Isothermal transient ionic current study of laminated electrochromic devices for smart window applications

The isothermal transient ionic current (ITIC) in three different kinds of laminated electrochromic devices has been determined. The devices consisted of one 300 nm thick layer of nickel oxide and one 300 nm thick layer of WO₃ deposited onto separate In₂O₃:Sn (ITO) covered glass substrates by DC magnetron sputtering at room temperature. They were then laminated with a polymeric ion conductor, acting as electrolyte, in symmetric and asymmetric configurations, i.e. WO₃/WO₃, NiO_xV_yH_z/NiO_xV_yH_z and WO₃/NiO_xH_y. The electrolyte was prepared by mixing polyethylene glycol of average molecular weight 400 (PEG 400) and lithium triflouromethanesulfonate (LiSO₃CF₃) for 12 h at 70°C and with a ratio oxygen/lithium (O/Li)=10. The samples were first polarized, i.e. the ions are transported to one of the electrodes, which in the asymmetric devices is the nickel oxide electrode. At the first applied potential step, the ions move through the electrolyte towards the opposite electrode. The potential is then switched and the ions move back to the first electrode. The ITIC curves are found to depend on the electrode material and in the asymmetric case also the direction of the ion current.     

Optical properties of electrochromic all-solid-state devices

We have investigated the optical properties of an all-thin-film electrochromic device, with a thin film of ZrO₂ acting as an ion conductor. The device also employed electrochromic layers of amorphous or crystalline WO₃ and NiV_xO_yH_z. Transmission (T) and reflection (R) spectra were recorded in the wavelength range 300–2500 nm at different intercalation levels, both for single films and complete devices. The results show that T decreases significantly upon intercalation in the WO₃ thin films as well as in the devices. The reflectance only shows minor changes.     

Design of passive backscattering RFID devices

The endeavors in realizing ubiquitous chips for ambient intelligence networks increased significantly over the past few years. In particular, the passive radio frequency identification (RFID) technology became a well known synonym for passive transponder devices. The increased attention is not only related to economical advantages, but also to the general technological potential. This article deals with the design of self-sustaining wireless transponders based on the backscattering technology. We explain the general architecture, present important design constraints and emphasize general characteristics of the backscattering radio-frequency (RF) front-end approach. Furthermore, we extend the common linear models by some important nonlinear figures of merit.     

3D Free‐Form Patterning of Silicon by Ion Implantation,Silicon Deposition,and Selective Silicon Etching

A method for additive layer‐by‐layer fabrication of arbitrarily shaped 3D silicon micro‐ and nanostructures is reported. The fabrication is based on alternating steps of chemical vapor deposition of silicon and local implantation of gallium ions by focused ion beam (FIB) writing. In a final step, the defined 3D structures are formed by etching the silicon in potassium hydroxide (KOH), in which the local ion implantation provides the etching selectivity. The method is demonstrated by fabricating 3D structures made of two and three silicon layers, including suspended beams that are 40 nm thick, 500 nm wide, and 4 μm long, and patterned lines that are 33 nm wide.     

Lateral base design rules for optimized low-frequency noise of differentially grown SiGe heterojunction bipolar transistors

The low-frequency noise dependence on lateral design parameters was investigated for SiGe heterojunction bipolar transistors fabricated by differential epitaxy. The low-frequency noise was found to vary substantially as a function of the extrinsic base design. The dominant noise sources were located either at the interface between the polycrystalline and epitaxial Si/SiGe base, in the epitaxial Si/SiGe base link region, in the base–emitter depletion region, or at the thin SiO₂ interface layer between the polysilicon and monosilicon emitter. Boron was found to passivate interfacial traps, acting as low-frequency noise sources. Generation–recombination noise with a strong dependence on the lateral electrical field was observed for some of the designs.     

Low-complexity BCH codes with optimized interleavers for DQPSK systems with laser phase noise

The presence of high phase noise in addition to additive white Gaussian noise in coherent optical systems affects the performance of forward error correction (FEC) schemes. In this paper, we propose a simple scheme for such systems, using block interleavers and binary Bose–Chaudhuri–Hocquenghem (BCH) codes. The block interleavers are specifically optimized for differential quadrature phase shift keying modulation. We propose a method for selecting BCH codes that, together with the interleavers, achieve a target post-FEC bit error rate (BER). This combination of interleavers and BCH codes has very low implementation complexity. In addition, our approach is straightforward, requiring only short pre-FEC simulations to parameterize a model, based on which we select codes analytically. We aim to correct a pre-FEC BER of around \(10^{-3}\). We evaluate the accuracy of our approach using numerical simulations. For a target post-FEC BER of \(10^{-6}\), codes selected using our method result in BERs around 3\(\times \) target and achieve the target with around 0.2 dB extra signal-to-noise ratio.     

