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This study describes the synthesis of delafossite, CuFeO2, as a primary photocatalytic material for hydrogen generation. A photoelectrode, CuFeO2/CuO/Cu, was prepared by combusting a Cu foil dipped in FeCl3 in ambient air. This photoelectrode showed excellent optical behavior for the hydrogen generation reaction from sewage water, producing 90 µmol/h of H2. The chemical structure was confirmed through XRD and XPS analyses, and the crystalline rhombohedral shape of CuFeO2 was confirmed using SEM and TEM analyses. With a bandgap of 1.35 ev, the prepared material displayed excellent optical properties. Electrochemical measurements for H2 gas generation were carried out using the CuFeO2/CuO/Cu photoelectrode, comparing the effect of light and dark and monochromatic wavelength light. The electrode exhibited significant enhancement in light compared to dark, with current density (Jph) values of −0.83 and −0.1 mA·cm−2, respectively. The monochromatic light also had a noticeable effect, with the Jph value increasing from −0.45 to −0.79 mA·cm−2 as the wavelength increased from 640 to 390 nm. This system is cheap and durable, making it a promising solution for hydrogen gas fuel generation in the industry.

Piezoceramics with composition (1–z) [Bi0.5(Na0.84K0.16)0.5TiO3]0.96–0.04SrTiO3–zLiTaO3 (z = 0.00–0.030) were formulated by ordinary firing process following by rapid quenching treatment. Effect of LiTaO3 on the structural, electrical and energy-storage properties were analyzed. For the composition with molar ratio 0.025, room temperature large-field piezoelectric coefficient (Smax/Emax = d33*) of 885 pm/V at 3.6 kV/mm was recorded. Furthermore, for compositions z = 0.025 and 0.030, broad temperature stable dielectric constants and low losses from ~135 to 350 °C with a small variation of ± 15% was observed. Additionally, the energy density for z = 0.025 was ~0.60 J/cm3 in the broader temperature range of 75–125 °C, along with the energy-storage efficiency of greater than 70%. These observations suggest that the studied piezo-material compositions are promising for the ceramic actuators and capacitor applications.

Lack of environmental sustainability is a growing and pivotal matter due to the issues such as disturbances associated with biodiversity pollution and climate change. Pollutants are the major cause of these environmental threats in the atmosphere. At present, nano-based photocatalysts are at the forefront of the author's interest because of their promising potential as a green chemical-based compound, high catalytic activity, suitable and controllable surface area for wastewater treatment. Semiconductor materials on a nano-sized scale have electronic and optical properties depending on their building block size, which plays a vital role in developing smart materials that are well-efficient for simultaneously destroying harmful chemical contaminants from our environment. This makes these materials useful in many possible industrial applications, such as water purification. In this review, we have reported the most significant results contributing to the progress in the area of environmental hazardous pollutant detection and removal focused on water purification especially through photocatalysis to give readers an overview of the present research trends. Moreover, we have analyzed previous studies to indicate key principles of photocatalysis and provide guidelines that can be used to fabricate more efficient photocatalysts.

In this study, pure cobalt ferrite (CoFe2O4) nanoparticles and europium doped CoFe2O4 (CoFe2−xEuxO4; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe3+) ions by trivalent rare earth europium (RE-Eu3+) ions on the microstructure, optical and magnetic properties of the produced CoFe2O4 nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu2O3 phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ1 and υ2) and tetrahedral A-site (υ3) around 415 cm−1, 470 cm−1 and 600 cm−1 respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu3+ ions within CoFe2O4 host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu3+ added to CoFe2O4 in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe2−xEuxO4, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe2O4 have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu3+ in CoFe2O4 lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe2O4 samples. Substitution of Fe3+ ions in CoFe2O4 nanoparticles with RE-Eu3+ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.

In this study, Titanium dioxide nanostructures were hydrothermally synthesized at different temperatures 130, 170 and 200 °C. The structural properties and crystallite size of TiO2 nanostructures were confirmed through XRD analyses. Moreover, the morphologies were confirmed using TEM analyses. These analyses confirmed the formation of single phase TiO2 nanostructures. The average crystallite size for the TiO2 nanostructures synthesized at different hydrothermal temperatures of 130, 170, and 200 °C was found to be 11.5 nm, 5.3 nm, and 5 nm, respectively. The impact of changes in these morphologies on the physical characteristics and photokilling activity of cancer cells has been studied. The results showed that the photokilling activity of TiO2 nanostructures is morphology dependent, with TiO2 nanowires having the highest activity and nanosheets having the lowest under our experimental conditions.

