Electron Dispersive X-ray Measurements Research Articles

Efficiency Enhancement by Insertion of ZnO Recombination Barrier Layer in CdS Quantum Dot-Sensitized Solar Cells.

In this investigation we report the formation of thin ZnO recombination barrier layer at TiO₂/CdS interface aimed for the improvement in performance of CdS sensitized solar cell. The film was deposited upon nanocrystalline mesoporous TiO₂ surface by following a simple chemical process and characterized, using UV-Visible spectroscopy, X-ray diffraction and electron dispersive X-ray measurements. The insertion of ZnO thin layer enhances the QDSC (Quantum dot sensitized solar cell) performance, contributed mainly by an increase in open circuit voltage (Voc) due to reduced electron back transfer from TiO₂ conduction band. Moreover, the analysis of photovoltaic characteristics upon increasing the thickness of the ZnO film reveals that the ZnO recombination barrier layer with optimum thickness at porous TiO₂/CdS interface proved to be an effective potential barrier for minimizing electron back recombination.

Role of Bi/Tm substitution in Bi-2212 system on crystal structure quality, pair wave function and polaronic states

This comprehensive study finds strongly out the crucial variations in the dc electrical resistivity, superconducting, crystal structural and flux pinning mechanisms with the partial replacement of homovalent Tm+3 inclusions by Bi+3 impurity in the active layers of Bi-2212 superconducting material. Materials of type Bi2.1-xTmxSr2.0Ca1.1Cu2.0Oy with molar ratio changes of 0.00 ≤ x ≤ 0.30 are prepared by conventional solid-state reaction route in atmospheric pressure and the characterizations are exerted by the bulk density, dc electrical resistivity (ρ-T), powder X-ray diffraction (XRD), critical current density (Jc), scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) experimental measurements. The combination of experimental results evaluated from the bulk density, dc electrical resistivity, XRD and EDX measurements points out that the Tm foreign impurities mostly incorporate successfully into the Bi-2212 crystal lattice. In fact, the EDX investigations verify that the thulium impurities may mostly be substituted for the bismuth sites in the crystal structure. All the experimental results declare that the characteristic features improve regularly with the increment in the Tm impurity level up to x = 0.07 beyond which the properties degrade dramatically. In this respect, the sample with x = 0.07 exhibits highest electrical conductive/metallic characteristics as a consequence of the refinement in the crystal structure quality and connectivity between the superconducting grains, being favored by bulk density and related relative degrees of granularity surveys. Likewise, the material presents the maximum offset-onset critical transition temperature values of 85.61 K–85.85 K due to the increment in the formation of effective and strong electron-phonon coupling probabilities and optimization of mobile hole carrier concentrations in the Cu-O2 consecutively stacked layers. In other words, the optimum content level leading to transit inherently over-doped nature into optimally doped state strengthens the amplitude of pair wave function for the Bi-2212 material. In more sophisticated interpretations, the presence of optimum dopant in the crystal structure changes the vibrational mode intensities of O (1)CuA1g, B1g phonons and O (2)SrA1g phonon so that the formation possibility of bipolaron out of two polarons increases strongly in a polarizable lattice (polaronic effect). Additionally, the highest self-field Jc of 95 A/cm2 confirms the fact that the optimum dopant augments the effective nucleation centers along the intragrain and inter-grain boundaries in the crystal system. Similarly, the material prepared with x = 0.07 presents the smoothest, densest, largest average crystalline distribution, lowest porosity and most uniform surface appearance with the finest connection between the superconducting grains. The XRD results (the increased high phase, c-axis length and average grain size but decreased a-axis length) also show the optimum dopant level of x = 0.07 for Bi-2212 crystal system. All in all, the paper developing a strong methodology about why the characteristic properties improve with the presence of Tm impurity in the Bi-2212 system may be a pioneering research to construct newly, novel and feasible market areas for the Bi-2212 superconducting ceramics in the universe economy.

