Highly Ordered Fe and Nb Stripe Arrays on Facetted α‐Al2O3 (10$ \bar 1 $0)

A process is described whereby highly ordered arrays of epitaxial thin‐film nano‐ and mesostripes can be grown using molecular beam epitaxy (MBE) techniques on M‐plane sapphire α‐Al₂O₃ (10 0) substrates. The planar sapphire substrate surface is unstable, and spontaneously forms primarily ( 101) and (1 02) nanofacets upon annealing at a high temperature. By employing this nanofacetted sapphire as a substrate for MBE growth at controlled shallow incident angles, perfect nano‐ and mesostripes can be produced by means of geometrical shadowing in conjunction with partial de‐wetting of the epilayer on the facets. Advantages over other stripe fabrication strategies include: epitaxial quality, tunable width, and the ability to grow superconducting and rare earth nanowires using well‐established MBE techniques. The process is demonstrated by the growth of regular arrays of 100 nm wide Nb nanostripes. Additionally, we have determined the epitaxy of Nb (111) on the Al₂O₃ ( 101) facet. The applicability of the periodic defect structure of Nb layers of uniform thickness on the facetted surface is exemplarily demonstrated for the study of the vortex dynamics of type II superconductors.     

From Bulk to Monolayer MoS2: Evolution of Raman Scattering

Molybdenum disulfide (MoS₂) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of and peaks vary monotonously with the layer number of ultrathin MoS₂ flakes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS₂ decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS₂. The asymmetric Raman peak at 454 cm^?1, which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS₂, is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ( ). Our findings suggest a clear evolution of the coupling between electronic transition and phonon when MoS₂ is scaled down from three‐ to two‐dimensional geometry.     

Growth,Cathodoluminescence and Field Emission of ZnS Tetrapod Tree‐like Heterostructures

We report the growth mechanism, cathodoluminescence and field emission of dual phase ZnS tetrapod tree‐like heterostructures. This novel heterostructures consist of two phases: zinc blende for the trunk and hexagonal wurtzite for the branch. Direct evidence is presented for the polarity induced growth of tetrapod ZnS trees through high‐resolution electron microscopy study, demonstrating that Zn‐terminated ZnS (111)/(0001) polar surface is chemically active and S‐terminated ( )/(000 ) polar surface is inert in the growth of tetrapod ZnS trees. Two strong UV emissions centered at 3.68 and 3.83 eV have been observed at room temperature, which are attributed to the bandgap emissions from the zinc blende trunk and hexagonal wurtzite branch, indicating that such structures can be used as unique electromechanical and optoelectronic components in potential light sources, laser and light emitting display devices. In addition, the low turn‐on field (2.66 Vµm⁻¹), high field‐enhancement factor (over 2600), large current density (over 30 mAcm⁻² at a macroscopic field of 4.33 Vµm⁻¹) and small fluctuation (∼1%) further indicate the availability of ZnS tetrapod tree‐like heterostructures for field emission panel display. This excellent field‐emission property is attributed to the specific crystallographic feature with high crystallinity and cone‐shape patterned branch with nanometer‐sized tips. Such a structure may optimize the FE properties and make a promising field emitter.     

Ionic Iridium(III) Complexes with Bulky Side Groups for Use in Light Emitting Cells: Reduction of Concentration Quenching

Here, the photophysics and performance of single‐layer light emitting cells (LECs) based on a series of ionic cyclometalated Ir(III) complexes of formulae and where ppy, bpy, and phen are 2‐phenylpyridine, substituted bipyridine and substituted phenanthroline ligands, respectively, are reported. Substitution at the N?N ligand has little effect on the emitting metal‐ligand to ligand charge‐transfer (MLLCT) states and functionalization at this site of the complex leads to only modest changes in emission color. For the more bulky complexes the increase in intermolecular separation leads to reduced exciton migration, which in turn, by suppressing concentration quenching, significantly increases the lifetime of the excited state. On the other hand, the larger intermolecular separation induced by bulky ligands reduces the charge carrier mobility of the materials, which means that higher bias fields are needed to drive the diodes. A brightness of ca. 1000 cd m^?2 at 3 V is obtained for complex 5, which demonstrates a beneficial effect of bulky substituents.     

