Leaky Behavior Research Articles

Investigations on structural, Mossbauer, dielectric, and ferroelectric properties of La doped barium hexaferrite

La substituted Barium hexaferrite, Ba(1-x)La(x)Fe12O19, (x = 0, 0.1, 0.15, 0.20) was synthesized using ball milling followed by heat treatment. Rietveld analysis of X-Ray diffraction patterns reveals the formation of a single-phase magnetoplumbite structure of barium hexaferrite for all prepared samples. Morphological studies using FESEM shows the formation of hexagonal plate-like grains with different grain size, and the average grain size decreases with La doping. Elemental analysis using EDS confirms that the observed elemental composition for all the samples is within the expected range within the experimental error. Density measurements observed that porosity decreases up to La content x = 0.15 and then slightly increases for x = 0.20. Mössbauer spectroscopy studies reveal no formation of Fe2+ ions but delocalization of electrons after La doping. There is not much variation in the hyperfine structure with La doping. It is observed from the dielectric spectroscopy that the highest dielectric constant and low loss are observed for La content x = 0.20. The P-E loop of the pristine sample shows small polarisation but leaky behavior, whereas La substitution shows both leaky and resistor circuit-type behavior but large polarization.

Enhanced magnetic and ferroelectric properties of La[formula omitted]M[formula omitted]FeO[formula omitted] (M = Dy and Y) nanoparticles: A comparison of A-site doping

The room temperature magnetic hysteresis (M-H) loops reveal ferromagnetic-like behavior in an antiferromagnetically ordered LaFeO3 (LFO) material system synthesized by the sol–gel method. The maximum magnetization (Mmax) for the undoped sample annealed at 800 °C is 1.08 emu/g, whereas, with the same annealing, materials that are Dy and Y doped (25%) exhibit four times higher magnetization. It is interesting to note that non-magnetic ion Y3+ doped LFO has the same magnetization as magnetic ion Dy3+ doped nanomaterials. Reduction of particle and crystallite size plays a significant role in enhancing the net magnetization of doped materials. While the magnetization in Y-doped materials is attributed to the anti-symmetric exchange interaction (AEI) through spin canting, the greater magnetization for Dy doped samples is related to the AEI as well as inherent magnetic moment of the Dy3+ ion. The quantified tilting angle (Fe–O–Fe) is higher and the bond length (Fe–O) is smaller for Y-doped compounds compared to Dy-doped samples. X-ray photoelectron spectroscopy for oxygen 1s spectra shows that the relative area of O1− is higher in Dy-doped LFO than Y-doped sample. Ferroelectric hysteresis loops exhibit spontaneous electric polarization with reduced leakage current for Y-doped LFO, while other compounds show leaky behavior.

Single- and Multilayered Perovskite Thin Films for Photovoltaic Applications.

Organic–inorganic lead halide perovskites materials have emerged as an innovative candidate in the development of optoelectronic and photovoltaic devices, due to their appealing electrical and optical properties. Herein, mix halide single-layer (~95 nm) and multilayer (average layer ~87 nm) CH3NH3PbIBr2 thinfilms were grown by a one-step spin coating method. In this study, both films maintained their perovskite structure along with the appearance of a pseudo-cubic phase of (200) at 30.16°. Single-layer and multilayer CH3NH3PbIBr2 thinfilms displayed leaky ferroelectric behavior, and multilayered thinfilm showed a leakage current of ~5.06 × 10−6 A and resistivity of ~1.60 × 106 Ω.cm for the applied electric field of 50 kV/cm. However, optical analysis revealed that the absorption peak of multilayered perovskite is sharper than a single layer in the visible region rather than infrared (IR) and near-infrared region (NIR). The band gap of the thinfilms was measured by Tauc plot, giving the values of 2.07 eV and 1.81 eV for single-layer and multilayer thinfilms, respectively. The structural analysis has also been performed by Fourier transform infrared spectroscopy (FTIR). Moreover, the fabricated CH3NH3PbIBr2 as an absorber layer for photoelectric cell demonstrated a power conversion efficiency of 7.87% and fill factor of 72%. Reported electrical, optical and photoelectric efficiency-based results suggest that engineered samples are suitable candidates for utilization in optoelectronic and photovoltaic devices.

