Effect of Ar+ irradiation on the electrical conductivity of BaCe0.9Y0.1O3−δ

The effects of 10 keV Ar⁺ ion irradiation on the electrical characteristics of BaCe_0.9Y_0.1O_2.95 subject to fluences of 0, 1.0 × 10¹⁷, 5.0 × 10¹⁷ and 1.0 × 10¹⁸ ions/cm² at room temperature, has been investigated using elastic recoil detection analysis (ERDA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and alternating current (AC) impedance measurements. It was confirmed from the ERDA results that the hydrogen concentration near the surface increased with increase of Ar⁺ ion fluence. This increase may be associated with the increasing quantities of hydrogen generated by interaction between oxygen vacancies, formed by irradiation, and H₂O from exposure to air. SEM images showed clearly that the number of surface defects due to modification increased with increasing fluence. In addition, the size of the defects showed a tendency to increase with increasing fluence. From the results of XPS analyses, providing information on the electronic states on the surface, it was evident that with increase in the Ar⁺ ion fluence, the quantity of excess oxygen, such as hydroxide, increased in the oxygen 1s XPS spectrum. In addition, it was indirectly found, from decomposition of the Ce 3d, spectrum that the concentration of oxygen vacancies increased with fluence, since the percentage of Ce³⁺ also increased. Accordingly, the surface modification led to the formation of more oxygen vacancies and a greater hydrogen concentration on the surface, since the H₂O interacted with some of them. From the results of the DC conductivity and AC impedance measurements, the proton conductivity was shown to predominate over the temperature range from 473 K to 823 K. It was concluded that the increase in these protons and vacancies generated from surface modification contributed to the increase of proton conductivity.     

SnO<Subscript>2</Subscript> nanowires bridged across trenched electrodes and their gas-sensing characteristics

By using a thermal chemical vapor deposition and Au-catalyzed in situ alignment and growth process, SnO₂ nanowires could be bridged across trenched electrodes. In this process, a complicated and individual alignment process could be avoided and a number of devices can be fabricated in one step in a wafer scale. The gas-sensing characteristics of the developed sensor were significantly better when compared to those of other types of NO₂ sensors reported in the literature. When the concentration of NO₂ was 5 ppm, the sensitivity was higher than 150. Especially, the reaction time of 8–14 s was noticeably fast, which is attributed to the microtrench structure beneath the nanowires. PACS 61.46.Fg; 85.35.Kt; 81.15.Gh     

A study on ac and dc conductivity characteristics of Y-doped BaCeO3 modified by Ar+ ion beam

The effects of surface modification on electrical characteristics in bulk, grain boundary and interface (electrolyte/electrode) of BaCe_0.9Y_0.1O_3-δ were investigated. The surface modification was performed by means of two processes: specimen was firstly irradiated by 10 keV Ar⁺ ion with dose of 1 × 10¹⁸ ions/cm² and then exposed to air. The modified surface was investigated by elastic recoil detection analysis (ERDA) for quantitative analysis of hydrogen concentration on the surface and alternating current (AC) and direct current (DC) conductivity measurements, respectively. The ERDA results showed that hydrogen concentration and reaction rate on the modified surface increased. The increase of hydrogen concentration was explained in terms of the increase of proton due to interaction between oxygen vacancy formed by modification and H₂O. In AC and DC electrical conductivity measurements, it concluded that the proton and electronic carrier generated on the surface by modification attributed to the increase of bulk, grain boundary and interface conductivity.     

Comparison of analytical methods for ozone precursors using adsorption tube and canister

Recently, ozone concentrations have increased dramatically as a result of vehicle usage in metropolitan areas. Ozone precursors are composed of hydrocarbons of organic compounds. Because hydrocarbons are indicative of ozone formation, they need to be monitored in ambient air. Since ozone precursor are present at very low levels (from ppb to ppt) in ambient air, they are difficult to analyze accurately. This study investigates ozone precursors in ambient air. The main purpose of this study is to compare analytical methods for the measurement of ozone precursors in atmosphere. Two measurement methods were evaluated using canister (Silco-canister) and adsorbent (300-mg Carbopack B+150-mg Carbosieve SIII) tube. Differences in measurements for total ozone precursor emissions were 54.1% between the adsorption tube and canister-GC/MS, 51.1% between adsorption tube and canister-GC/FID, and 16.3% between canister-GC/MS and canister-GC/FID.     