In the present work, we investigate the effect of Ni doping on the crystallite size (Dhkl), optical band gap ($$E_{\text{g}}^{\text{opt}}$$), Photoluminescence emission (PL) behavior, as well as the photocatalytic degradation efficiency of methylene blue (MB) by ZnS nanoparticles (NPs) catalyst. Undoped and Ni-doped ZnS NPs at Ni concentrations of 2, 4, 6, 8, and 10% are successfully synthesized with average Dhkl from 2.75 to 3.76 nm by the sonochemical technique. X-ray diffraction (XRD) patterns and high-resolution transmission electron microscope (HRTEM) images of all samples exhibit pure zinc-blende type of ZnS cubic structure. The increase in Ni content up to 4% results in an increase in the Dhkl and unit cell volume (V) accompanied by a decrease in $$E_{\text{g}}^{\text{opt}}$$. Meanwhile, a further increase in Ni content above 4% leads to a decrease in Dhkl and V and an increase in $$E_{\text{g}}^{\text{opt}}$$. The deconvoluted PL emission spectrum of the undoped sample at the excitation wavelength (λex) of 325 nm reveals emission bands centered at 3.41, 3.16, 2.89, and 2.26 eV, which are red-shifted with increasing λex to 370 nm. It is observed that the PL emission intensity is quenched with increasing Ni content without any noticeable change in the PL peak position. Ni-doped ZnS catalyst with 2% Ni exhibits maximum photo-degradation efficiency of 52.23% with a rate constant of 0.00396 min−1. The obtained results demonstrate that Ni doping can tune the optical band gap and photocatalytic efficiency of ZnS NPs that make it applicable for many optoelectronic applications.

Charge carrier modulation of graphene-based field effect transistors (GFETs) is the key factor to utilize and enhance its fascinating properties for technological applicability. Here, we have demonstrated the gate-dependent tweaking of electrical properties of graphene devices by application of honey as a top gate dielectric. Electrical characterization of dual-gated GFET is elucidated at different top and back-gate voltages. A charge neutrality point is fine-tuned by varying the top gate voltage (Vtg) from + 3 to − 4 V. The change in carrier density is clearly observed from 3.66 × 1012 to 2.15 × 1011 cm−2 at + 3 to − 4 Vtg. The charge carrier mobility of gel-gated GFET is increased significantly to 5376 cm2/V ⋅ sec by increasing top-gate voltages up to − 4 V. Result demonstrates a cost-effective, facile and rapid fabrication of top-gated devices and suggest natural dielectric materials as good candidate to replace conventionally available gate dielectrics in FET technology.

This paper reports the microstrcure, optical and electrical characteristics of undoped and Cu doped CdTe nanostructured thin films prepared on glass substrates by electron beam evaporation technique. The Crystallographic study of X-ray diffraction shows that CdTe and Cu doped CdTe films crystallize in the form of a cubic zinc blende structure. Microstructure analysis reveals that as the Cu doping level increases, the average crystallite size increases, while the microstrian decreases due to the improvement of the crystallinty, thereby reducing defects. XRD and AFM investigations confirmed the nanostructure characteristic of undoped and Cu doped films. It was found that the optical band gap energy increases from 1.485 eV to 1.683 eV as the Cu concentration increases from 0 wt. % to 10 wt. %, which may be related to the Burstein-Moss effect. The refractive index is calculated from the Swanepoel envelope method and found to decrease with the increase of the Cu doping due to the decrease in the prolizability. Similarly, the extinction coefficient decreases with the increase of Cu in CdTe matrix. The dc electrical conductivity is found to increase with increasing Cu doping, which is attributed to the increase in the grain size, thereby reducing the scattering of the grain boundary. Furthermore, two conduction mechanisms of the carrier transport in nanostrcutured undoped and Cu doped CdTe films were observed. The low temperature dependence of the conductivity of undoped and Cu doped CdTe nanostructured films is explained based on Mott’s variable range hopping conduction mechanism model (VRH). Interestingly, the calculated values of hopping distance R, the hopping energy W and the the density of states at the Fermi level N(EF) are consistent with the Mott's VRH. Finally, Hall effect measurements show that all the films have p- type conduction behavior. Besides, the results show that as Cu doping level increases, the carrier concentration and the Hall mobility increase due to the decrease in grain boundary scattering with the increase in grain size. Accordingly, it can be concluded that by increasing the Cu doping level in the CdTe film, the conductivity is increased, thereby improving the performance of the CdTe absorber layer in the solar cell structure.