Recognizing Spatiotemporal Features by a Neuromorphic Network with Highly Reliable Ferroelectric Capacitors on Epitaxial GeSn Film.

Epitaxial GeSn (epi-GeSn) shows the capability to form ferroelectric capacitors (FeCAPs) with a higher remanent polarization (Pr) than epi-Ge. With the interface engineering by a high-k AlON, the reliability of the epi-GeSn-based FeCAPs is enhanced. Using the highly reliable FeCAP in series with a resistor as the synapse and axon, a simplified neuromorphic network based on a differentiator circuit is proposed. The network not only holds the leaky integrate-and-fire (LIF) function but is also capable of recognizing the spatiotemporal features, which sets it apart from other LIF neurons arising from the FeCAP-modulated leaky behavior of the potential on the axon by spiking-time-dependent plasticity. Furthermore, it is more energy efficient to operate, nondestructive to read, and simpler to fabricate by employing FeCAPs, making it eligible for emergent spiking neural network hardware accelerators.

Effect of Hydrogen on Hafnium Zirconium Oxide Fabricated by Atomic Layer Deposition Using H2O2 Oxidant

Hafnium zirconium oxide (HZO) has been studied intensively due to its potential application to memory and logic devices based on its outstanding dielectric and ferroelectric properties. Because many process factors can significantly impact the properties of HZO thin film, an optimized process or post‐treatment is necessary to ensure its performance. Herein, the effect of hydrogen on HZO thin film can make the film degraded. Analysis of the polarization–voltage hysteresis loops and I–V measurements indicate a leaky behavior in the film. To address this issue, post‐oxygen‐plasma treatment is performed on the film, which results in the decrease in hydrogen ions inside the film and consequently reduces the leakage current density. This finding can provide new insight into the effect of hydrogen incorporation for HZO thin films and methodology to remove leaky components inside ferroelectric films using O2 plasma treatment.

Room temperature multiferroic properties of BiFeO3–MnFe2O4 nanocomposites

The novel functionalities of multiferroic magneto-electric nanocomposites have spawned substantial scope for fast-paced memory devices and sensor applications. Following this, herein we report the development of nanocomposites with soft ferromagnetic MnFe2O4 and ferroelectric BiFeO3 to fabricate a system with engineered multiferroic properties. A modified sol-gel route called Pechini method is demonstrated for the preparation of the (1-x) BiFeO3-x MnFe2O4 (x = 10%, 30%, 50%, 70%) nanocomposites. The crystallographic phase, structure, and morphology are characterized by XRD, FESEM, and HRTEM. The accurate crystallite size and lattice strain are determined by Williamson-Hall plot method and a comparative study with Scherer's equation is carried out. TEM image evidences the interface between BiFeO3 and MnFe2O4 nanoparticles in the composite. The room temperature magnetic response reveals the strong dependence of magnetic saturation, remanent magnetization, and coercivity of the nanocomposites on MnFe2O4 addition. The dielectric response and impedance analysis of the prepared nanocomposites are observed. The electrical performance of the composite is affected by grain, grain boundaries, and oxygen vacancies. The unsaturated P-E loops exhibit the leaky ferroelectric behavior for the nanocomposite. The intrinsic magnetoelectric coupling between ferroelectric BiFeO3 and ferromagnetic MnFe2O4 has been determined by varying Hdc/Hac and its maximum coupling coefficient (α) is found to be 25.39 mV/cmOe for 70% BiFeO3 -30% MnFe2O4 nanocomposite. These distinctive and achievable characteristics of the nanocomposite would enable the designing of magnetic field sensors, spintronic devices, and multiferroic memory devices.

