I.S. Yahia

Influence of temperature and illumination on the electrical properties of p-ZnTe/n-CdTe heterojunction grown by molecular beam epitaxy

A set of p-ZnTe/n-CdTe heterojunctions were grown on conducting GaAs substrates by molecular beam epitaxy. The current density–voltage (J–V) and capacitance–voltage (C–V) characteristics measured in the temperature range 300–400 K were analysed in order to reveal the dominant carrier transport mechanisms through the junctions. The C–V measurements show that the device is linearly graded. The temperature dependence of the built-in potential and the impurity gradient of the device were determined. The deep defect states govern the current flow through the junctions. The measurements under the lower voltage region (V 0.35 V), the space-charge-limited current governed the J–V characteristics with a single traps level, ΔEt = 0.55 eV. The p-ZnTe/n-CdTe device under different illumination intensities exhibit a significant photosensitivity proving that this kind of heterostructure can be regarded as a good candidate for photodiode applications.

A dual approach to study the electro-optical properties of a noncentrosymmetric L-asparagine monohydrate.

In this work we reports the experimental and theoretical investigation on an organic noncentrosymmetric monohydrated L-asparagine (LAM) molecule. LAM single crystals were grown in specially designed beaker for the first time. Structural confirmation was done by identifying the vibrational modes using IR and FT-Raman spectroscopic studies. The ultra violet-visible-near infrared absorbance, diffuse reflectance spectra were recorded in the spectral range 190-2500 nm. The optical transparency was calculated and found to be ∼80%. Its optical band gap was calculated found to be ∼5.100 eV. Density functional theory (DFT) was employed to optimize the molecular geometry of LAM using B3LYP/6-31G(∗) basis set of theory. The HOMO-LUMO energy gap of 6.047 eV and transition energy of 176 nm (f0=0.024) have been found in semi-quantitative agreement with our experimental results. The dipole moment, polarizability and first hyperpolarizability were calculated at the same level of theory. The obtained results reveals that the titled compound can be a decent contender for nonlinear applications.

How does hybrid bridging core modification enhance the nonlinear optical properties in donor-π-acceptor configuration? A case study of dinitrophenol derivatives

This study spotlights the fundamental insights about the structure and static first hyperpolarizability (β) of a series of 2,4‐dinitrophenol derivatives (1–5), which are designed by novel bridging core modifications. The central bridging core modifications show noteworthy effects to modulate the optical and nonlinear optical properties in these derivatives. The derivative systems show significantly large amplitudes of first hyperpolarizability as compared to parent system 1, which are 4, 46, 66, and 90% larger for systems 2, 3, 4, and 5, respectively, at Moller–Plesset (MP2)/6‐31G* level of theory. The static first hyperpolarizability and frequency dependent coupled‐perturbed Kohn–Sham first hyperpolarizability are calculated by means of MP2 and density functional theory methods and compared with respective experimental values wherever possible. Using two‐level model with full‐set of parameters dependence of transition energy (ΔΕ), transition dipole moment (μ0) as well as change in dipole moment from ground to excited state (Δμ), the origin of increase in β amplitudes is traced from the change in dipole moment from ground to excited state. The causes of change in dipole moments are further discovered through sum of Mulliken atomic charges and intermolecular charge transfer spotted in frontier molecular orbitals analysis. Additionally, analysis of conformational isomers and UV‐Visible spectra has been also performed for all designed derivatives. Thus, our present investigation provides novel and explanatory insights on the chemical nature and origin of intrinsic nonlinear optical (NLO) properties of 2,4‐dinitrophenol derivatives.

Modification of electrical properties of Al/p-Si Schottky barrier device based on 2′-7′-dichlorofluorescein

