Weighted average Q-factor calculation for single port filter-antenna measurement

Filter-antenna has many advantages like no need of match network, low insertion loss, ease of design, low cost and light weight. However, practical implementation of filter-antenna requires a precise value of \(Q\) -factor. Filter-antenna is a single device, handling radiating and filtering properties simultaneously, making it difficult to extract \(Q\) -factor for such device. Moreover, filter-antenna has single port and designer is required to calculate \(Q\) -factor from single port. As reported in literature that the available methods for calculation of \(Q\) -factor from single port seem inaccurate. This paper presents a novel \(Q\) -factor calculation method that outperforms existing methods for almost every case of filter-antenna. Experimental results verify the superior performance of proposed method relative existing methods.     

Effects of substrate orientation on opto-electronic properties in self-assembled InAs/GaAs quantum dots

Electronic structure and optical transition characteristics in (100), (110), and (111) oriented InAs/GaAs quantum dots (containing \({\sim }2\) million atoms) were studied using a combination of valence force-field molecular mechanics and 20-band \(sp^{3}d^{5}s^{*}\) atomistic tight-binding framework. These quantum dots are promising candidates for non-traditional applications such as spintronics, quantum cryptography and quantum computation, but suffer from the deleterious effects of various internal fields. Here, the dependence of strain and polarization fields on the substrate orientation is reported and discussed. It is found that, compared to the (100) and (110) oriented counterparts, quantum dots grown on the (111) oriented substrate exhibit a smaller splitting (non-degeneracy) in the excited \(P\) states and enhanced isotropy in the interband optical emission characteristics.     

Improving sequencing by tunneling with multiplexing and cross-correlations

Sequencing by tunneling is a next-generation approach to read single-base information using electronic tunneling transverse to the single-stranded DNA (ssDNA) backbone while the latter is translocated through a narrow channel. The original idea considered a single pair of electrodes to read out the current and distinguish the bases [1, 2]. Here, we propose an improvement to the original sequencing by tunneling method, in which \(N\) pairs of electrodes are built in series along a synthetic nanochannel. While the ssDNA is forced through the channel using a longitudinal field it passes by each pair of electrodes for long enough time to gather a minimum of \(m\) tunneling current measurements, where \(m\) is determined by the level of sequencing error desired. Each current time series for each nucleobase is then cross-correlated together, from which the DNA bases can be distinguished. We show using random sampling of data from classical molecular dynamics, that indeed the sequencing error is significantly reduced as the number of pairs of electrodes, \(N\) , increases. Compared to the sequencing ability of a single pair of electrodes, cross-correlating \(N\) pairs of electrodes exponentially improves this sequencing ability due to the approximate log-normal nature of the tunneling current probability distributions. We have also used the Fenton–Wilkinson approximation to analytically describe the mean and variance of the cross-correlations that are used to distinguish the DNA bases. The method we suggest is particularly useful when the measurement bandwidth is limited, allowing a smaller electrode gap residence time while still promising to consistently identify the DNA bases correctly.     

Computational analysis of the contributions to the piezoelectric coefficient e_{33} in ZnO nanowires: first-principles calculations

We investigated the piezoelectric coefficient, \(e_{33} \) , of ZnO nanowires, subdividing it into an ionic term, \(e_{33}^{\text {ion}} \) , and an electronic term, \(e_{33}^{\text {el}} \) , and calculated the effects of different diameters on its value using ab initio density functional theory calculations. The \(e_{33}^{\text {ion}} \) term was found to be dominant, with the innermost (outermost) atoms in the nanowires making the largest (smallest) contribution to the term. Moreover, the density of states (DOS) and projected DOS data revealed that the DOS tends to increase at the valence band maximum in the case of the outermost atoms, where the O \(2p\) and Zn \(3d\) orbital peaks increase in magnitude, resulting in hybridization and a decrease in bond length.     