Synthesis and multiferroic properties of high-purity CoFe2O4–BiFeO3 nanocomposites

CoFe2O4–BiFeO3 (CFO–BFO) nanocomposites of three different molar ratios (CFO:BFO = 2:2, 1.5:2, and 1:2) were synthesized by a combination hydrothermal/citric acid sol-gel method. This methodology allowed us to synthesize high-purity crystalline nanocomposites at a lower calcination temperature of 450 °C. Transmission electron microscopy (TEM) images revealed that the CFO and BFO nanocrystals are inter-embedded in each other. Room-temperature magnetic characterizations showed that the sintered sample of the 2:2 ratio had a high magnetization value of 40.5 emu/g at 20 kOe. The values of magnetization and coercivity indicated the presence of dipolar interaction between CFO and BFO. The electric-polarization change (ΔP) was estimated to be ~295 μC/m2 at a magnetic field strength of ~30 kOe at room temperature, although the polarization-electric field (P–E) loop measurements indicated that all of the samples manifested leaky behavior. The results presented herein offer a means of reliable magnetic-field control of electric polarization in high-purity multiferroic CFO–BFO nanocomposites.

Realization of high detectivity mid-infrared photodiodes based on highly mismatched AlInSb on GaAs substrates

We have systematically investigated highly mismatched AlInSb photodiodes grown on GaAs substrates operating in the mid-infrared range. A novel characterization method was introduced to analyze the recombination mechanism within an active layer of the devices, which revealed a high conductance stemming from the leaky behavior of dislocations. The introduction of a dislocation filter layer successfully reduced threading dislocations and improved resistance area product of photodiodes, leading to high detectivity at room temperature.

Experimental and Computational Investigation of Guided Waves in a Human Skull

We investigate guided (Lamb) waves in a human cadaver skull through experiments and computational simulations. Ultrasonic wedge transducers and scanning laser Doppler vibrometry are used respectively to excite and measure Lamb waves propagating in the cranial bone of a degassed skull. Measurements are performed over a section of the parietal bone and temporal bone spanning the squamous suture. The experimental data are analyzed for the identification of wave modes and the characterization of dispersion properties. In the parietal bone, for instance, the A0 wave mode is excited between 200 and 600 kHz, and higher-order Lamb waves are excited from 1 to 1.8 MHz. From the experimental dispersion curves and average thickness extracted from the skull computed tomography scan, we estimate average isotropic material properties that capture the essential dispersion characteristics using a semi-analytical finite-element model. We also explore the leaky and non-leaky wave behavior of the degassed skull with water loading in the cranial cavity. Successful excitation of leaky Lamb waves is confirmed (for higher-order wave modes with phase velocity faster than the speed of sound in water) from 500 kHz to 1.5 MHz, which may find applications in imaging and therapeutics at the brain periphery or skull–brain interface (e.g., for metastases). The non-leaky A0 Lamb wave mode propagates between 200 and 600 kHz, with or without fluid loading, for potential use in skull-related diagnostics and imaging (e.g., for sutures).

Leaky Lamb Wave Radiation from a Waveguide Plate with Finite Width

In this paper, leaky Lamb wave radiation from a waveguide plate with finite width is investigated to gain a basic understanding of the radiation characteristics of the plate-type waveguide sensor. Although the leaky Lamb wave behavior has already been theoretically revealed, most studies have only dealt with two dimensional radiations of a single leaky Lamb wave mode in an infinitely wide plate, and the effect of the width modes (that are additionally formed by the lateral sides of the plate) on leaky Lamb wave radiation has not been fully addressed. This work aimed to explain the propagation behavior and characteristics of the Lamb waves induced by the existence of the width modes and to reveal their effects on leaky Lamb wave radiation for the performance improvement of the waveguide sensor. To investigate the effect of the width modes in a waveguide plate with finite width, propagation characteristics of the Lamb waves were analyzed by the semi-analytical finite element (SAFE) method. Then, the Lamb wave radiation was computationally modeled on the basis of the analyzed propagation characteristics and was also experimentally measured for comparison. From the modeled and measured results of the leaky radiation beam, it was found that the width modes could affect leaky Lamb wave radiation with the mode superposition and radiation characteristics were significantly changed depending on the wave phase of the superposed modes on the radiation surface.

