Theoretical studies of poly(para-phenylene vinylene) (PPV) and poly(para-phenylene) (PPP)

The electroluminescence from PPV and the blue light emission from PPP constitute exciting subjects of study. The band gap of these semiconducting polymers can be engineered in a wide range from red to ultraviolet by structural changes made on them. In the present work, we present a theoretical approach based on semiempirical and ab initio total energy and force calculations of PPV and PPP. We perform a conformational analysis in order to investigate the connection between their structural, optical and electronic properties. We use the large cell approach, in connection with the semiempirical quantum method Extended Hückel (BICON-CEDiT code) and the density functional theory (DFT) within the full-potential linearized augmented-plane-wave method (FPLAPW) as implemented in the computational code WIEN2k. Our results are compared to other calculations and to optical absorption measurements.     

(Sr_(0.5)Ba_(0.5))_(1.9)Ca_(0.1)NaNb_(5–x)TaxO_(15)陶瓷的介电性能

通过Ta掺杂改性钨青铜陶瓷(Sr0.5Ba0.5)1.9Ca0.1NaNb5–xTaxO15(x=0～0.30),分析了Ta掺杂量对其烧结性能、微观结构及介电性能的影响。陶瓷的烧结温度随x的增大略有提高。当x<0.10时,陶瓷的tC和弛豫性变化不大;当x≥0.10时,tm(1kHz)明显降低,从270℃(x=0)降低至231℃(x=0.30)。且tm随频率增加向高温移动,弛豫性明显增强。认为Ta掺杂引起其性能变化是由于Ta—O键与Nb—O键键能的差异,导致陶瓷氧八面体中心离子位移量以及A位离子有序程度的变化所致。     

纳米复合(Nd,Pr)FeTiBC永磁合金的结构与磁性能

采用熔体快淬法制备了纳米复合(Nd1-xPrx)9.4Fe75.6Ti4B10.5C0.5(x为0,0.2,0.4,0.6,0.8和1.0)合金薄带,研究了Pr对合金薄带结构与磁性能的影响规律。结果表明:Pr降低了合金薄带的晶化温度,使合金薄带晶粒变得粗大,不利于合金矫顽力的提高。Pr对合金薄带磁性能的影响不大,不同Nd和Pr比例的合金薄带在最佳热处理条件下,剩磁Br在0.86 T与0.90 T之间,内禀矫顽力Hcj在1 000 kA/m左右,最大磁能积(BH)max介于130 kJ/m3与136 kJ/m3之间。     

Miniband spectra of (AlAs)M(GaAs)N(111) superlattices

Semiconductors - Electron states in the conduction band of (111)-oriented (AlAs)M(GaAs)N superlattices (SLs) with M≥N and N&;lt;10 are considered. The properties of such SLs are mainly...     

单层超晶格Ga_(0.47)In_(0.53)As/InP(110)及半导体合金Ga_(0.235)In_(0.765)P_(0.5)As_(0.5)的状态密度及介电常数(英文)

The DOS, JDOS and ε2(Ω) of monolayer superlattice Ga0.47ln0.53As/ InP(110) have been calculated by a tight-binding approach and compared with that of alloy Ga0.235ln0.765P0.5As0.5 which has the same stoi-chiometric composition as the monolayer superlattice. By using the techniques of the group theory we have obtained the expressions of momentum matrix elements between valence band states and conduction band states with four adjustable parameters. These parameters are determined by fitting the calculated values of ε2(Ω) with the experimental values for InP, GaAs and InAs. Our results show that the superlattice periodicity makes its DOS, JDOS and ε2(Ω) different from those of alloy in varying degree. Due to the folding of Brillouin zone, the JDOS of superlattice turns round in comparison with that of alloy. The momentum matrix elements have different effects for the superlattices and alloys.For the alloys, they can only change the amplitudes of peaks but not the positions of peaks; however, for the superlattices both amplitude and position can be changed.     

Electron-phonon interaction in short-period (GaAs) m (AlAs) n (001) superlattices

The deformation potentials of electron scattering at short-wavelength phonons for intervalley transitions in the conduction band of short-period (GaAs) _m (AlAs) _n (001) (m, n = 1, 2, 3) superlattices are determined by the electron density functional method. The dependences of the electron and phonon states and deformation potentials on the layer thickness in the superlattices are analyzed. The results of ab initio calculations are in good agreement with the data of empirical calculation of the deformation potentials integrated over phonons, but differ from data on the corresponding potentials for partial scattering channels because of approximations of the phenomenological model of interatomic binding.     