Cadmium telluride (CdTe) thin films were deposited by thermal evaporation method under base pressure 2 × 10−5 mbar on corning glass substrate. In this work, we study the effect of cadmium chloride (CdCl2) heat treatment in argon and oxygen (Ar + O2) atmosphere on the structural, morphological and optical properties of CdTe thin films to achieve high quality thin film absorber layer for solar cells applications. The structural characteristics were studied by X-ray diffraction (XRD). The microstructure parameters of the films such as average grain size (Davg), average lattice strain (eavg) and dislocation density (ρD) have been calculated via XRD line broadening analysis. XRD investigation revealed that, the samples show polycrystalline nature pronounced with cubic zinc blende structure with a strong preferentially (1 1 1) texture orientation. It has been found that the crystallinity of the films enhanced during (Ar + O2) annealing and CdCl2 heat treatment. The surface morphology of CdTe thin films was investigated by field emission scanning electron microscope (FE-SEM). XRD and FE-SEM results of CdCl2 treated films showed recrystallization and progressive increase in grain size. The optical properties of all samples were estimated using UV–vis–near-infrared (NIR) spectrophotometer. The Swanepoel envelope method has been employed to evaluate the various optical parameters of CdTe films such as refractive index and film thickness. The as-deposited films have a relatively high value of refractive index of 2.54, in contrast the CdCl2 treated films have a relatively low value of 2.1 in the whole wavelength range. The optical energy gap values slightly decrease from 1.56 eV for as-deposited films up to 1.54 eV for CdCl2 heat treated films. CdCl2 heat treatment in (Ar + O2) atmosphere is found to be a promising method to improve the physical properties of CdTe thin film solar cells.

ZnS film with various thicknesses (d ≈ 100–350 nm) deposited on the ITO coated glass substrate (ZnS/ITO/glass) by an electron beam evaporation process was examined structurally and optically. Different techniques were used to specify and analyze the optical characteristics of the film, such as spectroscopic ellipsometric (SE) and spectrophotometric (SP). The ZnS/ITO/glass films exhibit a wurtzite hexagonal type structure entrenched in the crystalline background of ITO film. XRD analysis revealed changes in structural and microstructural parameters, such as a decrease in lattice parameters, a reduction in microstrain, and a raise in crystallite size. The optical constants and the optical energy gap were extracted from SE by constructing an ellipsometric optical model, while the optical constants were calculated from SP by using Murmann's exact equations. It was seen that the overall behaviour of the refractive index n of the ZnS/ITO/glass films obtained from SE and SP increases with an increase in ZnS layer thickness, which is attributed to the increment of the size of the grain. It was additionally found that, the overall behaviour of the extinction coefficient k of the ZnS/ITO/glass films increases, when the thickness of the ZnS layer increments. Also, the direct optical transition was observed with energy band gap diminishes from 3.423 (d = 100 nm) eV to 3.287 eV (d = 350 nm) that is because of the rise in grain size, the decrease in microstrain, and reduction in lattice constants. Furthermore, it was found that the deposition of ZnS on ITO coated glass substrate increases the absorption compared with the ZnS/glass film and then reduces the transmittance and energy band gap. It was concluded that as the ZnS thickness increases, the optical constants of ZnS/ITO/glass films enhance. Finally, the overall behaviour of the optical constants within the experimental error range of the ZnS/ITO/glass films with different ZnS layer thicknesses obtained by SE was found to be consistent with that calculated from SP measurement.

