Luminescence properties of Tm co-doped Sr2Si5N8:Eu red phosphor

The Sr₂Si₅N₈:Eu²⁺ phosphors, both undoped and doped with Tm³⁺, were synthesized by high temperature solid-state method. The XRD pattern shows that only Sr₂Si₅N₈ phase is formed whatever Tm³⁺ was doped or not. The peak positions of both phosphors are centered at 612 nm which is assigned to the 4f⁶5d→4f⁷ transition of Eu²⁺. It implies that the crystal field, which affects the 5d electron states of Eu²⁺, is not changed dramatically after the phosphor is doped with Tm³⁺. The afterglow time is about 10 min after Tm³⁺ ion is introduced into the phosphor. The concentration of Tm³⁺ has little influence on the afterglow time of the phosphor. The depths of trap energy level of the two phosphors were calculated based on the TL spectra. The depths of Sr₂Si₅N₈:Eu²⁺ and Sr₂Si₅N₈:Eu²⁺, Tm³⁺ are 1.75 and 1.01 eV, respectively.     

Anisotropic characteristics of a-plane GaN films grown on γ-LiAlO2 (3 0 2) substrates by MOCVD

Single crystalline wurtzite a-plane GaN films were deposited on (3 0 2) LiAlO₂ (LAO) substrates by metal organic chemical vapor deposition (MOCVD). The high resolution X-ray diffraction (HRXRD) results and selected area electron diffraction (SAED) patterns in cross section indicated that the crystallographic orientation between LAO and wurtzite GaN was: [3 0 2]_LAO parallel to , parallel to and [0 1 0]_LAO parallel to [0 0 0 1]_GaN, the mismatches were −4.43%, −2.86% and −0.31%, respectively. When the incident beam parallel (or perpendicular) to the [0 0 0 1] direction of GaN, the FWHM values of ω-scans reached the minimum (or maximum). The a-GaN film was found to have steps along direction and strips coalesced parallel to [0 0 0 1] direction. The PL intensity of the emission peak around 364 nm reduced a lot when the polarization changed from E⊥c to E||c.     

Multiplicity results for semilinear resonant elliptic problems with discontinuous nonlinearities

In the present paper, some generalized critical points theorems for locally Lipschitz functions are given; as applications, some multiplicity results for zero-boundary-value elliptic resonant problems are obtained. Two classical important theorems are improved.     

Nucleophilic cosubstitution of poly(dichlorophosphazene) with alkyl ether and amino acid ester

The nucleophilic substitution reaction of poly(dichlorophosphazene) with sodium 2‐methoxyethoxide and glycine ethyl ester has been studied in detail. Polymers prepared with different methods have been characterized by ¹H NMR, and the results reveal that the addition sequence of the two nucleophilic reagents is an important factor in determining the structure of the resultant polymer. If alkyl ether is added first, the subsequently introduced amino acid ester not only reacts with residual P? Cl but also attacks the alkyl ether side units present by replacing either the whole group or just ? OCH₃. As a result, a new kind of side group (? OCH₂CH₂NHCH₂COOC₂H₅) can be detected in the macromolecule. To obtain polymers with desired compositions {poly[(methoxyethoxy)_x(ethylglycino)_yphosphazene]}, the amino acid ester should be introduced initially to react with poly(dichlorophosphazene), and it should be followed by the alkyl ether. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2417–2425, 2005     

Bi底层对FePt薄膜的影响

利用磁控溅射的方法，在玻璃基片上制备了以Bi为底层的FePt薄膜，经不同温度真空热处理得到L1₀-FePt薄膜.研究了Bi做底层对FePt薄膜的有序化温度及矫顽力H_c的影响.实验结果表明：以Bi做底层的FePt薄膜在350℃实现低温有序，同时其H_c也有大幅度提高，并且可以在更大成分范围内获得H_c较高的L1₀-FePt薄膜.利用X射线光电子能谱研究了薄膜中Bi原子的分布情况，利用X射线衍射研究了薄膜的晶体学结构变化.结果表明,Bi底层在退火过程中的扩散促进了FePt薄膜有序度的升高. 关键词： 0-FePt薄膜')" href="#">L1₀-FePt薄膜 有序化温度 底层 扩散     

具有垂直各向异性(Pt/Co)n/FeMn多层膜的交换偏置

采用磁控溅射方法制备了以Pt为缓冲层和保护层的具有垂直各向异性(Pt/Co)n/FeMn多层膜.研究结果表明,多层膜的垂直交换偏置场Hex和反铁磁层厚度的关系与其具有平面各向异性的交换偏置场随反铁磁层厚度变化趋势相近.随着铁磁层调制周期数的增加,垂直交换偏置场Hex相应减小,并且与铁磁层的调制周期数近似成反比关系.(Pt/Co)3/FeMn的垂直交换偏置场Hex已经达到22.3kA/m.为了进一步提高Hex,在Co/FeMn的界面插入Pt层,当Pt层厚度为0.4nm时,Hex达到最大值39.8kA/m.     