Boundary condition at the junction

When modeling a 2-d quantum network by a 1-d quantum graph one usually substitutes the 2-d vertex domains by the point-wise junctions with appropriate boundary conditions imposed on the boundary values $ \vec{\psi}(a) = (\psi_1 (a),\, \psi_2 (a),\, \psi_3 (a), \ldots \psi_n (a) ),\,\, \vec{\psi}' = (\psi'_1 (a),\, \psi'_2 (a),\, \psi'_3 (a), \ldots \psi'_n (a) ) $ of the wave-function on the leads $ \omega_1,\, \omega_2,\ldots \omega_n$ at the junction a. In particular Datta proposed parametrization of the boundary condition, for symmetric T-junction, by some orthogonal 1-d projection $ P_0: R_n \to R_n $ $$ P_0^{\bot}\,\,\vec{\psi}(a) = 0,\quad P_0\,\,\vec{\psi}'(a) = 0. $$ We consider an arbitrary junction, $ n \geq 3$ , of 2-d leads attached to a 2-d vertex domain $\Omega_{int}$ , in case, when there exist a resonance eigenvalue $\lambda_0 = 2 m^* E_f \,\hbar^{-2}$ of the Schrödinger operator $L_{int}$ . We derive, from the first principles, energy-dependent boundary conditions for thin, quasi-1-d, network, and obtain from it, in the limit of zero temperature, Datta-type boundary condition, interpreting the projection P ₀ in terms of the resonance eigenfunction $\psi_0: L_{int} \psi_0 = \lambda_0 \psi_0$ and geometry of the leads.     

Effects of acceptor dopants on the enhanced piezoelectric potential of ZnO nanowires: limiting free charge-carrier density through neutralizing donors

The piezoelectric potential of ZnO can be enhanced using acceptor dopants to neutralize the donor concentrations. In this study, unintentional n-type conductivity is assessed through modeling ZnO nanowires where the activation process of donors \((N_d^+)\) is given with a Fermi level \((E_F)\) close to the conduction band and followed by the introduction of an acceptor dopant \((N_a^-)\) in order to allow \(E_F\) to be within the optimum range of \(1\le E_F \le 3.2 \hbox { eV}\) , which corresponds to the maximum piezoelectric potential calculated. The finite element method simulation reveals that the maximal range of ZnO piezoelectric potential can be obtained due to the intrinsic characteristics of the ZnO nanowire transformed using acceptor dopants, which implies that the limitations on the free-charge carriers (i.e. free-carrier depletion) could reduce the screening effects on the piezoelectric potential. Furthermore, the difference \({\vert }N_d^+ -N_a^- {\vert }\) is calculated to approach zero near the mid-gap and the energy band structure, which deviates from the normal flat line within the optimal range of \(1\le E_F \le 3.2 \hbox { eV}\) under the external stress imposed.     

A novel SOI MESFET by \uppi -shaped gate for improving the driving current

This paper introduces a novel silicon-on-insulator (SOI) metal–semiconductor field-effect transistor (MESFET) with \(\uppi \) -shaped gate with triple workfunction ( \(\uppi \) -SOI MESFET) to improve the DC and radio frequency characteristics. The DC and radio frequency characteristics of the proposed structure are analyzed by 2-D ATLAS international simulator and compared with a conventional SOI MESFET (C-SOI MESFET). The simulated results show that the proposed SOI MESFET has excellent effect on the breakdown voltage and the driving current. The breakdown voltage of the \(\uppi \) -SOI MESFET structure gets 54 % enhancement compared with that of the C-SOI MESFET structure and also the driving current of the \(\uppi \) -SOI MESFET structure gets 66.66 % enhancement compared with that of the C-SOI MESFET structure. Other main characteristics such as maximum output power density, maximum oscillation frequency and maximum available gain have been evaluated and improved in the proposed structure.     

An impact of bias and structure dependent L_\mathrm{SD} variation on the performance of GaN HEMTs based biosensor

In this paper, we discussed the effect of different bias and structures in relation to S-D distance variation on the device electrical and expected biosensing performance. Devices with source to drain length ( \(L_{SD})\) variations from 3.5, 5.0, 8.0, 14.0, 26.0 to \(52~\upmu \) m were simulated at low and high bias voltages. Different structures having gate recess and finger variations were investigated for the complete range of \(L_{SD}\) variations. Small and very large \(L_{SD}\) variations in non-recessed structure showed good values of drain current \((I_{ds})\) and transconductances \((g_{m})\) at different low and high bias voltages respectively. Therefore expected response time and sensitivity could be improved by choosing a proper bias condition for different biosensing \(L_{SD}\) lengths. A gate recess structure showed better \(g_{m}\) values at low bias conditions for all \(L_{SD}\) lengths. However, \(I_{ds}\) degraded for these structures and hence the expected response time. The non-recessed structure variations in terms of number of fingers and gate width did not change the effective trends in \(L_{SD}\) variation.     

