Multifunctional core–shell nanoparticles: superparamagnetic,mesoporous, and thermosensitive

Multifunctional core–shell composite nanoparticles (NPs) have been developed by the combination of three functionalities into one entity, which is composed of a single Fe₃O₄ NP as the magnetic core, mesoporous silica (mSiO₂) with cavities as the sandwiched layer, and thermosensitive poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAAm-co-AAm)) copolymer as the outer shell. The mSiO₂-coated Fe₃O₄ NPs (Fe₃O₄@mSiO₂) are monodisperse and the particle sizes were varied from 25 to 95 nm by precisely controlling the thickness of mSiO₂-coating layer. The P(NIPAAm-co-AAm) were then grown onto surface-initiator-modified Fe₃O₄@mSiO₂ NPs through free radical polymerization. These core–shell composite NPs (designated as Fe₃O₄@mSiO₂@P(NIPAAm-co-AAm)) were found to be superparamagnetic with high r ₂ relaxivity. To manipulate the phase transition behavior of these thermosensitive polymer-coated NPs for future in vivo applications, the characteristic lower critical solution temperature (LCST) was subtly tuned by adjusting the composition of the monomers to be around the human body temperature (i.e. 37 °C), from ca. 34 to ca. 42 °C. The thermal response of the core–shell composite NPs to the external magnetic field was also demonstrated. Owing to their multiple functionality characteristics, these porous superparamagnetic and thermosensitive NPs may prove valuable for simultaneous magnetic resonance imaging (MRI), temperature-controlled drug release, and temperature-programed magnetic targeting and separation applications.     

Theoretical study on the Rocksalt structured positron annihilation in magnesium oxide

Based on the atomic superposition approximation （ATSUP） and first-principles pseudopotential plane-wave methods, the bulk and Mg mono-vacancy positron lifetime of magnesium oxide were calculated using Arponen-Pajamme and Borofiski-Nieminen positron-annihilation-rate interpolation formula respectively. The calculated values are in good agreement with experimental values and the first-principles method gives more convincing results. The positron annihilation density spectra analysis reveals that positrons mainly annihilate with valence electrons of oxygen atoms when the magnesium-vacancy appears within magnesium oxide.     

Electronic structures of alloy quantum dots with nonuniform composition

In this study, the significant effect of the nonuniform composition in alloy quantum dots (QDs) on electronic structure is analyzed in depth. The equilibrium composition profiles in experimentally observed dome and barn shaped GeSi/Si QDs are determined by combining the finite element method and the method of moving asymptotes. Due to the composition variation, the total band edge of heavy hole is dominated by the band offset and spin-orbit coupling rather than the strain effect. The numerical results reveal that the wave function of heavy hole trends to be localized in the Ge-rich region at the top of the large QD. Moreover, the size effect gradually compensates the composition effect as the size of QD decreases.     

Simultaneous low extinction and high local field enhancement in Ag nanocubes

We theoretically investigate surface plasmon resonance properties in Au and Ag cubic nanoparticles and find a novel plasmonic mode that exhibits simultaneous low extinction and high local field enhancement properties. We analyse this mode from different aspects by looking at the distribution patterns of local field intensity, energy flux, absorption and charge density. We find that in the mode the polarized charge is highly densified in a very limited volume around the corner of the nanocube and results in very strong local field enhancement. Perturbations of the incident energy flux and light absorption are also strongly localized in this small volume of the corner region, leading to both low absorption and low scattering cross section. As a result, the extinction is low for the mode. Metal nanoparticles involving such peculiar modes may be useful for constructing nonlinear compound materials with low linear absorption and high nonlinearity.     