The charge conduction mechanism and electrical properties of Al/p-Si Schottky barrier device based on 2′-7′-dichlorofluorescein (DCF) were investigated by current density–voltage (J–V) and capacitance–voltage (C–V) methods. Thin film of DCF organic compound was deposited on p-Si substrate as an interfacial layer by spin-coating technique. The dark J–V characteristics indicate that the rectifying junction is formed at DCF/Al interface. The ideality factor and barrier height of the Al/DCF/p-Si Schottky diode are higher than that of Al/p-Si Schottky diode. The effect of the thickness of the DCF organic layer was investigated by evaluating electrical parameters, such as the barrier height, ideality factor, series resistance, and interface state density. It is seen that the thickness of the DCF layer significantly affects the electrical properties by influencing the space charge region of the Al/DCF/p-Si Schottky junction. The interface state density of the diode was determined using low-high frequency C–V plots and was of order of ≈1011 eV−1cm−2. The order of the interface state density of Al/DCF/p-Si is lower than most of metal/organic compound/inorganic semiconductor devices. The values of the barrier height of the studied diodes are significantly larger than those of conventional Al/p-Si Schottky diodes. The J–V curves in the reverse direction are taken and interpreted via both Schottky and Poole–Frenkel effects. Poole–Frenkel effect was found to be dominant in the reverse direction.The charge conduction mechanism and electrical properties of Al/p-Si Schottky barrier device based on 2′-7′-dichlorofluorescein (DCF) were investigated by current density–voltage (J–V) and capacitance–voltage (C–V) methods. Thin film of DCF organic compound was deposited on p-Si substrate as an interfacial layer by spin-coating technique. The dark J–V characteristics indicate that the rectifying junction is formed at DCF/Al interface. The ideality factor and barrier height of the Al/DCF/p-Si Schottky diode are higher than that of Al/p-Si Schottky diode. The effect of the thickness of the DCF organic layer was investigated by evaluating electrical parameters, such as the barrier height, ideality factor, series resistance, and interface state density. It is seen that the thickness of the DCF layer significantly affects the electrical properties by influencing the space charge region of the Al/DCF/p-Si Schottky junction. The interface state density of the diode was determined using low-high frequency C–V plo...

p-ZnTe/n-CdMnTe/n-GaAs diluted magnetic diode for photovoltaic applications

A p-ZnTe/n-CdMnTe/n-GaAs diode was grown by MBE technology. The current–voltage characteristics of the grown device were analyzed under dark and illumination conditions. Thermionic emission and the space charge limited current were used to interpret the IV conduction mechanism through the heterostructure p-ZnTe/n-CdMnTe/n-GaAs at different temperatures. Photovoltaic parameters such as the short-circuit current Isc and open-circuit voltage Voc, power P = IV, maximum power Pmax, maximum current IM and maximum voltage VM were calculated at different light intensities. The dynamic IV characteristics under illumination exhibit the photovoltaic behavior of the investigated sample. Photosensitivity and the responsivity of the prepared device were calculated at different illumination intensities. p-ZnTe/n-CdMnTe/n-GaAs is a new promising candidate for photovoltaic devices.

Hydrothermal Preparation of -Doped Titanate Nanotubes: Magnetic Properties and Photovoltaic Performance

Pure and -doped titanate nanotubes (TNTs) materials were synthesized by a hydrothermal method. Their morphology, optical properties, thermal stability, and magnetic properties were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), UV-Vis spectroscopy, thermal analysis, and magnetic measurements. It was found that doping renders -TNT visible light active and results in smaller crystallite size and larger surface area as well as higher thermal stability compared to pure titanate nanotubes. The estimated magnetic moments point to presence of weak antiferromagnetic interaction. Application of the prepared -TNT for modifying conventional photoanodes in polymer solar cells was attempted. Preliminary results show slightly improved photovoltaic energy conversion efficiency in the devices containing the newly designed -doped nanotubes.

Facile microwave-assisted synthesis of Te-doped hydroxyapatite nanorods and nanosheets and their characterizations for bone cement applications

In this work, the authors have fabricated the nanorods and nanosheets of pure and Te-doped HAp with different Te concentrations (0.04, 0.08, 0.16, 0.24wt%) by microwave-assisted technique at low temperature. The crystallite size, degree of crystallinity and lattice parameters are calculated. FE-SEM study confirms that the fabricated nanostructures are nanorods of diameter about 10nm in undoped and at low concentration of Te doping. However, at and higher concentration, it becomes nanosheets of about 5nm thickness. X-ray diffraction, FT-IR and FT-Raman studies shows that the prepared products are of HAp and Te has been successfully incorporated. From EDX the Ca/P molar ratio of the pure HAp is about 1.740, while this ratio for 0.04, 0.08, 0.16, 0.24 wt% Te doped is about 1.53, 1.678, 1.724, 1.792, respectively. Crystallite size was found to be increased with Te doping from 15nm to 62nm. The value of dielectric constant is found to be enhanced at higher concentrations of Te. The values of linear absorption coefficient were also determined and show that the prepared material with Te doping is more absorbable than pure and will be highly applicable in radiation detection applications. Furthermore, the antimicrobial potential of pure and Te doped HAp was examined against some Gram- negative and positive bacteria and fungi by agar disk diffusion method. The results demonstrated that the antimicrobial activity of Te doped HAp is stronger than that of pure HAp where it exhibited the highest activity against Bacillus subtilis>Candida albicans>Shigella dysenteriae.

