Hydrogenation effect on enhancement of photoluminescence of Er and Si nanocrystallites in Er-doped SiO2 synthesized by laser ablation

Significant enhancement of photoluminescence (PL) was attained for Er ions and Si nanocrystallites (nc-Si) in SiO₂ films by two kinds of hydrogenation, using H₂ molecules or H atoms. Er-doped SiO₂ films containing Er impurities and a high density of nc-Si were fabricated by laser ablation of Er films deposited on Si substrate in an O₂ gas atmosphere, followed by annealing at high temperatures in flowing Ar gas. Hydrogenation at 300–500 °C was found to effectively increase the PL intensity of Er ions as well as that of nc-Si. In particular, the hydrogen atom treatment dramatically shortens the hydrogenation time for the enhancement of Er PL compared to the hydrogen molecule treatment. Spectra of electron spin resonance showed a decrease in residual defects, namely, P_b-type defects located at the interfaces between nc-Si and SiO₂ by hydrogenation. These results clearly show the effectiveness of hydrogen passivation for Si nanostructures; i.e., the increase in the Er PL and nc-Si PL due to hydrogen passivation of the nonradiative recombination centers located at the interfaces between nc-Si and SiO₂. PACS 78.67.Bf; 71.20.Eh; 76.30.Mi; 81.15.Fg     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Local-moment formation and metal-nonmetal transition in Ca1−x Y x VO3 and Ca1−x Y x TiO3

Electron-doped metallic states of Ca_1−x Y _x VO₃ and Ca_1−x Y _x TiO₃ change into non-metallic states around x∼0.4 and 0.6, respectively. The residual resistivity in the metallic states increases with increasing effective magnetic moment or coefficient of T ² term of resistivity. The effective moment reaches ∼ 0.5 μ_B/molecule in Ca_1−x Y _x VO₃ and also in Ca_1−x Y _x TiO₃ near the metal-nonmetal phase boundary. In these metallic states. ∼ 10% of 3d atoms seem to have large localized magnetic moments. In electron-doped metallic sample of Ca_1−x Y _x VO₃, the temperature dependence of resistance shows no resistance-minimum. However, weak negative magneto-resistance is observed for the sample with x=0.2 up to 50 Tesla at 4.2 K.     

Accurate quantitation of salivary and pancreatic amylase activities in human plasma by microchip electrophoretic separation of the substrates and hydrolysates coupled with immunoinhibition

A high-performance determination system for alpha-amylase isoenzyme activities in human plasma involving microchip electrophoresis with a plastic chip was developed. The combination of microchip electrophoresis for substrate and hydrolysate separation and an immunoinhibition method for the differentiation of isoenzyme activities using antihuman salivary amylase (S-AMY) mAb allowed the highly selective determination of amylase isoenzyme (S-AMY and pancreatic amylase (P-AMY)) activities even in a complex matrix such as a crude plasma sample. We used 8-aminopyrene-1,3,6-trisulfonic acid (APTS)-labeled maltohexaose (G6) as a substrate. Amylase in a human plasma sample hydrolyzed APTS-G6 into APTS-maltotriose (G3) and G3, which was measured as the fluorescence intensity of APTS-G3 on microchip electrophoresis. A double logarithm plot revealed a linear relationship between amylase activity and fluorescence intensity in the range of 5-500 U/L of amylase activity (r2=0.9995, p<0.01), and the LOD was 4.38 U/L. Amylase activities in 13 subjects determined by the present method were compared with the results obtained by conventional methods with nitrophenylated oligosaccharides as substrates, respectively. Good correlations were observed for each method on simple linear regression analysis (both p<0.01). The reproducibilities of within-days for total amylase and P-AMY were 2.98-6.27 and 3.83-6.39%, respectively, and these between-days were 2.88-5.66 and 3.64-5.63%, respectively. This system enables us to determine amylase isoenzyme activities in human plasma with high sensitivity and accuracy, and thus will be applicable to clinical diagnosis.     

Aqueous noncovalent functionalization and controlled near-surface carbon doping of multiwalled boron nitride nanotubes

Noncovalent functionalization of boron nitride nanotubes (BNNTs) in aqueous solution was achieved by means of pi-stacking of an anionic perylene derivative, through which carboxylate-functionalized BNNTs were prepared for the first time. Starting from the functionalized nanotubes, an innovative methodology was designed and demonstrated for the controlled near-surface carbon doping of BNNTs. As a result of such delicate doping, novel B-C-N/BN coaxial nanotubes have been fabricated, and their p-type semiconducting behaviors were elucidated through gate-dependent transport measurements.     

Propane reacts with O2 and H2 on gold supported TS-1 to form oxygenates with high selectivity

Gold nanoparticles supported on a microporous titanosilicate (TS-1) were found to be highly selective (95%) towards the formation of acetone and isopropanol from propane, O(2), and H(2) at moderate temperatures (443 K).     

Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment

Although tremendous effort has been directed to synthesizing advanced TiO₂, it remains difficult to obtain TiO₂ exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO₂ particles, and photoexcited electron transfer and subsequent charge separation at the anatase–rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO₂, which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO₂ exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO₂, inspired by a recently burgeoning zeolite design, promises to make TiO₂ applications more feasible and effective.