Influences of Connecting Unit Architecture on the Performance of Tandem Organic Light‐Emitting Devices

The present work investigates the influence of the n‐type layer in the connecting unit on the performance of tandem organic light‐emitting devices (OLEDs). The n‐type layer is typically an organic electron‐transporting layer doped with reactive metals. By systematically varying the metal dopants and the electron‐transporting hosts, we have identified the important factors affecting the performance of the tandem OLEDs. Contrary to common belief, device characteristics were found to be insensitive to metal work functions, as supported by the ultraviolet photoemission spectroscopy results that the lowest unoccupied molecular orbitals of all metal‐doped n‐type layers studied here have similar energy levels. It suggests that the electron injection barriers from the connecting units are not sensitive to the metal dopant used. On the other hand, it was found that performance of the n‐type layers depends on their electrical conductivities which can be improved by using an electron‐transporting host with higher electron mobility. This effect is further modulated by the optical transparency of constituent organic layers. The efficiency of tandem OLEDs would decrease as the optical transmittance decreases.     

Highly Improved Sb2S3 Sensitized‐Inorganic–Organic Heterojunction Solar Cells and Quantification of Traps by Deep‐Level Transient Spectroscopy

The light‐harvesting Sb₂S₃ surface on mesoporous‐TiO₂ in inorganic–organic heterojunction solar cells is sulfurized with thioacetamide (TA). The photovoltaic performances are compared before and after TA treatment, and the state of the Sb₂S₃ is investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, and deep‐level transient spectroscopy (DLTS). Although there are no differences in crystallinity and composition, the TA‐treated solar cells exhibit significantly enhanced performance compared to pristine Sb₂S₃‐sensitized solar cells. From DLTS analysis, the performance enhancement is mainly attributed to the extinction of trap sites, which are present at a density of (2–5) × 10¹⁴ cm^?3 in Sb₂S₃, by TA treatment. Through such a simple treatment, the cell records an overall power conversion efficiency (PCE) of 7.5% through a metal mask under simulated illumination (AM 1.5G, 100 mW cm^–2) with a very high open circuit voltage of 711.0 mV. This PCE is, thus far, the highest reported for fully solid‐state chalcogenide‐sensitized solar cells.     

Constructing Conductive Interfaces between Nickel Oxide Nanocrystals and Polymer Carbon Nitride for Efficient Electrocatalytic Oxygen Evolution Reaction

Combining transition metal oxide catalysts with conductive carbonaceous material is a feasible way to improve the conductivity. However, the electrocatalytic performance is usually not distinctly improved because the interfacial resistance between metal oxides and carbon is still large and thereby hinders the charge transport in catalysis. Herein, the conductive interface between poorly conductive NiO nanoparticles and semi‐conductive carbon nitride (CN) is constructed. The NiO/CN exhibits much‐enhanced oxygen evolution reaction (OER) performance than corresponding NiO and CN in electrolytes of KOH solution and phosphate buffer saline, which is also remarkably superior over NiO/C, commercial RuO₂, and mostly reported NiO‐based catalysts. X‐ray photoelectron spectroscopy and extended X‐ray absorption fine structure spectrum reveal that a metallic Ni–N bond is formed between NiO and CN. Density functional theory calculations suggest that NiO and CN linked by a Ni–N bond possess a low Gibbs energy for OER intermediate adsorptions, which not only improves the transfer of charge but also promotes the transmission of mass in OER. The metal–nitrogen bonded conductive and highly active interface pervasively exists between CN and other transition metal oxides including Co₃O₄, CuO, and Fe₂O₃, making it promising as an inexpensive catalyst for efficient water splitting.     

Simulations and experiments for optimal deployment of an RFID‐based location‐aware system

The proliferation of communication and mobile computing devices and local‐area wireless networks has cultivated a growing interest in location‐aware systems and services. An essential problem in location‐aware computing is the determination of physical locations. RFID technologies are gaining much attention, as they are attractive solutions to indoor localization in many healthcare applications. In this paper, we propose a new indoor localization methodology that aims to deploying RFID technologies in achieving accurate location‐aware undertakings with real‐time computation. The proposed algorithm introduces means to improve the accuracy of the received RF signals. Optimal settings for the parameters in terms of reader and reference tag properties were investigated through simulations and experiments. The experimental results indicate that our indoor localization methodology is promising in applications that require fast installation, low cost and high accuracy. Copyright © 2009 John Wiley & Sons, Ltd.     

