Compensation phenomena by ion implantation doping of an electroactive polymer,poly(para-phenylene)

We have shown that poly(para-phenylene) (PPP) can be obtained either n-type or p-type by ion implantation at low energy (E ≦ 50 keV); PPP is primarily an insulator pellet obtained from compacted powder synthetised by the Kovacic method. To compare with the chemical doping effect, we have studied the conductivity and thermopower of PPP samples after two successive ion implantations with Cs⁺ and I⁺. The experimental results show that we clearly obtain reversible doping only in the case of an initially I⁺-doped sample: the thermopower sign is changed after a Cs⁺ implantation with a fluence equal to 3 × 10¹⁴ ions cm^?2. In the other case (Cs⁺ initial implantation) we observe the change in thermopower sign at higher fluence (2 × 10¹⁶ I⁺ ions cm^?2). This last effect can be attributed to a metal transition induced by the accumulation of defects in the material because of too high implantation parameters (graphitisation).     

Study of thermal conversion and patterning of a new soluble poly (p-phenylenevinylene) (PPV) precursor

The investigation of conversion of new soluble poly(p-phenylenevinylene) (PPV) precursor and PPV patterns by irradiation with UV light of a film is reported. We obtained patterns by this method with well-defined edges and channel width up to 10 μm. Also, it was found that the PPV precursor polymer is a photoresist material. This allows the fabrication of PPV patterns, which can directly act as luminescent structures in organic light-emitting diodes (OLEDs). Using the atomic force microscopy (AFM) technique, investigations on the PPV thin films show that at 200 °C well-defined crystalline domains of PPV are detected, thus indicating the complete transformation of the precursor into the final polymer. The current–voltage characteristics of single and double PPV layer devices indicate that turn-on voltages around 9 and 8 V were recorded for double and single PPV layer devices, respectively. From the electroluminescence–voltage plot, an onset voltage at 10 V is detected for two PPV layers OLED. In addition, we investigate the optical, electrical and EL characteristics of pyrrolo[1,2-a][1,10]phenanthroline derivatives [Leontie L, Druta I, Danac R, Rusu GI. Synth Met 2005;155/1:138; Zugravescu I, Petrovanu M. 3+2 Dipolar cycloaddition. Bucharest: Roman Academic Publishing House; 1987 [in Romanian]; Druta I, Andrei M, Aburel P. Tetrahedron 1998;54:2107; Druta I, Dinica R, Bacu E, Humelnicu I. Tetrahedron 1998;54:10811; Dinica R, Druta I, Pettinari C. Synlett 2000;7:1013; Danac R, Rotaru A, Drochioiu G, Druta I. J Heterocyclic Chem 2003;40:283; Druta I, Danac R, Barbieru R, Tapu D, Andrei M. Sci Ann Al I Cuza Univ Iasi S Chem 2001;IX:149] as potential candidates for OLED applications. In this case, PPV was used as the hole-transport layer (HTL) and pyrrolo[1,2-a][1,10]phenanthroline derivatives, which were spin coated onto PPV, as the emissive layer. The structure of all PPV devices reported in this paper was fabricated using UV light for patterning.     

Conformational properties of quasi-particles in poly(p-phenylene vinylene)

We investigate the quasi-particle conformational defects (excitons, polarons and bipolarons) in phenylene vinylene oligomers (PVOs) consisting of up to 12 repeat units. The conformations are determined by minimisation of the total Hartree–Fock energy calculated at 3-21G level. The Hartree–Fock calculations of the excited states are followed by the CI–Singles calculation. The bond length alternation along the oligomer chain is discussed. On the basis of these results the vibrational transitions are calculated. To correct the basis set truncation error, the vibrational frequencies are multiplied by a uniform scaling factor. The types of vibrations are assigned. The theoretical spectra are in good agreement with the experimental infrared vibrational spectrum of poly(p-phenylene vinylene) (PPV). © 1998 John Wiley & Sons, Ltd.     

光码分多址全光网络实现方案

本文提出一种利用时域编码的光码分多址(OCDMA)技术构造全光通信网络的实现方案.给出了OCDMA全光接入网,OCDMA光交叉连接、光交换、光上下路、光复用的具体实现方法,给出了OCDMA全光网络体系结构.     

H、F、Cl/Si(111)化学吸附的半经验CNDO法研究

我们已把研究分子性质的半经验CNDO自治场分子轨道法用于计算模拟共价半导体的集团X_3X_(12)＇(X代表硅、金刚石或锗原子,X＇是集团边界上相应的虚拟原子),经过重新确定成键参数和恰当地选取边界原子的电负性参数,所得结果能比较满意地描写晶体的一些性质.本文报道用相同的计算方案研究氢、氟和氯原子在Si(111)表面上化学吸附性质的结果.与其它理论研究的结果比较表明,这种修改后的CNDO方案可以用于研究共价半导体表面上的化学吸附问题.     