Integrating the self‐growing concept in a self‐organizing wireless network for topology optimization

The concept of self‐organizing networks is considered one of the most promising approaches for the efficient management of future wireless networks that will support a large number of nodes and a plethora of services with diverse characteristics. Today, different types of networks (e.g. WLANs, wireless sensor networks) are deployed to serve different needs but do not interoperate. Their possible loose integration will provide opportunities that could be exploited through collaborative approaches to devise novel solutions to extend the capabilities and improve the performance of these networks. The self‐growing paradigm addresses this challenge by extending network nodes to dynamically evolve in terms of purpose and operational features. In this paper we describe the CONSERN architecture, which targets the realization of the self‐growing concept in the context of self‐organized networks. To test our ideas we designed and implemented a WLAN topology optimization scheme that provides the best coverage at a minimum energy consumption, through dynamic access point (AP) deactivation and reactivation. Using self‐growing mechanisms and typical motion detectors we present how the operation of the proposed topology optimization mechanism can be improved. The reduced energy consumption attained under the proposed scheme at the AP side, as well as the efficient utilization of network resources, are evaluated via a proof‐of‐concept implementation that we have deployed in a real office environment that consists of WLAN APs and motion sensors. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation and design of beaconing in mobile wireless networks

One of the intrinsic problems of mobility in wireless networks is the discovery of mobile nodes. A widely used solution for this problem is to use different variations of beacons, such as hello packets. Although a poorly designed beaconing scheme may lead to unnecessary energy usage or poor throughput, a systematic approach to analyze and select beaconing parameters is not provided in the literature. Here, we propose a model to study the beaconing efficiency using some measures such as the link lifetime, the probability of link establishment, and the delay to discover a new neighbor. The model is general and does not adhere to any particular mobility model; the only input from the mobility is the distribution of physical link durations, which not only abstracts away the mobility details but also all effects that contribute to the link stability such as non-perfectly omni-directional antennas and the path loss exponents. Among our results, we prove that the periodic beaconing (which is widely used owing to its simplicity) is the best in terms of beacon hits; we compare one-way and two-way beaconing schemes and study beaconing energy optimization. Finally, the model is applied to three cases of ad hoc, delay-tolerant, and sensor networks, and a simple rule of thumb is proposed to efficiently adjust the beacon interval.     

Near‐Infrared Emitting and Pro‐Angiogenic Electrospun Conjugated Polymer Scaffold for Optical Biomaterial Tracking

Noninvasive tracking of biomaterials is vital for determining the fate and degradation of an implant in vivo, and to show its role in tissue regeneration. Current biomaterials have no inherent capacity to enable tracing but require labeling with, for example, fluorescent dyes, or nanoparticles. Here a novel biocompatible fully conjugated electrospun scaffold is described, based on a semiconducting luminescent polymer that can be visualized in situ after implantation using fluorescence imaging. The polymer, poly [2,3‐bis‐(3‐octyloxyphenyl)quinoxaline‐5,8‐diyl‐alt‐thiophene‐2,5‐diyl] (TQ1), is electrospun to form a fibrous mat. The fibers display fluorescence emission in the near‐infrared region with lifetimes in the sub‐nanosecond range, optimal for in situ imaging. The material shows no cytotoxic behaviors for embryonic chicken cardiomyocytes and mouse myoblasts, and cells migrate onto the TQ1 fibers even in the presence of a collagen substrate. Subcutaneous implantations of the material in rats show incorporation of the TQ1 fibers within the tissue, with limited inflammation and a preponderance of small capillaries around the fibers. The fluorescent properties of the TQ1 fibers are fully retained for up to 90 d following implantation and they can be clearly visualized in tissue using fluorescence and lifetime imaging, thus making it both a pro‐angiogenic and traceable biomaterial.     

Downscaling and Charge Transport in Nanostructured Ferroelectric Memory Diodes Fabricated by Solution Micromolding

Ferroelectric polymer memory diodes are interface devices where charge injection into the organic semiconductor is controlled by the stray electric field of the ferroelectric polymer. Key to high current density and current modulation is the areal density of well‐defined interfaces. Here, bistable diodes are fabricated by using the soft lithography method solution micromolding. First, the semiconducting polymer poly(9,9‐dioctylfluorene) is patterned into linear gratings. Subsequently, bilinear arrays are obtained by backfilling with the ferroelectric polymer poly(vinylidenefluoride‐co‐trifluoroethylene). The lateral feature size is scaled down from 2 μm to 500 nm. Comprising memory diodes show rectifying J–V characteristics with an On‐current density larger than 10³ A m^?2 and an On/Off current ratio exceeding 10³. The charge transport is explained by 2D numerical simulations. Since the dependence of polarization on electric field is explicitly taken into account, entire J–V characteristics can be quantitatively described. The simulations reveal that rectifying J–V characteristics are inherently related to the concave shape of the patterned ferroelectric polymer. It is argued that the exponential increase in current density with decreasing feature size can be due to confinement of the semiconductor. High On‐current density combined with downscaling, rectification, and simple fabrication yield new opportunities for low‐cost integration of high‐density solution‐processed memories.