Low loss broadband polarization independent fishnet negative index metamaterial at 40 GHz

We present a polarization independent fishnet negative index metamaterial at 40 GHz. The structure is investigated theoretically using finite element method simulations and experimentally by measuring the amplitude and phase of the S-parameters. The experimental setup for free space measurements of both transmission and reflection is hereby introduced. The internal properties are thereafter retrieved and show the double-negative behavior of the structure. This negative index metamaterial exhibits very high transmission (?0.13 dB), low reflection (?33.1 dB) and a high figure of merit (FOM = |Re(n)/Im(n)| = 42), where the real part of the refractive index is nearly ?1 (Re(n) = ?0.93) at 40 GHz.     

High spatial resolution imaging in a clipping Kagomé lattice photonic crystal

In this paper, a two-dimensional Kagomé lattice photonic crystal (PC) made of GaAs (ɛ = 12.96) dielectric rods in air is considered. This Kagomé lattice PC has an effective refractive index n_eff = −1 at a low normalized frequency ω = 0.187 × 2πc/a. Imaging quality and the capability of the super-resolution of two point sources are studied for a superlens made of such PC structure. In order to achieve a high quality image and to improve the spatial super-resolution of two sources, a clipping Kagomé lattice PC is designed. Results simulated by finite-difference time-domain method show that imaging quality and super-resolution of two sources can be enhanced greatly as the perfect Kagomé lattice structure are superseded by the clipping Kagomé lattice structure. Coupled-mode theory analysis gives an explanation why the clipping structure is superior to the perfect one for both the imaging quality and the capability of the super-resolution of two sources. This clipping Kagomé lattice PC structure would be widely used in optical devices and integrated circuit.     

Electrical properties of a nanoparticle-networked film

We have developed a new technique for the preparation of conducting nanoparticle films, which consisted of gold nanoparticles networked with binding molecules such as butanethiol, pentanehtiol, hexanethiol, and heptanethiol, on a polystyrene substrate through a one-step straightforward procedure. The film conductivity became significantly higher with a decrease in the alkylchain length, depending on the number of carbon atoms (n) of the binder molecule between adjacent Au nanoparticles, in which it was changed from an insulator (n > 10) to conductor (n = 4). The film resistivity (2.1 μΩ cm) prepared using butanethiol corresponds to that of planar gold (1.3 μΩ cm).     

Electrical and structural properties of stepped,partially reconstructed Au(11n) surfaces in HClO4 and H2SO4 electrolytes

We have studied the interface capacitance and the voltammograms of Au(11n) (n = 5, 7, 11, 17) and of Au(100) electrodes in 5 mM HClO₄ and 5 mM H₂SO₄ after immersion into the electrolyte solution at ?0.4 V versus a saturated calomel electrode. The minima of the capacitance curves measured in positive sweeps continuously shift towards positive potentials as function of 1/n. All voltammograms, even that of Au(1 1 5), display peaks that are characteristic for lifting of surface reconstructions, albeit at different potentials. Thus, all vicinal surfaces appear to have at least sections that allow reconstruction. This inference is consistent with STM-profiles of an Au(1 1 9) surface which displays a wide range of local inclination angles corresponding to local (11n)-orientations with 3.5 < n < ∞. A numerical analysis of the voltammograms shows the existence of three different ranges of transition potentials for the lifting of the reconstruction. The transition potentials are assigned to three different structures of the reconstructed phase as either observed by experiment or proposed by theory.     

Current–voltage characteristics of Al/Rhodamine-101/n-GaAs structures in the wide temperature range

The forward bias current–voltage (I–V) characteristics of Al/Rhodamine-101/n-GaAs structure have been investigated in the temperature range of 80–350 K. It has been seen a decrease in ideality factor (n) and an increase in the zero-bias barrier height (BH) with an increase in temperature. It has been seen that such a behavior of the BH and n obey Gaussian distribution of the BHs due to the BH inhomogeneities at the metal/semiconductor (MS) interface. The very strong temperature dependence of ideality factor of the structure has shown that the current processes occurring in the organic layer at the MS interface would be a possible candidate such as trap-charge limited conduction in determining the current at the intermediate and high bias regimes. Furthermore, it has been show that the Rh101 can be used to vary effective BHs for the metal/GaAs Schottky diodes. As a result, it has been determined that the BH value for conventional Al/n-GaAs SBD is remarkably higher than our own values of 0.68 eV obtained for the Al/Rh101/n-GaAs at 290 K.     

