Origin of unusual work function change upon forming Tl nanoclusters on Si(111)-7x7 surface

We report an unusual behavior of the work function that remains unchanged while increasing the coverage (θ) of thallium (Tl) nanoclusters regularly arranged on a Si(111)-7×7 surface. Such a constant work function with increasing θ is understood in terms of a θ-dependent inter-cluster interaction that cancels the change induced by dipoles due to Tl nanoclusters. The spectral changes of Si 2p and Tl 5d_5/2 core-levels as a function of θ strongly indicates the presence of such an inter-clusters interaction, which is further supported by our theoretical calculation revealing a significant charge redistribution. PACS 73.20.-r; 73.30.+y; 68.47.Fg; 79.60.-i; 73.20.Hb     

Synthesis and characterization of LiMnBO3 cathode material for lithium ion batteries

LiMnBO₃ with enhanced powder density was successfully synthesized by a commercially available spray-drying process. A monoclinic-LiMnBO₃ single phase was experimentally substantiated by an X-ray diffractometer with crystallinity investigated by Rietveld refinement method (Bragg R-factor and RF-factor <10). The dense LiMnBO₃ powder prepared by the spray drying process showed spherical morphology. The electrochemical property of LiMnBO₃ was extensively investigated, positively revealing that 0.27 Li⁺ (Li_0.27MnBO₃) was stoichiometrically extracted from the host LiMnBO₃ material at first cycle.     

High space harmonic perturbations in travelling wave tubes

Stability properties of the free streaming mode in an electron beam propagating through a cylindrical waveguide loaded with a tape helix are investigated, including influence of high space harmonic perturbations. Closed algebraic dispersion relation of the free streaming mode are obtained. Properties of the high space harmonic perturbations are numerically investigated in connection with application on a high frequency microwave amplifier. One of the most important features in this analysis is that instability of high harmonic perturbations occurs at a very large value of microwave frequency. In this regard, millimeter microwave can be easily attainable by reducing the helix radius to a subcentimeter.     

The effects of non-thermal atmospheric pressure plasma jet on cellular activity at SLA-treated titanium surfaces

Titanium (Ti) is a primary material used for dental implants, and the sandblasted, large-grit, and acid-etched (SLA) surface treatment is commonly used on titanium to promote early osseointegration. Despite their benefits, SLA-treated Ti surfaces are disadvantaged by their hydrophobic property, and much research has been performed to address this problem. In current study, we hypothesized the effects of a nitrogen-based non-thermal atmospheric pressure plasma jet (NTAPPJ) treatment on SLA-treated Ti would increase hydrophilicity and cellular activity. Samples with and without the NTAPPJ treatment were analyzed using a field emission scanning electron microscope, optical surface roughness system, X-ray photoelectron spectroscope, and water contact angle measuring system. MC3T3-E1 cells (murine osteoblastic cell line) attachments and proliferations were examined by the MTT and BrdU colorimetry assay. Cell immunofluorescent microscopic images were observed by a confocal laser scanning microscope for a morphological analysis. This study found that the nitrogen-based NTAPPJ treatment on SLA-treated Ti significantly increased the hydrophilicity and MC3T3-E1 cell attachments and proliferations. Hence, it was concluded that an additional procedure of nitrogen-based NTAPPJ treatment just prior to implantation of SLA-treated Ti into oral defect sites could improve the success of dental implant surgery.     

On the origin of reactive Pd catalysts for an electrooxidation of formic acid

We investigated the origin of the reactive surface of Pd catalysts during the electrocatalytic oxidation of formic acid. XPS analysis was the primary tool adapted to characterize the surface changes in Pd catalysts arising from interactions with formic acid. Pd catalysts showed fast deactivation, though their activity could be simply recovered by applying a reduction potential at which hydrogen evolution reaction can occur. XPS analysis revealed that the surface of Pd catalysts is significantly affected by interaction with formic acid, thus confirming that the surface coverage of oxygen species plays an important role in formic acid electrooxidation on the Pd catalysts. At the same time, mass transfer of formic acid also has an effect on the deactivation of Pd catalysts.     

Breakdown mechanism of an atmospheric-pressure radio-frequency capacitive argon discharge in parallel-plate bare metal electrodes

The breakdown behavior of an atmospheric-pressure radio-frequency capacitively coupled argon plasma discharge at 13.56 MHz is investigated in order to produce a stable and homogeneous atmospheric-pressure argon glow discharge. It is found that the electrode separation distance plays a pivotal role in exciting argon discharge whether in mobility-controlled electric breakdown or in diffusion-controlled breakdown and the discharge mode (arc discharge, α-mode glow discharge, or γ-mode glow discharge) immediately following breakdown is closely related to the breakdown mechanism.     

Synthesis of titanium dioxide in O2/Ar/SO2/TiCl4 microwave torch plasma and its band gap narrowing

Titanium dioxide (TiO₂) nanoparticles were synthesized directly by injecting gas-phase titanium tetrachloride (TiCl₄) bubbled with a mixture of Ar and SO₂ into a 2.45 GHz microwave torch plasma operated in O₂ gas at atmospheric pressure. The absorption edge of the as-produced TiO₂ powders in the UV–Visible spectrum shifted from 457 nm to 483 nm as the SO₂ gas content in the mixture gas carrying the TiCl₄ was increased. According to X-ray photoelectron spectroscopy (XPS) and UV–Visible spectroscopy, the band gap narrowing was due to the incorporation of sulphur (S) species from the Ar and SO₂ mixture in the oxygen microwave torch plasma into the O site of TiO₂.     

A single-step approach to create nano-pottery structures for efficient water electrocatalysis

We have introduced a simple fabrication process to create Ni nano-pottery structure using a well-controlled electrodeposition process into a nanoporous alumina template. The nanostructures were then applied as a stable and effective cathode catalyst for hydrogen evolution reaction (HER) in alkaline water electrolysis. Their catalytic activity was compared to that of the Ni nano-rod and film and the result shows that the HER activity was greatly enhanced when using the Ni nano-pottery structure which mainly resulted from both larger and higher numbers of surface reactive sites.     

Generalization of Wilemski-Fixman-Weiss decoupling approximation to the case involving multiple sinks of different sizes, shapes, and reactivities

We generalize the Wilemski-Fixman-Weiss decoupling approximation to calculate the transient rate of absorption of point particles into multiple sinks of different sizes, shapes, and reactivities. As an application we consider the case involving two spherical sinks. We obtain a Laplace-transform expression for the transient rate that is in excellent agreement with computer simulations. The long-time steady-state rate has a relatively simple expression, which clearly shows the dependence on the diffusion constant of the particles and on the sizes and reactivities of sinks, and its numerical result is in good agreement with the known exact result that is given in terms of recursion relations.     

Metal‐Insulator Transition‐Induced Adsorption‐Resistant Behavior of Small Au Nanoparticles

Smaller nonmetallic nanoparticles are more inert: Metal–insulator transition of Au nanoparticles on silica is closely related to the metal–support charge transfer, which has a strong influence on chemisorption reactivity of Au. Smaller nonmetallic Au nanoparticles are more resistant towards butanethiol chemisorption (see picture and graph).