Structural, dielectric, and electrical characteristics of selenium-modified BiFeO3–(BaSr)TiO3 ceramics

The selenium (Se)-modified 0.5BiFeO3–0.5(BaSr)TiO3 was synthesized employing a high-temperature solid-state technique. Structural analysis (through Rietveld refinement) of the room-temperature X-ray diffraction pattern and data of the material confirms the tetragonal (P4mm) symmetry of the compound. Studies of scanning electron micrograph (SEM) and energy dispersive X-ray spectroscopy (EDS) data reveal the nature and characteristics (i.e., size, shape and distribution of grains, grain boundaries, voids and presence of elements, etc.,) of surface morphology and structure of the compound. Detailed analysis of temperature and frequency dependence of dielectric and impedance data exhibits the relaxor type of ferroelectric behavior and semiconductor (negative temperature coefficient of resistance) nature of the material. The material is found to have high resistivity and low dielectric (tangent) loss. Study of the temperature dependence of leakage current characteristics (i.e., electric field dependent current density) shows the leaky behavior of the material. The Se-modified 0.5BiFeO3–0.5(BaSr)TiO3 (BFBST), compared to its components (BFBST and pure BiFeO3), material possesses different types of conduction process, like space charge limited (SCLC), Ohmic, Hopping type. Poole–Frenkel emission (PFE) and Schottky emission (SE) fitted data give an evidence/idea about the bulk-limited and interface-limited conduction mechanism present in the system. The energy gap values (Eg) of Se substituted BFBST and BiFeO3 are found to be 0.55 eV and 0.78 eV, respectively, in the low-temperature range.

In situ grown single crystal aluminum as a nonalloyed ohmic contact to n-ZnSe by molecular beam epitaxy

Novel ohmic contacts to n-ZnSe are demonstrated using single crystal Al films deposited on epitaxially grown ZnSe (100) by molecular beam epitaxy. Electron backscatter diffraction confirmed the single crystalline structure of the Al films. The (110)-oriented Al layer was rotated 45° relative to the substrate to match the ZnSe (100) lattice constant. The as-grown Al-ZnSe contact exhibited nearly ideal ohmic electrical characteristics over a large doping range of n-ZnSe without any additional treatment. The contact resistances are in a range of 10−3Ωcm2 for even lightly doped ZnSe (∼1017cm−3). Leaky Schottky behavior in lightly doped ZnSe samples suggested that Al-ZnSe formed a low-barrier height, Schottky limit contact. In situ grown Al could act as a simple metal contact to n-ZnSe regardless of carrier concentration with lower resistance compared to other reported contacts in literary studies. The reported novel metallization method could greatly simplify the ZnSe-based device fabrication complexity and lower the cost.

Numerical simulation of a highly directional optical leaky wave antenna using diamond-shaped graphene perturbations.

We present a graphene-based optical leaky wave antenna (OLWA) with diamond-shaped perturbations. The leaky wave antenna is created by applying diamond-shaped graphene perturbations to a Si3N4 waveguide. The leaky wave behavior is observed by changing the graphene chemical potential. Results in the form of leakage power, normalized directivity, and reflectance, transmittance, leakage power, normalized directivity, and normalized E-field are presented. The half power beamwidth (HPBW) of 1.2° is achieved by this antenna. The reflectance and transmittance are in a very low wavelength range between 1.4 and 1.6 µm throughout. The leakage of power is more for the lower graphene chemical potential. The graphene-based design is also compared to a gold-based design and silicon-based design to show the leakage comparison. The designed graphene-based OLWA can be used in medical sensing devices.

Enabling Spike-Based Backpropagation for Training Deep Neural Network Architectures.