A theoretical study on photoexcitations in poly(p-phenylene vinylene)

By applying a femtosecond electric pump pulse to a poly(p-phenylene vinylene) (PPV) molecule, we theoretically investigate the photoexciting process. The simulations are performed within the framework of an extended version of one-dimensional Su–Schrieffer–Heeger tight-binding model combined with a nonadiabatic evolution method. We obtain excitons, biexcitons, as well as high-energy excitons. Their yields are calculated and it is found that they are determined by the photoexciting energy. Especially, we obtain a relation between their photogenerations and the photoexciting energies, which is helpful for optoelectronic applications of organic semiconductors. In addition, effect of the photoexciting intensity on the photogeneration of high-energy excitons, which contribute to free charges generation, is discussed.     

Determination of the electroaffinity and potential barrier heights at polymer/ metal interfaces of poly(4,7-benzothiophene vinylene) (PBTV)

In this paper we determine the LUMO level position of poly(4,7-benzothiophene vinylene) (PBTV), a heterocyclic poly(phenylene vinylene) (PPV) analogue, using tunnelling current measurements. We compare the energy level positions with those measured for PPV and determine their shifts. The experimental results are compared with theoretical predictions and good agreement is observed. © 1998 John Wiley & Sons, Ltd.     

Radar cross section of complex targets

A summary of the development and verifications of a computer code, RECOTA (return from complex target), developed at Boeing Aerospace for calculating the radar cross section of complex targets is presented. The code utilizes a computer-aided design package for modeling target geometry in terms of facets and wedges. It is based on physical optics, physical theory of diffraction, ray tracing, and semiempirical formulations, and it accounts for shadowing, multiple scattering and discontinuities for monostatic calculations     

Photoinduced charge separation in poly(1,4-phenylenevinylene) derivatives studied by electron paramagnetic resonance

We report a study of photoinduced charge separation in poly(1,4-phenylenevinylene) (PPV) derivatives with enhanced exciton dissociation using light-induced electron paramagnetic resonance (EPR). Four polymers were studied; all contained alkoxy and fluorenyl side chain units, and two of them also contained a nitro group on the 7-positon of the fluorenyl moieties. Pulsed EPR detected a light induced polaron for all the polymers with the intensity significantly higher for those with nitro groups. A second center was observed for these materials and spectra could be fitted assuming a radical anion was localized on the nitro groups. The fraction of radical anion and polaron centers was comparable, consistent with intramolecular exciton dissociation for the PPV derivatives containing the nitro groups.     

Si(113)表面电子结构的研究

采用Si_(16)H_(21)和Si_(31)H_(39)原子集团分别模拟Si(113)和Si(111)表面;通过半经验自洽CNDO法计算了两个体系的电子结构.结果表明,Si(113)具有与Si(111)不同的表面态特征.Si(113)表面台阶和台面原子上电荷重新分布,与悬键相关的表面电子态都强烈地定域在表面Si原子上,尤其局域在悬键方向上,并且具有比(111)面上更高的悬健态密度.理论计算结果能解释以前的光电子谱实验.     

一种新的光码分多址技术

提出了一种新的、实现光ＣＤＭＡ的方案。它采用平衡发射和接收技术同时使用Ｍａｃｈ－Ｚｅｈｎｄｅｒ干涉链来进行地址编码。该ＣＤＭＡ系统接近波分复用的性能,但是也面临一些有待解决的问题,例如多用户时的谱干扰,散弹噪声等。而本系统可以在非相干调制光系统中得到地址码的真正正交,从而改善系统的性能。     

Photoluminescence evaluation of pseudomorphic high electron mobility transistor device waters

Photoluminescence (PL) has been used for some time the evaluation of pseudomorphic high electron mobility transistor material structures. Among the results routinely obtained from these structures are estimates of electron sheet density in the InGaAs channel, either from empirical relationships or from first principles (from direct observation of the Fermi level). We present a semiempirical line shape model for the study of PL line shapes at low temperatures. We show that the primary source of error for optical measurement of the sheet density is in the filling of the channel by electrons injected by the incident laser. We also demonstrate the potential for extraction of structural parameters such as channel composition and thickness from careful observation of variations in PL transition energies.     

PPP一致性测试研究

PPP协议(Point to Point Protocol)作为目前Internet上所广泛采用协议,它在单机入网和路由器之间互连具有非常重要的作用.在这样的背景下,就需要一种手段来检验和保证各种互连设备中的PPP模块实现的正确性.本文在扼要地介绍PPP协议的基础上,分析了PPP的测试组织、测试方法和测试集的设计,提出了适合于PPP一致性测试的测试结构,并对实际的路由器进行了PPP一致性测试.     