Electronic transport across a layered structure of Fe/\upbeta -poly vinylidene fluoride/Fe using DFT calculations

Quantum electronic transport across a \(\upbeta \) -poly(vinylidene fluoride) ( \(\upbeta \) -PVDF) ferroelectric barrier structured between two ferromagnetic Fe layers is explored using DFT calculations. The multifunctional junction is organized in capacitor like structure, as FM (ferromagnetic metal)/FE (ferroelectric)/FM to understand the mechanism of electron transfer by controlling the spin polarization of the electrodes and also the ferroelectric polarization of the barrier. These studies are carried on a single bcc layer of Fe atoms in both the electrodes and two monomers of PVDF is utilized as a barrier. We investigated the dependence of total density of states (DOS), projected DOS, transmission coefficient and I–V characteristics on applied bias voltage using SIESTA & TRANSIESTA package.     

Superhigh frequency magnetic properties and electromagnetic attenuation applications for \mathrm { BaMn_{x}Ti_{x}Fe_{12-2x}O_{19}} composites

Superhigh frequency microwave magnetic properties and attenuation characteristics at K and Ka bands have been studied for M-type barium hexaferrite $\mathrm {BaMn_{x}Ti_{x}Fe_{12-2x}O_{19}}$ ( $x=0.4-1.0$ ) composites with c-axis anisotropy. The complex permeability of the composites has resonancelike dispersion with relatively large imaginary permeability $\mu ''_{\max }$ of 1.1 and high resonance frequency $f_{R}$ of 20–28 GHz. $f_{R}$ is determined by the anisotropy fields $H_{a}$ . The composites show good attenuation properties with percentage bandwidth of 30–40 % and small thickness of 0.08–0.1 cm at K and Ka bands, thus being potential candidates for electromagnetic attenuation applications.     

Electrical properties of rutile-type relaxor ferroelectric-like Fe0.9W0.05TiMO6 (M = Ta,Nb) ceramics

Electrical properties of rutile-type $\mathrm {Fe}_{0.9}{\kern 1pt} \mathrm {W}_{0.05}\\\mathrm {TiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ ceramics were measured at and above room temperature and the results are compared with those gained previously on rutile-type relaxor ferroelectrics $\mathrm {FeTiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ . The aliovalent ${\rm W}^{6+}$ cationsin the current compounds might change the suggested polar nanodomains, giving rise to very high dielectric constant $\epsilon (\omega )$ , and further electrical quantities can possibly shed additional light on the nature of the mechanism leading to extraordinary values in $\epsilon (\omega )$ . In part similar electrical data were established such as very high $\epsilon (\omega )$ but also different results were noted. Apart from $\epsilon (\omega )$ , the electrical response was analysed by measuring losses, dissipation factor $\tan \delta $ , DC conductivity $\sigma _{DC}$ and AC conductivity $\sigma _{AC}(\omega )$ using impedance spectroscopy, and thermopower; the results are discussed in conjunction with literature data. The role of grain boundaries and sample-electrode processes was investigated in particular with respect to the sample capacitance. Eventual microstructural local inhomogeneities were checked by means of ⁵⁷Fe Mössbauer spectroscopy. For both compounds, the temperature dependence of bulk $\sigma _{DC}$ showed Arrhenius behaviour with activation energy ${E_{A}}\sim $ 0.35 eV and $\sigma _{DC}$ (295 K) $\sim 5\times 10^{-5} \Omega ^{-1}\text{cm}^{-1}$ ; grain boundaries exhibited slightly higher ${E_{A}}$ but the value of $\sigma _{DC}$ was a factor of up to $\sim 10$ lower at all temperatures. From $\sigma _{AC}(\omega )$ data, a power law frequency dependence of grain boundary conductivity was derived. Relaxation processes were established from loss and $\tan \delta $ data. The thermopower is negative and varies weakly with temperature, pointing to long-range charge transfer by a hopping-type mechanism of electron polarons.     

First-principles versus semi-empirical modeling of global and local electronic transport properties of graphene nanopore-based sensors for DNA sequencing

Using first-principles quantum transport simulations, based on the nonequilibrium Green function formalism combined with density functional theory (NEGF+DFT), we examine changes in the total and local electronic currents within the plane of graphene nanoribbon with zigzag edges (ZGNR) hosting a nanopore which are induced by inserting a DNA nucleobase into the pore. We find a sizable change of the zero-bias conductance of two-terminal ZGNR + nanopore device after the nucleobase is placed into the most probable position (according to molecular dynamics trajectories) inside the nanopore of a small diameter \(D=1.2\) nm. Although such effect decreases as the nanopore size is increased to \(D=1.7\) nm, the contrast between currents in ZGNR + nanopore and ZGNR + nanopore + nucleobase systems can be enhanced by applying a small bias voltage \(V_b \lesssim 0.1\) V. This is explained microscopically as being due to DNA nucleobase-induced modification of spatial profile of local current density around the edges of ZGNR. We repeat the same analysis using NEGF combined with self-consistent charge density functional tight-binding (NEGF+SCC-DFTB) or self-consistent extended Hückel (NEGF+SC-EH) semi-empirical methodologies. The large discrepancy we find between the results obtained from NEGF+DFT vs. those obtained from NEGF+SCC-DFTB or NEGF+SC-EH approaches could be of great importance when selecting proper computational algorithms for in silico design of optimal nanoelectronic sensors for rapid DNA sequencing.     

