Electromigration in fine-line conductors (0.45–2 μm)

The electromigration behaviour of various metallization systems has been tested on Si, GaAs and GaInAs substrates. Lifetime dependence on temperature and current density has been measured by accelerated lifetime tests. Linewidth was between 0.45 μm and 2 μm. The best electromigration resistance was found for electroplated gold lines, however also the system Al on Ti showed a as much as 40 times better performance than standard Al metallization. For linewidths of 0.45 μm a steep increase in stability has been found.     

Probing Bias‐Dependent Electrochemical Gas–Solid Reactions in (LaxSr1–x)CoO3–δ Cathode Materials

Spatial variability of bias‐dependent electrochemical processes on a (La_0.5Sr_0.5)₂CoO_4±δ modified (La_xSr_1–x)CoO_3–δ surface is studied using first‐order reversal curve method in electrochemical strain microscopy (ESM). The oxygen reduction/evolution reaction (ORR/OER) is activated at voltages as low as 3–4 V with respect to bottom electrode. The degree of bias‐induced transformation as quantified by ESM hysteresis loop area increases with applied bias. The variability of electrochemical activity is explored using correlation analysis and the ORR/OER is shown to be activated in grains at relatively low biases, but the final reaction rate is relatively small. At the same time, at grain boundaries, the onset of reaction process corresponds to larger voltages, but limiting reactivity is much higher. The reaction mechanism in ESM of mixed electronic‐ionic conductor is further analyzed. These studies both establish the framework for probing bias‐dependent electrochemical processes in solids and demonstrate rich spectrum of electrochemical transformations underpinning catalytic activity in cobaltites.     

Controlled Pattern Formation of Poly[2‐methoxy‐5‐(2′‐ethylhexyloxyl)–1,4‐phenylenevinylene] (MEH–PPV) by Ink‐Jet Printing

A detailed survey on the processing of poly[2‐methoxy‐5‐(2′‐ethylhexyloxyl)–1,4‐phenylenevinylene] (MEH–PPV) solutions via ink‐jet printing and the subsequent characterization of the resulting films is reported. The printability of MEH–PPV dissolved in different solvents, and with varied concentrations, is studied. Limitations of the printability of highly concentrated polymer solutions are overcome by using ultrasonication. The pattern formation of the resulting lines is explained in relation to the contact angle formed by the MEH–PPV solution on the substrate and interchain interactions. A uniform thickness distribution of MEH–PPV films is obtained when toluene is used as the solvent. Further improvement on the surface quality of the lines is achieved by optimizing the printing parameters. The line stability as a function of the print‐head velocity is also studied. Additionally, current–voltage (I–V) characteristics and the morphology of the MEH–PPV films, as determined by atomic force microscopy, are discussed.     

Synthesis of Microscale Raft‐shaped Zinc(II)–Phenylalanine Complexes and Zinc(II)–Phenylalanine/dye Hybrid Bundles with New Optical Properties

Novel raft‐like zinc(II)–phenylalanine complexes and zinc(II)–phenylalanine/acid green 27 (AG27) hybrid radial bundles have been successfully synthesized by a simple refluxing reaction. The formation processes of the morphologies and the superstructures of the hybrid bundles were proposed based on the time‐dependent evolution process. The AG27 molecules act as both the inclusion compound and the controller of the morphologies and the superstructures of the final hybrid. The combination of the zinc(II)–phenylalanine complex and AG27 leads to distinct optical properties compared with the individual component materials. This approach opens a new and effective way for the fabrication of amino acid/dye hybrid materials with unique optical properties and is expected to allow access to other organic/organic hybrid materials with structural specificity and functional novelty.     

Percolation Mechanism and Characterization of (CdO)y(ZnO)1–y Thin Films

(CdO)_y(ZnO)_1–y thin films have been prepared by the sol–gel process, based on precursor solutions used separately for such oxides. The Cd/(Cd + Zn) atomic ratio in solution ranged from 0 to 0.32. These compositions were selected on the basis of an observed abrupt fall, of ca. four orders of magnitude, in the resistivity of the films within this range. Such a resistivity drop, with a threshold value of around y = 0.17, is consistent with a percolation mechanism in a three‐dimensional, random, two‐phase system composed of isotropic, sphere‐like, conducting CdO regions embedded in a highly resistive ZnO matrix. Optical measurements show that the films are highly transparent, above 90 % transmission, for wavelengths ≥600 nm. The optical absorption edge shifts to longer wavelengths as the Cd content in the film increases. On the basis of the percolation mechanism observed in the multicomponent system (CdO)_y(ZnO)_1–y, possible future pathways are proposed for the design and construction of highly efficient, transparent, conducting oxides.     