Spiking Neural Networks (SNNs) have recently emerged as a prominent neural computing paradigm. However, the typical shallow SNN architectures have limited capacity for expressing complex representations while training deep SNNs using input spikes has not been successful so far. Diverse methods have been proposed to get around this issue such as converting off-the-shelf trained deep Artificial Neural Networks (ANNs) to SNNs. However, the ANN-SNN conversion scheme fails to capture the temporal dynamics of a spiking system. On the other hand, it is still a difficult problem to directly train deep SNNs using input spike events due to the discontinuous, non-differentiable nature of the spike generation function. To overcome this problem, we propose an approximate derivative method that accounts for the leaky behavior of LIF neurons. This method enables training deep convolutional SNNs directly (with input spike events) using spike-based backpropagation. Our experiments show the effectiveness of the proposed spike-based learning on deep networks (VGG and Residual architectures) by achieving the best classification accuracies in MNIST, SVHN, and CIFAR-10 datasets compared to other SNNs trained with a spike-based learning. Moreover, we analyze sparse event-based computations to demonstrate the efficacy of the proposed SNN training method for inference operation in the spiking domain.

Extracellular methemoglobin promotes cyto-adherence of uninfected RBC to endothelial cells: Insight into cerebral malaria pathology.

The endothelial cell barrier is tightly regulated, and disruption or the leaky behavior of the barrier leads to pathology. Disturbance of blood-brain barrier is observed during viral infection, cerebral malaria, and acute hemorrhagic encephalitis. Red blood cells (RBCs) bind to the endothelial cells (ECs) and their affinity towards ECs enhances in the presence of Plasmodium falciparum infection. ECs stimulated with methemoglobin (MetHb; 20 µM) for 1 hour exhibit high levels of cyto-adherence receptors CD36 and ICAM-1 on their cell surface compared with unstimulated cells. These ECs have acquired affinity towards uninfected RBCs in flow at arterial shear stress. SEM analysis indicates that EC-RBC cyto-adherence involved multiple attachment points. Initially, ECs bind single layer of RBCs and the number of RBCs increases over time to give high-order cyto-adherence with more than 30 RBCs adhered to each endothelial cell. The cyto-adherence complexes are stable to high shear stress and can withstand shear stress up to 450 dyne/cm 2 . MetHb-treated ECs exhibited high reactive oxygen species level, and preincubation of ECs with antioxidant (NAC or mannitol) abolished the formation of EC-RBC cyto-adherence complexes. In addition, gallic acid (present in red wine) and green tea extract has inhibited the formation of EC-RBC cyto-adherence complex. A better understanding of gallic acid and tea polyphenol targeting pathological cyto-adherence may allow us to develop a better adjuvant therapy for cerebral malaria and other noninfectious diseases.

Surprisingly high magneto-electric coupling in cubic Co0.7Fe2.3O4-SrTiO3 nano-composites

Magnetoelectric (ME) coupling of (x)SrTiO3-(1-x)Co0.7Fe2.3O4 synthesized by the sol-gel method is presented in this study. The presence of constituent phases of Co0.7Fe2.3O4 (CFO) and SrTiO3(STO), and their strain mechanism in the composites were studied by x-ray diffraction. The field emission scanning electron micrographs confirmed well-distributed CFO and STO phases in the composites. The dielectric constant (ε′) and loss tangent (tanδ) of the composites were studied as a function of frequency. CFO and all the composites exhibit typical ferromagnetic hysteresis loops whereas their ferroelectric hysteresis loops show leaky behavior. CFO and STO lattices experiences compressive and tensile strain respectively that further promoting magnetostriction and electrostrictions in CFO and STO respectively. Strain mediated high magnetoelectric coefficient, αME = 9.1 mV/cm Oe is obtained for the composite having 50% STO and 50% CFO content. These results demonstrate that the lead free STO-CFO could be effective as magnetoelectric composite and may provide an alternative option over toxic lead contain materials for environmentally friendly ME device application.

Completeness and divergence-free behavior of the quasi-normal modes using causality principle

A fundamental feature of the quasi-normal modes (QNMs), which describe light interaction with open (leaky) systems like nanoparticles, lies in the question of the completeness of the QNMs representation and in the divergence of their field profile due to their leaky behavior and complex eigenfrequency. In this article, the QNMs expansion is obtained by taking into consideration the frequency dispersion and the causality principle. The derivation based on the complex analysis ensures the completeness of the QNMs expansion and prevents from any divergence of the field profile. The general derivation is tested in the case of a one-dimensional open resonator made of a homogeneous absorptive medium with frequency dispersion given by the Lorentz model. For a harmonic excitation, the result of the QNMs expansion perfectly matches the exact formula for the field distribution outside as well as inside the resonator.