Tunable characteristics of one dimensional magnetic photonic crystal composed with single-negative materials

In this paper, we present the study of dispersion and transmittance characteristics of one dimensional magnetic photonic crystal composed by single negative indexed materials. For this structure, we have considered magnetic negative (MNG) with ? = 1 and μ < 0 and electric negative (ENG) with ? < 0 and μ = 4. We used simple transfer matrix method and Bloch's theorem for its analytical explanations. Analyzing transmittance characteristics of the proposed structure, we obtain the tunneling of certain frequency range where as the dispersion characteristic shows total forbidden for the same range for TM mode. The tunable property is found inside the band structure due to zero-?, zero-μ and magnetic behavior of the material. To identify zero-? and zero-μ of the structure, we have calculated the dispersion and the transmittance of the magnetic structure of MNG–ENG on different angles of incidence and thickness of layers.     

Inorganic polymer phosphazene disulfide as cathode material for rechargeable lithium batteries

Novel inorganic network polymer phosphazene disulfide [(NPS₂)₃]_n was synthesized by a solution cross-link method. IR and element content analysis confirmed the polymer's molecular structure. The polymer has an average particle size of d_0.5 = 7.7 μm and the specific surface area is 57.4 m² g^− 1. TG/DTA analysis showed that [(NPS₂)₃]_n underwent a decomposition reaction from 200 to 300 °C. When used as cathode material in lithium batteries, its initial discharge capacity was 459.1 mAh g^− 1, which is almost 93.5% of theoretical specific capacity (490.9 mAh g^− 1). After 30 charge–discharge cycles, the discharge capacity of [(NPS₂)₃]_n stabilized at approximately 400.1 mAh g^− 1 which revealed an excellent cyclic ability. Therefore [(NPS₂)₃]_n is of great potential as cathode material for secondary lithium batteries.     

Design optimization of porous fibrous material for maximizing absorption of sounds under set frequency bands

In this paper, a methodology is proposed for designing porous fibrous material with optimal sound absorption under set frequency bands. The material is assumed to have a rigid frame and a hexagonal arrangement of fibers, and the analytical model derived by Johnson, Champoux and Allard (“JCA model”) is used to investigate the influences of the micro-structural parameters (fiber radius r and gap w) on sound absorption performance, and the macro-acoustic parameters used in JCA model is determined via finite element analysis for the hexagonal micro-structure. Moreover, a mathematical model is constructed to obtain the optimized micro-structure design, with fiber radius and gap as design parameters and average absorption performance of the porous fibrous material under set frequency band as target. Utilizing the constructed optimization model, the microstructure parameters are derived with optimal sound absorption under low frequency (20 ⩽ f < 500 Hz), medium frequency (500 ⩽ f < 2000 Hz) and high frequency (2000 ⩽ f < 15,000 Hz), respectively. On top of that, for a given thickness of porous fibrous material layer, the analytical relationship between fiber radius and optimal porosity under set frequency bands is constructed.     

Effects of fluoride treatment on phosphoric acid-etching in primary teeth: An AFM observation

