Hafedh Belmabrouk

Magnetic, magnetocaloric and critical behavior investigation of La0.7Ca0.1Pb0.2Mn1−x−yAlxSnyO3 (x, y = 0.0, 0.05 and 0.075) prepared by a sol–gel method

A systematic study on the magnetic, magnetocaloric and critical behavior properties of polycrystalline La0.7Ca0.1Pb0.2Mn1−x−yAlxSnyO3 prepared via a sol–gel method are studied. These compounds present a single magnetic transition from a ferromagnetic (FM) to paramagnetic (PM) phase with decreasing temperature. The critical exponents are estimated using various techniques, such as a modified Arrott plot, the Kouvel–Fisher method and critical isotherm analysis based on the data of static magnetic measurements recorded around the Curie temperature, TC. The estimated critical exponent values are found to be consistent and comparable to those predicted by the 3D-Ising model for x, y = 0.0 and by the mean field model for x, y = 0.05 and 0.075. We have confirmed the obtained critical exponents with the single scaling equation: M(μ0H,e) = eβf ± (μ0H/eβ+γ), where e = (T − TC)/TC is the reduced temperature. We have investigated the validity and usefulness of theoretical modeling in our compound La0.7Ca0.1Pb0.2Mn1−x−yAlxSnyO3 based on the mean-field analysis of the magnetic entropy change (−ΔSM) versus the magnetization data. For comparison, the MSp has been also deduced from the classical extrapolation of the Arrott plot. We obtain an excellent agreement between the spontaneous magnetization determined from the entropy change (−ΔSM vs. M2) and the Arrot curves (μ0H/M vs. M2), confirming the validity of the magnetic entropy change approach in order to estimate the spontaneous magnetization MSp in a ferromagnetic system.

Nanoheat Conduction Performance of Black Phosphorus Field-Effect Transistor

Black phosphorus (BP) has arisen as the preferred material with great applications in electronics devices. Nanoinvestigation of the thermal properties and thermal stability of BP transistors at the nanoscale is extremely challenging. This paper reports nanothermal investigation of BP MOSFET transistors, using the dual-phase-lagging (DPL) model including the phonon scattering. The thermal properties of the BP including the thermal conductivity and volumetric heat generation rate considered depend on the temperature. The results are compared with those obtained from the classical silicon MOSFET. Using the finite-element method, we have demonstrated that the temperature variation of the BP MOSFET does not exceed 305 K instead of 319 K in the case of a classical MOSFET. This paper not only exposes various novel properties of BP transistors, but also demonstrates the great usefulness of the BP transistors.

Optimization of microfluidic biosensor efficiency by means of fluid flow engineering

Binding reaction kinetics of analyte-ligand at the level of a sensitive membrane into a microchannel of a biosensor has been limited by the formation of the boundary diffusion layer. Therefore, the response time increases and affects the overall performance of a biosensor. In the present work, we develop an approach to engineer fluid streams into a complex configuration in order to improve the binding efficiency. We investigate numerically the flow deformations around a parallelepiped with square cross-section inside the microfluidic channel and exploit these deformations to simulate the analyte transport to the sensitive membrane and enhance both association and dissociation processes. The effect of several parameters on the binding reaction is provided such as: the obstacle location from the inlet of the microchannel, the average flow velocity, and the inlet analyte concentration. The optimal position of the obstacle is determined. An appropriate choice of the inlet flow velocity and inlet analyte concentration may reduce significantly the response time.