Synthesis,Morphology, and Properties of Poly(3‐hexylthiophene)‐block‐Poly(vinylphenyl oxadiazole) Donor–Acceptor Rod–Coil Block Copolymers and Their Memory Device Applications

Novel donor–acceptor rod–coil diblock copolymers of regioregular poly(3‐hexylthiophene) ( P3HT )‐block‐poly(2‐phenyl‐5‐(4‐vinylphenyl)‐1,3,4‐oxadiaz‐ole) ( POXD ) are successfully synthesized by the combination of a modified Grignard metathesis reaction ( GRIM ) and atom transfer radical polymerization ( ATRP ). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low‐lying highest occupied molecular orbital (HOMO) energy level (–6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT‐ b ‐POXD exhibits a non‐volatile bistable memory or insulator behavior depending on the P3HT / POXD block ratio and the resulting morphology. The ITO/ P3HT₄₄ ‐b‐ POXD₁₈ /Al memory device shows a non‐volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor‐acceptor rod‐coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications.     

Network Effects in the Academic Market: Mechanisms for Hiring and Placing PhDs in Communication (2007–2014)

We analyze hiring and placement dynamics across communication PhD programs using data collected in 2014. We assess changes compared to data collected in 2007, and identify factors that underlie the formation of recruitment ties. Our findings challenge prior conclusions that faculty‐hiring patterns offer a proxy to the quality of doctoral education. Instead, we find evidence that the recruitment network results from interorganizational dynamics likely to emerge from faculty mobility; these dynamics, endogenous to the network, manifest in the form of reciprocity, transitivity, and cumulative advantage. Once we control for these characteristics, exogenous factors such as institutional prestige, faculty seniority, and reputational rankings modestly drive the creation of recruitment ties—appearing as secondary forces in the formation of faculty‐hiring networks.     

Facile Controlled Synthesis and Spectroscopy of CdS1−xSex Alloy and (CdS)1−x@(CdSe)x Core–Shell Nanotetrapods

Nanotetrapods of alloy CdS_1?xSe_x and core–shell (CdS)_1?x@(CdSe)_x are fabricated easily in water using ethylenediamine as a solvent‐coordinating molecular template, and then their optical properties are investigated using diverse static and time‐resolved spectroscopic methods. The arms of the alloy nanotetrapods have single‐crystalline structures of CdS_1?xSe_x without showing staking faults, while the arms of the core–shell nanotetrapods display polycrystalline shell structures of CdSe. The optical properties of CdS_1?xSe_x, where Se atoms are isolated in the CdS lattice, are very different from those of (CdS)_1?x@(CdSe)_x, where banded CdSe passivates the CdS core. Compared with pure CdS nanotetrapods, the photoluminescence of CdS_0.9Se_0.1 shifts to the red by 40 nm, whereas that of (CdS)_0.9@(CdSe)_0.1 does so only by 5 nm. Although the mean luminescence lifetime of alloy CdS_1?xSe_x is shorter than that of pure CdS, it is still much longer than that of core‐shell (CdS)_1?x@(CdSe)_x.     

Harnessing Structure–Property Relationshipsfor Poly(alkyl thiophene)–Fullerene Derivative Thin Filmsto Optimize Performance in Photovoltaic Devices

Nanoscale bulk heterojunction (BHJ) systems, consisting of fullerenes dispersed in conjugated polymers have been actively studied in order to produce high performance organic photovoltaics. How the BHJ morphology affects device efficiency, is currently ill‐understood. Neutron reflection together with grazing incidence X‐ray and neutron scattering and X‐ray photoelectron spectroscopy are utilized to gain understanding of the BHJ morphology in functional devices. For nine model systems, based on mixtures of three poly(3‐alkyl thiophenes, P3AT) (A = butyl, hexyl, octyl) blended with three different fullerene derivatives, the BHJ morphology through the film thickness is determined. It is shown that fullerene enrichment occurs at both the electrode interfaces after annealing. The degree of fullerene enrichment is found to strongly correlate with the short circuit current (J_SC ) and to a lesser degree with the fill factor. Based on these findings, it is demonstrated that by deliberately adding a fullerene layer at the electron transport layer interface, J_SC can be increased by up to 20%, resulting in an overall increase in power conversion efficiency of 5%.     

Analysis and performance evaluation of new coding options for space telecommand links – part II: jamming channels

In this paper, we study the performance of telecommand space links affected by pulsed, continuous wave and pseudo‐noise jamming. Countermeasures include coding, interleaving, and direct sequence spread spectrum. Binary and non‐binary low‐density parity‐check codes, parallel turbo codes, and soft‐decision decoded BCH codes are considered. We investigate the impact of different decoding algorithms, also taking into account the role of jamming state information, spreading processing gain and interleaving. The results show that significant gains (up to more than 10 dB) can be achieved in a number of interesting scenarios. Copyright © 2014 John Wiley & Sons, Ltd.     

