Electronic properties of nanocrystalline tin oxide dispersed in monolithic mesoporous silica

This paper is devoted to the study of the electrical properties of nanocrystalline tin oxide dispersed in the mesoporous silica. By immersing the silica in precursor solutions with different concentrations and heat-treatment, different samples were obtained. With precursor concentrations increasing from 0.1 to 4.0 M, the resistivities of the samples decrease from 3.15×10⁶ to 2.43×10³ Ω cm. The resistivity changes with the measurement time, and the deviations from Ohm's law in the voltage–current (V–I) measurements illustrate the capacitance property of these nanocomposites. For this new kind of nanocomposites, the obtained results provide experimental evidence of the conducting mechanism for tin oxide nanoparticles.     

Coaxial ZnO/SiO<Subscript>2</Subscript> nanocables fabricated by thermal evaporation/oxidation

ZnO/SiO₂ coaxial nanocables have been synthesized on silicon substrates by simply evaporating zinc powder under an argon and argon/oxygen mixed atmosphere sequentially. The diameters of these nanocables vary from 50 to 100 nm and the lengths up to several millimeters. Electron microscopy and chemical composition investigations reveal that the nanocable consists of a crystalline ZnO core surrounded by an amorphous silica sheath. The electron diffraction pattern proves that the long-axis direction of ZnO cores grows along the [0001] direction. Silica nanotubes with wall structures have been obtained by the selective dissolution of the cores with hydrochloric acid. PACS 81.10.Bk; 81.05.Hd     

Preparation and spectroscopic properties of Nb2O5 nanorods

Nb₂O₅ nanorods have been prepared using water/ethanol media. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption and photoluminescence spectroscopy. The as-prepared Nb₂O₅ nanorods appeared to be single pseudohexagonal (TT-Nb₂O₅) phase. From the photoluminescence spectrum, two emission bands at 407 and 496 nm, respectively, were observed. The origin of the luminescence was discussed in detail.     

Diode-pumped intra-cavity doubled Nd:LuVO4 laser at 458 nm

We have demonstrated a diode-pumped intra-cavity frequency doubling Nd:LuVO₄ laser operating at 916 nm with a Z-folded cavity. A 10-mm long LBO crystal, cut for critical type I phase matching at 912 nm, is used for the experiment. A maximum output power of 330 mW at 458 nm has been achieved at pump power of 22 W. The optical-to-optical conversion efficiency and slope efficiency is 1.5% and 2.3%, respectively. The power instability at the maximum output power in 30 min is better than 3%.     

Chemical tuning by 5-Methyl and N-Methyl-substitution in heptanuclear complexes effects multistability investigated by Mössbauer spectroscopy

The precursors [Fe^(III)(^N???R???L)Cl] (^N???R???LH₂=N,N′-bis(2′-hydroxy- 5′-methyl-benzyliden)-1,7-diamino-4-R-4-azaheptane, R ?=? H, methyl(Me)) are high-spin (S?=?5/2) complexes. The Lewis-acidic precursors are combined with Lewis- Base-bridging-units [M(CN) _x ] ^y??? (M = Fe^(II), Ru^(II), Co^(III)) to form heptanuclear star-shaped [M{CN-Fe^(III)(^N???R???L)} _x ]Cl _y molecular switches. The star-shaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the compounds exhibit multistability, i.e. several iron(III) centers within a molecule switch to the low-spin state as shown by Mössbauer spectroscopy.     

Hartree-Fock ground state of the three-dimensional electron gas

In 1962, Overhauser showed that within Hartree-Fock (HF) the electron gas is unstable to a spin-density wave state. Determining the true HF ground state has remained a challenge. Using numerical calculations for finite systems and analytic techniques, we study the unrestricted HF ground state of the three-dimensional electron gas. At high density, we find broken spin symmetry states with a nearly constant charge density. Unlike previously discussed spin wave states, the observed wave vector of the spin-density wave is smaller than 2k(F). The broken-symmetry state originates from pairing instabilities at the Fermi surface, a model for which is proposed.     

基于响应面模型的高超声速低温喷管优化

 建立了高超声速低温(HYLTE)喷管的响应面模型,样本点设计矩阵采用正交试验设计法构造,样本数据通过3维粘性NS方程计算喷管光腔耦合段的多组分混合流场获得。基于HYLTE喷管响应面模型,对喷管进行了多目标优化,定义了综合性能参数,优化后喷管混合性能显著改善,综合性能明显提高。计算表明,基于响应面模型的优化策略,能够满足喷管优化对计算精度和计算量的要求。运用多学科设计优化软件框架iSIGHT作为建模和优化的辅助工具,提高了优化设计的实现效率。     

Scaling law of anomalous Hall effect in Fe/Cu bilayers

The scaling of anomalous Hall resistivity on longitudinal resistivity has been intensively studied in different magnetic systems, including multilayer and granular films, to examine whether a skew scattering or a side jump mechanism dominates in the origin of anomalous Hall effect (AHE). The scaling law is based on the premise that both resistivities are a consequence of electron scattering by the imperfections in the materials. By studying the anomalous Hall effect in the simple Fe/Cu bilayers, it was demonstrated that the measured anomalous Hall effect should not follow the scaling laws derived from skew scattering or side jump mechanism due to the short-circuit and shunting effects of the non-magnetic layers.     

Exciplex emission in the blend of two blue luminescent materials

Organic light-emitting diodes (OLEDs) based on the blend of two blue luminescent materials N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-diphenyl-4,4′-diamine (NPB) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) were fabricated. The electroluminescence (EL) spectra of this device showed a new emission that is different from their intrinsic exciton emission. Compared with the photoluminescence (PL) spectra of single layer NPB and PBD, respectively, there was an apparent red shift in that of their blend. Thus the exciplex formation in the blend can be concluded due to the similar emission in both PL and EL spectra. The exciplex formation process and the effect of applied voltage were analyzed by Gaussian fitting.