Operational results of grid‐connected photovoltaic system with different inverter's sizing factors (ISF)

This paper presents operational results of a 11·07 kWp grid‐connected photovoltaic system. This system is made up by eight groups with different relationships between the inverter's rated power and the PV generator's maximum power (P / P) . The obtained results led to the verification that the different studied relationships, P / P between 55 and 102%, do not affect significantly the final yields (Y_F). Copyright © 2006 John Wiley & Sons, Ltd.     

On the electro-optic properties of single crystals of sodium,potassium and rubidium acid phthalates

The linear electro-optic (Pockels) effect in a series of alkali metal acid phthalate crystals has been studied. Single electro-optic coefficients r and r for sodium (NaAP), potassium (KAP) and rubidium (RbAP) acid phthalates have been measured by employing the modified Mach–Zehnder interferometric technique. The best electro-optic crystal in this series is RbAP with r = 9.10 × 10^?12 m V^?1, r = 3.05 × 10^?12 m V^?1 and a sizable figure of merit for electro-optic phase retardation, comparable with that of KDP. The dispersion properties of the electro-optic coefficients for KAP are discussed in detail.     

ZnO Hierarchical Micro/Nanoarchitectures: Solvothermal Synthesis and Structurally Enhanced Photocatalytic Performance

A novel ZnO hierarchical micro/nanoarchitecture is fabricated by a facile solvothermal approach in an aqueous solution of ethylenediamine (EDA). This complex architecture is of a core/shell structure, composed of dense nanosheet‐built networks that stand on a hexagonal‐pyramid‐like microcrystal (core part). The ZnO hexagonal micropyramid has external surfaces that consist of a basal plane (000 ) and lateral planes {0 11}. The nanosheets are a uniform thickness of about 10 nm and have a single‐crystal structure with sheet‐planar surfaces as {2 0} planes. These nanosheets interlace and overlap each other with an angle of 60° or 120°, and assemble into a discernible net‐ or grid‐like morphology (about 100 nm in grid‐size) on the micropyramid, which shows a high specific surface area (185.6 m² g^?1). Such a ZnO micro/nanoarchitecture is new in the family of ZnO nanostructures. Its formation depends on the concentration of the EDA solution as well as on the type of zinc source. A two‐step sequential growth model is proposed based on observations from a time‐dependent morphology evolution process. Importantly, such structured ZnO has shown a strong structure‐induced enhancement of photocatalytic performance and has exhibited a much better photocatalytic property and durability for the photodegradation of methyl orange than that of other nanostructured ZnO, such as the powders of nanoparticles, nanosheets, and nanoneedles. This is mainly attributed to its higher surface‐to‐volume ratio and stability against aggregation. This work not only gives insight into understanding the hierarchical growth behaviour of complex ZnO micro/nanoarchitectures in a solution‐phase synthetic system, but also provides an efficient route to enhance the photocatalytic performance of ZnO, which could also be extended to other catalysts, such as the inherently excellent TiO₂, if they are of the same hierarchical micro/nanoarchitecture with an open and porous nanostructured surface layer.     

Atomic‐Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers

The optical conductance of monolayer graphene is defined solely by the fine structure constant, α = (where e is the electron charge, is Dirac's constant and c is the speed of light). The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero‐gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, use of atomic layer graphene as saturable absorber in a mode‐locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the graphene thickness. These results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth, and wideband tunability.     

Engineering of Facets,Band Structure,and Gas‐Sensing Properties of Hierarchical Sn2+‐Doped SnO2 Nanostructures

Hierarchical SnO₂ nanoflowers, assembled from single‐crystalline SnO₂ nanosheets with high‐index (11$ \bar 3 $ ) and (10$ \bar 2 $ ) facets exposed, are prepared via a hydrothermal method using sodium fluoride as the morphology controlling agent. Formation of the 3D hierarchical architecture comprising of SnO₂ nanosheets takes place via Ostwald ripening mechanism, with the growth orientation regulated by the adsorbate fluorine species. The use of Sn(II) precursor results in simultaneous Sn²⁺ self‐doping of SnO₂ nanoflowers with tunable oxygen vacancy bandgap states. The latter further results in the shifting of semiconductor Fermi levels and extended absorption in the visible spectral range. With increased density of states of Sn²⁺‐doped SnO₂ selective facets, this gives rise to enhanced interfacial charge transfer, that is, high sensing response, and selectivity towards oxidizing NO₂ gas. The better gas sensing performance over (10$ \bar 2 $ ) compared to (11$ \bar 3 $ ) faceted SnO₂ nanostructures is elucidated by surface energetic calculations and Bader analyses. This work highlights the possibility of simultaneous engineering of surface energetics and electronic properties of SnO₂ based materials.     