Process windows for low-temperature Au wire bonding

The process windows are presented for low-temperature Au wire bonding on Au/Ni/Cu bond pads of varying Au-layer thicknesses metallized on an organic FR-4 printed circuit board (PCB). Three different plating techniques were used to deposit the Au layers: electrolytic plating, immersion plating, and immersion plating followed by electrolytic plating. Wide ranges of wire bond force, bond power, and bond-pad temperature were used to identify the combination of these processing parameters that can produce good wire bonds, allowing the construction of process windows. The criterion for successful bonds is no peel off for all 20 wires tested. The wire pull strengths and wire deformation ratios are measured to evaluate the bond quality after a successful wire bond. Elemental and surface characterization techniques were used to evaluate the bond-pad surfaces and are correlated to wire bondability and wire pull strength. Based on the process windows along with the pull strength data, the bond-pad metallization and bonding conditions can be further optimized for improved wire bondability and product yields. The wire bondability of the electrolytic bond pad increased with Au-layer thickness. The bond pad with an Au-layer thickness of 0.7 μm displayed the highest bondability for all bonding conditions used. The bondability of immersion bond pads was comparable to electrolytic bond pads with a similar Au thickness. Although a high temperature was beneficial to wire bondability with a wide process window, it did not improve the bond quality as measured by wire pull strength.     

The microwave power performance comparisons of Al/sub x/Ga/sub 1-x/As/In/sub 0.15/Ga/sub 0.85/As (x=0.3, 0.5, 0.7, 1.0) doped-channel HFETs

The properties of doped-channel field-effect transistors (DCFET) have been thoroughly investigated on Al/sub x/Ga/sub 1-x/As/InGaAs (x= 0.3, 0.5, 0.7, 1) heterostructures with various Al mole fractions. In this study, we observed that by introducing a 200-/spl Aring/-thick Al/sub 0.5/Ga/sub 0.5/As (x=0.5) Schottky layer can enhance the device power performance, as compared with the conventional x=0.3 AlGaAs composition system. However, a degradation of the device power performance was observed for further increasing the Al mole fractions owing to their high sheet resistance and surface states. Therefore, Al/sub 0.5/Ga/sub 0.5/As Schottky layer design provides a good opportunity to develop a high power device for power amplifier applications.     

Enhanced space-time block coded systems by concatenating turbo product codes

The BER performance of a turbo product code (TPC) based space-time block coding (STBC) wireless system has been investigated. With the proposed system, both the good error correcting capability of TPC and the concurrent large diversity gain characteristic of STBC can be achieved. The BER upper bound has been derived taking BPSK modulation as an example. The simulation results show that the proposed system with the concatenated codes outperforms the one with only TPC or STBC and other reported schemes that concatenate STBC with convolutional Turbo codes or trellis codes.     

Nonvolatile flash memory device using Ge nanocrystals embedded in HfAlO high-/spl kappa/tunneling and control oxides: Device fabrication and electrical performance

We fabricated a nonvolatile Flash memory device using Ge nanocrystals (NCs) floating-gate (FG)-embedded in HfAlO high-/spl kappa/ tunneling/control oxides. Process compatibility and memory operation of the device were investigated. Results show that Ge-NC have good thermal stability in the HfAlO matrix as indicated by the negative Gibbs free energy changes for both reactions of GeO/sub 2/+Hf/spl rarr/HfO/sub 2/+Ge and 3GeO/sub 2/+4Al/spl rarr/2Al/sub 2/O/sub 3/+3Ge. This stability implies that the fabricated structure can be compatible with the standard CMOS process with the ability to sustain source-drain activation anneal temperatures. Compared with Si-NC embedded in HfO/sub 2/, Ge-NC embedded in HfAlO can provide more electron traps, thereby enlarging the memory window. It is also shown that this structure can achieve a low programming voltage of 6-7 V for fast programming, a long charge retention time of ten years maintaining a 0.7-V memory window, and good endurance characteristics of up to 10/sup 6/ rewrite cycles. This paper shows that the Ge-NC embedded in HfAlO is a promising candidate for further scaling of FG Flash memory devices.     

An integrated content and metadata based retrieval system for art

A new approach to image retrieval is presented in the domain of museum and gallery image collections. Specialist algorithms, developed to address specific retrieval tasks, are combined with more conventional content and metadata retrieval approaches, and implemented within a distributed architecture to provide cross-collection searching and navigation in a seamless way. External systems can access the different collections using interoperability protocols and open standards, which were extended to accommodate content based as well as text based retrieval paradigms. After a brief overview of the complete system, we describe the novel design and evaluation of some of the specialist image analysis algorithms including a method for image retrieval based on sub-image queries, retrievals based on very low quality images and retrieval using canvas crack patterns. We show how effective retrieval results can be achieved by real end-users consisting of major museums and galleries, accessing the distributed but integrated digital collections.