Effect of annealing temperature on the electrostrictive properties of 0.94(Na0.5Bi0.5)TiO3-0.06BaTiO3 thin films

0.94(Na_0.5Bi_0.5)TiO₃-0.06BaTiO₃ (NBT-BT6) thin films were fabricated by metal-organic decomposition (MOD) at the different annealing temperatures. Based on the electrostrictive effect and converse piezoelectric effect, the phenomenological approach is provided to characterize the electrostrictive properties of the perovskite relaxor, and it is used to determine the effective electrostriction coefficients $ Q_{33}^{\mathrm{eff}} $ and electrostrictive strains $ {S_3} $ of NBT-BT6 thin films annealed at the range of 650?C800?°C. After the microstructure, ferroelectric, dielectric and piezoelectric properties of the thin films were determined, the maximum values of $ Q_{33}^{\mathrm{eff}} $ and $ {S_3} $ of NBT-BT6 thin film annealed at 750?°C are respectively determined as 0.0289?m⁴/C² and 0.26?% under the bipolar driving field of 391?kV/cm. They are strongly influenced by annealing temperature due to the bismuth evaporation and crystallization of perovskite phase, and the enhanced electrostrictive properties could make NBT-based thin film a promising candidate to the design and application of stacked actuators, microangle-adjusting devices, and oil pressure servo valves.     

Band-gap properties of 2D photonic crystal made by silica matrix doped with magnetic nanoparticles

We present a study of the band gaps of a variety of two-dimensional photonic crystal made by \(\text {SiO}_{2}/\text {ZrO}_{2}\) and \(\text {SiO}_{2}/\text {TiO}_{2}\) matrix doped with magnetic nanoparticles as function of the filling factor parameter for different refractive index contrasts. The results obtained are useful for better designs of magneto photonic crystal devices.     

1 Tb/s high quality factor NAND gate using quantum-dot semiconductor optical amplifiers in Mach–Zehnder interferometer

The performance of all-optical logic NAND gate realized by employing quantum-dot semiconductor optical amplifiers (QD-SOAs)-based Mach–Zehnder interferometers (MZI) is numerically simulated. Boolean NAND operation is achieved by a series combination of properly configured and driven QD-SOAs-MZIs. The theoretical study is carried out by taking into account the effect of amplified spontaneous emission. The dependence of the output \(Q\) -factor on data signals and QD-SOA parameters is investigated and discussed. The obtained results indicate that the NAND gate is capable of operating at 1 Tb/s with high output quality factor ( \(Q\) -factor) provided that these parameters are properly optimized.     

Calculating the steady-state polarizations of quantum cellular automata (QCA) circuits

We present on the use of well-known stochastic methods for computing the steady-state polarizations of quantum cellular automata (QCA) circuits. Typically, a Boltzmann distribution, which requires the exploration of the complete configuration space of an \(N\) -cell QCA circuit, is used to compute the \(2^N\) steady-states of the QCA circuit. However, the exponential growth in states as the circuit size grows makes computing the Boltzmann distribution infeasible for large circuits. Thus, we approximate the Boltzmann distribution of a QCA circuit by conducting a partial exploration of the complete configuration space by means of a Monte Carlo method, simulated annealing, and a genetic algorithm. The approximated Boltzmann distribution from each method was able to compute the steady-state polarizations with a very high degree of accuracy, with the simulated annealing algorithm producing the best results.     

