Processes to achieve high spatial resolution ion implantation induced quantum well intermixing in GaAs/AlGaAs superlattices have been developed. Ion implantation has been carried out using various doses of 4 MeV As2+ ion beam, followed by rapid thermal annealing at various temperatures for 60 s. Low temperature photoluminescence measurements reveal a blue-shift up to 90 nm in the energy band-gap. Propagation losses have been characterized in the intermixed waveguides, and losses as low as 0.55 cm−1 have been observed for 0.5 × 1013 cm−2 implantation dose which gives a blue-shift of 68 nm when annealed at 775 °C. The spatial resolution of ~1.2 μm has been observed at the depth of 2 μm inside the epitaxial structure.

The quantum confined Stark effect (QCSE) has been investigated in detail in GaAs/AlGaAs and InAs/GaAs/AlGaAs HEMTs structures grown by molecular beam epitaxy on (1 0 0) oriented GaAs substrates. A power dependent photoluminescence (PL) study allowed to highlight the QCSE caused by the internal electric field in the GaAs channel then a piezoelectric field reinforce the red-shift. Increasing the Si-δ-doping leads to; first a red-shift then a blue shift at high excitation power due to the stabilize quantum well structures tendency and the saturation phenomenon. The HEMT band structures and the theoretical activated electron densities at 10 K have been studied using the finite difference method and the simultaneously solve of the Schrödinger and the Poisson equations written within the Hartree approximation.

An experimental methodology compliant with industrial constraints was deployed to uncover the origin of soft breakdown events in large planar silicon-based NMOS capacitors. Complementary advanced failure analysis techniques were advantageously employed to localize, isolate and observe structural defects at nanoscale. After an accurate localization of the failing area by optical beam-induced resistance change (OBIRCH), focused ion beam (FIB) technique enabled preparing thin specimens adequate for transmission electron microscopy (TEM). Characterization of the gate oxide microstructure was performed by highresolution TEM imaging and energy-filtered spectroscopy. A dedicated experimental protocol relying on iterative FIB thinning and TEM observation enabled improving the quality of electron imaging of defects at atom scale. In that way, the gate oxide integrity was evaluated and an electrical stress-induced silicon epitaxy was detected concomitantly to soft breakdown events appearing during constant voltage stress. The growth of silicon hillocks enables consuming a part of the breakdown energy and may prevent the soft breakdown event to evolve towards a hard breakdown that is catastrophic for device functionality.

In this work, PANI:PVDF composites films were prepared with different PANI contents (p = 1, 2, 3, 4 and 5%). The resulting films were dried at various temperatures such as 30, 90 and 120 °C. The alternating current mechanisms and dielectric relaxation and of PANI:PVDF films were studied using complex impedance spectroscopy over a wide range of temperature (303–453 K) and a frequency range (1 kHz to 1 MHz). We found that the ac conductivity in PANI:PVDF composite is governed by correlated barrier hopping (CBH) model. In dielectric loss modulus study, two relaxation processes were identified. The first peak was associated to Maxwell Wagner-Sillas (MWS) relaxation whereas the second one which obtained at higher frequency was attributed to the αc relaxation. For PANI:PVDF film which dried at 30 °C, the MWS relaxation appears only at higher temperature. The temperature dependence of αc relaxation was suitably fitted according to Vogel Flucher Temman model whereas MWS relaxation follows Arrhenius type behavior. The effect of drying temperature on microstructure and phase crystallization of PVDF in the composites was carried out using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. These results were used to find a reasonable correlation between microstructure and electrical properties.

In this paper, carrier dynamics in N,N′-diphenyl-N,N′bis(1,1′-biphenyl)-4,4′-diamine (NPB) was studied using impedance spectroscopy (IS) and particle swarm optimization algorithm (PSO). We applied PSO to fit the frequency dependence of impedance spectroscopy of NPB, and achieved the charge-carrier transit time and the dispersive parameters of NPB, and then obtained carrier mobility. The impacts of the dispersive degree on the impedance had been analyzed. Though PSO, the three unknown parameters, charge-carrier transit time τdc and dispersive degree M, α in the admittance model were achieved simultaneously. The results verified the reliability of this method. Furthermore, we have presented the advantages of PSO compared with the traditional nonlinear least squares algorithm. In our limited knowledge, this paper begins the work to study materials in the deep level of algorithm

The properties of electronic transport in graphene superlattices which consist of symmetrical period potentials have been studied. It is found that such structures possess an unusual tunneling state inside the original forbidden gaps. Furthermore, the position of tunneling mode is highly dependent on the lattice constant and potential voltage but insensitive to period number, and a theoretical explanation for this phenomenon is proposed. Finally it is revealed that the electronic conductance is greatly enhanced and the Fano factor is strongly suppressed near the energy of the tunneling state. The characteristics of electron transport over symmetrical graphene superlattices may facilitate the development of many graphene-based electronics.

