Thermoelectric properties and electronic structure of Al-doped ZnO

Impure ZnO materials are of great interest for high temperature thermoelectric application. In this work, we present the effects of Al-doping on the thermoelectric properties and electronic structures of a ZnO system. We find that, with increasing Al concentrations, the electrical conductivity increases and the thermal conductivity decreases significantly, whereas, the Seebeck coefficient decreases slightly. Nevertheless, the figure of merit (ZT) increases owing to high electrical conductivity and low thermal conductivity. On the other hand, the electronic band structures show that the position of the Fermi level is moved upwards and the bands split near the valence-band top and conduction-band bottom. This is due to the interaction between the Al3p and Zn4s orbitals, which drive the system towards semimetal. Besides, the Density Of States (DOS) analysis shows that the introduction of Al atom obviously reduces the slope d(DOS)/dE near the Fermi level. Based on the calculated band structures, we are able to explain qualitatively the measured transport properties of the Al-doped ZnO system.     

Photoluminescence of patterned arrays of vertically stacked InAs/GaAs quantum dots

We report on photoluminescence measurements of vertically stacked InAs/GaAs quantum dots grown by molecular beam epitaxy on focused ion beam patterned hole arrays with varying array spacing. Quantum dot emission at 1.24 eV was observed only on patterned regions, demonstrating preferential nucleation of optically active dots at desired locations and below the critical thickness for dot formation at these growth conditions. Photoluminescence measurements as a function of varying focused ion beam irradiated hole spacing showed that the quantum dot emission intensity increased with decreasing array periodicity, consistent with increasing dot density.     

Possible coexistence of superconductivity and magnetism in intermetallic NiBi3

NiBi₃ polycrystals were synthesized via a solid state method. X-ray diffraction analysis shows that the main phase present in the sample corresponds to NiBi₃ in a weight fraction of 96.82 % according to the refinement of the crystalline structure. SEM - EDS and XPS analysis reveal a homogeneous composition of NiBi₃, without Ni traces. The powder superconducting samples were studied by performing magnetic measurements. The superconducting transition temperature and critical magnetic fields were determined as , Oe and Oe. The superconducting parameters were , , and κ=5.136. Isothermal measurements below the transition temperature show an anomalous behavior. Above the superconducting transition the compound presents ferromagnetic characteristics up to 750 K, well above the Ni Curie temperature.     

Multiferroic magnetoelectric coupling and relaxor ferroelectric behavior in 0.7BiFeO3-0.3BaTiO3 nanocrystals

The structural, microstructural, polarization, magnetization, dielectric constant, and relaxor characteristics of 0.7BiFeO₃-0.3BaTiO₃ (BF-BT) nanocrystals have been studied. BF-BT nanocrystals were prepared by a chemical route using polyvinyl alcohol as surfactant. The phase structure is confirmed by X-ray diffraction and average particle size by transmission and scanning electron microscopy. The magnetoelectric coupling is studied by polarization hysteresis loops under the influence of applied magnetic field and the phase transition anomaly. The diffuse phase transition is studied by modified Curie-Weiss law and relaxor characteristics by Vogel-Fulcher relation.     

Singular orbital magnetism of graphene

The origin of the singular diamagnetic susceptibility at the Dirac point is probed through the study of effects of band-gap opening and spatially varying magnetic field. In the presence of a band gap, the susceptibility is nonzero only inside the band gap and exhibits a discrete jump at the band edges down to zero in the conduction and valence bands. The jump height is understood in terms of the pseudo-spin paramagnetism arising from valley degree of freedom. In spatially varying magnetic field with wave vector q, the susceptibility becomes nonzero only in a finite energy region containing the Dirac point, determined by q. This behavior is understood in terms of electronic states numerically calculated in periodic magnetic field.     

Film thickness dependence of electro-optic effect in epitaxial BaTiO3 thin films

Based on the phenomenological Landau-Devonshire theory, we investigate the film thickness dependence of ferroelectric and electro-optic properties of epitaxial BaTiO₃ thin films grown on SrTiO₃ and MgO substrates. By using the effective substrate lattice parameter concept, the film thickness dependence of misfit strain is incorporated into the theory. Therefore, the film thickness dependence of ferroelectric and electro-optic properties in epitaxial BaTiO₃ thin films can be explained. Moreover, a large quadratic electro-optic effect was obtained in the BaTiO₃ thin films, which is in good agreement with the experimental result of BaTiO₃ thin films on the MgO substrate.     

Na2GdPO4F2:Tb3+绿色荧光粉阴极射线发光研究

通过高温固相法制备Na2GdPO4F2:Tb3+绿色荧光粉,并利用X射线粉末衍射(XRD)和阴极射线光谱分别对其物相、阴极射线发光性能进行研究.结果表明,Tb3+作为绿色发光中心进入到Na2Gd2PO4F2的晶格中取代Gd3+的格位,在低电子束(0.5～5 kV)激发下主要表现出Tb3+的特征跃迁(5D3.4→7FJ,J=6～2),其中以5D4→7F5跃迁(546 nn)为主.样品Na2Gd0.95Tb0.05PO4F2在阴极射线激发下的色坐标为(0.240 3,0.438 6).随着电压、电流和掺杂量的增加,荧光粉的发光强度逐渐提高,其中,最佳的样品为Na2Gd0.9Tb0.1PO4F2.     

X射线荧光光谱研究粮食中生命有机碳与碳化学循环

采用X射线荧光光谱(XRF)方法测定六种粮食:稻谷(大米)、小麦(面粉)、黄豆、小米、高粱和玉米中生命有机碳含量和化学元素组成,建立一种新方法测定它们的蛋白质含量.粮食中生命有机碳平均含量约为44%.黄豆中的蛋白质含量最高(42.74%),小米蛋白质含量28.56%,麦子蛋白质含量27.57%,玉米蛋白质含量24.99...     

Effect of annealing on structural and electrical properties of the Li–Mn–O thin films, prepared by high frequency RF magnetron sputtering

Li–Mn–O thin film cathode materials are prepared by high frequency (27.12 MHz) RF magnetron sputtering. The high RF frequency gives higher deposition rates without compromising on the quality of the films. This investigation focuses on the effects of post-annealing on the micro-structural, morphological and electrical properties of Li–Mn–O films. It is observed that with the increase of annealing temperature the crystallinity as well as the electrical conductivity of the films increases. The films annealed at 600–700 °C are found to have high structural perfection and good electrical properties.     

退火处理对W:Bi4Ge3O12和Bi12GeO20晶体发光性能的影响

通过提拉法制备了W:Bi4 Ge3 O12和Bi12GeO20晶体,测试了晶体的吸收光谱、光致发光谱和发光衰减时间等.W:Bi4 Ge3 O12的可见光发光强度比纯Bi4 Ge3 O12有所增强,而且N2中退火处理对W:Bi4Ge3O12发光有进一步增强作用.Bi12GeO20在N2中退火处理后在745 nm附近有发光...