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.     

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 .     

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.     

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.     

New Time‐Domain Decoder for Correcting both Errors and Erasures of Reed‐Solomon Codes

A new time‐domain decoder for Reed‐Solomon (RS) codes is proposed. Because this decoder can correct both errors and erasures without computing the erasure locator, errata locator, or errata evaluator polynomials, the computational complexity can be substantially reduced. Herein, to demonstrate this benefit, complexity comparisons between the proposed decoder and the Truong‐Jeng‐Hung and Lin‐Costello decoders are presented. These comparisons show that the proposed decoder consistently has lower computational requirements when correcting all combinations of ν errors and μ erasures than both of the related decoders under the condition of , where d_min denotes the minimum distance of the RS code. Finally, the (255, 223) and (63, 39) RS codes are used as examples for complexity comparisons under the upper bounded condition of . To decode the two RS codes, the new decoder can save about 40% additions and multiplications when as compared with the two related decoders. Furthermore, it can also save 50% of the required inverses for .     

Structural Origins of Silk Piezoelectricity

Uniaxially oriented, piezoelectric silk films are prepared by a two‐step method that involves first air drying aqueous, regenerated silk fibroin solutions into films, and then drawing the silk films to a desired draw ratio. The utility of two different drawing techniques—zone drawing and water‐immersion drawing—is investigated for processing the silk for piezoelectric studies. Silk films zone drawn to a ratio of λ 5 2.7 display relatively high dynamic shear piezoelectric coefficients of d₁₄ 5 –1.5 pC N²¹, corresponding to an increase in d₁₄ of over two orders of magnitude due to film drawing. A strong correlation is observed between the increase in silk II, β‐sheet content with increasing draw ratio as measured by FTIR spectroscopy (C_b $ \propto $ e^2.5λ), the concomitant increasing degree of orientation of β‐sheet crystals detected via wide‐angle X‐ray diffraction (full width half maximum (FWHM) = 0.22° for λ = 2.7), and the improvement in silk piezoelectricity (d₁₄ $ \propto $ e^2.4λ). Water‐immersion drawing leads to a predominantly silk I structure with a low degree of orientation (FWHM 5 75°) and a much weaker piezoelectric response compared to zone drawing. Similarly, increasing the β‐sheet crystallinity without inducing crystal alignment, e.g., by methanol treatment, does not result in a significant enhancement of silk piezoelectricity. Overall, a combination of a high degree of silk II, β‐sheet crystallinity and crystalline orientation are prerequisites for a strong piezoelectric effect in silk. Further understanding of the structural origins of silk piezoelectricity provides important options for future biotechnological and biomedical applications of this protein.     

Inter‐annual variability,risk and confidence intervals associated with propagation statistics. Part II: parameterization and applications

This set of two companion papers aims at providing a model for the inter‐annual variability of earth‐space propagation statistics and for the inherent risk and CIs. In part I, it was proposed to model the yearly variance σ² of empirical complementary CDFs so that where is the variance of estimation, the inter‐annual climatic variance and p the long‐term probability. Particularly, an analytical formulation of was derived and parameterized from synthetic rain attenuation data. Considering the statistical framework developed in part I, this part II is specifically devoted to the parameterization of the variance of estimation from experimental data of rain attenuation and rainfall rate. Then, a methodology to model and parameterize worldwide the inter‐annual climatic variance is presented. The model of yearly variance of the empirical complementary CDFs is finally compared against yearly experimental variances derived from data collected worldwide. The knowledge of this variability is very useful for system design as it allows the risk on a required availability and associated with a given propagation margin to be quantified. Copyright © 2013 John Wiley & Sons, Ltd.     

Accurate Tunable‐Gain 1/x Circuit Using Capacitor Charging Scheme

This paper proposes an accurate tunable‐gain 1/x circuit. The output voltage of the 1/x circuit is generated by using a capacitor charging time that is inversely proportional to the input voltage. The output voltage is independent of the process parameters, because the output voltage depends on the ratios of the capacitors, resistors, and current mirrors. The voltage gain of the 1/x circuit is tuned by a 10‐bit digital code. The 1/x circuit was fabricated using a 0.18 μm CMOS process. Its core area is , and it consumes 278 μW at and . Its error is within 1.7% at to 1 V.     