Diamond like carbon (DLC) and composite nickel incorporated diamond-like carbon (Ni-DLC) films have been synthesized on ITO coated glass substrates using low voltage electrodeposition method. Modifications of structural and optical properties of thin films have been investigated with varying Ni concentration. Average grain size of Ni-DLC granules is found to decrease with increasing molarity of Ni in electrolytic solution. XRD pattern depicts multi-phase nature of Ni-DLC film. Incorporation of Ni nanoparticles in DLC matrix has been confirmed by TEM. Interestingly optical bandgap energy decreases from 2.31 to 1.58 eV with decrease in nickel content in the electrolytic bath. Simultaneously Urbach energy exhibits an increasing trend from 1.972 to 2.374 eV. Presence of sp2 and sp3 bonded carbons has been indicated by FTIR spectra. The number of sp2 bonding in carbon matrix is enhanced with dilution of electrolyte. The peaks in the range of ~600–750 cm−1 in Ni-DLC films have been attributed to metal incorporation into DLC matrix. Study reveals that the bandgap and the particle size of carbon nanocomposite films can be tailored by controlling the amount of nickel in the electrolyte.

We present a method to control the length and diameter of Bi2Se3 nanowires through laser-cutting. Nanowires of the topologically insulating and thermoelectric material Bi2Se3 were grown using the vapor-liquid-solid method, and cut using a 532-nm-laser operating at a minimum power of 1 μW. The cutting process can be controlled through laser intensity and exposure time, and is based upon evaporation of Se from the nanowires. This method has many applications from pure research to device engineering.

Nanocrystalline zinc oxide (ZnO) aerogel powders were synthesized using a modified sol-gel process. Ethanol, acetone and methanol were used as supercritical drying fluids. Effects of co-solvent on morphological and structural properties were investigated. The as prepared powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The XRD results show that drying in solvents mixture affects the crystalline quality and acts as a compression agent by exerting stress on the lattice parameters. SEM micrographs demonstrate that co-solvent plays a key role in controlling ZnO nucleation and favors the particles agglomeration with increasing the pressure and the temperature. The EDAX analysis shows that the obtained ZnO nanopowder with ethanol and acetone as co-solvent is pure with different stoichiometries (an excess of oxygen (O) with ethanol and zinc (Zn) atoms with acetone). However, when methanol is used as supercritical drying fluid, the obtained nanopowder contains an excess of carbon (C) atoms. FTIR absorption bands are more intense for aerogel synthesized by drying in methanol indicating the presence of more C-H bounds responsible of the low rate agglomeration of the ZnO crystallites.

Within the framework of the effective-field theory (EFT) with correlations, the differential operator technique has been used to study the phase diagrams of a ferroelectric nanoparticle described by the transverse field Ising model. The dependence of the phase diagrams on two types surface parameters modifications, modifications of the surface transverse field and the surface exchange interaction, is calculated numerically in the (Tc, Js) coordinates or the (Tc, Ωs) coordinates. The crossover features, from the ferroelectric-dominant phase diagram (FPD) to the paraelectric-dominant phase diagram (PPD), for interaction parameters of a ferroelectric nanoparticle with a size S are determined. Meanwhile, the critical behaviours are also examined for the ferroelectric nanoparticle system.

External applied field effect in magnetization process by pulsed field (PFM) method of rectangular bulk superconductor is analysed by solving the A-V magnetic equation coupled to the thermal one in order to show the influence of the amplitude of the external field on the trapped magnetic field of bulk superconductor. A numerical model based on the control volume method (CVM) has been developed, which uses a power-law model with temperature dependency and magnetic field dependence on critical current density. For low cooling temperature Tco = 20 K, a good distribution of the trapped magnetic field of the bulk superconductor is obtained when we applied high external field.

Cobalt doped ZnO nanoparticles were synthesized by microwave irradiation technique for their structural and magnetic properties. Initially the samples were exhibit single phase standard ZnO wurtzite structure (x ≤ 0.1) further Co concentration increase Co3O4 phase was confirmed by X-ray diffraction analysis. The average crystallite sizes of cobalt doped ZnO particles were calculated by Debye-Scherrer formula and are nearly 25 nm. The hexagonal wurtzite structure of ZnO and destroyed cubical Co3O4 were identified in the TEM images. The presence of metal oxide was confirmed by Fourier transform infrared spectral analysis result. The micro-Raman analysis confirmed the existence of Co3O4 phase. Magnetization measurements performed by using vibrating sample magnetometer determine the paramagnetic behavior for the synthesized samples.

Bright- and dark-field images are reconstructed by extracting the intensities of selected spots from a succession of digitalized electron diffraction patterns collected using a transmission electron microscope by scanning the focused beam over the area of interest. The procedure is similar to the generation of the scanning-transmission electron microscopy images. Several examples are shown to illustrate the flexibility and potentiality of such numerical off-line reconstruction.