Nanowire Structural Evolution from Fe3O4 to ϵ‐Fe2O3

The ?‐Fe₂O₃ phase is commonly considered an intermediate phase during thermal treatment of maghemite (γ‐Fe₂O₃) to hematite (α‐Fe₂O₃). The routine method of synthesis for ?‐Fe₂O₃ crystals uses γ‐Fe₂O₃ as the source material and requires dispersion of γ‐Fe₂O₃ into silica, and the obtained ?‐Fe₂O₃ particle size is rather limited, typically under 200 nm. In this paper, by using a pulsed laser deposition method and Fe₃O₄ powder as a source material, the synthesis of not only one‐dimensional Fe₃O₄ nanowires but also high‐yield ?‐Fe₂O₃ nanowires is reported for the first time. A detailed transmission electron microscopy (TEM) study shows that the nanowires of pure magnetite grow along [111] and <211> directions, although some stacking faults and twins exist. However, magnetite nanowires growing along the <110> direction are found in every instance to accompany a new phase, ?‐Fe₂O₃, with some micrometer‐sized wires even fully transferring to ?‐Fe₂O₃ along the fixed structural orientation relationship, (001) ∥ (111), [010] ∥ <110>. Contrary to generally accepted ideas regarding epsilon phase formation, there is no indication of γ‐Fe₂O₃ formation during the synthesis process; the phase transition may be described as being from Fe₃O₄ to ?‐Fe₂O₃, then to α‐Fe₂O₃. The detailed structural evolution process has been revealed by using TEM. 120° rotation domain boundaries and antiphase boundaries are also frequently observed in the ?‐Fe₂O₃ nanowires. The observed ?‐Fe₂O₃ is fundamentally important for understanding the magnetic properties of the nanowires.     

Nano‐ and Mesoscale Structure of Na$_{1 \over 2}$Bi$_{1 \over 2}$TiO3: A TEM Perspective

The room‐temperature structure of Na Bi TiO₃ (NBT) ceramics was studied using several transmission electron microscopy (TEM) techniques. High‐angle annular dark field imaging in a scanning TEM confirmed an essentially random distribution of Bi and Na, while electron diffraction revealed significant disorder of the octahedral rotations and cation displacements. Diffraction‐contrast dark‐field and Fourier‐filtered high‐resolution TEM images were used to develop a model that reconciles local and average octahedral tilting in NBT. According to this model, NBT consists of nanoscale twin domains which exhibit a^?a^?c⁺ tilting. The coherence length of the in‐phase tilting, however, is limited to a few unit cells and is at least one order of magnitude shorter than that of anti‐phase tilting. Assemblages of such nanodomains are proposed to exhibit an average a^?a^?c^? tilt system. Diffuse sheets of intensity in electron diffraction patterns are attributed to local cation displacements correlated along both 〈111〉 and 〈100〉 chains and suggest partial polar ordering of these displacements. Overall, the TEM data indicate significant chemical, cation‐displacement and tilt disorder of the NBT structure at the nano and mesoscale and support the premise that the Cc symmetry recently proposed from powder diffraction refinements is an averaged “best fit” cell.     

Providing and finding k‐road‐coverage efficiently in wireless sensor networks

In this paper, we study k‐road‐coverage problems in wireless sensor networks (WSNs). Assume there is a 2‐dimensional area Ω with a given road map = (V,E) where E contains all road segments and V consists of all intersection points on Ω. The first question we study is about ‘sensor deployment’, i.e., how to deploy a minimum number of sensor nodes on Ω such that each path (each road segment) on is k‐covered when all sensor nodes have the same sensing range. When sensors can only be deployed in a set of discrete locations, we propose an efficient method with the approximation ratio 6 + ϵ for the special case where k = 1 and O(k) generally. If sensors can be deployed in arbitrary locations, we propose an efficient method with the approximation ratio 24 + ϵ when k = 1 and O(k) generally. The second question we study is about ‘path query’, i.e., how to find the k‐covered path or k‐support path connecting any given source/destination pair of points on the road map . Basically, given any source/destination pair of points S and D, we present two algorithms which can efficiently find a k‐covered path connecting S and D and a k‐supported path connecting S and D, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Multi‐regional query scheduling in wireless sensor networks with minimum latency