Large magnetocaloric effect and critical behavior in La0.7Ba0.2Ca0.1Mn1−xAlxO3

The structural, magnetic and magnetocaloric properties of La0.7Ba0.2Ca0.1Mn1−xAlxO3 (0 ≤ x ≤ 0.1) perovskite manganite oxides have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement has shown that all of the samples under investigation crystallize with a rhombohedric structure in the Rc space group (N°167). Paramagnetic (PM) to ferromagnetic (FM) transitions have been observed in all of the synthesized samples. In addition, the maximum magnetic entropy change (ΔSmaxM) for the x = 0 sample was found to reach ∼5.8 J kg−1 K−1 under an applied magnetic field of 5 T, which is sufficient for potential applications in magnetic refrigeration. For the same applied magnetic field (μ0H = 5 T), the relative cooling power (RCP) value is found to be 167 J kg−1. The critical properties of manganites La0.7Ba0.2Ca0.1Mn1−xAlxO3 (0 ≤ x ≤ 0.1) are investigated through various techniques, such as modified Arrott plots, Kouvel–Fisher methods and critical isotherm analyses around the paramagnetic–ferromagnetic phase transition (Tc). The values of critical exponents, derived from magnetic data using the above methods, yield 0.246 ≤ β ≤ 0.253, 1.01 ≤ γ ≤ 1.12 and 4.76 ≤ δ ≤ 4.9 with a Tc of 300–350 K. The exponent values are close to those expected for tricritical mean field model ferromagnets with short-range dipole–dipole interactions.

Enhancing Efficiency of InGaN Nanowire Solar Cells by Applying Stress

In photovoltaic solar cells, p-n junctions have been considered a very promising structure to improve the carrier collection efficiency and accordingly the conversion efficiency. The basic processes for a solar cell to work are the generation of electron–hole pairs, separation, and recombination of those carriers in external circuits. The step of critical importance here is the electron–hole pair separation. The inner piezopotential, formed in the crystal by applying a stress which is called piezophototronic effect, interferes directly in the separation and recombination process, and consequently affects the solar cell performance. Recently, elaborated models including the piezophototronic effect were proposed to simulate metal/semiconductor and a p-n junction based in ZnO, but discussion of results has been limited to the output and the open-circuit voltage. In the present work, we will attempt to extend systematically the modeling of photovoltaic conversion on solar cell. The piezophototronic effect is included both in transport equation and photocurrent. Finally, the experimental results of organic solar cells support our theoretical model. Using the piezoelectric effect created by external stress, our study not only provides the first basic theoretical understanding about the piezophototronic effect on the characteristics of an inorganic solar cell, but also assists the design for higher performance solar cells.

Finite-Element Simulations of the pH-ElecFET Microsensors

This paper presents a COMSOL Multiphysics 2-D axisymmetric model of a pH-sensitive electrochemical field effect transistor (pH-ElecFET) microsensor. This device combines an integrated microelectrode with a pH-sensitive chemical field effect transistor (pH-ChemFET). Thus, by triggering electrolysis phenomena owing to the integrated microelectrode, associated local pH variations in microvolumes are monitored thanks to the pH-ChemFET microdevice. Taking into account (electro) chemical reactions and diffusion phenomena in the liquid phase, the proposed model points out the role of the ElecFET geometrical design (microelectrode width w, gate sensitive radius re and distance between the pH-ChemFET gate and the microelectrode d), as well as polarization parameters, (polarization voltage Vp and time tp), on the microsensor response. It is first applied to water electrolysis in order to validate pH impulsional variations in microvolume. Then, the oxidation of hydrogen peroxide in phosphate buffer (PBS, pH0 = 7.2) solutions is studied, evidencing the H2O2 potentiometric detection in the [10-100 mM] concentration range. This developed model paves new ways for sensor applications, opening several new opportunities for pH-ElecFET devices for H2O2-related enzymatic detection of biomolecules.

Numerical investigation of microfluidic flow under AC applied electric field: Enhanced of binding reaction for a biosensor

Binding reaction is a natural characteristic that is applied to design biosensors. In this study we simulate the binding reaction kinetics between the immobilized antibody and the targeted antigen in a reaction chamber (microchannel) of a biosensor under AC applied electric field. The diffusion boundary layer on the sensitive area of the biosensor would hinder the binding reaction from association and dissociation. We studied the influence of the shape and position of reaction surface under AC applied voltage on the binding reaction. The electrothermal force, produced by the AC electric field can induce a pair of vortices to stir the flow field over the reacting surface allowing accelerate the binding reaction. Our approach may contribute to efficient development and optimization of a biosensor for medical applications.