Magnetodielectric coupling in a Ru-based 6H-perovskite, Ba3NdRu2O9

A large spin-orbit coupling is a way to control strong magnetodielectric (MD) coupling in a higher d-orbital materials. However reports are rare on such compounds due to often leaky conductive behavior. Here, we demonstrate MD coupling in a Ru-based 6H-perovskite system, Ba3NdRu2O9. The rare-earth ion in a 6H-perovskite makes the system insulating enough to carry out MD investigation. The compound is ferromagnetically ordered below 24 K (TC), followed by another magnetic feature at T~ 17 K (T2). The dielectric constant clearly traces the magnetic ordering, manifesting a peak at the onset of TC, which is suppressed by the application of an external magnetic field (H). The results indicate the presence of MD coupling in this compound, which is further confirmed by the H-dependence of the dielectric constant. Interestingly, a cross-over of the sign of MD coupling is observed at T ~ T2. We conclude that two different mechanism controls the MD coupling which yields positive and negative coupling, respectively. Both mechanisms are competing as a function of temperature and magnetic field. This brings us a step closer to design and control the magnetodielectric effect in 6H-perovskites containing higher d-orbital elements.

Modeling of self-assembled monolayers (SAMs) of Octadecanethiol and Hexadecanethiol on gold (Au) and silver (Ag)

This work proposes a modeling of self-assembled monolayers (SAMs) to assess the quality of SAM layers in terms of their leaky behavior. In the modeling, electrochemical impedance spectroscopy (EIS) and a conceptual and simplified resistance-resistance-capacitance (RRC) electrical model from an electrochemical setup were demonstrated. Based on the model, Matlab-based simulation was carried out to find out the suggestive low frequency measurement for analyzing the defective monolayers. Finally, the developed electrical model facilitated the interpretation of the EIS spectra measured in the range of 10Hz to 100kHz and provided the capacitance, resistance and thickness of the monolayer. Thus the proposed model could be considered as a powerful tool to characterize the defective SAMs, which was very specific to determine the resistive behavior of the self-assembled monolayers prepared for shorter adsorption time.

Investigation on structural, Mössbauer and ferroelectric properties of (1−x)PbFe0.5Nb0.5O3–(x)BiFeO3 solid solution

In this study, (1−x)PbFe0.5Nb0.5O3(PFN)–(x)BiFeO3(BFO) multiferroic solid solutions with x=0.0, 0.1, 0.2, 0.3 and 0.4 were synthesized through single step solid state reaction method and characterized thoroughly through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR), Raman, Mössbauer spectroscopy and ferroelectric studies. The room temperature (RT) XRD studies confirmed the formation of single phase with negligible amount of secondary phases (x=0.2 and 0.4). The zoomed XRD patterns of (1−x)PFN–(x)BFO solid solutions showed the clear structural phase transition from monoclinic (Cm) to rhombohedral (R3c) at x=0.4. The Raman spectra of the (1−x)PFN–(x)BFO solid solutions showed the composition dependent phase transition from monoclinic (Cm) to rhombohedral (R3c). With increasing x in PFN, the modes related monoclinic symmetry changes to those of rhombohedral symmetry. The RT Mössbauer spectroscopy results evidenced the existence of composition dependent phase transition from paramagnetic to weak antiferromagnetic ordering and weak antiferromagnetic to antiferromagnetic ordering. The Mössbauer spectroscopy showed paramagnetic behavior with a doublet for x=0.0, 0.1 and 0.2 are shows the weak antiferromagnetic with paramagnetic ordering. For x=0.3 and 0.4 shows the sextet pattern and it is a clear evidence of antiferromagnetism. The ferroelectric (P–E) loops at RT indicate the presence of small polarization, as the x concentration increases in PFN, the remnant polarization and coercive field were decreased, which may due to the increase in the conductivity and leaky behavior of the samples.