Conjugated Polymers: High‐Resolution Scanning Near‐Field Optical Lithography of Conjugated Polymers (Adv. Funct. Mater. 17/2010)

The fabrication of high‐resolution nanostructures in both poly(p‐phenylene vinylene), PPV, and a crosslinkable derivative of poly(9,9′‐dioctylfluorene), F8, using scanning near‐field optical lithography, is reported. The ability to draw complex, reproducible structures with 65000 pixels and lateral resolution below 60 nm (< λ/5) is demonstrated over areas up to 20 μm × 20 μm. Patterning on length‐scales of this order is desirable for realizing applications both in organic nanoelectronics and nanophotonics. The technique is based on the site‐selective insolubilization of a precursor polymer under exposure to the confined optical field present at the tip of an apertured near‐field optical fiber probe. In the case of PPV, a leaving‐group reaction is utilized to achieve insolubilization, whereas the polyfluorene is insolubilized using a photoacid initiator to create a crosslinked network in situ. For PPV, resolubilization of the features is observed at high exposure energies. This is not seen for the crosslinked F8 derivative, r‐F8Ox, allowing us to pattern structures up to 200 nm in height.     

光通信中基于SCG(4,k)码的一类改进LDPC码构造方法

针对SCG(4,k)码构造方法的分析与研究,提出一种适用于光通信系统中改进的新颖低密度奇偶校验(LDPC)码构造方法.该方法在保留SCG(4,k)构造方法的基础上,采用类似于准循环的构造形式,使生成的码字不受短环干扰,并具有良好的围长特性;并且与改进前的SCG(4,k)码相比,该构造方法具有硬件实现方面节省存储空间和降低计算复杂度等优点.采用该方法构造了码率为93.7％的LDPC(3969,3720)码.仿真结果表明:这种码的净编码增益(NCG)比广泛用于光通信系统中的经典RS(255,239)码提高了1.99 dB.     

On the Pless-construction and ML decoding of the (48,24,12) quadratic residue code

We present a method for maximum likelihood decoding of the (48,24,12) quadratic residue code. This method is based on projecting the code onto a subcode with an acyclic Tanner graph, and representing the set of coset leaders by a trellis diagram. This results in a two level coset decoding which can be considered a systematic generalization of the Wagner rule. We show that unlike the (24,12,8) Golay code, the (48,24,12) code does not have a Pless-construction which has been an open question in the literature. It is determined that the highest minimum distance of a (48,24) binary code having a Pless (1986) construction is 10, and up to equivalence there are three such codes.     

可溶性聚对苯乙炔衍生物非线性光学效应研究

以对甲氧基苯酚和溴代烷为原料,经过脱氯化氢反应合成了三种可溶性非对称烷氧基取代聚对苯乙炔 (PPV)衍生物,分别为聚(2 甲氧基 5 丁氧基)对苯乙炔(PMOBOPV)、聚[2 甲氧基 5 (3′ 甲基)丁氧基]对苯乙炔 (PMOMBOPV)和聚(2 甲氧基 5 辛氧基)对苯乙炔(PMOCOPV)。利用后向式简并四波混频(DFWM)研究了它们 的三阶非线性光学性质。结果表明PMOBOPV,PMOMBOPV和PMOCOPV的三阶非线性极化率(χ(3))分别为 3.14×10-10,5.96×10-10和3.71×10-10esu,相应的二阶分子超极化率(γ)分别为4.22×10-28,7.78×10-28和 5.00×10-28esu。分析了分子结构对聚对苯乙炔衍生物非线性光学性质的影响。采用分光光度计对三种材料的 光学禁带宽度(Eg)进行了测量,线性拟合的结果表明PMOBOPV,PMOMBOPV和PMOCOPV的Eg值分别为 2.08,2.03及2.05eV。     

游程长度受限码RLL (4 ,13) 的研究

提出了一种新的RLL(4，13)游程长度受限码。给出RLL(4，13)码的构造方法和编解码步骤。比较了不同游程长度受限码的主要性能参数。RLL(4，13)码的硬件复杂度低，密度率高，适用于高密度光存储系统。     

VCSEL design using the bidirectional beam-propagation method

We present an optical modeling approach for calculating vertical-cavity surface emitting laser (VCSELs) modes based on the bidirectional beam propagation method. Compared with existing approaches, it is flexible, efficient, and convenient. To demonstrate and validate the approach, we examined several design problems for oxide-confined VCSEL devices. Specifically, we modeled the blue-shift phenomenon in small oxidized VCSELs and compared our calculations with previous results. We also examined the dependence of the threshold gain on different oxide-aperture shaped designs and on the thickness and placement of an aperture layer