In the present work, we synthesized CoxZn1-xFe2O4 spinel ferrite nanoparticles (x= 0, 0.1, 0.2, 0.3 and 0.4) via the precipitation and hydrothermal-joint method. Structural parameters were cross-verified using X-ray powder diffraction (XRPD) and electron microscopy-based techniques. The magnetic parameters were determined by means of vibrating sample magnetometry. The as-synthesized CoxZn1-xFe2O4 nanoparticles exhibit high phase purity with a single-phase cubic spinel-type structure of Zn-ferrite. The microstructural parameters of the samples were estimated by XRD line profile analysis using the Williamson–Hall approach. The calculated grain sizes from XRPD analysis for the synthesized samples ranged from 8.3 to 11.4 nm. The electron microscopy analysis revealed that the constituents of all powder samples are spherical nanoparticles with proportions highly dependent on the Co doping ratio. The CoxZn1-xFe2O4 spinel ferrite system exhibits paramagnetic, superparamagnetic and weak ferromagnetic behavior at room temperature depending on the Co2+ doping ratio, while ferromagnetic ordering with a clear hysteresis loop is observed at low temperatures (5K). We concluded that replacing Zn2+ ions with Co2+ ions changes both the structural and magnetic properties of ZnFe2O4 nanoparticles., This research was funded by Spanish “Ministerio de Economía y Competitividad” (MAT2016-78155-C2-1-R, MAT2013-40950-R, MAT2011-27573-C04-02 and FPI grant BES-2011-046948 to MSM.A.), “Gobierno del Principado de Asturias” (GRUPIN14-060) and FEDER.

The current work focused on studying the optical and structural properties of (CdS)1-x (ZnS)x thin films fabricated by thermal vacuum evaporation approach. The evaporation was implemented at room temperature from bulk samples synthesis by sintering approach. The energy gap, index of refraction, extinction coefficient and absorption coefficient were estimated from the experiment and employed in our theoretical model to estimate quantitatively the solar cell efficiency and short-circuit current density of CdS:ZnS/CdTe structure. The calculations of cell efficiency as well as short-circuit current density were computed on the bases of the optical losses caused by reflection at interfaces and absorption process occurred in the frontal charge-collecting and window layers and the recombination losses at front and back surface of CdTe. The XRD analysis showed that the intensity and position of predominant peak of CdS gradually changes with increasing the ZnS content indicating a success of forming CdS:ZnS alloy. The films exhibited direct band-to-band transitions and the optical energy gap increased from 2.40 eV to 3.10 eV with increasing of ZnS content up to x = 0.50. The short-circuit current density increased from 16.50 mA/cm2 to 21 mA/cm2 and the cell efficiency increased from 13.10% to 17.10% due to the increase of the ZnS content from x = 0 to x = 0.50.

In this study, pure cadmium oxide (CdO) nanoparticles and mixed gadolinium oxide (Gd2O3)–CdO nanocomposites with different Gd2O3 contents (0–15%) were synthesized by a facile precipitation technique followed by calcined treatment. The X-ray diffraction analysis illustrated that all samples had high cubic-phase purity and a good crystallinity. Further support for the formation of highly pure CdO and Gd2O3 phases was obtained via infrared spectroscopy. The morphologies of pure CdO and mixed Gd2O3–CdO nanoparticles were probed by scanning electron and transmission electron microscopy, which demonstrated that the collected samples consisted of individual semi-spherical shaped entities of different particle sizes (23–31 nm). The optical band gap of the developed samples was computed based on the Tauc equation and showed a decrease from 3.41 to 2.75 eV upon increasing the Gd2O3 content. The 3D fluorescence analysis showed that the quenching in the emission peak intensity with increasing Gd2O3 content was due to the high separation efficiency of photogenerated electron–hole pairs. Moreover, the Gd2O3(15%)–CdO nanocomposite showed superior photodegradation efficiency (89.1%) of methylene blue compared to 44.4% for pure CdO. At pH 11.5, >3-fold enhancement in degradation rate (0.044 min −1) was obtained compared to natural pH 9.6. Reusability study showed stability of the Gd2O3–CdO photocatalyst in four cycles of methylene blue degradation. Trapping experiment of holes and electrons revealed extensive contribution of holes rather than electrons in producing active oxidizing species.