Influence of deposition temperature on the crystallinity of Al-doped ZnO thin films at glass substrates prepared by RF magnetron sputtering method

Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by RF magnetron sputtering method under different substrate temperatures. The microstructural, electrical and optical properties of AZO films were investigated in a wide temperature range from room temperature up to 350 °C by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), High-Resolution Transmission Electron Microscopy (HRTEM), Hall measurement, and UV–visible meter. The nature of AZO films is polycrystalline thin films with hexagonal wurtzite structure and a preferred orientation along c-axis. The crystallinity and surface morphologies of the films are strongly dependent on the growth temperature, which in turn exerts a great effect on microstructural, electrical and optical properties of the AZO films. The atomic arrangement of AZO film having an wurtzite structure was indeed identified by the HRTEM as well as the Selected Area Electron Diffraction (SAED). The defect density of AZO film was investigated by HRTEM. The film deposited at 100 °C exhibited the relatively well crystallinity and the lowest resistivity of 3.6 × 10⁻⁴ Ω cm. The average transmission of AZO films in the visible range is all over 85%. More importantly, the low-resistance and high-transmittance AZO film was also prepared at a low temperature of 100 °C.     

Effects of the spin–orbit coupling on magnetic and superconducting properties in iron-based superconductors

We analyze the magnetic properties through two-orbital Hubbard model with the spin–orbit coupling (SOC) interaction in the iron-based superconductors. With the help of the Ising approximation for the Hund’s coupling between the itinerant electrons and the localized spins, we give a self-consistent account of the various magnetic orders observed in pnictides and the pairing symmetry. We also calculate the local density of states (LDOS) of the vortex state when a magnetic field is applied. The LDOS without SOC shows no resonant peak at the vortex core center in the superconducting state, while it shows an obvious resonant peak when SOC is applied.     

Preparation of solution-based YBCO films with BaSnO3 particles

The YBCO films with BaSnO₃ (BSO) particles were prepared on LAO (0 0 1) substrates by metal organic deposition using trifluoroacetates (TFA-MOD) via introducing SnCl₄ powders into the YBCO precursor solution. It was found that with the increase of the SnCl₄ contents, the slower decomposition and higher temperature for nucleation during the reaction were requested compared to that of pure YBCO film. The YBCO films with different contents of Sn with dense surface and well c-alignment were obtained under optimized heat treatment, and the BaSnO₃ phases were detected by XRD analysis. Litter effect of BSO particles on the T_c and J_c values of YBCO films was found. All YBCO films with BSO particles had T_c values over 90 K and J_c values over 1 MA/cm². A significant enhancement of J_c was observed for YBCO films with BSO particles compared to that of pure YBCO film by the field dependence of J_c values. The best property was obtained for YBCO film with 6 mol.% Sn at 77 K under magnetic field. The results showed that the J_c value of YBCO film with 6 mol.% Sn was enhanced by a factor of 2 in 2 T, and over a factor of 10 beyond 4 T compared to that of pure YBCO film.     

Growth and thermoelectric properties of FeSb<Subscript>2</Subscript> films produced by pulsed laser deposition

Thermoelectric FeSb₂ films were produced by pulsed laser deposition on silica substrates in a low-pressure Ar environment. The growth conditions for near phase-pure FeSb₂ films were confirmed to be optimized at a substrate temperature of 425°C, an Ar pressure of 2 Pa, and deposition time of 3 h by ablating specifically prepared compound targets made of Fe and Sb powders in atomic ratio of 1:4. The thermoelectric transport properties of FeSb₂ films were investigated. Pulsed laser deposition was demonstrated as a method for production of good-quality FeSb₂ films.     

银杏叶中硒与多糖的季节分布

银杏叶中总硒和各种溶解形态硒含量随着季节而变化,实验研究了不同采摘期银杏叶中总硒及不同溶解态硒含量分布.7月、9月和霜降之后采摘的银杏叶总硒的含量分别为1.873,2.136,0.815 mg·kg-1,硒的形态以水溶态硒为主.银杏叶粗多糖含量分布依次为9月＞7月＞11月.7月份采集的银杏叶中得到粗多糖为棕褐色固体粉末...