Sr_(0.3)Ba_(0.7)Bi_(3.7)La_(0.3)Ti_4O_(15)铁电陶瓷的烧结及介电性能

采用两步烧结工艺制备Sr0.3Ba0.7Bi3.7La0.3Ti4O15铁电陶瓷,研究了烧结工艺对陶瓷的晶相和介电性能的影响。结果表明:适当提高最高温度、保温温度和保温时间可改善陶瓷的介电性能。当最高温度为1180～1200℃,在1050～1080℃保温5～15h时,其εr为238～262,tanδ小于10–2,σ为1.0×10–11～10–12S·m–1。该烧结工艺可减少铋的挥发,降低氧空位浓度,因而减弱了陶瓷的高温低频耗散现象。随着保温时间的增加,高温电导得到有效抑制,在1050℃保温15h样品的σ降低了一个数量级,在280℃时为5.2×10–9S·m–1。     

全球信息基础设施总体概念问题(上)

本文讨论了电信技术、网络形态和发展电信技术的指导思想,目的是从技术机理和工程应用方面说明GII网络形态的总体概念.     

sol-gel法制备Ba_(3.99)Sm_(9.34)Ti_(18)O_(54)微波介质陶瓷

以柠檬酸为络合剂,通过sol-gel法制备了Ba3.99Sm9.34Ti18O54陶瓷前驱体;经1100℃预烧2h压片成型后,再在1300℃保温3h,即得到了烧结致密的陶瓷样品。与传统固相法相比,其烧结温度降低了50℃,且陶瓷晶粒细小,晶粒分布均匀,具有更加优良的微波介电性能:εr=79.56,Q·f=9636GHz(4.71GHz),τf=–1.23×10–6/℃。     

复合量子阱Ge_(0.3)Si_(0.7)/(Ge_(0.3)Si_(0.7))_m-(Si)_m/Ge_(0.3)Si_(0.7)的电子能带结构

采用建立在经验赝历势基础上的推广k·P方法计算了复合量子阱Ge0.3Si0.7／（Ge0.3Si0.7）m-（Si）m／Ge0.3Si0.7的电子束缚能组及其活界面方向的色激关系,并与通常的单带模型下的包络函数方法的计算结果进行了比较。结果表明由于超晶格中子能带的形成,邻近能带间的互作用使通常单带模型下的包络函数方法不再能适用于复合量子阱的计算。计算结果也表明复合量子阱的电子束缚能级沿界面方向在kx＜0.1（2π/a）范围内基本上不随kx变化。     

Electromagnetic interference (EMI) of system-on-package (SOP)

Electromagnetic interference (EMI) issues are expected to be crucial for next-generation system-on-package (SOP) integrated high-performance digital LSIs and for radio frequency (RF) and analog circuits. Ordinarily in SOPs, high-performance digital LSIs are sources of EMI, while RF and analog circuits are affected by EMI (victims). This paper describes the following aspects of EMI in SOPs: 1) die/package-level EMI; 2) substrate-level EMI; 3) electromagnetic modeling and simulation; and 4) near electromagnetic field measurement. First, LSI designs are discussed with regard to radiated emission. The signal-return path loop and switching current in the power/ground line are inherent sources of EMI. The EMI of substrate, which work as coupling paths or unwanted antennas, is described. Maintaining the return current path is an important aspect of substrate design for suppressing EMI and for maintaining signal integrity (SI). In addition, isolating and suppressing the resonance of the DC power bus in a substrate is another important design aspect for EMI and for power integrity (PI). Various electromagnetic simulation methodologies are introduced as indispensable design tools for achieving high-performance SOPs without EMI problems. Measurement techniques for near electric and magnetic fields are explained, as they are necessary to confirm the appropriateness of designs and to investigate the causes of EMI problems. This paper is expected to be useful in the design and development of SOPs that take EMI into consideration.     

Sm~(3+)掺杂Co_(0．6)Zn_(0．4)Ni_(0．8)Fe_(1．2)O_4红外辐射陶瓷材料的研究

用常规固相合成法成功地制备出Sm3 掺杂Co0.6Zn0.4Ni0.8Fe1.2O4红外辐射陶瓷材料,并通过XRD、FT-IR和IRE-2型红外发射率测量仪测试了材料的微观结构,分析了材料的结构特征与红外辐射性能的关系,发现Sm3 的掺杂导致Sm3 以一定的配位形式进入Co0.6Zn0.4Ni0.8Fe1.2O4体系中,并形成了有限置换型固溶体结构.数据分析可知,Sm3 掺杂浓度对材料的红外辐射性能存在一定的影响,样品Sm0.1在全波段的积分发射率为0.74,而在>8μm波段的平均发射率最高值可达0.94.     

溶胶–凝胶法制备NBT-KBT系陶瓷及其电性能

采用sol-gel法制备(1–x)Na0.5Bi0.5TiO3-xK0.5Bi0.5TiO3(x=0.12~0.50)系无铅压电陶瓷。XRD分析表明,当x=0.18~0.30时陶瓷具有三方–四方相共存的晶体结构,为该陶瓷的准同型相界(MPB)。在MPB附近存在最佳的电性能:d33为150pC/N,kp为36.7%,ε3T3/ε0为1107,tanδ为1.1×10–2,Qm为168.8,Np为2949.7Hz·m。与常规固相法相比,sol-gel法有利于提高该陶瓷的电性能。分析了该陶瓷材料在1,10和100kHz下的介电温谱,发现该陶瓷是一类弛豫型铁电体材料。     

钛酸锶钡/铋锌铌多层复合薄膜的制备及性能

采用溶胶一凝胶法在Pt/Ti/SiO2/Si衬底上制备了钛酸锶钡/铋锌铌多层复合薄膜样品.研究了不同退火温度下多层复合薄膜的结构、微观形貌及介电性能.结果表明:在退火温度高于700℃时,所得复合薄膜中会出现立方焦绿石结构的铋锌铌和钙钛矿结构的钛酸锶钡.750℃退火处理得到的多层复合薄膜,表面致密,无裂纹,其相对介电常数...     

