Hussain Alawadhi

Magnetic susceptibility and compositional dependence of the energy gap in Cd1-xCoxTe

Single crystals of the diluted magnetic semiconductor Cd1-xCoxTe grown by the vertical Bridgman technique are characterized by wavelength-modulated reflectivity and magnetization measurements. Low-temperature magnetization and high-temperature magnetic susceptibility analysis were used to extract the exchange integrals for up to third-neighbour Co2+ pairs in the CdTe host: J1/kB = -25pm7 K, J2/kB = -3.0pm1.5 K, and J3/kB = -1.3pm0.3 K. These values correspond well to the values obtained for other Co-based II-VI diluted magnetic semiconductors and are a clear manifestation of the unusually large Co2+-Co2+ antiferromagnetic interaction. The excitonic energy gap Eg(x) of Cd1-xCoxTe in the wavelength-modulated reflectivity shows a linear monotonic increase with increasing x in the composition range studied.

Reduced Graphene Oxide Thin Film on Conductive Substrates by Bipolar Electrochemistry.

Recent years have shown an increased interest in developing manufacturing processes for graphene and its derivatives that consider the environmental impact and large scale cost-effectiveness. However, today’s most commonly used synthesis routes still suffer from their excessive use of harsh chemicals and/or the complexity and financial cost of the process. Furthermore, the subsequent transfer of the material onto a substrate makes the overall process even more intricate and time-consuming. Here we describe a single-step, single-cell preparation procedure of metal-supported reduced graphene oxide (rGO) using the principle of bipolar electrochemistry of graphite in deionized water. Under the effect of an electric field between two stainless steel feeder electrodes, grapheme layers at the anodic pole of the wireless graphite were oxidized into colloidal dispersion of GO, which migrated electrophoretically towards the anodic side of the cell, and deposited in the form of rGO (d(002) = 0.395 nm) by van der Waals forces. For substrates chemically more susceptible to the high anodic voltage, we show that the electrochemical setup can be adapted by placing the latter between the wireless graphite and the stainless steel feeder anode. This method is straightforward, inexpensive, environmentally-friendly, and could be easily scaled up for high yield and large area production of rGO thin films.Recent years have shown an increased interest in developing manufacturing processes for graphene and its derivatives that consider the environmental impact and large scale cost-effectiveness. However, todays most commonly used synthesis routes still suffer from their excessive use of harsh chemicals and/or the complexity and financial cost of the process. Furthermore, the subsequent transfer of the material onto a substrate makes the overall process even more intricate and time-consuming. Here we describe a single-step, single-cell preparation procedure of metal-supported reduced graphene oxide (rGO) using the principle of bipolar electrochemistry of graphite in deionized water. Under the effect of an electric field between two stainless steel feeder electrodes, grapheme layers at the anodic pole of the wireless graphite were oxidized into colloidal dispersion of GO, which migrated electrophoretically towards the anodic side of the cell, and deposited in the form of rGO (d(002) = 0.395 nm) by van der Waals forces. For substrates chemically more susceptible to the high anodic voltage, we show that the electrochemical setup can be adapted by placing the latter between the wireless graphite and the stainless steel feeder anode. This method is straightforward, inexpensive, environmentally-friendly, and could be easily scaled up for high yield and large area production of rGO thin films.

Structure and energy gap of Cd1?xCaxTe and Cd1?yCaySe as a function of Ca2+ incorporation

Single crystals of Cd1?xCaxTe and Cd1?yCaySe ternaries, grown by the Bridgman technique and characterized by microprobe and x-ray techniques, showed the upper limit of x and y to be 0.05. The excitonic energy gap, determined from the derivative signature of free excitons in wavelength modulated reflectivity, shows a linear increase with increasing Ca2+ concentration in both ternary alloys. The near-band gap emissions of donor-bound and of acceptor-bound excitons observed in photoluminescence, investigated as a function of alloy composition, reveal blue shifts of donor-bound excitonic signatures, in good agreement with those observed for free excitons. The Raman spectra of Cd1?xCaxTe reveal the clear presence of CaTe-like LO phonons, confirming that the Ca incorporation has indeed resulted in a ternary Cd1?xCaxTe with a characteristic two-mode behaviour.

Production of Size-Selected CuXSn1-X Nanoclusters

Composites of copper–tin (CuxSn1-x) nanoclusters were synthesized using the magnetron dc sputtering gas–condensation technique. Targets with controlled ratios of Sn to Cu were used to produce CuxSn1-x with different compositions. The effects on the nanocluster size and yield of the sputtering discharge power, inert gas flow rate, and aggregation length were investigated using a quadrupole mass filter. The sputtering discharge power was optimized to maximize the nanocluster yield. The results show that as the inert gas flow rate increases the nanocluster size increases and then decreases. These dependences could be understood in terms of the dominant nanocluster production mechanisms. This work demonstrates the ability of controlling the CuxSn1-x nanoclusters’ size and composition by optimizing the source operation conditions.