In this study, low-dimensional (LD) MgO nanostructured thin films with three different morphologies, namely, nanowires (NWs), nanotubes (NTs) and nanoparticles (NPs) were fabricated by a vapor transport method on quartz and silicon substrates under optimum growth conditions. It was found that the deposition parameters have great influences on the morphology, optical, photoluminescent, electrical, gas sensing and magnetic behavior of the resulting products. X-ray diffraction analysis illustrated that all three LD MgO nanostructures have five expected Bragg peaks of cubic MgO phase purity with well crystalline nature. The morphology and diameter of LD MgO nanostructures were probed by scanning electron and transmission electron-microscopes. The optical band gap values for LD MgO nanostructure films varies between 3.65 eV and 3.95 eV depending on growth conditions. It was found that all MgO films exhibit two distinguishing PL peaks related to the near band edge luminescence of LD MgO nanostructures and defect levels produced by oxygen vacancies, respectively. It was found that the dependence of electrical conductivity on film morphology can be attributed to the defect levels produced by O2- ion vacancies during the synthesis process. NH3 gas sensing efficiency of LD MgO nanostructures with various morphologies were carried out at different operating temperatures from 25 °C to 300 °C. The MgO film with NWs structure has the highest sensor response value of 27 at 100 °C and the film with NPs structure has the lowest response value of 12 at 150 °C. Ferromagnetic order has been recorded for all morphologies at room temperature with clear hysteresis loop and different magnetic parameters depending on growth conditions. Thus, our results present a direct route for the growth of high-quality and diverse LD MgO nanostructures developed via vapor transport for many technological applications.

Sandy soils under arid and semi-arid conditions are characterized by poor physical and biochemical properties such as low water retention, rapid organic matter decomposition, low nutrients use efficiency, and limited crop productivity. Addition of organic amendments is crucial to develop soil properties and consequently enhance nutrients use efficiency and lessen organic carbon decomposition. Two years field experiments were developed to investigate the feasibility of using poultry manure and its derived biochar integrated with different levels of N fertilizer as a soil amendment for newly reclaimed sandy soils in Western Desert of El-Minia Governorate, Egypt. Results of this research revealed that poultry manure and its derived biochar addition induced pronounced effects on soil moisture content at saturation point, field capacity (FC) and consequently available water. Data showed that application of poultry manure (PM) or PM-derived biochar (PMB) in combination with inorganic N levels had caused significant changes on a range of the investigated sandy soil biochemical properties including pH, EC, mineral N, dissolved organic carbon (DOC), dissolved organic N (DON) and quotient DOC/DON. Overall, the impact of PMB on soil physical properties was detected to be superior than the impact of PM, regardless the inorganic N levels. In addition, the obtained results showed that PM and PM application had the capacity to stimulate vigorous growth, nutritional status, production levels of wheat and sorghum, and to increase soil organic matter content and N uptake and recovery compared to control. By contrast, comparing between PM and PMB at different levels of inorganic N, the obtained results showed higher relative increases in both grain and straw yields of wheat in plots treated with PM than in those treated with PMB. The interesting feature of this research is that the biochar derived from PM increased treated sandy soil organic carbon (SOC) 1.75 times more than soil treated with PM itself at the end of cropping seasons albeit double-applied amount of PM. This was attributed to the higher carbon stability of biochar treated sandy soils increasing soil persistence for carbon decomposition in comparison with PM labile carbon. It could be concluded that organic manures applied to sandy soils under arid and semi-arid conditions are subjected to high decomposition and mineralization rates through crop seasons. Biochar derived from organic wastes considers as a source of stable carbon and could be very hopeful choice for substituting easily decomposable organic manures under arid conditions. Therefore, sustainable agriculture and productivity in newly reclaimed sandy soils desire one high rate addition of biochar derived from organic manures instead of frequent addition of such organic amendments.

The structural and electrical properties of the as-prepared and annealed In45Sb35Se20−xTex thin films with different compositions (x = 2.5, 5, 7.5, 10, 12.5 and 15 at.%) prepared by electron beam evaporation method are studied. The XRD patterns of the as-prepared thin film show that the investigated compositions have amorphous and polycrystalline structure depending on the Te content. After annealing the In35Sb45Se20−xTex thin films, at 473 K for 10 min, crystalline peaks are obtained. The electrical measurements were taken during heating in the range from 300 to 600 K. It was found that the resistivity decreases with increasing temperature for all the compositions indicating that these films have a semiconducting behavior. After annealing it was found that the room temperature resistivity of the investigated films were found depend on annealing temperature which cause a reduction by five orders of magnitude. These can be attributed to the amorphous–crystalline transformation, which is accompanied by a pronounced change in the electronic structure.