Architecture of Conjugated Donor–Acceptor (D–A)‐Type Polymer Films with Cross‐Linked Structures

A series of new donor–acceptor (D–A)‐type semiconducting conjugated polymers (SCPs), which can form cross‐linked structural and supramolecular assembly films by hydrogen‐bonding, is successfully synthesized. The microstructures of supramolecular assembly films are further investigated by X‐ray diffraction (XRD), high‐ resolution transmission electron microscopy (HRTEM), and variable‐temperature Fourier transform infrared (FT‐IR) absorption spectra. As electronic transmission (ET) materials, the SCPs demonstrate superior properties by means of fabricating electron‐only devices with the configuration of ITO/ET (SCPs)/Ca/Al. According to space‐charge‐limited current (SCLC) measurements, fluorine‐containing SCPs exhibit much smaller threshold voltages and much higher electron mobilities than Alq₃. Meanwhile, a significant enhancement for their luminescence properties is verified by the photoluminescence (PL) and electroluminescent (EL) spectra of cross‐linked‐type SCPs, compared to non‐cross‐linked‐type SCPs. The fabricated polymer light‐emitting diodes (PLEDs) with the configuration of ITO/PEDOT:PSS/EML (SCPs)/BCP/LiF/Al are able to emit the color from green to red with moderately low turn‐on voltages. These results suggested that cross‐linked D–A‐type SCP can become a potential candidate as a kind of multifunctional materials applied in the field of optoelectronic devices.     

Designed Autonomic Motion in Heterogeneous Belousov–Zhabotinsky (BZ)‐Gelatin Composites by Synchronicity

Critical technologies from medicine to defense are highly dependent on advanced composite materials. Increasingly there is a greater demand for materials with expanded functionality. The state of the art includes a wide range of responsive composites capable of impressive structural feats such as externally triggered shape morphing. Here a different composite concept is presented, one in which a portion of the constituent materials feed off of ambient energy and dynamically couple to convert it to mechanical motion in a cooperative, biomimetic fashion. Using a recently developed self‐oscillating gel based on gelatin and the oscillating Belousov–Zhabotinsky (BZ) reaction, a technique is demonstrated for producing continuous patterned heterogeneous BZ hydrogel composites capable of sustained autonomic function. The coupling between two adjacent reactive patches is demonstrated in an autonomic cantilever actuator which converts chemical energy into amplified mechanical motion. The design of heterogeneous BZ gels for motion using a basic finite element model is discussed. This work represents notable progress toward developing internally responsive, bio‐inspired composite materials for constructing modular autonomic morphing structures and devices.     

A Highly Stable,New Electrochromic Polymer: Poly(1,4‐bis(2‐(3′,4′‐ethylenedioxy) thienyl)‐2‐methoxy‐5‐2″‐ethylhexyloxybenzene)

A highly stable new electrochromic polymer, poly(1,4‐bis(2‐(3′,4′‐ethylenedioxy)thienyl)‐2‐methoxy‐5‐2″‐ethylhexyloxybenzene) (P(BEDOT‐MEHB)) was synthesized and its electrochemical and electrochromic properties are reported. P(BEDOT‐MEHB) showed a very well defined electrochemistry with a relatively low oxidation potential of the monomer at + 0.44 V versus Ag/Ag⁺, E_1/2 at – 0.35 V versus Ag/Ag⁺ and stability to long‐term switching up to 5000 cycles. A high level of stability to over‐oxidation has also been observed as this material shows limited degradation of its electroactivity at potentials 1.4 V above its half‐wave potential. Spectroelectrochemistry showed that the absorbance of the π–π* transition in the neutral state is blue‐shifted compared to PEDOT, displaying a maximum at 538 nm (onset at 640 nm), thus giving an almost colorless, highly transparent oxidized polymer with a bandgap of 1.95 eV. Different colors observed at different oxidation levels and strong absorption in the near‐IR make this polymer a good candidate for several applications.     

Controlling Phase Assemblage in a Complex Multi‐Cation System: Phase‐Pure Room Temperature Multiferroic (1−x)BiTi(1−y)/2FeyMg(1−y)/2O3–xCaTiO3

A room temperature magnetoelectric multiferroic is of interest as, e.g., magnetoelectric random access memory. Bulk samples of the perovskite (1?x)BiTi_(1?y)/2Fe_yMg_(1?y)/2O₃–xCaTiO₃ (BTFM–CTO) are simultaneously ferroelectric, weakly ferromagnetic, and magnetoelectric at room temperature. In BTFM–CTO, the volatility of bismuth oxide, and the complex subsolidus reaction kinetics, cause the formation of a microscopic amount of ferrimagnetic spinel impurity, which complicates the quantitative characterization of their intrinsic magnetic and magnetoelectric properties. Here, a controlled synthesis route to single‐phase bulk samples of BTFM–CTO is devised and their intrinsic properties are determined. For example, the composition x = 0.15, y = 0.75 shows a saturated magnetization of 0.0097μ_B per Fe, a linear magnetoelectric susceptibility of 0.19(1) ps m^?1, and a polarization of 66 μC cm^?2 at room temperature. The onset of weak ferromagnetism and linear magnetoelectric coupling are shown to coincide with the onset of bulk long‐range magnetic order by neutron diffraction. The synthesis strategy developed here will be invaluable as the phase diagram of BTFM–CTO is explored further, and as an example for the synthesis of other compositionally complex BiFeO₃‐related materials.