The aim of this study was to examine the effect of fluoride application on 37% phosphoric acid-etching by atomic force microscopy (AFM) in primary tooth samples based on a clinical protocol used in a pediatric dental hospital. Enamel samples were prepared from 36 exfoliated and non-carious primary teeth. Primary tooth samples were randomly assigned to one of the four groups based on the timing of acid-etching with 37% phosphoric acid after an acidulated phosphate fluoride (APF) pre-treatment. Group 1 received no fluoride application, Group 2 was pre-treated with fluoride and then received acid-etching 2 weeks later. One week separated the fluoride treatment and the acid-etching in Group 3, while Group 4 received acid-etching immediately after the fluoride treatment. The vestibular enamel surfaces of each primary tooth sample were scanned in air at a resolution of 512 × 512 pixels and a scan speed of 0.8 line/s. On the enamel surfaces of the primary teeth after APF pre-treatment, debris were observed although the teeth were smoother than they were prior to APF. As a result, it was concluded that APF treatment is responsible for decreased primary tooth surface roughness. The enamel surfaces etched for 20 s showed that acid-etching was effective not only in removing scratches and debris, but also for evaluating enamel rod characteristics. Primary tooth enamel surfaces after etching showed minute structures caused by the decreased hydroxyapatite nanoparticle space, compared to those before etching. Also, acid-etching showed significantly increased roughness effects (p < 0.0001, n = 9). Finally, as more time elapsed after APF pre-treatment, the roughness was decreased to a lesser degree (p = 0.005, n = 9). We suggest that primary teeth etching 2 weeks after APF pre-treatment used clinically in pediatric hospitals may be effective to obtain properly etched enamel surfaces.     

Effects of trench oxide and field plates on the breakdown voltage of SOI LDMOSFET

To improve the breakdown voltage, we propose a SOI-based LDMOSFET with a trench structure in the drift region. Due to the trench oxide and underneath boron implanted layer, the surface electric field in the drift region effectively reduced. These effects resulted in the increment of breakdown voltage for the trenched LDMOS more than 100 V compared with the conventional device. However, the specific on-resistance, which has a trade-off relationship, is slightly increased. In addition to the trench oxide on the device performance, we also investigated the influence of n− drift to n+ drain junction spacing on the off-state breakdown voltage. The measured breakdown voltages were varied more than 50 V with different n− to n+ design spaces and achieved a maximum value at L_DA = 2.0 μm. Moreover, the influence of field plate on the breakdown voltage of trench LDMOSFET was investigated. It is found that the optimum drain field plate over the field oxide is 8 μm.     

A comparative study of the Ruddlesden-Popper series,Lan+1NinO3n+1 (n = 1, 2 and 3), for solid-oxide fuel-cell cathode applications

A comparative investigation of the much-studied La₂NiO_4+δ (n = 1) phase and the higher-order Ruddlesden-Popper phases, La_n+1Ni_nO_3n+1 (n = 2 and 3), has been undertaken to determine their suitability as cathodes for intermediate-temperature solid-oxide fuel cells. As n is increased, a structural phase transition is observed from tetragonal I4/mmm in the hyperstoichiometric La₂NiO_4.15 (n = 1) to orthorhombic Fmmm in the oxygen-deficient phases, La₃Ni₂O_6.95 (n = 2) and La₄Ni₃O_9.78 (n = 3). High temperature d.c. electrical conductivity measurements reveal a dramatic increase in overall values from n = 1, 2 to 3 with metallic behavior observed for La₄Ni₃O_9.78. Impedance spectroscopy measurements on symmetrical cells with La_0.9Sr_0.10Ga_0.80Mg_0.20O_3−δ (LSGM-9182) as the electrolyte show a systematic improvement in the electrode performance from La₂NiO_4.15 to La₄Ni₃O_9.78 with ∼ 1 Ω cm² observed at 1073 K for the latter. Long-term thermal stability tests show no impurity formation when La₃Ni₂O_6.95 and La₄Ni₃O_9.78 are heated at 1123 K for 2 weeks in air, in contrast to previously reported data for La₂NiO_4.15. The relative thermal expansion coefficients of La₃Ni₂O_6.95 and La₄Ni₃O_9.78 were found to be similar at ∼ 13.2 × 10^− 6 K^− 1 from 348 K to 1173 K in air compared to 13.8 × 10^− 6 K^− 1 for La₂NiO_4.15. Taken together, these observations suggest favourable use for the n = 2 and 3 phases as cathodes in intermediate-temperature solid-oxide fuel cells when compared to the much-studied La₂NiO_4+δ (n = 1) phase.     

AlH3 between 65 and 110 GPa: Implications of electronic band and phonon structures

A first-principles density-functional-theory method has been used to reinvestigate the mechanical and dynamical stability of the metallic phase of AlH₃ between 65 and 110 GPa. The electronic properties and phonon dynamics as a function of pressure are also explored. We find electron–phonon superconductivity in the cubic Pm-3n structure with critical temperature T_c = 37 K at 70 GPa which decreases rapidly with the increase of pressure. Further unlike a previously calculated T_c-value of 24 K at 110 GPa, we do not find any superconductivity of significance at this pressure which is consistent with experimental observation.     