Efficient gene delivery in differentiated human embryonic stem cells

Human embryonic stem (hES) cells are capable of differentiating into pluralistic cell types, however, spontaneous differentiation generally gives rise to a limited number of specific differentiated cell types and a large degree of cell heterogeneity. In an effort to increase the efficiency of specified hES cell differentiation, we performed a series of transient transfection of hES cells with EGFP expression vectors driven by different promoter systems, including human cellular polypeptide chain elongation factor 1 alpha (hEF1alpha), human cytomegalo-virus, and chicken beta-actin. All these promoters were found to lead reporter gene expression in undifferentiated hES cells, but very few drug-selectable transfectants were obtained and failed to maintain stable expression of the transgene with either chemical or electroporation methods. In an attempt to increase transfection efficiency and obtain stable transgene expression, differentiated hES cells expressing both mesodermal and ectodermal markers were derived using a defined medium. Differentiated hES cells were electroporated with a hEF1alpha promoter-driven EGFP or human noggin expression vector. Using RT-PCR, immunocytochemistry and fluorescence microscopy, the differentiated hES cells transfected with foreign genes were confirmed to retain stable gene and protein expression during prolonged culture. These results may provide a new tool for introducing exogenous genes readily into hES cells, thereby facilitating more directed differentiation into specific and homogenous cell populations.     

Effects of Electrolytes on the Transport Phenomena in a Cation-Exchange Membrane

The effect of electrolyte solutions on the characteristics of the current-voltage (I-V) curve in a cation-exchange membrane (CMX membrane, Tokuyama Soda, Inc.) was studied based on the concentration polarization and electroconvection theory. The study includes the limiting current density (LCD), plateau length, and the ratio of resistance of region III to region I of the I-V curve (R(3rd)/R(1st)). Different electrolyte solutions, HCl, LiCl, NaCl, KCl, CaCl(2), MgCl(2), and AlCl(3), were used in this study. The LCD values of the electrolytes were correlated with the diffusion coefficient of the cation (D(+)) and valence of the cation and anion (z(+), z(-)). Except for the HCl solution, the LCD values of the electrolytes increased linearly with D(+)(1-z(+)/z(-)), implying that the current in this region was governed by the concentration polarization phenomena. The deviation of the HCl solution from the linearity is due to a particular transport mechanism of the proton called the Grotthuss-type transport. The differences in the plateau length and the resistance ratio, R(3rd)/R(1st), with the electrolytes were explained by the Péclet number (Pe) representing a transport pattern in the electroconvection theory. The Péclet number is proportional to the Stokes radius of an ion. An electrolyte with a large Stokes radius has a shorter plateau length and a lower ratio of R(3rd)/R(1st) than those of an electrolyte with a small Stokes radius. Water-splitting measurements for the different electrolyte solutions in the CMX membrane revealed that the contribution of water splitting to the overlimting current was insignificant regardless of the electrolytes used in this study. However, when metal hydroxides, such as Al(OH)(3), formed on the surface of the membrane, significant water splitting was observed. Copyright 2001 Academic Press.     

Synthesis and structural characterization of novel ruthenium(II) complexes featuring an N,N,O-scorpionate ligand: A versatile synthetic precursor for open-face scorpionatoruthenium(II) complexes

The syntheses and characterization of novel ruthenium(II) complexes containing bis(3,5-dimethylpyrazol-1-yl)acetato (bdmpza), a new class of scorpionate ligands, are reported herein. [RuCl(bdmpza)(η⁴-1,5-cyclooctadiene)] (1) was found to be a versatile precursor to synthesize a wide range of new ruthenium(II) complexes with the bdmpza ligand. The treatment of 1 with pyridine (py), diphenylphosphinoethane (dppe), 2,2′-bipyridyl (bpy), 1,10-phenanethroline (phen), or bispicolylamine (Hbpica) in refluxing N,N-dimethylformamide resulted in displacement of the 1,5-cyclooctadiene ligand to afford [RuCl(bdmpza)(py)₂] (2), [RuCl(bdmpza)(dppe)] (3), [RuCl(bdmpza)(bpy)] (4), [RuCl(bdmpza)(phen)] (5), and [Ru(bdmpza)(Hbpica)]Cl (6Cl) in good yields, respectively. The structures of 1–4, and 6 were determined by X-ray structure analyses.     

Field-emission properties of patterned ZnO nanowires on 2.5D MEMS substrate

We fabricated a nanowire-based field-emission display (FED) device on a 2.5D substrate using a photolithography, lift-off, thermal-evaporation, and plasma-etching process. We first fabricated a 3×3 array of microholes (diameter = 400???m and depth = 50???m) on a Si substrate and fabricated ZnO nanowires inside the microholes by using a thermal CVD process. The field-emission pattern image of the 3×3 array of microholes was clearly apparent. The threshold emission field was ca. 5.6?V/??m and we obtained considerable brightness when the applied voltage was 1900?V (i.e. 6.3?V/??m). Because the fabrication processes used in this study are standard semiconductor fabrication routes, the study suggests the feasibility of mass producing a nanowire-based FED device.