InGaAsP/InP photodetectors targeting on 1.06 μm wavelength detection

InP-based InGaAsP photodetectors targeting on 1.06 μm wavelength detection have been grown by gas source molecular beam epitaxy and demonstrated. For the detector with 200 μm mesa diameter, the dark current at 10 mV reverse bias and R₀A are 8.89 pA (2.2 × 10⁻⁸ A/cm²) and 3.9 × 10⁵ Ω cm² at room temperature. The responsivity and detectivity of the InGaAsP detector are 0.30 A/W and 1.45 × 10¹² cm Hz^1/2 W⁻¹ at 1.06 μm wavelength. Comparing to the reference In_0.53Ga_0.47As detector, the dark current of this InGaAsP detector is about 570 times lower and the detectivity is more than ten times higher, which agrees well with the theoretical estimation.     

An ignition-temperature model with two free interfaces in premixed flames†

In this paper we consider an ignition-temperature zero-order reaction model of thermo-diffusive combustion. This model describes the dynamics of thick flames, which have recently received considerable attention in the physical and engineering literature. The model admits a unique (up to translations) planar travelling wave solution. This travelling wave solution is quite different from those usually studied in combustion theory. The main qualitative feature of this travelling wave is that it has two interfaces: the ignition interface where the ignition temperature is attained and the trailing interface where the concentration of deficient reactants reaches zero. We give a new mathematical framework for studying the cellular instability of such travelling front solutions. Our approach allows the analysis of a free boundary problem to be converted into the analysis of a boundary value problem having a fully nonlinear system of parabolic equations. The latter is very suitable for both mathematical and numerical analysis. We prove the existence of a critical Lewis number such that the travelling wave solution is stable for values of Lewis number below the critical one and is unstable for Lewis numbers that exceed this critical value. Finally, we discuss the results of numerical simulations of a fully nonlinear system that describes the perturbation dynamics of planar fronts. These simulations reveal, in particular, some very interesting ‘two-cell’ steady patterns of curved combustion fronts.     

Synthesis of tunable core–shell nanostructures based on TiO2-graphene architectures and their application in the photodegradation of rhodamine dyes

We present the synthesis of core–shell nanostructural materials with multi-component architectures based on TiO₂ and graphitic layers. The composites have been synthesized by chemical vapor deposition with methane as the carbon source, for 5, 10, 30 and 45 min. The final products were characterized by a combination of analytical approaches which include: electron microscopy, Raman, FT-IR and UV–vis spectroscopy as well as thermogravimetric analysis. The amount of graphene shells covering the TiO₂ surfaces was found to vary linearly with the reaction time. Furthermore, the compounds were shown to have excellent stability and photocatalytic activity towards the UV degradation of rhodamine (RhB) dye solution at room temperature. These composites could have major applications in the area of environmental cleaning of various pollutants, electrochemistry or nanomedicine.     

Multiple mobility edges in a 1D Aubry chain with Hubbard interaction in presence of electric field: Controlled electron transport

Electronic behavior of a 1D Aubry chain with Hubbard interaction is critically analyzed in presence of electric field. Multiple energy bands are generated as a result of Hubbard correlation and Aubry potential, and, within these bands localized states are developed under the application of electric field. Within a tight-binding framework we compute electronic transmission probability and average density of states using Green's function approach where the interaction parameter is treated under Hartree–Fock mean field scheme. From our analysis we find that selective transmission can be obtained by tuning injecting electron energy, and thus, the present model can be utilized as a controlled switching device.     

Waiting times of entangled electrons in normal–superconducting junctions

We consider a normal–superconducting junction in order to investigate the effect of new physical ingredients on waiting times. First, we study the interplay between Andreev and specular scattering at the interface on the distribution of waiting times of electrons or holes separately. In that case the distribution is not altered dramatically compared to the case of a single quantum channel with a quantum point contact since the interface acts as an Andreev mirror for holes. We then consider a fully entangled state originating from splitting of Cooper pairs at the interface and demonstrate a significant enhancement of the probability to detect two consecutive electrons in a short time interval. Finally, we discuss the electronic waiting time distribution in the more realistic situation of partial entanglement.     