Low-bias,high-temperature operation of an InAs–InGaAs quantum-dot infrared photodetector with peak-detection wavelength of 11.7 μm

We report on a low-bias InAs–InGaAs quantum-dot (QD) infrared photodetector (QDIP) with operating temperature of 150 K. Longwave-infrared (LWIR) detection at the peak wavelength of 11.7 μm was achieved. Peak specific photodetectivity D¹ of 1.7 × 10⁹ and 9.0 × 10⁷ cm Hz^1/2/W were obtained at the operating temperature T of 78 K and 150 K, respectively. A large photoresponsivity of 8.3 A/W and high photoconductive gain of 1100 were demonstrated at a low-bias voltage of V = 0.5 V at T = 150 K. The low-bias and high-temperature performance demonstration based on InAs–GaAs material systems indicates that the QDIP technology is promising for LWIR sensing and imaging.     

The first cytogenetic characterization of the poisonous black widow spider Latrodectus gr. curacaviensis from Brazil,with chromosomal review of the family Theridiidae (Arachnida,Araneae)

In this paper we present, for the first time, cytogenetical data on Latrodectus gr. curacaviensis (Theridiidae) from Brazil, as well as the first data on meiosis and sex chromosome system of this genus. Testes were submitted to colchicine, hypotonic, and fixation treatment, and chromosomal preparations were stained with Giemsa solution. The analysis showed 2n = 26 telo/acrocentric chromosomes in spermatogonial metaphases. Metaphase I exhibited 12 autosomal bivalents and two sex chromosome univalents (12II + X₁X₂). All bivalents revealed one terminal chiasma. Metaphases II confirmed the sex chromosome system, showing 12 autosomes or 12 autosomes plus two X chromosomes, respectively. Male karyotype prevailing in theridiids is formed by 2n = 22 chromosomes, including sex chromosome system X₁X₂ in all species. The Latrodectus species of the geometricus clade analyzed until now showed smaller diploid number (2n♀ = 16 and 2n♀ = 18) than the species of the mactans clade (2n♀ = 24 and 2n♀ = 26). Thus, according to the chromosome number, the examined Latrodectus species seems to be related to the mactans clade.     

Compact WDM demultiplexer for seven channels in photonic crystal

We demonstrate a new device concept for wavelength division demultiplexing based on planar photonic crystal waveguides. The filtering of wavelength channels is realized by shifting the cutoff frequency of the fundamental photonic bandgap mode in consecutive sections of the waveguide. The shift is realized by modifying the size of the border holes.The proposed demultiplexer has an area equal to (16.5 μm × 6.5 μm) and thus it is verified that this structure is very small and can be integrated easily into optical integrated circuits with nanophotonic technologies. The output wavelengths of designed structure can be tuned for communication applications, around 1550 nm. The wavelengths of demultiplexer channels are λ₁ = 1.590 μm, λ₂ = 1.566 μm, λ₃ = 1.525 μm, λ₄ = 1.510 μm, λ₅ = 1.484 μm, λ₆ = 1.450 μm, λ₇ = 1.400 μm respectively. Designs offering improvement of number of the separate wavelengths (seven), miniaturization of the structure (107.25 μm²) is our aim in this work.In our structure, we consider that the 2D triangular lattice photonic crystal is composed of air holes surrounded by dielectric. Its parameters are: radius of holes (r = 0.130 μm), lattice constant (a = 0.380 μm), and index of membrane (n = 3.181:InP). The numerical model used to simulate the structure of the demultiplexer is based on the finite difference time domain (FDTD).     

