Nonthermal and selective crystal bridging of ZnO grains by irradiation with electron beam as nonequilibrium reaction field.

Ceramic particles, such as titanium oxide and indium tin oxide, are expected to be used as electric or catalytic materials for various applications. In this work, we progressed to employ the irradiation with an electron beam as the nonequilibrium reaction field for ceramic composition, and we successfully obtained the basic technology for a ceramic thin-film fabrication using a field emission (FE) electron beam with low energy resolution having a half width under 100 meV that had a homogeneous planar electron emission as the nonequilibrium reaction field. In particular, ZnO particles synthesized by electron beam irradiation show selective crystal bridging along the c-axis during FE electron beam irradiation, which is important for synthesizing poly-ZnO crystals without a heating process, because the energy fluctuations of FE electron beams are small and affect the directionality of ZnO crystal growth along the c-axis. This accomplishment may make a significant contribution to the analysis of the formation mechanism of ZnO particles with a uniform morphology and crystal structure by the FE electron beam during the crystallization. Moreover, we will be able to provide basic elements for next-generation nanodevices with highly functional properties by controlling each terminal crystal interface of metals, ceramics, and semiconductors with this technique.

Uneven damage on head and liner contact surfaces of a retrieved Co-Cr-based metal-on-metal hip joint bearing: An important reason for the high failure rate.

Detailed metallurgical investigations have been performed on a used Co-Cr-based metal-on-metal (MoM) hip joint bearing containing a type of liner that is commonly used in such joints. The damage on the metal-liner sliding surface was considerably more severe than that on the metal head counterpart, in terms of wear-scar density and width and microcrack frequency. Cross-sectional transmission electron microscopy revealed that a thick (>3 µm) nanocrystalline layer formed on the sliding surface of the head, whereas the liner had coarse carbides embedded in it and nanocrystals were formed in a very limited region no deeper than 1 µm. Comparative investigation of an unused head and a liner of identical type showed that although the chemical compositions of the liner and head were nearly identical, their microstructures were significantly different. Specifically, the grain size in the liner was larger than that in the head on average, and the grain boundaries of the liner were decorated with coarse carbides. Moreover, X-ray diffraction analysis revealed a large tensile residual stress only in the liner. These differences are possibly responsible for the wear damage on the liner being more serious than that on the head.

Localization Effect on Pt-Loaded Ce0.5Zr0.5O2 Nanoparticles Inserted Into Mesoporous SBA-16 by Hydrothermal Processing.

We succeeded to use hydrothermal treatment to insert prefabricated Pt-loaded Ce0.5Zr0.5O2 (PtCZ) nanoparticles into the mesopores of the SBA-16 mesoporous silica without disordering of the mesoporous structure. Samples prepared by the hydrothermal treatment exhibited superior oxygen storage capacity compared to that of simple dry mixed sample. The oxygen storage capacity of the hydrothermally treated PtCZ is attributed to the localized PtCZ nanoparticles inside the mesopores of the SBA-16. FTIR analysis suggested that the PtCZ nanoparticles inside the mesopores possess the Si-O-Zr linkages that are bonded to the inner walls of the SBA-16 host. This linkage is the key reason for the superior oxygen storage capacity of PtCZ localized in the mesopores by hydrothermal treatment. It is considered that the formation of the Si-O-Zr linkage in the hydrothermally treated samples resulted in crystalline distortions of Ce0.5Zr0.5O2 nanoparticles inside the mesopores, and which contribute to enhance the oxygen storage capacity of PtCZ.

Numerical analysis of electron emission site distribution of carbon nanofibers for field emission properties.

To obtain optimal field emission (FE) properties, it is important to evaluate FE parameters including the electron emission site α and the field enhancement factor ß. However, it is difficult to evaluate α quantitatively because the emitting electrons cannot be observed directly. The authors have aimed to analyze this site using an original architecture with a computation system tool based on the surface charge method, and a three-dimensional model has been employed to calculate FE properties with high accuracy. In this study, to analyze α for determining FE properties, each carbon nanofiber (CNF) model separated by Cr islands which include the minimum area for calculating electric fields by the surface charge method was constructed on the surface of a Ni catalyst. The FE current was simulated with a Fowler-Nordheim formula using the calculated electric fields, followed by a simulation performed using all CNFs on a field emitter cathode. The electron emission site α was determined by comparing the simulation and experimental results of the FE current. It was found that α depends on the morphology of the CNF bundles, and a close quantitative correspondence between the experimental and the computation results of FE properties was obtained. In summary, a method of analyzing FE properties was established using an original architecture, making it possible to predict FE properties with a computational tool based on the surface charge method.

Semiconducting cross-linked polymer nanowires prepared by high-energy single-particle track reactions.

High-energy charged particle irradiation of cross-linking polymers gives nanowires formed by cross-linking reactions along the ion track trajectories. Here, the direct formation of nanowires consisting of a conjugated polymer by single-particle nanofabrication technique (SPNT) is investigated. Poly(9,9'-di-n-octylfluorene) (PFO), regioregular poly(3-hexylthiophene) (rrP3HT), and poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) underwent an efficient cross-linking reaction upon irradiation, resulting in the formation of 1-dimensional nanostructures with high and desired aspect ratio reaching up to ∼200. The size of nanowires was perfectly interpreted by well-sophisticated theoretical aspects based on the statistical theory of polymer backbone configurations, suggesting that simple cross-linking reactions of the polymers determine the size and structure of nanowires. PFO based nanostructures exhibited sharp and intense emission with high fluorescence quantum yield indicating the absence of any significant inter/intra polymer chromophore interactions in the nanowires assemblies.

Crystal growth of thiol-stabilized gold nanoparticles by heat-induced coalescence.

A monolayer of dodecanethiol-stabilized gold nanoparticles changed into two-dimensional and three-dimensional self-organized structures by annealing at 323 K. Subsequent crystal growth of gold nanoparticles occurred. Thiol molecules, although chemisorbed, form relatively unstable bonds with the gold surface; a few thiols desorbed from the surface and oxidized to disulfides at 323 K, because the interaction energy between thiol macromolecules is larger than that between a thiol and a nanoparticle. The gold nanoparticles approached each other and grew into large single or twinned crystals because of the van der Waals attraction and the heat generated by the exothermic formation of disulfides.

Effect of the wavelength of infrared heaters on the inactivation of bacterial spores at various water activities.

Bacterial spores (Bacillus subtilis subsp. subtilis NBRC 16183) inoculated onto a stainless steel Petri dish and treated at nine levels of water activity (a(w)) for 2 days were inactivated by infrared radiation heating (IRH) using three kinds of infrared heaters with different radiation spectra. The peak wavelengths used were 950, 1,100 and 1,150 nm. In general, the inactivating efficacy of IRH treatment against bacterial spores with shorter wavelength heater (950 nm) was greater than that with other heaters. The decimal reduction times (D value) calculated using the linear portion of survival curves were affected by both the initial a(w) values and the spectra of the infrared rays. Spores at approximately 0.9, 0.7 and 0.6 a(w) were most resistant to IRH at wavelengths of 950, 1,100 and 1,150 nm, respectively. The a(w) values that led to maximum D values for bacterial spores increased as the wavelength was shortened. Optimum a(w) values were identified for the inactivation of bacterial spores by IRH. Spore resistance to IRH could also be affected by the spectral characteristics of the infrared absorption, which varied with the a(w) of bacterial spores.