True random bit generators based on current time series of contact glow discharge electrolysis

Random bit generators (RBGs) in todays digital information and communication systems employ a high rate physical entropy sources such as electronic, photonic, or thermal time series signals. However, the proper functioning of such physical systems is bound by specific constrains that make them in some cases weak and susceptible to external attacks. In this study, we show that the electrical current time series of contact glow discharge electrolysis, which is a dc voltage-powered micro-plasma in liquids, can be used for generating random bit sequences in a wide range of high dc voltages. The current signal is quantized into a binary stream by first using a simple moving average function which makes the distribution centered around zero, and then applying logical operations which enables the binarized data to pass all tests in industry-standard randomness test suite by the National Institute of Standard Technology. Furthermore, the robustness of this RBG against power supply attacks has been examined and verified.

Electrodeposited Dendritic Structures of Copper Oxide as Solar Selective Absorbers in the UV–Vis Range

We report the electrodeposition of copper from a 0.2 M H2SO4 + 0.4 M CuSO4 · 5H2O aqueous solution on a copper substrate, and its subsequent oxidation in air for selective solar thermal absorbers applications. A thorough study of the morphological properties and crystalline structure of the deposited layer through SEM-EDS and powder XRD revealed self-assembled dendritic microstructures, crystallized into fcc copper oxides, Cu2O. The building blocks of these dendrites are spherically-shaped particles of an average diameter of ca. 1 μm. The copper oxide layer was optically examined by virtue of a spectrometer in the spectral UV–Vis range. The surface roughness induced by the existence of the dendrites has been seen to enhance the absorptance of the material: fourfolds enhancement of optical surface absorption in the wavelength range of 400–1,000 μm versus an air-grown copper oxide.

Assessment of Photoelectrode Material Based on (TiO2)1-x / (Al65Cu24Fe11)x in Dye-Sensitized Solar Cell Applications

This paper presents the results obtained for incorporating the Al65Cu24Fe11 material with the conventional TiO2 as the electron injection layer in dye-sensitized solar cells. The icosahedral phase of the Al-Cu-Fe system has attractive physical and optical properties at the target composition, and is obtained by synthesizing the material via the facile high energy ball milling process to ensures the highest possible interdiffusion of elemental powders, followed by heat treatment. The evolution of the i-phase is confirmed via X-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. The optical absorption and electrical properties of the compound are investigated by spectrometry, four probe measurement and Mott-Schottky analysis, respectively. Different cells with different percentages (x value) of (TiO2)1-x/(Al65Cu24Fe11)x are constructed and tested to obtain the electrical characteristic curves, efficiency and fill factor to quantify the effect of the proposed material mixture.

Acid-functionalized carbon nanofibers for high stability, thermoelectrical and electrochemical properties of nanofluids

Carbon-based nanofluids are viewed as promising thermal fluids for heat transfer applications. However, other properties, such as electrical conductivity and electrochemical behavior, are usually overlooked and rarely investigated despite their importance for the overall performance characterization of a given application. In this study, we synthesized PAN-based carbon nanofibers (CNF) by electrospinning, and characterized them using electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis. Thermoelectrical and electrochemical measurements were carried out on nanofluids. We found that, although CNF nanofluids exhibit good thermal and electrical properties with a negligible corrosive effect, the suspensions tend to sediment within a few days. However, acid treatment of CNF (F-CNF), which resulted in the shortening of the fibers and the appearance of surface-oxygenated species, made F-CNF-based nanofluids exhibit superior stability in water that extended for more than 90 days, with consistent and superior thermal and electrical properties.

Copper Nanoparticles Induced Genotoxicty, Oxidative Stress, and Changes in Superoxide Dismutase (SOD) Gene Expression in Cucumber (Cucumis sativus) Plants

With the increased use of metal nanoparticles (NPs), their access to the food chain has become a main concern to scientists and holds controversial social implications. This research particularly sheds light on copper nanoparticles (CuNP), as they have been commonly used in several industries nowadays. In this study, we investigated the phytotoxicity of CuNP on cucumber (Cucumis sativus) plants grown hydroponically. Atomic Absorption Spectroscopy (AAS), X-Ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM) analysis confirmed that C. sativus treated with CuNP accumulated CuNP in the plant tissues, with higher levels in roots, with amounts that were concentration dependent. Furthermore, genotoxicity was assessed using Random amplified polymorphic DNA (RAPD) technique, and our results showed that CuNP caused genomic alterations in C. sativus. Phenotypical, physiological, and biochemical changes were assessed by determining the CuNP treated plant’s total biomass, chlorophyll, H2O2 and MDA contents, and electrolyte leakage percentage. The results revealed notable adverse phenotypical changes along with decreased biomass and decreased levels of the photosynthetic pigments (Chlorophyll a and b) in a concentration-dependent manner. Moreover, CuNP induced damage to the root plasma membrane as determined by the increased electrolyte leakage. A significant increase in H2O2 and MDA contents were detected in C. sativus CuNP treated plants. Additionally, copper-zinc superoxide dismutase (Cu-Zn SOD) gene expression was induced under CuNP treatment. Overall, our results demonstrated that CuNP of 10–30 nm size were toxic to C. sativus plants. This finding will encourage the safe production and disposal NPs. Thus, reducing nano-metallic bioaccumulation into our food chain through crop plants; that possesses a threat to the ecological system.