Strong Spin‐Lattice Coupling Through Oxygen Octahedral Rotation in Divalent Europium Perovskites

First‐principles calculations reveal that in divalent europium perovskites EuMO₃ (M = Ti, Zr, and Hf), antiferromagnetic superexchange interactions via nd states of the B‐site M cations (n = 3, 4, and 5, respectively) are enhanced by rotations of the MO₆ octahedra. The octahedral rotations involved in a structural change from cubic $ Pm{\bar 3}m $ to orthorhombic Pbnm structures not only reduce energy gaps between the Eu 4f and M nd bands but also point the M nd orbitals at the Eu sites, leading to a significant overlap between the M nd and Eu 4f orbitals. These results reveal that the octahedral rotations are indispensable for antiferromagnetic ordering observed for EuZrO₃ and EuHfO₃, and put these perovskites into a class of materials exhibiting a novel type of strong coupling between their magnetism and octahedral rotations.     

Efficient Computation of Eta Pairing over Binary Field with Vandermonde Matrix

This paper provides an efficient algorithm for computing the η_T pairing on supersingular elliptic curves over fields of characteristic two. In the proposed algorithm, we deploy a modified multiplication in using the Vandermonde matrix. For , the proposed multiplication method computes β · F · G instead of F · G with some because β is eliminated by the final exponentiation of the η_T pairing computation. The proposed multiplication method asymptotically requires only 7 multiplications in as n → ∞, while the cost of the previously fastest Karatsuba method is 9 multiplications in . Consequently, the cost of the η_T pairing computation is reduced by 14.3%.     

Surface Micromachined Pressure Sensor with Internal Substrate Vacuum Cavity

A surface micromachined piezoresistive pressure sensor with a novel internal substrate vacuum cavity was developed. The proposed internal substrate vacuum cavity is formed by selectively etching the silicon substrate under the sensing diaphragm. For the proposed cavity, a new fabrication process including a cavity side‐wall formation, dry isotropic cavity etching, and cavity vacuum sealing was developed that is fully CMOS‐compatible, low in cost, and reliable. The sensitivity of the fabricated pressure sensors is 2.80 mV/V/bar and 3.46 mV/V/bar for a rectangular and circular diaphragm, respectively, and the linearity is and for these two diaphragms. The temperature coefficient of the resistances of the polysilicon piezoresistor is to per degree of Celsius according to the sensor design. The temperature coefficient of the offset voltage at 1 atm is 0.0019 mV and 0.0051 mV per degree of Celsius for a rectangular and circular diaphragm, respectively. The measurement results demonstrate the feasibility of the proposed pressure sensor as a highly sensitive circuit‐integrated pressure sensor.     

Influence of a Single Grain Boundary on Domain Wall Motion in Ferroelectrics

Epitaxial tetragonal 425 and 611 nm thick Pb(Zr_0.45Ti_0.55)O₃ (PZT) films are deposited by pulsed laser deposition on SrRuO₃‐coated (100) SrTiO₃ 24° tilt angle bicrystal substrates to create a single PZT grain boundary with a well‐defined orientation. On either side of the bicrystal boundary, the films show square hysteresis loops and have dielectric permittivities of 456 and 576, with loss tangents of 0.010 and 0.015, respectively. Using piezoresponse force microscopy (PFM), a decrease in the nonlinear piezoelectric response is observed in the vicinity (720–820 nm) of the grain boundary. This region represents the width over which the extrinsic contributions to the piezoelectric response (e.g., those associated with the domain density/configuration and/or the domain wall mobility) are influenced by the presence of the grain boundary. Transmission electron microscope (TEM) images collected near and far from the grain boundary indicate a strong preference for (101)/(01) type domain walls at the grain boundary, whereas (011)/(01) and (101)/(01) are observed away from this region. It is proposed that the elastic strain field at the grain boundary interacts with the ferro‐electric/elastic domain structure, stabilizing (101)/(01) rather than (011)/(01) type domain walls, which inhibits domain wall motion under applied field and decreases non‐linearity.     

Circularly Polarized Dielectric‐Loaded Antennas: Current Technology and Future Challenges

In the last few years, dielectric loaded antennas (DLAs) have emerged as a viable solution for high‐gain reception at microwave frequencies for handheld devices such as satellite phones, radios, and global positioning systems. This article compares the performance, cost, and volumetric efficiencies of the two dominant designs, namely the dielectrically loaded quadrifilar‐helix and microstrip patch antennas. The current and future material requirements for DLAs are discussed and an example is given of a recently developed castable glass ceramic based on BiNbO₄, which is suitable in terms of properties and glass formability for the single‐step fabrication of net‐shape antenna cores.