Ultrasonically cleaned glass slides are used as substrates for receiving the different thickness of Zinc selenide (ZnSe) films. The deposition processes of our investigated films were done at room temperature using physical thermal evaporation mechanism under vacuum ≈2 × 105 mbar. We investigated the optical and structural parameters of ZnSe thin films in correlation with film thickness (200–650 nm). Various techniques such as UV–vis-NIR spectrophotometer, x-ray diffraction lines and field emission scanning electron microscope were used to investigate aforementioned parameters. Structural analysis indicate that the films exhibited cubic preferred orientation along the plane (111) and the crystallinity and crystallite size of films increases linearly with film thickness. The optical band gap ranges from 2.69 to 2.81 eV and it is founded that it increases with film thickness. According to the applied Swanepoel’s approach, it is possible to estimate the optical parameters and average thickness of the ZnSe thin films of different thicknesses with higher accuracy.

In this study, we report the preparation of different Sb 2 S 3 morphologies in the same experimental setup. We utilized the method of vapor phase transport with direct evaporation of high purity Sb 2 S 3 powder on quartz and Si (100) substrates. The deposited Sb 2 S 3 nanostructures showed different morphologies and crystallinities without using metal catalyst seed layers. The successfully formed Sb 2 S 3 morphologies were nanowires, nanorods, nanodendrites and nanoparticles, as verified by the scanning electron microscopy and transmission electron microscopy analysis. We found that the physical characteristics of the final product are a function of the differential temperature inside the furnace tube. The X-ray diffraction analysis confirmed the formation of the orthorhombic pure phase of crystalline stibnite-Sb 2 S 3 . The energy-dispersive X-ray spectroscopy spectra validated the high purity of the synthesized products. Moreover, the relation of the morphology and the optical and electrical properties of Sb 2 S 3 thin films have been studied by various techniques. The optical analysis by UV–vis–near-infrared (NIR) spectroscopy shows that the optical band gaps of the different synthesized films range from 1.64 to 1.92 eV. The refractive indices ( n ) of Sb 2 S 3 thin films were found to be morphology dependent. The film with nanoparticles morphology has the highest n value of 2.1 and the film with nanowires morphology has the lowest n value of 1.97. In all prepared samples photoluminescence (PL) spectra exhibit a distinct emission peak at 615 nm (⁓ 2.02 eV) in terms of intensity and FWHM. The dc-electrical conductivity of various Sb 2 S 3 nanostructures is thermally activated according to Arrhenius law with two types of conduction mechanisms. The conduction in the high temperature and lower temperature zones is due to the hopping conduction via localized states and the thermionic emission respectively. The study provides a framework for future research in semiconductor nanomaterials with controllable morphologies for applications of optoelectronics.

The low-temperature softening of the TO1 phonon of SrTiO3 (STO), which determines its incipient ferroelectricity, is known to be partially hindered either in the bulk under strong electric fields, or in thin STO films. Here we show, by terahertz (THz) reflectivity measurements, that a similar effect is produced in bulk STO and at zero static field by ultrathin metallic films on its surface, like a 10-nm-thick film of SrRuO3 (SRO), or the two-dimensional electron system (2DES) present at the interface with LaAlO3. In SRO/STO, the observed hardening is well explained by the depolarizing action of the SRO free electrons which follow adiabatically the ion motion. In LAO/STO, a weaker TO1 hardening could be detected by patterning the 2DES in the form of microstripes and using a polarized THz field parallel (E-) or orthogonal (E-) to the stripes. At 10 K, when TO1 is excited together with the free electrons by E-, its absorbance is harder by about 7 cm-1 than that measured when TO1 is coupled to the plasmon-polariton confined within the stripes, being excited by E-.

Physical properties of In 35 Sb 45 Se 20− x Te x thin films with different compositions ( x =2.5, 5, 7.5, 10, 12.5 and 15 at %) prepared by electron beam evaporation method are studied. X-ray diffraction results indicate that the as-evaporated films depend on the Te content and the crystallized compounds consist mainly of Sb 2 Se 3 with small amount of Sb 2 SeTe 2 . Transmittance and reflectance of the films are found to be thickness dependent. Optical-absorption data indicate that the absorption mechanism is direct transition. Optical band gap values decrease with increase in Te content as well as with increase in film thickness.