Query scheduling as one of the most important technologies used in query processing has been widely studied recently. In this paper, we investigate the Minimum Latency Multi‐Regional Query Scheduling (ML‐MRQS) problem in wireless Sensor Networks (WSNs), which aims to generate a scheduling plan with minimum latency under a more practical query model called Multi‐Regional Query (MRQ). An MRQ targets at interested data from multiple regions of a WSN, where each region is a subarea. Because the ML‐MRQS problem is NP‐hard, we propose a heuristic scheduling algorithm Multi‐Regional Query Scheduling Algorithm (MRQSA) to solve this problem. Theoretical analysis shows that the latency of MRQSA is upper bounded by 23A + B + C for an MRQ with m query regions , where is the maximum latency for non‐overlapped regions, is the maximum latency for overlapped regions, and is the accumulated latency for data transmission from the accessing nodes to the sink. Simulation results show that MRQSA reduces latency by 42.7% to 51.63% with respect to different number of query regions, network density, region size, and interference/transmission range compared with C‐DCQS, while guaranteeing energy efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

Cadmium(II) (8‐Hydroxyquinoline) Chloride Nanowires: Synthesis,Characterization and Glucose‐Sensing Application

Luminescent cadmium(II) (8‐hydroxyquinoline) chloride (CdqCl) complex nanowires are synthesized via a sonochemical solution route. The results of X‐ray photoelectron spectroscopy, energy dispersive X‐ray analysis, infrared spectroscopy, elemental analysis (EA), and atomic absorption spectroscopy demonstrate that the chemical composition of the product is Cd(C₉H₆NO)Cl. Transmission electron microscopy and scanning electron microscopy images show that the CdqCl product is wire‐like in structure, with a diameter of approximately 50 nm and an approximate length of 2–4 µm. The morphology and composition of the product can be transformed from Cdq₂ micrometer‐scaled flakes to CdqCl nanowires by increasing the ratio of CdCl₂/q. A new fluorescent sensing strategy for detecting H₂O₂ and glucose is developed and is based on the combination of the luminescent nanowires and the biocatalytic growth of Au nanoparticles. The quenching effects of Au nanoparticles and on the fluorescence of CdqCl nanowires are investigated. The dominant factor for the fluorescence quenching of CdqCl nanowires is that the Stern–Volmer quenching constant of Au nanoparticles is larger than that of .     

Strain Mapping at the Atomic Scale in Highly Mismatched Heterointerfaces

A complete characterization of dislocation network in a highly mismatched interface with high spatial resolution has been performed. The interface between InN quantum dots and a (0001) GaN substrate contains three noninteracting sets of regularly‐spaced misfit dislocations lying along <110> directions. The network has a “Star of David” form, with each star bounding a hexagonal region which is pseudomorphic. These misfit dislocations form a threading dislocation network at the island edges due to free surface forces.     

Simultaneous Electrical and Thermoelectric Parameter Retrieval via Two Terminal Current–Voltage Measurements on Individual ZnO Nanowires

The thermoelectric parameters, in particular the thermal conductivity and dimensionless figure of merit ZT, of ZnO nanowires, are estimated via two terminal current–voltage measurements. The measurements are carried out in situ in a transmission electron microscope and negative differential conductance is observed on individually suspended ZnO nanowires. From the low bias region of the current–voltage curve, the electrical parameters, including carrier concentration and mobility, are obtained by fitting the experimental data using a metal–semiconductor–metal model. The thermal conductivity is extracted from the high bias region of the same current–voltage curve using a self‐consistent method, which combines the self‐heating thermal conduction and electrical transport properties of ZnO nanowires. It is shown that the thermal conductivity of ZnO nanowires is suppressed significantly in comparison with that of bulk ZnO, which is attributed to the strong surface scattering of phonons. The thermal conductivity is also found to decrease more steeply than the expected $ {1 \mathord{\left/{\vphantom {1 T}} \right.} T} $ trend, but does obey a $ {1 \mathord{\left/{\vphantom {1 {\left({\alpha T + \beta T^2} \right)}}} \right. } {\left({\alpha T + \beta T^2} \right)}} $ relation; this is shown to result from four‐phonon processes at high temperatures. The dimensionless figure of merit ZT is determined to be about 0.1 at 970 K. Finally, the thermoelectric properties of individual ZnO nanowires are also discussed, indicating that ZnO nanowires are promising high temperature thermoelectric materials.     

