Upconversion and Phase Transition Characteristics in Erbium(III)- and Ytterbium(III)-Codoped Vanadium(IV) Oxide

Vanadium(IV) dioxide has emerged as a promising thermochromic material for smart window application through metal–insulator transition, which simultaneously involves an abrupt change in optical, electrical, and magnetic properties. Here, Er³⁺ or Yb³⁺-codoped vanadium(IV) dioxide has been prepared by a hydrothermal and annealing process. The structure, metal–insulator transition, and upconversion luminescence characterizations have been evaluated using X-ray diffraction, differential thermal analysis, and fluorescence spectral analysis. The samples exhibit unique properties, including enhancing the intensity of upconversion emission, decreasing the metal–insulator transition temperature to 41.4°C, and emitting bright green upconversion emission along with extremely weak emission in the red region under 980?nm excitation. Moreover, green upconversion luminescence intensity increased by an order of magnitude from the low-temperature monoclinic structure of vanadium(IV) dioxide to the high-temperature rutile structure of vanadium(IV) dioxide for the first time, which will pave a new pathway for researching the application of photoluminescence in smart materials.     

Electron transport near the Mott transition in n-GaAs and n-GaN

In this paper, we study the temperature dependence of the conductivity and the Hall coefficient near the metal–insulator phase transition. A theoretical investigation is performed within the effective mass approximation. The variational method is used to calculate the eigenvalues and eigenfunctions of the impurity states. Unlike previous studies, we have included nonlinear corrections to the screened impurity potential, because the Thomas–Fermi approximation is incorrect for the insulator phase. It is also shown that near the phase transition the exchange interaction is essential. The obtained temperature dependencies explain several experimental measurements in gallium arsenide (GaAs) and gallium nitride (GaN).     

钙钛矿锰氧化物La0.7Sr0.3MxMn1-xO3(M=Cr,Fe)的巨磁电阻效应与磁性

研究了溶胶 -凝胶法制备氧化物巨磁电阻材料的工艺 ,制备了La0 .7Sr0 .3 CrxMn1-xO3 (x =0 ,0 .10 ,0 .15 )和La0 .7Sr0 .3 FexMn1-xO3 (x =0 .0 5 ,0 .10 ,0 .16 )两系列的单相钙钛矿锰氧化物多晶样品 ,并研究了Cr ,Fe替代La0 .7Sr0 .3 MnO3 中部分Mn后对其结构、磁性和巨磁电阻性质的影响 .观察到La0 .7Sr0 .3 Cr0 .15Mn0 .85O3 和La0 .7Sr0 .3 Fe0 .0 5Mn0 .95O3 两个样品的电阻 温度曲线都出现了双峰 .定性讨论了可能产生双峰的机制 .随Cr(或Fe)替代量的增加 ,材料的居里温度很快下降 ,铁磁性减弱 ,导电性降低 ,巨磁电阻效应增强 .但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小 .     

A new metallic state in two dimensions

We report the discovery of a new and unexpected kind of metal in two dimensions (2D), which exists in the presence of scattering by local magnetic moments. The experiment was carried out on a 2D electron system in silicon, where the local magnetic moments have been induced by disorder and their number was varied using substrate bias (V_sub). In the new metal, the conductivity decreases as σ(n_s,T)=σ(n_s,T=0)+A(n_s)T² (n_s – carrier density) to a non-zero value as temperature T→0. In three dimensions, this T² dependence is well known, and results from Kondo scattering by local magnetic moments. In 2D, however, the existence of a metal with dσ/dT>0 is very surprising. As the number of local moments is reduced, the range of temperatures [T<T_m(V_sub)] where they dominate transport becomes smaller. For T>T_m, we observe the usual 2D metallic behavior with dσ/dT<0.     

以陶瓷厚膜为绝缘层的红色ZnS:Sm,Cl电致发光器件

报道采用高介电常数的陶瓷厚膜作绝缘层、ＺｎＳ：Ｓｍ,Ｃｌ作为发光层的红色薄膜电致发光器件。测量了器件的电致发光光谱和亮度电压曲线,研究了发光机理和效率电压等特性。制备的器件在电驱动下１６Ｖ启亮,最大亮度为１８．４ｃｄ／ｍ＾２,最大效率为０．０６１ｍ／Ｗ。     

The Effect of Annealing Temperature on Electrical Properties of SrBi2Ta2O9/Insulators/Si(MFIS) Structure for NDRO-type FRAM Devices

We have fabricated Pt/SBT/insulator/Si structure for the transistor gate in MFIS-FET and investigated the electrical properties of MFIS structure with various insulator materials. SrBi₂Ta₂O₉ films as a ferroelectric layer were deposited by metal organic decomposition (MOD) technique, on various insulator structures including SiON, and Al₂O₃ as well as on Pt/Ti/SiO₂/Si structures. The effect of annealing temperature on the electrical properties of MFIS structures was investigated in order to analyze the applicability to conventional CMOS process. Although the remnant polarization of SBT films for MFM structure was increased with increasing annealing temperature, the memory window which has a relationship with remnant polarization of ferroelectrics was differently displayed with insulator structure in MFIS structure.     

Effects of thermal aging on cellulose pressboard using terahertz time-domain spectroscopy

We demonstrate a method for examining the effects of thermal aging of cellulose pressboard using terahertz time-domain spectroscopy. The change of refractive indexes at the frequencies of pulsed terahertz waves while applying heat reveals that the degree of thermal aging and the condition of thermal breakdown can be clearly analyzed by performing terahertz measurements. The visual examination method only allows evaluation of the degree of blackness on the external surfaces of cellulose pressboard. However, using terahertz techniques for non-destructive inspection enables determination of the dielectric integrity to check the strength of the electrical insulation inside the cellulose pressboard. The results indicate that the terahertz techniques could be very useful, especially in the electric power industry, which requires a variety of methods for internal non-destructive testing to ensure the safety and reliability of insulation materials in electric power facilities and components.     

Sizable band gap in organometallic topological insulator

Based on first principle calculation when Ceperley–Alder and Perdew–Burke–Ernzerh type exchange-correlation energy functional were adopted to LSDA and GGA calculation, electronic properties of organometallic honeycomb lattice as a two-dimensional topological insulator was calculated. In the presence of spin–orbit interaction bulk band gap of organometallic lattice with heavy metals such as Au, Hg, Pt and Tl atoms were investigated. Our results show that the organometallic topological insulator which is made of Mercury atom shows the wide bulk band gap of about ∼120 meV. Moreover, by fitting the conduction and valence bands to the band-structure which are produced by Density Functional Theory, spin–orbit interaction parameters were extracted. Based on calculated parameters, gapless edge states within bulk insulating gap are indeed found for finite width strip of two-dimensional organometallic topological insulators.     

Magnetically Controlled Electronic Transport Properties of a Ferromagnetic Junction on the Surface of a Topological Insulator

We have investigated the transport properties of the Dirac fermions through a ferromagnetic barrier junction on the surface of a strong topological insulator.The current-voltage characteristic curve and the tunneling conductance are calculated theoretically.Two interesting transport features are predicted:observable negative differential conductances and linear conductances tunable from unit to nearly zero.These features can be magnetically manipulated simply by changing the spacial orientation of the magnetization.Our results may contribute to the development of high-speed switching and functional applications or electrically controlled magnetization switching.