Electrical conductivity of some dibenzoylme- thane arylhydrazones (DBMAH) were measured during heating and reheating runs. The observed variation of the conductance of the polycrystalline sample during thermal agitation was found to depend on the ordering and disor- dering of molecules which in turn cause the lattice dipole to distort. A semiconducting behavior was detected for these systems as it was deduced from their conductance values (1.7 9 10 -6 - 8.25 9 10 -7 ohm -1 cm -1 ). The presence of substituents affects markedly the measured electrical conductivity and calculated activation energy values.

The electrical and thermal properties of some acetylacetone-(I) and benzoylacetone-(II) arylhydrazone derivatives have been investigated. The results obtained show semiconductor behavior as evident from the positive temperature coefficient of electrical conductivity (dG/dT). Values of activation energy (ΔE) have been calculated in each case. The electrical conductivity increases with the introduction of either electron-donating or electron-withdrawing substituents to the phenyl ring. Differential thermal analysis curves showed sharp well-defined peaks at the melting point of the investigated compounds. The latent heats of fusion were calculated from these thermograms.

The Raman spectrum of ${\mathrm{Ba}}_{2}{\mathrm{CuGe}}_{2}{\mathrm{O}}_{7}$, a tetragonal insulator which develops Dzyaloshinskii-Moriya helical magnetism below ${T}_{N}=3.2\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, has been detected at temperatures varying from 300 to 80 K in a single crystal, with the radiation polarized either in the $ab$ plane or along the $c$ axis of its tetragonal cell. Twenty-nine phonon lines out of the 35 allowed by the Raman selection rules for the present geometry were observed, and their vibrational frequencies were found in overall good agreement with those provided by shell-model calculations. Together with the previous report on the infrared-active phonons [A. Nucara et al., Phys. Rev. B 90, 014304 (2014)], the present study provides an exhaustive description, both experimental and theoretical, of the lattice dynamics in ${\mathrm{Ba}}_{2}{\mathrm{CuGe}}_{2}{\mathrm{O}}_{7}$.

${\mathrm{BiMnO}}_{3}$ (BMO), ferromagnetic (FM) below ${T}_{c}\ensuremath{\simeq}100\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, was believed to also be ferroelectric (FE) due to a noncentrosymmetric $C2$ structure, until diffraction data indicated that its space group is the centrosymmetric $C2/c$. Here we present infrared phonon spectra of BMO, taken on a mosaic of single crystals, which are consistent with $C2/c$ at any $Tg10\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, as well as room-temperature Raman data which strongly support this conclusion. We also find that the infrared intensity of several phonons increases steadily for $T\ensuremath{\rightarrow}0$, causing the relative permittivity of BMO to vary from 18.5 at 300 K to 45 at 10 K. At variance with FE materials of the displacive type, no appreciable softening has been found in the infrared phonons. Both their frequencies and intensities, moreover, appear insensitive to the FM transition at ${T}_{c}$.

Cadmium sulphide (CdS) thin films have been grown on corning glass substrate by thermal evaporation technique under base pressure 2 × 105 mbar. In this study we investigate the influence of Cadmium chloride (CdCl2) heat treatment and argon and oxygen (Ar + O2) annealing on the structural, morphological optical and electrical properties of CdS thin films to achieve high quality thin films for solar cells applications. X-ray diffraction (XRD), Field Emission scanning electron microscope (FE-SEM) and UV–Vis-NIR spectrophotometer were used to confirm and investigate the different physical properties of CdS films. The quality of CdS thin films crystallinity including the average grain size (D avg), the average lattice strain (e ls) and the dislocation density (ρ D) were extracted via XRD line broadening analysis. XRD analysis revealed that the samples are polycrystalline in nature with a mixed (hexagonal + cubic) structure and the crystallinity of the films increases with both (Ar + O2) annealing and CdCl2 heat treatment. After (Ar + O2) annealing and CdCl2 heat treatment processes the mean values of the grain size indicating the grain growth of CdS films. The surface morphology of the CdS films was examined by (FE-SEM) analysis; which confirmed the nano-crystalline nature of the CdS films with uniform coverage of the substrate surface; The optical properties of as-deposited, (Ar + O2) annealed and CdCl2 treated CdS films were discussed in detail. The optical energy gap was calculated using Tauc plot extrapolation. It was found to be increased from 2.43 eV for as-deposited film to 2.45 for CdCl2 treated CdS film. Swanepoel method was employed to estimate the thicknesses and extract the refractive index of the CdS films. The Room temperature resistivity decreased from 13.4 Ω cm for as-deposited CdS film to 2 and 0.8 Ω cm for (Ar + O2) annealed and CdCl2 treated CdS films respectively. The CdCl2 treated CdS film has the highest figure of merit value of 29 × 10−4 Ω−1. The obtained results confirm that the CdCl2 heat treatment process in (Ar + O2) atmosphere can enhance the physical properties of CdS thin films as a promising window layer or buffer layer material for CdS/CdTe and Cu(In,Ga)Se2 solar cells.