Alternating beam method (ABM) in photothermal microscopy (PTM) and photoacoustic microscopy (PAM)

In measuring thermal properties of nearly uniform surfaces, it is often difficult to resolve small differences in the surfaces. The letter reports a differential method to measure small variations with the detector operating as a null detector. This method is applied to measure the thickness of plasma-sprayed coatings.     

High-resolution transmission electron microscopy study of Ca(3)Co(4)O(9)

The crystal structure of Ca(3)Co(4)O(9) was investigated using high-resolution transmission electron microscopy (HRTEM) and the image-simulation method. The c(*) was 10.8A and the b parameters were 4.56A for the Ca(2)CoO(3) block and 2.82A for the CoO(2) sheet. The [110] zone axis HRTEM images confirmed that Ca(3)Co(4)O(9) has a modulated layered structure with modulation. For the first time, the atomic positions of the Ca and Co atoms in the Ca(2)CoO(3) block were identified, corresponding to three rows of dark spots in the [110] direction. The observed HRTEM images for Ca(2)CoO(3) agreed well with the calculated images based on the structural model obtained by the Rietveld refinement method.     

An 88 nm gate-length In_(0.53)Ga_(0.47)As/In_(0.52)Al_(0.48)As InP-based HEMT with f_(max) of 201 GHz

正An 88 nm gate-length In_(0.53)Ga_(0.47)As/In_(0.52)Al_(0.48)As InP-based high electron mobility transistor (HEMT) was successfully fabricated with a gate width of 2×50μm and source-drain space of 2.4μm.The T-gate was defined by electron beam lithography in a trilayer of PMMA/A1/UⅧ.The exposure dose and the development time were optimized,and followed by an appropriate residual resist removal process.These devices also demonstrated excellent DC and RF characteristics:the extrinsic maximum transconductance,the full channel current, the threshold voltage,the current gain cutoff frequency and the maximum oscillation frequency of the HEMTs were 765 mS/mm,591 mA/mm,-0.5 V,150 GHz and 201 GHz,respectively.The HEMTs are promising for use in millimeter-wave integrated circuits.     

The growth of (InGa)As quantum wells on GaAs(111)A, (211)A and (311)A substrates

The ability to grow high quality (InGa)As on the (111)A surface is essential for the production of a wide range of optoelectronic devices, but the topic has so far received little attention. What work there has been shows it to be highly problematic, reflected in the very broad photoluminescence (PL) peaks observed for GaAs:(InGa)As multiple quantum well structures. The origin of this broadening is unclear but is certainly related to the difficulty in choosing appropriate conditions for the growth of III-Vs on the (111)A surface. We have undertaken a study of the growth of (InGa)As on the GaAs(111)A, (211)A and (311)A surfaces with the goal of achieving high quality quantum well structures, the test being the ability to obtain narrow PL line widths. We have demonstrated that 80 Å 15% InGaAs(111)A single quantum wells with 12K PL peak widths of less than 8 meV can be obtained by growth at 400°C under a V:III ratio of 5:1.     

背入射Al_(0.42)Ga_(0.58)N/Al_(0.40)Ga_(0.60)N异质结p-i-n太阳光盲紫外探测器

在蓝宝石上用MOCVD生长的材料制备了背入射Al0.42Ga0.58N/Al0.40Ga0.60N异质结p-I-n太阳光盲紫外探测器.从器件的正向Ⅰ-Ⅴ特性曲线计算了理想因子n与串联电阻Rs分别为3和93?器件在零偏压下275nm峰值波长处的外量子效率与探测率分别为9%和4.98×1011cm·Hz1/2/W,分析表明Al0.42Ga0.58N窗口层在275nm波长处的透过率仅为15.7%,是器件外量子效率和探测率偏低的原因之一.     

微波烧结Ba_(6-3x)Sm_(8+2x)Ti_(18)O_(54)陶瓷材料的初步研究

研究了Ba_(6-3x)Sm_(8+2x)Ti_(18)O_(54)(x=0.67,BST)陶瓷材料的微波烧结情况,从烧结特性、微结构与相组成及微波介电性能等方面对微波烧结的样品与传统工艺制得的样品进行了对比.结果表明, 与传统制备工艺相比,微波烧结BST陶瓷缩短了烧结周期,并促进了样品的致密化,其物相组成和传统烧结的样品没有区别,且晶粒细小分布均匀.微波烧结BST陶瓷可获得较优的微波介电性能:介电常数ε_r=82.89,品质因数与频率之积Qf=8 450 GHz(频率f=4.75 GHz),谐振频率温度系数τ_f=22.58×10~(-6)/℃.