Theoretical designing of novel heterocyclic azo dyes for dye sensitized solar cells

Since, the organic dyes that harness sunlight are generally considered as the heart of the dye sensitized solar cells (DSSC), the present study was carried out with the aim to design heterocyclic azo dyes that can be potentially used in DSSC application. Hereby, the analysis based on density functional theory (DFT) and time-dependent DFT calculations of the geometries, electronic structures and absorption spectra of the dyes before and after binding to titanium oxide \((\hbox {TiO}_{2})\) were carried out and investigated in detail. The data obtained from these analyses were then used to determine the open-circuit photovoltage \((\hbox {V}_\mathrm{OC})\) , and to measure the important parameters such as the light harvesting efficiency (LHE) and the electron injection efficiency associated with the short-circuit photocurrent density \((\hbox {J}_\mathrm{SC})\) . Our investigation reveals that all dyes showed absorbance in the visible region (469–521 nm) with high oscillator strength \((f)\) (1.076–1.564) and LHE (0.9176–0.973). Moreover, we found that the dyes after binding to titanium oxide displayed slightly red-shifted absorption (475–527 nm) with improved oscillator strength \((f)\) (1.121–1.664) and LHE (0.921–0.979). In addition, all dyes showed high \(\hbox {V}_\mathrm{OC}\) (1.068–2.232 eV) and high driving force for the electron injection, thus leading to the larger \(\hbox {J}_\mathrm{SC}\) . Our findings indicate that the heterocyclic azo dyes investigated in the current study can display better light to power conversion efficiency if used in the DSSC system, where the origin or their better performance can be attributed to the high \(\hbox {J}_\mathrm{SC}\) and \(\hbox {V}_\mathrm{OC}\) values found for these potential dyes. Based on the detailed study and investigation, we believe that the theoretical criteria used in the present study can be employed as an initial screening tool not merely to assess the properties of other organic dyes, but also to potentially design the organic azo dyes for their potential application in the DSSC systems.     

Poisson–Nernst–Planck model for an ionic transistor based on a semiconductor membrane

In this paper we developed a Poisson–Nernst–Planck model of an ionic current flowing through a nanopore in a layered solid-state membrane made of a single highly-doped \(n\) -Si layer sandwiched between two thick oxide layers which we call the ionic transistor. We studied this layered membrane for a range of source-drain voltages while keeping the gate (the semiconductor membrane) voltage fixed at a certain value, which was later varied too. We find that for this ionic transistor to be effective in controling the ion fluxes through the nanopore, the gate voltage must be kept relatively large. Another solution could be to increase the surface negative charge on the membrane or to replace the outer oxide layers with the semiconductor material, such as the \(p\) -Si material. The developed model can be applied to study ionic filtering and separation properties of membranes of different composition and nanopore geometries.     

Oxygen incorporation in porous thin films of strontium doped lanthanum ferrite

Electrical conductivity relaxation measurements were carried out on thin films of (La_0.6Sr_0.4)_0.99 FeO_3????? deposited on MgO (100) substrates by pulsed laser deposition in order to determine the surface exchange coefficient, k _Ex, of the oxygen incorporation process in the temperature range 550?C700°C. The composition of the films was verified using wavelength dispersive x-ray and Rutherford backscattering spectroscopy. Scanning electron microscopy showed small triangular crystallites with the largest dimension 80 nm and the smallest dimension 10 nm. X-ray diffraction showed a cubic perovskite structure and significant texturing. At a constant temperature, k _Ex was found to be a function only of the final $p_{\mathrm{O_{2}}}$ of the $p_{\mathrm{O_{2}}}$ -changes the sample was subjected to during conductivity relaxation experiments, confirming that the magnitude of the exchange coefficient was not influenced by changes in ionic defect concentrations. The k _Ex-values determined for these thin films were significantly lower than for bulk samples. A value of 3.6 × 10^???6 cm s^???1 was obtained at 702°C and a final $p_{\mathrm{O_{2}}}$ of 0.048 atm, approximately a factor of six lower than that obtained for bulk samples. An activation energy of 282 ± 20 kJ mol^???1 was found for the surface exchange coefficient at $p_{\mathrm{O_{2}}}$ =?0.048 atm. Possible reasons for the reduced magnitude of k _Ex are discussed including the role of thermal history in influencing surface morphology and chemistry.     

A fast \vec{k}\cdot\vec{p} solver for hole inversion layers with an efficient 2D \vec{k} -space discretization

An efficient discretization of the 2 dimensional (2D) $\vec{k}$ -space and parallelization of the $\vec{k}\cdot \vec{p}$ solver for hole inversion layers is proposed. The 6×6 $\vec{k}\cdot \vec{p}$ Schrödinger equation is solved in parallel for only a small number of grid points in the 2D $\vec{k}$ -space. The subband energy and the generalized probability density function for an arbitrary in-plane wave vector are determined by interpolation based on the resultant eigen states. The fast approach results in accurate inversion densities and also low-field mobilities of holes in unstrained and uniaxially stressed Si channel double-gate MOS structures.