In this study, Monoclinic bismuth oxide nanorods (α-Bi2O3 NRs) were successfully synthesized by a simple one-step hydrothermal route using (water: ethanol) (1:1) as a mixed solvents at optimum conditions. The Bi2O3 nano-powder was characterized in detail by different techniques in terms of their structural, morphological, compositional, optical and photocatalytic properties. X-ray diffraction (XRD) analysis indicated that the as-synthesized Bi2O3 NRs exhibited high purity with monoclinic structure (α-Bi2O3) and good crystallinity. The Transmission electron microscope (TEM), Energy dispersive x-ray spectroscopy (EDXS) and Field Emission scanning electron microscope (FE-SEM) analysis clearly confirmed the high purity and the nanorod morphology of the as-synthesized Bi2O3 sample. The optical band gap of α-Bi2O3 NRs was estimated using the UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS) analysis according to the Kubelka–Munk theory. The optical band gap of α-Bi2O3 NRs was found to be 3.55 eV for an indirect allowed transition and 3.63 eV for a direct allowed transition. The Fourier transfer infrared spectroscopy (FTIR) was employed to check the structure as well as to evaluate the phonon vibration modes corresponding to Bi2O3. Photocatalytic activity of α-Bi2O3 NRs was investigated using UV source lamp. The as-synthesized α-Bi2O3 NRs photocatalyst exhibited better performance for degradation and decolorization of Methylene blue (MB) under ultraviolet (UV) irradiation. MB was completely photodegraded after 210 min under UV irradiation using α-Bi2O3 NRs as photocatalyst.

The lattice dynamics of Ba2CuGe2O7, a compound which develops Dzyaloshinsky-Moriya helical magnetism below TN=3.2 K, has been studied by measuring the infrared reflectivity of a single crystal with the radiation polarized both in the ab plane and along the c axis of its tetragonal cell, from 7 to 300 K. In this compound, where the unit cell has no inversion symmetry, 14 E phonon modes of the ab plane, out of the 18 predicted, and nine B2 modes of the c axis, out of the ten predicted, have been observed. They have been assigned to the atomic motions by a comparison with shell-model calculations, which provided vibrational frequencies in good agreement with the experiment, while most calculated intensities turned out to be much lower than the experimental values. This discrepancy has been tentatively explained by assuming strong electron-phonon interactions, a hypothesis supported by the failure of the f-sum rule if restricted to the phonon region. Indeed, we observe a remarkable increase in the oscillator strengths between 300 and 200 K for the phonons of the ab plane (between 300 and 100 K for the c axis), which implies an increase in the dielectric constant of Ba2CuGe2O7 below room temperature.

Lanthanum manganites with a massive concentration of La defects can be stabilized in the form of thin films, by exploiting the structural stress produced by a substrate such as SrTiO3. They undergo an insulator-to-metal transition (IMT) like those doped by divalent ions, which is here studied by measuring the optical conductivity of LaxMnO films with x = 0.66, 0.88, 0.98 and 1.10, and with , from the far infrared to the near ultraviolet, and between 20 and 300 K. The IMT is here a slow process which continues down to 100 K at least, more than 250 K below its onset at the Curie temperature Tc and at the TIMT measured from the dc resistivity. The metallization is here monitored through the increase of the Drude term and a transfer of spectral weight from a 'hard' midinfrared band MIR-2 peaked between 3000 and 5000 cm−1 at room temperature, to a 'soft' midinfrared band MIR-1 at ~ 1000 cm−1 and to the Drude term. This evidence is in good agreement with a model of phase separation below Tc, where insulating and paramagnetic regions of small polarons coexist with conducting and ferromagnetic regions populated by large polarons and free carriers.