An improved model for the cantilever NEMS actuator including the surface energy,fringing field and Casimir effects

The influence of the surface energy on the instability of nano-structures under the electrostatic force has been investigated in recent years by different researchers. It appears that in all prior research, the response of all structures becomes softer due to the surface effects. In the present study, the pull-in instability of a NEMS device incorporating the electrostatic force and Casimir intermolecular attraction for different values of the surface parameter is investigated by the Duan–Rach method of determined coefficients (MDC) in order to identify the remarkable effect of the surface energy. Although the obtained results verify the behavior of such structures in presence of the fringing field and the Casimir attraction same as the previous investigations, however the incremental effects of the surface energy cause the aforementioned structures to behave more stiffly in contrast.     

On the photon-drag effect of photocurrent of surface states of topological insulators

The photocurrent of surface states of topological insulator due to photon-drag effect is computed, being based on pure Dirac model of surface states. The scattering by disorder is taken into account to provide a relaxation mechanism for the photocurrent. The Keldysh–Schwinger formalism has been employed for the systematic calculation of photocurrent. The helicity dependent photocurrent of sizable magnitude transverse to the in-plane photon momentum is found, which is consistent with experimental data. Other helicity independent photocurrents with various polarization states are also calculated.     

Structural characterization and X-ray analysis by Williamson–Hall method for Erbium doped Aluminum Nitride nanoparticles,synthesized using inert gas condensation technique

We have synthesized AlN nanoparticles (NPs) doped in-situ with Er (AlN:Er) using inert gas condensation technique. Using x-ray diffraction (XRD) peak broadening analysis with the Williamson–Hall (W–H) Uniform Deformation Model (UDM) the crystallite size of the NPs and the strain in NPs were found to be 80±38 nm and 3.07×10⁻³±0.9×10⁻³ respectively. In comparison, using the Debye–Scherrer's (DS) formula, we have inferred that the crystallite size of the NPs was 23±6 nm and the average strain was 4.3×10⁻³±0.4×10⁻³. The scanning electron microscopy images show that the NPs are spherical and have an average diameter of ∼300 nm. The crystallite size is smaller than the size of the NPs revealing their polycrystalline behavior. In addition, the NPs strain, stress and energy density were also calculated using W–H analysis combined with the Uniform Deformation Stress Model (UDSM) and the Uniform Deformation Energy Density Model (UDEDM). Suggested by the spherical geometry and polycrystalline nature of the AlN NPs, the strain computed from UDM, UDSM and UDEDM were in agreement confirming an isotropic mechanical nature of the particle. Luminescence measurements revealed the temperature dependence of the optical emission of the Er³⁺ ions, confirming the use of AlN:Er NPs for nano-scale temperature sensing.     

Reprint of : Spin polarization induced by an electric field in the presence of weak localization effects

We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.     

Dielectric properties and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in Bis(4-acetylanilinium) tetrachlorocuprate(II) compound

In the present work, the synthesis and characterization of the Bis(4-acetylanilinium) tetrachlorocuprate(II) compound are presented. The structure of this compound is analyzed by X-ray diffraction which confirms the formation of single phase and is in good agreement the literature. Indeed, the Thermo gravimetric Analysis (TGA) shows that the decomposition of the compound is observed in the range of 420–520 K. However, the differential thermal analysis (DTA) indicates the presence of a phase transition at T=363 k. Furthermore, the dielectric properties and AC conductivity were studied over a temperature range (338–413 K) and frequency range (200 Hz–5 MHz) using complex impedance spectroscopy. Dielectric measurements confirmed such thermal analyses by exhibiting the presence of an anomaly in the temperature range of 358–373 K. The complex impedance plots are analyzed by an electrical equivalent circuit consisting of resistance, constant phase element (CPE) and capacitance. The activation energy values of two distinct regions are obtained from log σT vs 1000/T plot and are found to be E=1.27 eV (T<363 K) and E=1.09 eV (363 K<T).The frequency dependence of ac conductivity, σ_ac, has been analyzed by Jonscher's universal power law σ(ω)=σ_dc+Aω^s. The value of s is to be temperature-dependent, which has a tendency to increase with temperature and the non-overlapping small polaron tunneling (NSPT) model is the most applicable conduction mechanism in the title compound.