Fabrication of hydrophobic surface of titanium dioxide films by successive ionic layer adsorption and reaction (SILAR) method

Titanium dioxide (TiO₂) films were fabricated on fluorine doped tin oxide (FTO) coated glass substrate using successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction, scanning electron microscopy, transmission electron microscopy, optical absorption and contact angle measurement were applied to study the structural, surface morphological, optical and surface wettability properties of the as-deposited and annealed TiO₂ films. The X-ray diffraction studies revealed both as-deposited and annealed TiO₂ films are amorphous. Irregular shaped spherical grains of random size and well covered to the fluorine doped tin oxide coated glass substrates were observed from SEM studies with some cracks after annealing. The optical band gap values of virgin TiO_2, annealed, methyl violet and rose bengal sensitized TiO₂ were found to be 3.6, 3.5, 2.87 and 2.95 eV, respectively. Surface wettability studied in contact with liquid interface, showed hydrophobic nature as water contact angles were greater than 90°. The adsorption of dyes, as confirmed by the photographs, is one of the prime requirements for dye sensitized solar cells (DSSC).     

Coevolutionary extremal dynamics on gasket fractal

We considered a Bak-Sneppen model on a Sierpinski gasket fractal. We calculated the avalanche size distribution and the distribution of distances between subsequent minimal sites. To observe the temporal correlations of the avalanche, we estimated the return time distribution, the first-return time, and the all-return time distribution. The avalanche size distribution follows the power law, P(s)∼s−τ, with the exponent τ=1.004(7). The distribution of jumping sites also follows the power law, P(r)∼r−π, with the critical exponent π=4.12(4). We observe the periodic oscillation of the distribution of the jumping distances which originated from the jumps of the level when the minimal site crosses the stage of the fractal. The first-return time distribution shows the power law, Pf(t)∼t−τf, with the critical exponent τf=1.418(7). The all-return time distribution is also characterized by the power law, Pa(t)∼t−τa, with the exponent τa=0.522(4). The exponents of the return time satisfy the scaling relation τf+τa=2 for τf?2.     

Pore formation in in situ processed MgB2 superconductors

MgB₂ bulks were prepared by an in situ process which utilizes the reaction between boron and magnesium powder. The reaction time was fixed at 0.5 h and the temperature was changed from 600 °C to 1000 °C. The density decrease due to pore formation and mass (mainly magnesium) loss during the formation reaction of MgB₂ was observed in all samples. In addition to the pore formation, a pellet expansion which can be explained by the outgrowth of MgB₂ grains was also observed. Two different mechanisms were adopted to explain the pore formation; Kirkendall pores formed at a temperature below the melting point (m.p.) of magnesium by a difference in the diffusivity between magnesium and boron, and the pores formed at a temperature above the m.p. by melting of magnesium and a capillary movement. The density, T_c and J_c results suggest that the current carrying capacity can be improved by a careful control of the process parameters regarding a pore evolution.     

Luminescence enhancement of Eu-doped calcium magnesium silicate blue phosphor for UV-LED application

(Ca_1−x,Eu_x)MgSi_2yO_6+δ blue phosphor was prepared by spray pyrolysis and the photoluminescence properties were optimized by controlling concentration of Si element and the activator content. At y=1.0, the concentration quenching in the luminescent intensity appeared when the Eu²⁺ content (x) was 0.01 (1 at%). Such quenching concentration was changed with the concentration of silicon (y), which was increased with an increase in the quantity of excess Si (y>1.0). The highest luminescent intensity was achieved when the Eu²⁺ content (x) and the Si concentration (y) were 0.04 and 1.3, respectively. According to X-ray diffraction (XRD) analysis, the tetragonal SiO₂ phase was formed as a minor phase when the y value was larger than 1.3. The formation of SiO₂ phase, however, did not reduce but increased the luminescent intensity when the Eu²⁺ content was optimized again. As a result, the luminescent intensity of the phosphor particles optimized in the content of both Si and Eu²⁺ was about 150% improved compared with that of the CaMgSi₂O₆:Eu sample (x=0.01, y=1.0).     

Effect of Ni doping on the phase stability and conductivity of scandia-stabilized zirconia

The effect of Ni doping on the phase stability and conductivity of scandia-stabilized zirconia (SSZ) thick film was studied. A free-standing 10SSZ thick-film (10 mol% Sc₂O₃-stabilized zirconia, ~ 10 μm thick) that was previously in contact with a Ni layer during co-firing was fabricated. The 10SSZ thick-film showed a cubic phase in contrast to the rhombohedral phase shown for a bulk 10SSZ sample. The Ni content in the SSZ thick film was ~ 1.7 mol%. The effect of Ni on the cubic phase formation was also confirmed by the similar observation of the cubic phase in the Ni-doped bulk 10SSZ sample. The observed conductivity behavior also supported the XRD observation. Ni was found to hinder the transformation of the cubic phase to the rhombohedral on cooling in 10SSZ samples after a reduction treatment.     