Calibration-free laser induced breakdown spectroscopy (CF-LIBS) was used for the determination of elemental composition and quantitative analysis of the Košice meteorite by means of time resolved and broadband emission spectroscopy (200–1000 nm). The electron temperature was determined using the Saha-Boltzmann plot method and the electron density from Stark broadening of the hydrogen Hα line (656 nm). Apart from magnesium, silicon and iron, which are the main elemental constituents of examined meteorite fragments, elements such as aluminum, nickel, potassium, sodium, chromium, calcium and manganese were also identified in the obtained LIBS spectra. Concentrations of Al, Ca, Cr, Fe, Mg, Mn, Na, Ni and Si were calculated using the calibration free approach and results were compared with ones obtained from the ICP-MS analyses. For the increase of the CF-LIBS accuracy, a selection of spectral lines was performed. Considering the transition probability, the population of absorbing level, the degree of ionization and predicted elemental concentration we calculated the probability of self-absorption and, consequently, spectral lines with highest self-absorption probability were rejected. CF-LIBS can be used as an alternative method for the meteorite fragments analysis (including the inner part and crust), because this method is quasi non-destructive and therefore analysis of all found fragments with minimal destruction is possible.

Despite numerous investigations during recent decades in the field of antimicrobial treating textile fibers using silver, many obscurities remain regarding the durability and dyeing ability and the influences of dyeing on the antimicrobial effectiveness of silver-treated fibers. In this research work, the cotton fabrics were sputtered using DC magnetron sputtering system for different times of exposure by silver. Then the silver coated samples were dyed by different classes of synthetic and natural dyes. The dye ability of coated samples was compared with untreated cotton. The reflective spectrophotometer was used for this purpose. The morphology of the cotton fabrics before and after dyeing was observed using a scanning electron microscope (SEM). The antibacterial activity of samples before and after dyeing, were investigated and compared. For antibacterial investigation, the antibacterial counting tests were used. It was concluded that, dyeing does not have any negative effect on antibacterial activity of coated samples and very good antibacterial activity was achieved after dyeing.

The heat transfer and thermal performance of a single pass solar air heater a smooth plate was investigated experimentally. In the present paper, energy and heat transfer analysis of a solar air collector with smooth plate, this technique is used to determine the optimal thermal performance of flat plate solar air heater by considering the different system and operating parameters to obtain maximum thermal performance. Thermal performance is obtained for different mass flow rate varying in the array 0.0108–0.0202 kg/s with five values, solar intensity; tilt angle and ambient temperature. We discuss the thermal behavior of this type of collector with new design and with my proper construction. An experimental study was carried out on a prototype installed on the experimental tests platform within the University of Biskra in the Algeria. The effects of air mass flow rate, emissivity of channel plates and wind heat transfer coefficient on the accuracy of the criterion are also investigated.

Electromechanical model of an energy harvester that is comprised of 64 identical pairs of cantilever beams has been built in this work. Each pair consists of a short and a long cantilever with the same width and thickness. All the beams are bi-layer structures that include a piezoelectric layer and a substrate layer, which are coupled by the overhang part. The model is focused on analyzing the nonlinear dynamic behavior of the device, specifically when it is operated at intrinsic localized mode (ILM). The electrical charge generated on the surface of the piezoelectric layer has been derived using the beam theory and the piezoelectric equations. It has been found from numerical simulations that spatiotemporal chaos, in particular ILMs can arise during abrupt frequency changes of the external driving source, which could potentially be used to achieve high/concentrated energy output.

With the evolution of integrated circuit technology, the interconnect parasitics can be the limiting factor in high speed signal transmission. With increasing frequency of operation, length of interconnect and fast transition time of the signal, the RC models are not sufficient to estimate the delay accurately. To mitigate this problem, accurate delay models for coupled interconnects are very much required. This paper proposes an analytical model for estimating propagation delay in lossy coupled RLC interconnect lines for simultaneously switching scenario. To verify the proposed model, the analytical results are compared with those of FDTD and SPICE results for the two cases of inputs switching under consideration. An average error of 2.07% is observed which shows an excellent agreement with SPICE simulation and FDTD computations.

Equipment used in hybrid or electric vehicles (HEVs) must meet certain requirements. Beyond issues of electro-magnetic compatibility (EMC), it’s necessary to assess the risks related to the exposure of the passengers to electromagnetic field inside an HEV. At low frequencies, using the electromagnetic shielding as protection is inefficient. The compliance can be achieved done by defining the harness’s architecture or by the use of permeable materials. In this paper, we will focus on the prediction of the shielding effectiveness of materials subjected to a near magnetic field source at low frequency (9 kHz–10 MHz).We will focus our study on two cases. In the first case, we will work on the numerical modeling of an enclosure with and without opening. The result from the model is compared to the measurement’s results obtained with a test bench developed in our laboratory. In the second case, the impact of the slot in the enclosure will be studied. An analytical method based on magnetic moments approximation is developed to predict the shielding effectiveness for infinite plane with slot. The results obtained with the latter are compared with the numerical results.