Combinatorial aspects of geometric graphs

As a special case of our main result, we show that for all L> 0, each k-nearest neighbor graph in d dimensions excludes K_h as a depth L minor if h = Ω(L^d). More generally, we prove that the overlap graphs defined by Miller, Teng, Thurston and Vavasis (1993) have this combinatorial property. By a construction of Plotkin, Rao and Smith (1994), our result implies that overlap graphs have “good” cut-covers, answering an open question of Kaklamanis, Krizanc and Rao (1993). Consequently, overlap graphs can be emulated on hypercube graphs with a constant factor of slow-down and on butterfly graphs with a factor of O(log^* n) slow-down. Therefore, computations on overlap graphs, such as finite element and finite difference methods on “well-conditioned” meshes and image processing on k-nearest neighbor graphs, can be performed on hypercubic parallel machines with a linear speed-up. Our result, in conjunction with a result of Plotkin, Rao and Smith, also yields a combinatorial proof that overlap graphs have separators of sublinear size. We also show that with high probability, the Delaunay diagram, the relative neighborhood graph, and the k-nearest neighbor graph of a random point set exclude K_h as a depth L minor if h = Ω(L^d/2 log n).     

有机薄膜电致发光器件在反向偏压下的电致发光

合成了性能优良的聚合物--聚对苯乙烯,并采用甩胶方法制备了单层薄膜电致发光器件ITO/PPV/Al.在所制备的器件上观察到反向偏压下的电致发光现象,记录了在不同反向偏压下的电致发光光谱,测量了在反向偏压下的电流和发光强度,初步讨论了有机发光器件在反向偏压下的发光机理.     

Gasdynamic characteristics of toroidal shock and detonation wave converging

The modified CCW relation is applied to analyzing the shock, detonation wave converging and the role of chemical reactions in the process. Results indicate that the shock wave is strengthened faster than the detonation wave in the converging at the same initial Mach number. Euler equations implemented with a detailed chemical reaction model are solved to simulate toroidal shock and detonation wave converging. Gasdynamic characteristics of the converging are investigated, including wave interaction patterns, observable discrepancies and physical phenomena behind them. By comparing wave diffractions, converging processes and pressure evolutions in the focusing area, the different effects of chemical reactions on diffracting and converging processes are discussed and the analytic conclusion is demonstrated through the observation of numerical simulations.     

Microstructure and oxidation of hot-dip aluminized titanium at high temperature

High-temperature diffusion of a hot-dip aluminized titanium is conducted to study microstructure changes and oxidation behavior of the aluminized titanium. After aluminizing, the titanium substrate is covered by a black layer in which tiny block-shaped TiAl₃ particles are scattered in aluminum matrix. Based on the diffusion experiment results, the thickness of the aluminum diffusion layer at 800 °C increases with diffusion time. However, the aluminum diffusion layer at 900 °C grows and reaches its maximum thickness in 6 h, and then the thickness of the aluminum diffusion layer is reduced with prolonged diffusion time. An inversion of the diffusion layer thickness versus time appears for the aluminized titanium treated at 1000 °C, and the thickness of the diffusion layer keeps declining with diffusion time. The phases present in the outer and middle sublayers are titanium-rich TiAl₃ and equilibrium TiAl₃, respectively. However, the phase in inner sublayer changes from titanium-rich TiAl₃ to TiAl₂ and TiAl as diffusion temperature and time increase. Through energy-dispersive X-ray and X-ray diffraction analysis, the oxides formed in the oxidation process are Al₂O₃ and Al₂TiO₅. Although the oxide scale formed on the surface of the aluminized titanium has an insufficient stability and integrity, the thermal oxidation resistance of the aluminized titanium is still improved by over 5 times compared with that of the pure titanium.