Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping

ABSTRACT: Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV).PACS: 81.15.Gh.     

Exploring Hypermedia Processor Design Space

Distributed hypermedia systems that support collaboration are important emerging tools for creation, discovery, management and delivery of information. These systems are becoming increasingly desired and practical as other areas of information technologies advance. A framework is developed for efficiently exploring the hypermedia design space while intelligently capitalizing on tradeoffs between performance and area. We focus on a category of processors that are programmable yet optimized to a hypermedia application.The key components of the framework presented in this paper are a retargetable instruction-level parallelism compiler, instruction level simulators, a set of complete media applications written in a high level language, and a media processor synthesis algorithm. The framework addresses the need for efficient use of silicon by exploiting the instruction-level parallelism found in media applications by compilers that target multiple-instruction-issue processors.Using the developed framework we conduct an extensive exploration of the design space for a hypermedia application. We find that there is enough instruction-level parallelism in the typical media and communication applications to achieve highly concurrent execution when throughput requirements are high. On the other hand, when throughput requirements are low, there is little value in multiple-instruction-issue processors. Increased area does not improve performance enough to justify the use of multiple-instruction-issue processors when throughput requirements are low.The framework introduced in this paper is valuable in making early architecture design decisions such as cache and issue width trade-off when area is constrained, and the number of branch units and instruction issue width.     

Alternating phenylenevinylene and thienylenevinylene copolymers with cyano groups: Synthesis,photophysics and photovoltaics

Two alternating conjugated copolymers TTP and TTT were synthesized by Heck coupling of 2,3-bis-(5-bromothiophene-2-yl)acrylonitrile with 1,4-dihexyloxy-2,5-divinylbenzene and 3-hexyl-2,5-divinylthiophene, respectively. The absorption spectra of the copolymers in THF solution showed three maxima around 270, 370 and 460 nm with optical band gaps of 2.30–2.34 eV. The electrochemically estimated band gaps of copolymers were 2.04–2.10 eV. The thin film absorption spectra were broad and extended about from 250 to 600 nm with a long wavelength maximum near 470 nm. The copolymers emitted yellow-orange light with maximum at 528–551 nm in THF solution and 567–610 nm in thin film. TTP showed the most red shifted emission maximum between the copolymers. The performance of the photovoltaic cells which were fabricated using blends of the copolymers with 6,6-phenyl C61-butyric acid methyl ester (PCBM) (1:1 and 1:4, w/w) as well as pure copolymers was investigated.     

Synthesis of Hyperbranched Polymers with Rhenium(I) Bis(Stilbazoylimino)Acephthalene Complexes at the Branching Units

Two hyperbranched polymers that contains chlorotricarbonyl rhenium(I) bis(stilbazoylimino)acenaphthene complexes were synthesized. The AB₂ typed monomers are based on 3- or 4-stilbazoylimino groups that coordinated to the rhenium center as the bidentate ligands. Self-polymerization could be initiated by the addition of silver triflate that activated the rhenium center by removing the chloride ligand. The sizes of the polymers were studied by various methods including gel permeation chromatography and light scattering, and atomic force microscopy. Addition of electrolyte to the polymer solutions resulted in decrease in molecular size, but after a critical concentration (ca. 10 mM), the sizes increased due to the formation of aggregates. These polymers were fabricated into multilayer films by the layer-by-layer electrostatic self-assembly with another polyanion. The multilayer films could function as the active layer in photovoltaic cells. The open-circuit voltage, short circuit current, and fill factor of the best device were measured to be 0.62 V, 3.7 μA/cm², and 0.17, respectively. The power conversion efficiencies of the cells were in the order of 10⁻⁴ %. The contribution of metal complex in the photosensitization process was confirmed by the plot of incident photon-to-electron conversion efficiency as the function of incident light wavelength. This paper is dedicated to Professor Didier Astruc and his scientific accomplishments.     

Digital circuit macromodeling with PSPICE

Ordinary algebra is used to represent Boolean algebra on logic variables with states 0 and 1, so to achieve a unify approach to simulated both digital and analog circuit in PSPICE. Result on mixed A/D simulation shows a save in memory but generally longer run time.     

Charge balance materials for homojunction and heterojunction OLED applications

In a homojunction device, a single organic layer assumes the multiple roles of hole, electron transportation, and emitter. Its ease in processing is highly desirable from the manufacturing point of view. In this paper, we shall describe the synthesis of a range of bipolar small molecules and conductive vinyl polymers for application in homojunction and heterojunction organic light emitting diodes (OLEDs). The bipolar materials, in general, consist of three basic building blocks: an arylamine, a 1,3,4-oxadiazole, and a polycyclic aromatic moiety. The achievement of charge balance can be validated either by direct measurement of electron/hole mobility or indirectly via optimization of device properties.A series of conductive vinyl copolymers containing hole transporting N-(4-methoxyphenyl)-N-(4-vinylphenyl)naphthalen-1-amine (4MeONPA) and electron transport-ing 2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (OXA) at different compositions was applied for heterojunction and homojunction OLEDs. For heterojunction devices employed the copolymers as the hole transporting layer and Alq3 as the electron transporting and emitting layer,a maximum luminance and current efficiency of over 23000 cd/m2 and 4.2 cd/A (PL of Alq3), respectively, were achieved at the charge balance composition. Homojunction devices for the copolymers were demonstrated by the addition ofrubrene as a dopant. The single layer devices at the optimal copolymer composition has ca 1500 cd/m2 and 0.74 cd/A.     

一种改进的无线传感器网络动态密钥管理方案

无线传感器网络是由大量资源有限的传感器节点组成。为了保证传感器节点间的安全通信,找到一种有效的密钥管理方式是十分重要的。针对无线传感器节点能量低,存储空间有限的特点,提出了一种改进的密钥管理方案。该方案采用或运算及异或运算生成共享密钥对,计算量小、耗能低,并且密钥可更新。最后通过对比分析,该方案比其他方案具有更强的安全性和更低的能量消耗。     

A distance-based group decision-making methodology for multi-person multi-criteria emergency decision support

In this paper, a distance-based group decision-making (GDM) methodology is proposed to solve unconventional multi-person multi-criteria emergency decision-making problems. In this model, some decision-makers are first identified to formulate a group decision-making framework. Then a standard multi-criteria decision-making (MCDM) process is performed on specific decision-making problems and different decision results are obtained from different decision-makers. Finally, these different decision results are aggregated into a group consensus to support the final decision-making. For illustration and verification purposes, a numerical example and a practical unconventional emergency decision case are presented. Experimental results obtained demonstrate that the proposed distance-based multi-criteria GDM methodology can improve decision-making objectivity and emergency management effectiveness.     

Locomotion and depth control of robotic fish with modular undulating fins

This paper presents an environmental-friendly robotic system mimicking the undulating fins of a fish. To mimic the actual flexible fin of real fish, a fin-like mechanism with a series of connecting linkages is modeled and attached to the robotic fish, by virtue of a specially designed strip. Each link is able to turn and slide with respect to the adjacent link. These driving linkages are then used to form a mechanical fin consisting of several fin segments, which are able to produce undulations, similar to those produced by the actual fish fins. Owing to the modular and re-configurable design of the mechanical fin, we are able to construct biomimetic robotic fish with various swimming modes by fin undulations. Some qualitative and workspace observations by experiments of the robotic fish are shown and discussed.