Sample preparation toward seamless 3D imaging technique from micrometer to nanometer scale.

Three-dimensional (3D) imaging techniques, such as x-ray computed tomography (XCT), serial sectioning method, transmission electron microtomography (TEMT) and 3D atom probe (3DAP), provides 3D internal structures and external form of objects. In order to obtain the 3D images of one object from the synchrotron-XCT (SR-XCT), FIB-SEM serial sectioning, TEMT and 3DAP, in the present study, the common sample holder and improvement in the TEM tomography retainer were made. We report the sample holder, the TEM retainer, and the sample preparation method using focused ion beam (FIB) and show the 3D images obtained from SR-XCT, FIB-SEM and TEMT of quartz sample containing fluid inclusions.The present common sample holder was made from tungsten needle and copper pipe. The tungsten needle was made from the wire by electropolishing in aqueous ammonia and salt as molten material. A micro-sample of quartz containing fluid inclusions was picked up from the thin section using a focused ion beam (FIB) system (FEI, Quanta 200 3DS), Kyoto University. The FIB system used a Ga(+) ion gun at the condition of 30 kV and 3-65 nA. After a specific area (ca. several ten µm on a side) of the quartz was cut out to a depth of 10 - 30 µm by FIB, it was held at a tip of tungsten needle with platinum deposition (Figure 1a) [1]. Then it was observed by imaging tomography system using a Frenel zone plate at BL47XU, SPring-8, Japan [2]. The size of voxel (pixel in 3D) was 50-80 nm, which gave the effective spatial resolution of ∼200 nm. The characteristic of this method (FIB-XCT) is that the XCT sample can be exactly picked up from a specific area from thin section and bulk specimen after the observation using optical microscopy and/or scanning electron microscopy (SEM). After the FIB-XCT observation, the sample held at a tip of tungsten needle was directly inserted into the FIB-SEM system and the cross-section surface were observed by FIB-SEM. Figure 1b shows a snap shot of the cross-section surface. 3D image was reconstructed from the obtained surface image series and the spatial resolution of this 3D image is higher than XCT although it is depended on the spatial resolution of FIB and SEM. When we obtain TEMT image from the specific area after FIB-XCT and FIB-SEM, TEMT specimen is picked up during FIB-SEM processing and is attached to another tungsten needle. TEMT specimen can be also made from the remaining sample of FIB-SEM held at same holder. Then TEMT specimen was carefully milled into a sharp rod-form with annular-mask by FIB (Figure 1c). This specimen can be analysis by 3DAP. The tungsten needle with rod specimen at the top was mounted in the specimen retainer which was shaped by nipper to achieve the ± 90 ° tilt without any impedimenta and was dug the channel by femto-second laser system to fix the tungsten needle. TEMT experiments were carried out using a JEM-2100F (JEOL LTD., Japan) at Kyoto University. The acceleration voltage was 200kV. The inclusion of about 20 to 100 nm in quartz, which could not be detected by FIB-XCT, was clearly identified in a TEM and TEMT image (Figure 1d).jmicro;63/suppl_1/i24/DFU055F1F1DFU055F1Fig. 1.(a) FIB-XCT sample held at a tip of tungsten needle. (b) A snap shot of the cross-section surface by FIB-SEM at tilt = 52°. The hole observed in the center is the trace of fluid inclusion. (c) Sharp rod-formed TEMT specimen at a tip of tungsten needle. (d) Bright field TEM image of quartz TEMT specimen. The inclusion of about 50 × 100 nm (inside of dashed line circle) was observed in quartz.

Hydrogen storage in Pd nanocrystals covered with a metal-organic framework.

Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5-benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating.

Solid solution alloy nanoparticles of immiscible Pd and Ru elements neighboring on Rh: changeover of the thermodynamic behavior for hydrogen storage and enhanced CO-oxidizing ability.

Pd(x)Ru(1-x) solid solution alloy nanoparticles were successfully synthesized over the whole composition range through a chemical reduction method, although Ru and Pd are immiscible at the atomic level in the bulk state. From the XRD measurement, it was found that the dominant structure of Pd(x)Ru(1-x) changes from fcc to hcp with increasing Ru content. The structures of Pd(x)Ru(1-x) nanoparticles in the Pd composition range of 30-70% consisted of both solid solution fcc and hcp structures, and both phases coexist in a single particle. In addition, the reaction of hydrogen with the Pd(x)Ru(1-x) nanoparticles changed from exothermic to endothermic as the Ru content increased. Furthermore, the prepared Pd(x)Ru(1-x) nanoparticles demonstrated enhanced CO-oxidizing catalytic activity; Pd0.5Ru0.5 nanoparticles exhibit the highest catalytic activity. This activity is much higher than that of the practically used CO-oxidizing catalyst Ru and that of the neighboring Rh, between Ru and Pd.

Enhanced magnetization in highly crystalline and atomically mixed bcc Fe-Co nanoalloys prepared by hydrogen reduction of oxide composites.

