using a multi-slice simulation. Additional spots in the simulated diffraction patterns accurately reconstructed the experimental data. We also considered the possibility of the real-space analysis of local structures using spherical aberration corrected transmission electron microscopy.

Changes in the crystal structure and grain modifications in titanium oxide (TiO2) thin films were observed during the photocatalytic oxidation of hydrocarbons. When the hydrocarbon and collodion films were irradiated, single crystalline titanium oxide transformed into polycrystals. The titanium oxide films gradually became network aggregates. These changes were analyzed with a dedicated in situ transmission electron microscope and observed three dimensionally by electron tomography. A detailed analysis of electron energy loss spectra of the samples also revealed that the changes were associated with the loss of oxygen atoms in the TiO2 crystal lattice. Correlations between the polycrystalline grain size of TiO2 and its catalyst activity were discussed based on the measured data. (C) 2006 American Institute of Physics.

Ultraviolet light was used to irradiate hydrocarbons on TiO2 thin film in high-resolution transmission electron microscopy (TEM). The hydrocarbon was decomposed by photocatalysis of titanium oxide. Reaction processes were studied by using an in situ TEM observation system which was newly constructed for the present study. For measuring photocatalytic activities, electron energy loss spectroscopy (EELS) was used. We developed a new TEM method for observing crystal structures of TiO2 and quantifying photocatalytic activities concurrently. We succeeded in measuring the photodecomposition activity of hydrocarbons on TiO2 films in a submicron area. The spatial resolutions of the present method were compared with those of other methods for measuring photocatalytic activity.

Photocatalytic TiO2 materials have been one of the strong subjects of investigation for these ten years among various kinds of advanced functional materials. For studying the catalytic reaction by physical science techniques, a kind of transmission electron microscope technique is presented and applied to the study of photocatalysis on TiO2 films by UV light. Using the technique, we visualized in situ the decomposition process of hydrocarbons deposited on the TiO2 films in atomic level and elucidated a mechanism of the decomposition process. (C) 2004 American Institute of Physics.