     

Real‐Time Locomotion Mode Recognition Employing Correlation Feature Analysis Using EMG Pattern

This paper presents a new locomotion mode recognition method based on a transformed correlation feature analysis using an electromyography (EMG) pattern. Each movement is recognized using six weighted subcorrelation filters, which are applied to the correlation feature analysis through the use of six time‐domain features. The proposed method has a high recognition rate because it reflects the importance of the different features according to the movements and thereby enables one to recognize real‐time EMG patterns, owing to the rapid execution of the correlation feature analysis. The experiment results show that the discriminating power of the proposed method is 85.89% when walking on a level surface, 96.47% when going up stairs, and 96.37% when going down stairs for given normal movement data. This makes its accuracy and stability better than that found for the principal component analysis and linear discriminant analysis methods.     

Supercapacitive Properties of Composite Electrode Consisting of Activated Carbon and Di(1‐aminopyrene)quinone

Di(1‐aminopyrene)quinone (DAQ) as a quinone‐containing conducting additive is synthesized from a solution reaction of 1‐aminopyrene and hydroquinone. To utilize the conductive property of DAQ and its compatibility with activated carbon, a composite electrode for a supercapacitor is also prepared by blending activated carbon and DAQ (3:1 w/w), and its supercapacitive properties are characterized based on the cyclic voltammetry and galvanostatic charge/discharge. As a result, the composite electrode adopting DAQ exhibits superior electrochemical properties, such as a higher specific capacitance of up to at , an excellent high‐rate capability of up to , and a higher cycling stability with a capacitance retention ratio of 82% for the 1,000th cycle.     

An approximate stochastic analysis of the packet‐pair probing technique for available bandwidth estimation

The packet‐pair probing algorithm for network‐bandwidth estimation is examined and an approximate model is proposed for predicting its behaviour. The model replaces the Poisson arrival process with a Gaussian distribution and resolves the queue‐size profile into two separate components: A transient component representing the buffer‐emptying process and an equilibrium component representing the return to steady‐state behaviour. Comparison with discrete‐event simulation results shows that the model is accurate in single‐hop paths when utilization is ?70% when the cross‐traffic packets are ?½ the size of the probe packets. When extended to two‐hop paths, the model remains accurate for smaller cross‐traffic packets ($\leq\frac{1}{10}-\frac{1}{5}The packet‐pair probing algorithm for network‐bandwidth estimation is examined and an approximate model is proposed for predicting its behaviour. The model replaces the Poisson arrival process with a Gaussian distribution and resolves the queue‐size profile into two separate components: A transient component representing the buffer‐emptying process and an equilibrium component representing the return to steady‐state behaviour. Comparison with discrete‐event simulation results shows that the model is accurate in single‐hop paths when utilization is ?70% when the cross‐traffic packets are ?½ the size of the probe packets. When extended to two‐hop paths, the model remains accurate for smaller cross‐traffic packets ($\leq\frac{1}{10}-\frac{1}{5}$ the probe‐packet size). Copyright © 2008 John Wiley & Sons, Ltd.     

Defect‐Related Emissions and Magnetization Properties of ZnO Nanorods

A clear correlation between defect‐related emissions and the magnetization of ZnO nanorods synthesized by a one‐step aqueous chemical method is demonstrated. The relative contribution of the emission bands arising from various types of defects is determined and found to be linked with the size of the nanorods and annealing conditions. When the size of the nanorods and the annealing temperature are increased, the magnetization of pure ZnO nanorods decreases with the reduction of a defect‐related band originating from singly charged oxygen vacancies ($V_{\rm o}^ +$ ). With a sufficient increase of annealing temperature (at 900 °C), the nanorods show diamagnetic behavior. Combining with the electron paramagnetic resonance results, a direct link between the magnetization and the relative occupancy of the singly charged oxygen vacancies present on the surface of ZnO nanorods is established.     

Generation and Detection of Terahertz Waves Using Low‐Temperature‐Grown GaAs with an Annealing Process

In this letter, we present low‐temperature grown GaAs (LTG‐GaAs)‐based photoconductive antennas for the generation and detection of terahertz (THz) waves. The growth of LTG‐GaAs and the annealing temperatures are systematically discussed based on the material characteristics and the properties of THz emission and detection. The optimum annealing temperature depends on the growth temperature, which turns out to be 540°C to 580°C for the initial excess arsenic density of to .     

Non‐resonant Element in Slotted Ground Plane for Multiband Antenna Operation

New ways of achieving small, multiband, multifunctional, and standard solutions for mobile handset antennas are demanded in the current wireless market. A non‐resonant element of , a matching network, and a slotted ground plane are proposed to satisfy mobile market demands that require multiband operation and small antenna solutions. The main advantage of the proposed design is that with only one non‐resonant element of considerably small size (0.015λ, 900 MHz), the handset is capable of providing operation at mobile bands.     

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.