Diffused reflectance and structure analysis for the nano-matrix (ZnO(1−x)SiO2(x)) system

Optical and structural properties of the investigated matrix ZnO(1-x)SiO2(x) system were characterized by various techniques such as X-ray analysis and UV-VIS-NIR absorption. The structural changes of the studied nano-matrix ZnO(1-x)SiO2(x) with the concentration of nanosilica are checked by X-ray analysis measurement. The crystal structures for ZnO, (ZnO)0.75(SiO2)0.25, (ZnO)0.50(SiO2)0.50 and (ZnO)0.25(SiO2)0.75 and pure SiO2 are hexagonal, monoclinic, tetragonal, orthorhombic and amorphous respectively and detailed crystal parameters are obtained. The electronic properties of ZnO(1-x)SiO2(x) are investigated, where the optical band gaps for the five studied systems are 3.22eV, 3.24eV, 3.27eV, 3.30eV and 4.5eV respectively. It is clear that the band gap increases with increasing SiO2 content. Mixing the ZnO with SiO2 enhance the UV response of these materials which is confirmed by diffused reflectance spectrum used to analyze the UV response of the studied systems.

Controlling of conduction mechanism and electronic parameters of silicon–metal junction by mixed Methylene Blue/2′-7′-dichlorofluorescein

Abstract Al/p-Si junction based on Organic Mixed Layer (OML) Methylene Blue (MB) and 2′-7′-dichlorofluorescein (DCF) was fabricated and the current–voltage ( I – V ) and the capacitance–voltage measurements of the structure have been obtained at room temperature. This combination resulted in both a good rectifying behavior and low leakage current. The characteristic parameters of the structure such as barrier height, ideality factor, interface states density and series resistance were determined from the electrical measurements. Also, Cheung functions and Norde method were used to evaluate the I – V characteristics and to obtain the characteristic parameters of the Schottky contact. High-low frequency capacitance–voltage characteristics have been observed to have a maximum. The maximum value of the capacitance is decreased with increasing frequency. The higher values of capacitance at low frequencies were attributed to interface states and the excess capacitance resulting from the interface states in equilibrium with the Si that can follow the alternating current signal. The J – V curves in the reverse direction are taken and interpreted via both Schottky and Poole–Frenkel effects. Poole–Frenkel effect was found to be dominant in the reverse direction.

Novel and facile microwave-assisted synthesis of Mo-doped hydroxyapatite nanorods: Characterization, gamma absorption coefficient, and bioactivity

In the current work, the authors report the microwave-assisted synthesis Molybdenum-doped (from 0.05 to 5wt%) hydroxyapatite (HAp) for the first time. The morphology of Mo-doped HAp is nanorods of diameter in the range of 25-70nm and length in the range of 25nm to 200nm. The good crystalline nature was confirmed from X-ray diffraction patterns and also lattice parameters, grain size, strain and dislocation density were determined. The crystallite size was found to be in the range 16 to 30nm and crystallinity was found to be enhanced from 0.5 to 0.7 with doping. The field emission SEM micrographs show that the morphology of the synthesized nanostructures of pure and Mo-doped HAp are nanorods of few nanometers. The vibrational modes were identified using the FT-Raman and FT-IR spectroscopy. The dielectric properties were studied and the AC electrical conductivity was found to be increased with increasing the concentration of Mo ions doping in HAp. Moreover, antimicrobial studies were also carried out to understand the anti-bacterial and anti-fungi properties. The results suggest that it may be a good bio-ceramics material for bio-medical applications. Mo-doped HAp was subjected to the gamma irradiation produced from Cs-137 (662keV) and its related parameters such as linear absorption coefficient, the half-value layer (HVL) and the tenth value layer TVL were calculated and analyzed.