Fe(x)Co(100-x) nanoalloys (NAs) with 20 ≤ x ≤ 80 were prepared by hydrogen reduction of Fe-Co oxide nano-composites, which were composed of mixed phases (or domains) of Fe(2)O(3) and CoO. In situ X-ray diffraction (XRD) measurements using synchrotron radiation clearly showed development of a solid-solution Fe-Co phase by hydrogen reduction from the oxide composites. High-resolution transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM and powder XRD revealed that Fe-Co NAs form a single crystal structure and the two elements are mixed homogeneously. The saturation magnetization depends on the size and metal composition and shows the highest value (250 emu g(-1)) for the Fe(70)Co(30) NA in the size range of 30-55 nm, which is comparable to that of the Fe(70)Co(30) bulk alloy (245 emu g(-1)). This high magnetization is attributable to high crystallinity and homogeneous mixing of constituent atoms, which are attained by thermal treatment of oxide phases under a hydrogen atmosphere.

Nanosize-induced drastic drop in equilibrium hydrogen pressure for hydride formation and structural stabilization in Pd-Rh solid-solution alloys.

We have synthesized and characterized homogeneous solid-solution alloy nanoparticles of Pd and Rh, which are immiscible with each other in the equilibrium bulk state at around room temperature. The Pd-Rh alloy nanoparticles can absorb hydrogen at ambient pressure and the hydrogen pressure of Pd-Rh alloys for hydrogen storage is dramatically decreased by more than 4 orders of magnitude from the corresponding pressure in the metastable bulk state. The solid-solution state is still maintained in the nanoparticles even after hydrogen absorption/desorption, in contrast to the metastable bulks which are separated into Pd and Rh during the process.

Microstructures and electrical properties of TiO(2)-doped Al(2)O(3) ceramics.

Microstructures of TiO(2)-doped alpha-Al(2)O(3) ceramics used as electrostatic chucks (ESC) were investigated by transmission electron microscopy including energy-dispersive spectrometry (EDS) and electron energy loss spectroscopy (EELS) analyses in connection with their electrical properties. The lattice parameters of sintered Al(2)O(3) grains are almost independent of TiO(2) content as well as the sintering temperature, indicating immiscibility of the additive with Al(2)O(3). Scanning transmission electron microscopy (STEM)-EDS revealed that the grain boundaries of alpha-Al(2)O(3) are slightly enriched with Ti. It was shown in EELS that the segregated Ti is in a partially reduced state. The Ti-enriched grain boundaries, therefore, play a role as a conductive network, which is responsible for considerable improvement of electronic conductivity with TiO(2) doping. STEM-EDS and electron diffraction analyses confirmed that micrometre-sized TiO(2) particles are dispersed in the alpha-Al(2)O(3) when sintering is operated at 1300 degrees C or lower, while the particles transform into Al(2)TiO(5) at higher temperature. EELS revealed that the TiO(2) grains are partially reduced into non-stoichiometric TiO(2-y), while Al(2)TiO(5) grains are in the fully oxidized state. The TiO(2-y)-dispersed alpha-Al(2)O(3) shows no dielectric relaxation and quite smooth dissipation of the electrostatic condensed charges. In contrast, alpha-Al(2)O(3) with Al(2)TiO(5) grains possesses pronounced dielectric relaxation, and the electrostatic dissipation takes such a longer time as 30 s. The former is preferable to application to ESC in terms of quick response.

Maximum diameter of the rod-shaped specimen for transmission electron microtomography without the "missing wedge".

In our recent study, the complete rotation of a rod-shaped specimen during transmission electron microscopy (TEM) has been successfully carried out, yielding a truly quantitative three-dimensional (3D) structure of a ZrO(2)/polymer nano-composite. This result allows the further development of transmission electron microtomography (TEMT) for materials science. The diameter of the rod-shaped specimen was about 150 nm, which may not be statistically large enough to evaluate structural parameters, e.g., volume fraction of Zr nano-particles. Thus, it is preferable to image rods with larger diameters in 3D. In this study, several rod-shaped specimens whose diameters ranged from 150 to 530 nm were subjected to the "distortion-free TEMT". The maximum diameters, l, observable under 200 and 300 kV-TEMTs were, respectively, 460-470 and 600-670 nm (corresponding the maximum relative diameters, l/lambda (lambda: mean free path), were ca. 2.2 and 2.7-3.0).

Microstructure of metal-filled carbon nanotubes.

Catalysts are usually required to produce carbon nanotubes (CNTs) and play important roles during the growth process. Any catalysts that remain after processing are expected to add extra properties and removal of the catalysts is usually required to achieve the original properties of CNTs. Recently, CNTs have been filled incidentally by catalysts, such as Pb, Sn, Ni and Bi. This has led to success in obtaining additional properties and a few models have been proposed to describe the encapsulating mechanisms. In the present study, CNTs were filled with palladium by a microwave plasma-assisted chemical vapor deposition method. Detailed structural and compositional investigations of these metal-filled CNTs were carried out by transmission electron microscopy to elucidate the growth mechanisms.