Metal-directed supramolecular assembly of metal(II) benzoates (M = Co,Ni, Cu,Zn, Mn,and Cd) with 4,4′-bipyridine: Effects of metal coordination modes and novel catalytic activities

Six polymeric metal(II)-benzoate complexes of formula [Co₂(O₂CPh)₄(4,4′-bpy)₂]_n (1-Co), [Ni(O₂CPh)₄(H₂O)₂(4,4′-bpy)]_n (2-Ni), [Cu₂(O₂CPh)₄(4,4′-bpy)]_n (3-Cu), [Zn₂(O₂CPh)₂(OH)₂(4,4′-bpy)₂]_n (4-Zn), [Zn₃(O₂CPh)₄(μ-OH)₂(4,4′-bpy)₂]_n (5-Zn), and [Cd₂(O₂CPh)₄(4,4′-bpy)₂]_n (6-Cd) have been synthesized and characterized (4,4′-bpy = 4,4′-bipyridine). 1-Co and 6-Cd show ladder-type double chains, 2-Ni does a helical structure, 3-Cu does a one-dimensional chain containing paddle-wheel units, 4-Zn does a zigzag chain, and 5-Zn does two-dimensional sheets. Since different structures provide different coordination geometry of each metal ion, it is clear that selection of appropriate metal ions can control the coordination geometry of each metal ion to form different crystal structures. Reactivity study of the compounds 1–7 for the transesterification of a variety of esters has shown that 4-Zn and 5-Zn are very efficient and the best among them. The catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, also catalyzed efficiently the transesterification of a variety of esters, and its reactivity is comparable to 4-Zn and 5-Zn. Moreover, the redox-active metal-containing polymers, 1-Co, 3-Cu, and 7-Mn, have shown efficient catalytic reactivities for the transesterification reactions, while 2-Ni has displayed a very slow conversion. The reactivities of the compounds used in this study are in the order of 5-Zn > 4-Zn > 6-Cd > 7-Mn ∼ 3-Cu > 1-Co > 2-Ni, indicating that the non-redox metal-containing compounds (5-Zn, 4-Zn, and 6-Cd) show better activity than the redox-active metal-containing compounds (7-Mn, 3-Cu, 1-Co, and 2-Ni). These results suggest that it is possible to tune the catalytic activities by changing from Zn to those metals such as Cd, a kinetically inert metal, or Cu, Mn, and Co, the redox-active metals.     

Energetic Ethylene‐ and Propylene‐Bridged Bis(nitroiminotetrazolate) Salts

High energy density materials with ethylene‐ and propylene bis(5‐nitroiminotetrazolate) as the anions are reported; all salts were fully characterized by IR, and ¹H, ¹³C, and ¹⁵N NMR spectroscopy as well as elemental analyses. In addition, the heats of formation (ΔH_f) and the detonation pressures (P) and velocities (D) were calculated.

     

Enantioselective α-hydrazination of α-fluoro-β-ketoesters catalyzed by chiral nickel complexes

The catalytic enantioselective electrophilic α-hydrazination promoted by chiral nickel complexes is described. Treatment of α-fluoro-β-ketoesters with azodicarboxylates as electrophilic amination reagents under mild reaction conditions afforded the corresponding α-amino α-fluoro-β-ketoesters with high yields (80-96%) and enantioselectivities (up to 78% ee).     

Computational study of carbon atom (3P and 1D) reaction with CH2O. Theoretical evaluation of 1B1 methylene production by C (1D)

Singlet and triplet free energy surfaces for the reactions of C atom ((3)P and (1)D) with CH(2)O are studied computationally to evaluate the excited singlet ((1)B(1)) methylene formation from deoxygenation of CH(2)O by C ((1)D) atom as suggested by Shevlin et al. Carbon atoms can react by addition to the oxygen lone pair or to the C=O double bond on both the triplet and singlet surfaces. Triplet C ((3)P) atoms will deoxygenate to give CO plus CH(2) ((3)B(1)) as the major products, while singlet C ((1)D) reactions will form ketene and CO plus CH(2) ((1)A(1)). No definitive evidence of the formation of excited singlet ((1)B(1)) methylene was found on the singlet free energy surface. A conical intersection between the (1)A' and (1)A' ' surfaces located near an exit channel may play a role in product formation. The suggested (1)B(1) state of methylene may form via the (1)A' ' surface only if dynamic effects are important. In an effort to interpret experimental observation of products trapped by (Z)-2-butene, formation of cis- and trans-1,2-dimethylcyclopropane is studied computationally. The results suggests that "hot" ketene may react with (Z)-2-butene nonstereospecifically.