Low loss propagation in slow light photonic crystal waveguides at group indices up to 60

We have designed slow light photonic crystal waveguides operating in a low loss and constant dispersion window of Δλ = 2 nm around λ = 1565 nm with a group index of n_g = 60. We experimentally demonstrate a relatively low propagation loss, of 130 dB/cm, for waveguides up to 800 μm in length. This result is particularly remarkable given that the waveguides were written on an electron-beam lithography tool with a writefield of 100 μm that exhibits stitching errors of typically 10–50 nm. We reduced the impact of these stitching errors by introducing “slow–fast–slow” mode conversion interfaces and show that these interfaces reduce the loss from 320 dB/cm to 130 dB/cm at n_g = 60. This significant improvement highlights the importance of the slow–fast–slow method and shows that high performance slow light waveguides can be realised with lengths much longer than the writing field of a given e-beam lithography tool.     

Intercomparison of Fluctuation Induced Conductivity of Cu0.5Tl0.5Ba2Can−1CunO2n+4−y (n = 2, 3, 4) superconductor thin films

An intercomparison of Fluctuation Induced Conductivity (FIC) of Cu_0.5Tl_0.5Ba₂Ca_n?1Cu_nO_2n+4?y (n = 2, 3, 4) [CuTl-12(n ? 1)n] superconductor thin films is given. We tried to find any correlation between the critical temperature and the parameters extracted from the excess conductivity data i.e. cross-over temperature, pseudogap temperature and fluctuation amplitudes. We found that the critical temperature seems to depend on the fluctuation amplitude; greater the fluctuation amplitude higher is the critical temperature.     

Layer optimization in wight organic light emitting diodes (WOLEDs) to reduce the portion of guided waves in ITO/Glass interface

In this paper, our main attempt was to reduce Total Internal Reflection (TIR) happening at Indium Tin Oxide (ITO, n_ito = 1.8 + 0.01i) and Glass (n_glass = 1.51) interface, which is due to ITO's higher index in comparison with Glass's, that makes light guided in ITO layer, 50% of generated light in Wight Organic Light Emitting Diodes (WOLED) are trapped in ITO layer; here we tried to reduce this portion of trapped light by implying 12-fold quasi-photonic crystal to the mentioned interface. With some gentle changes in 12-fold's structure we could reduce TIR in this interface to less than 9%. Also, far field results before and after adding the structure to WOLED were studied, which represents suitability of using this structure for lighting applications.     

Resonances in the final Rydberg state population of multiply charged ions ArVIII,KrVIII, and XeVIII escaping solid surfaces

The appearance of resonances (pronounced maxima at n_A = n_res) in the probability distributions for the population of the Rydberg state (n_A, l_A, m_A) of multiply charged ions (Z ? 1) escaping solid surfaces at intermediate velocities (v ≈ 1 a.u.) is discussed. Within the framework of the time-symmetrized two-state vector model, in which the state of a single active electron is described by two wave functions Ψ₁ and Ψ₂, the resonances are explained by means of an electron tunneling in the very vicinity of the ion–surface potential barrier top. To include this specific feature of electron transitions into the model, the appropriate etalon equation method is used in the calculation of the function Ψ₁. We consider the ions ArVIII, KrVIII, and XeVIII with the same core charges Z = 8 a.u., but with different core polarizations. The effect of the ionic core polarization is associated with the function Ψ₂. The population probabilities for n_A ≈ n_res are complemental to those obtained recently for n_A < n_res, and in sufficiently good agreement with available beam-foil experimental data. The pronounced resonances in the final population distributions are recognized only in the case of ArVIII ion and for the lower values of the solid work function (argon anomaly).     

First-principles investigations of low-coverage Ca-induced reconstructions on the Si(001) surface

Using the pseudopotential method and the local density approximation of density functional theory we have investigated the stability, atomic geometry, and electronic states for low-coverage Ca adsorbates on the Si(001) surface within the (2 × n) reconstructions with n = 2, 3, 4, 5. Our total energy calculations suggest that the (2 × 4) phase represents the most energetically stable structure with the Ca coverage of 0.375 ML. Within this structural model, each Ca atom is found to form a bridge with the inner two Si–Si dimers. The inner Si–Si dimers become elongated and symmetric (untilted). The band structure calculation indicates that the system is semiconducting with a small band gap. Significant amount of charge transfer from the Ca atoms to neighbouring Si atoms has been concluded by analysing the electronic charge density and simulation of scanning tunnelling microscopy images. The highest occupied and lowest unoccupied electronic states are found to arise from the inner and outer Si–Si dimer components, respectively.