The capacity of multi‐channel multi‐interface wireless networks with multi‐packet reception and directional antenna

The capacity of wireless networks can be improved by the use of multi‐channel multi‐interface (MCMI), multi‐packet reception (MPR), and directional antenna (DA). MCMI can provide the concurrent transmission in different channels for each node with multiple interfaces; MPR offers an increased number of concurrent transmissions on the same channel; DA can be more effective than omni‐DA by reducing interference and increasing spatial reuse. This paper explores the capacity of wireless networks that integrate MCMI, MPR, and DA technologies. Unlike some previous research, which only employed one or two of the aforementioned technologies to improve the capacity of networks, this research captures the capacity bound of the networks with all the aforementioned technologies in arbitrary and random wireless networks. The research shows that such three‐technology networks can achieve at most capacity gain in arbitrary networks and capacity gain in random networks compared with MCMI wireless networks without DA and MPR. The paper also explored and analyzed the impact on the network capacity gain with different , θ, and k‐MPR ability. Copyright © 2012 John Wiley & Sons, Ltd.     

Electrical Transport Properties of Large,Individual NiCo2O4 Nanoplates

Understanding the electrical transport properties of individual semiconductor nanostructures is crucial to advancing their practical applications in high‐performance nanodevices. Large‐sized individual nanostructures with smooth surfaces are preferred because they can be easily made into nanodevices using conventional photolithography procedures rather than having to rely on costly and complex electron‐beam lithography techniques. In this study, micrometer‐sized NiCo₂O₄ nanoplates are successfully prepared from their corresponding hydroxide precursor using a quasi‐topotactic transformation. The Co/Ni atomic arrangement shows no changes during the transformation from the rhombohedral LDH precursor (space group R$ \bar 3 $ m) to the cubic NiCo₂O₄ spinel (space group Fd $ \bar 3 $ m), and the nanoplate retains its initial morphology during the conversion process. In particular, electrical transport within an individual NiCo₂O₄ nanoplate is further investigated. The mechanisms of electrical conduction in the low‐temperature range (T < 100 K) can be explained in terms of the Mott's variable‐range hopping model. At high temperatures (T > 100 K), both the variable‐range hopping and nearest‐neighbor hopping mechanisms contribute to the electrical transport properties of the NiCo₂O₄ nanoplate. These initial results will be useful to understanding the fundamental characteristics of these nanoplates and to designing functional nanodevices from NiCo₂O₄ nanostructures.     

An Efficient Parallel Algorithm for Merging in the Postal Model

Given two sorted lists A = (a0, a1 ^…, al-1) and B = (b0, b1, ^…, bm-¹), we are to merge these two lists into a sorted list C = (c0, c1, ^…, cn-1), where n = l + m. Since this is a fundamental problem useful to solve many problems such as sorting and graph problems, there have been many efficient parallel algorithms for this problem. But these algorithms cannot be performed efficiently in the postal model since the communication latency …, which is of prime importance in this model, is not needed to be considered for those algorithms. Hence, in this paper we propose an efficient merge algorithm in this model that runs in time by using a new property of the bitonic sequence which is crucial to our algorithm. We also show that our algorithm is near-optimal by proving that the lower bound of this problem in the postal model is , where      

Novel Solid Acid Catalysts: Sulfonic Acid Group‐Functionalized Mesostructured Polymers

Novel solid acid catalysts have been prepared from Fudan University (FDU)‐type mesoporous polymers with the Ia d and P6mm mesostructures through a carefully controlled sulfonation procedure. Various techniques have been adopted to characterize throughout their structures, porosity, acidity as well as the information related to the sulfonic acid groups. The sulfonic acid group‐functionalized mesopolymers prove to be efficient heterogeneous catalysts in the reactions such as liquid‐phase Beckmann rearrangement of cyclohexanone oxime and condensation of ethylene glycol with the aldehydes having different molecular sizes.