Tunable Anisotropic Absorption of Ag-Embedded SiO2 Thin Films by Oblique Angle Deposition

Ag-embedded SiO2 thin films are prepared by oblique angle deposition. Through field emission scanning electron microscopy （SEM）, an orientated slanted columnar structure is observed. Energy-dispersive x-ray （EDX） analysis shows the Ag concentration is about 3% in the anisotropic SiO2 matrix. Anisotropic surface plasma resonance （SPR） absorption is observed in the Ag-embedded SiO2 thin films, which is dependent on polarization state and incidence angle of two orthogonal polarized lights and the deposition angle. This means that optical properties and anisotropic SPR absorption can be tunable in Ag-embedded SiO2 thin films. Broadband polarization splitting is also observed and the transmission ratio Tp/Ts between p- and s-polarized lights is up to 2.7 for thin films deposited at a = 70°, which means that Ag-embedded SiO2 thin films are a promising candidate for thin film polarizers.     

Effect of the main-group elements on the electronic structures and magnetic properties of Heusler alloys Mn2NiZ (Z=In, Sn, Sb)

The magnetic properties and electronic structure of Mn₂NiZ (Z=In, Sn, Sb) have been studied. The magnetic structure of these alloys is mainly determined by the main-group element Z instead of the distance between the Mn atoms. Electronic structure calculations suggest that Mn₂NiIn and Mn₂NiSn are both ferrimagnets with antiparallel alignment between the Mn moments. But this antiferromagnetic coupling is weakened by the increasing number of valence electrons of the Z atoms. When it comes to Mn₂NiSb, a ferromagnetic coupling between the Mn atoms is observed. Mn₂NiSn and Mn₂NiSb have been synthesized successfully. Their M_s at 5 K agree well with the theoretical value.     

Influence of impurity-induced spin-orbit scattering on persistent spin helix

The persistent spin helix discovered in intrinsic spin-orbit coupled systems previously is reexamined using the motion equations of Green's functions by considering the effect of extrinsic impurity-induced spin-orbit coupling. We find both the intrinsic and extrinsic spin-orbit couplings can increase the excitation energy of spin helix. They together can reduce drastically the lifetime of the spin helix, making it severely departure from the ideal infinite value. The effect of impurity density on spin helix is also analyzed. The results may be helpful to understand experimental measurements on spin helix.     

An efficient co-doping of Eu and Er in CaAl2O4 aluminate phosphor

CaAl₂O₄:Eu²⁺ co-doped with varying concentrations of Er³⁺ was prepared by solid-state reaction method. Prepared materials with 1 mol% Eu²⁺ and 2-10 mol% of Er³⁺ were investigated for their photoluminescence properties. Phase, morphology and crystalline structure were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Broad band UV-excited luminescence was observed for CaAl₂O₄:Eu²⁺, Er³⁺ in the blue region (λ_max=440 nm) due to transitions from 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. The Er³⁺ ion co-doping generates deep traps, which results in longer decay time for phosphorescence.     

Long silicon nitride nanowires synthesized in a simple route

Long silicon nitride (Si₃N₄) nanowires with high purity were synthesized by heating mixtures of SiO₂ powders and short carbon fibers at 1430°C for 2 h in a flowing N₂ atmosphere. The nanowires had the length of 1–2 millimeters and the diameters of 70–300 nm, and were mainly composed of ⍺-Si₃N₄, growing along the [001] direction. The vapor–solid (VS) mechanism was employed to interpret the nanowires growth.     

A statistical evaluation of the field emission for copper oxide nanostructures

A statistical data analysis methodology was developed to evaluate the field emission properties of many samples of copper oxide nanostructured field emitters. This analysis was largely done in terms of Seppen-Katamuki (SK) charts, field strength and emission current. Some physical and mathematical models were derived to describe the effect of small electric field perturbations in the Fowler-Nordheim (F-N) equation, and then to explain the trend of the data represented in the SK charts. The field enhancement factor and the emission area parameters showed to be very sensitive to variations in the electric field for most of the samples. We have found that the anode-cathode distance is critical in the field emission characterization of samples having a non-rigid nanostructure.     

Effects of Annealing on Microstructure and Optical Properties of TiO2 Sculptured Thin Films

The evolution of microstructure and optical properties of TiO2 sculptured thin films under thermal annealing is reported. XRD, field emission SEM, UV-Vis-NIR spectra are employed to characterize the microstructural and optical properties. It is found that the optimum annealing temperature for linear birefringence is 500℃. The maximum of transmission difference for linear birefringence is up to 18%, which is more than twice of that in as-deposited thin films. In addition, the sample annealed at 500℃ has a minimum of column angle about 12℃. The competitive process between the microstructural and optical properties is discussed in detail. Post-annealing is a useful method to improve the linear birefringence in sculptured thin films for practical applications.     

Room-Temperature Ferromagnetism in Semiconducting TiO2-δ Nanoparticles

TiO2-δ nanoparticles are synthesized by the sol-gel method and annealed under different reducing atmosphere. The x-ray diffraction patterns show that anatase is the dominant phase with small amounts of the futile phase of TiO2-δ for all the samples. Magnetic measurements indicate that the samples annealed in reducing atmosphere exhibit unprecedented room-temperature ferromagnetism, in particular, the saturation magnetization Ms is up to about 8.6 × 10^-3 emu/g for the sample annealed in H2/Ar mixture. Analysis of the x-ray photoelectron spectroscopy spectra for the samples processed under different conditions indicates that the amounts of Ti^3＋ or Ti^2＋ cations, namely, the concentration of oxygen vacancies, increase with intensifying reducing atmosphere during processing, which shows that ferromagnetism in this material strongly depends on the concentration of oxygen vacancies. The relationships between the ferromagnetism and the crystal structure as well as the grain size in this material are also discussed.     

Ab initio prediction of half-metallic ferromagnetism in Zn(TM)O2 (TM=Cr,Mn, Fe,Co, Ni) compounds

From the results of first principles tight-binding linear muffin-tin orbital (TB-LMTO) calculations, half-metallic ferromagnetism is proposed in Zn(TM)O₂ with a chalcopyrite structure. The calculated electronic and magnetic property shows that consistent with the integer value for the total magnetic moment, half metallicity is obtained for ZnCrO₂, ZnMnO₂, ZnFeO₂, ZnCoO₂ and ZnNiO₂. A careful analysis of the spin density reveals the ferromagnetic coupling between the p–d states and the cation dangling-bond p states, which is believed to be responsible for the stabilization of the ferromagnetic phase. The calculated heat of formation, bulk modulus and cohesive energy are reported.     

Effect of Cr on the electronic structure of Co3Al intermetallic compound: A first-principles study

The effect of doping with Cr on the electronic structure and magnetism of Co₃Al has been studied by density functional calculations. It has been found that the Cr atom has a strong site preference for the B-site in Co₃Al. With the substitution of Cr for Co, the total densities of states (DOS) change obviously: A DOS peak appears at E_F in the majority spin states and an energy gap is opened in the minority spin states. The effect of Cr in Co₃Al is mainly to push the antibonding peak of the Co (A,C) atoms high on the energy scale and to form the energy gap around E_F, and also to contribute to the large DOS peak at E_F in the majority spin direction. The calculations indicate a ferromagnetic alignment between the Co and Cr spin moments. The calculated total magnetic moment decreases and becomes closer to the Slater–Pauling curve with increasing Cr content. This is mainly due to the decrease of the Co (A,C) spin moments. At the same time, the moments of Co (B) and Cr (B) only change slightly.