AlxGa1−xN/GaN/AlN heterostructures grown on Si(1 1 1) substrates by MBE for MSM UV photodetector applications

AlxGa1−xN/GaN/AlN heterostructures on silicon (Si) substrate was developed by nitrogen plasma-assisted molecular beam epitaxy (MBE) and their properties were investigated by scanning electron microscopy (SEM), electron dispersive X-ray (EDX), atomic force microscopy (AFM), high resolution X-ray diffraction (XRD), Raman spectroscopy and Hall effect measurements. High purity gallium (7N) and aluminum (6N5) were used in the Knudsen cells. High purity nitrogen with 7N purity was supplied to radio frequency (RF) source to generate reactive nitrogen species. The nitrogen pressure and a discharge power were kept at 1.5×10−5Torr and 300W, respectively. From SEM measurements, the surface morphology of samples presented 2- and 3-dimensional growth modes. The EDX measurements showed that there were no foreign elements in the grown samples. The HR-XRD measurement has confirmed that the AlxGa1−xN/GaN/AlN heterostructures samples were epitaxially grown on Si substrate. All the dominant E2 phonon modes were found in Raman spectra results. Lastly, AlxGa1−xN/GaN/AlN heterostructures based metal–semiconductor–metal (MSM) UV photodetectors were fabricated and the electrical characteristics of the devices were investigated by using current–voltage (I–V) and photo-conductivity measurements. The devices presented good I–V and photoconductivity characteristics.

Structural and mechanical properties of ZnMgO nanoparticles

This study reports the effect of annealing temperature on the structure and mechanical properties of Zn0.95Mg0.05O bulk samples by using digital Vickers microhardness tester, X-ray diffraction analysis, scanning electron microscopy and electron dispersive X-ray measurements. The samples were prepared using Zn and Mg based alkoxed by the sol–gel technique and annealed at various temperatures (500, 600, 700 and 800°C). Vickers microhardness, elastic modulus, yield strength and fracture toughness values of Zn0.95Mg0.05O bulk samples were separately calculated and compared with each other. The experimental results of hardness measurements were analyzed using Meyer's law, Proportional Specimen Resistance (PSR) and Elastic/Plastic Deformation (EPD) models and Hays–Kendall (HK) approach. Finally, it was seen that HK approach is the most successful model for the microhardness analysis of these materials.

Beginning point of metal to insulator transition for Bi-2223 superconducting matrix doped with Eu nanoparticles

Abstract This comprehensive study examines the change of the microstructural, electrical and superconducting properties of the Eu doped Bi1.8Pb0.4EuxSr2Ca2.2Cu3.0Oy ceramic cuprates (with x ⩽ 0.7) produced by the conventional solid state reaction method at the constant annealing temperature of 840 °C for 24 h with the aid of the standard characterization measurements such as bulk density, dc resistivity (ρ-T), transport critical current density (Jc), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) examinations. For the full characterization of the pure and Eu doped Bi-2223 samples, the degree of granularity (from the bulk density and porosity measurements); the room temperature resistivity, onset–offset critical transition temperature, variation of transition temperature, hole carrier concentration, spin-gap opening temperature and thermodynamic fluctuations (from the dc resistivity experiments); the texturing, crystal structure, crystallite size, phase purity and cell parameters (from the XRD investigations); the variation of the flux pinning centers and the boundary weak-links between the superconducting grains (from the critical current density values); the crystallinity, specimen surface morphology, grain connectivity between the superconducting grains and grain size distribution (from the SEM examinations), the elemental compositions and distributions (from EDX measurements) of the samples are determined and discussed clearly. The results obtained confirm that all the properties degrade with the enhancement of the Eu concentration in the Bi-2223 superconducting matrix up to x = 0.5 beyond which they are destroyed surprisingly due to not only the distortion between the Bi-2223 slabs but also the increase in the porosities and grain boundary weak-links. For example; the onset (offset) critical temperature decreases from 117.6 K (109.9 K) to 68.1 K (14.8 K) with the impurity content. The critical temperatures ( T c onset and T c offset ) are not measurable for the sample doped with the Eu content level of x = 0.7 as a consequence of the metal to insulator transition (MIT). On the other hand, the critical current density (Jct) is measured in the range from 3201 A/cm2 (for the pure sample) to 29 A/cm2 (for the sample doped with x = 0.5). For the sample doped with x = 0.7, each value is not measurable due to the nonsuperconducting behavior. Besides, the SEM pictures display that the surface morphology and grain connectivity degrade considerably with the Eu concentration. Moreover, the XRD measurements show that the Eu inclusions enter into the crystal structure by reducing the formation velocity of the Bi-2223 phase. Similar to the XRD evidences, the EDX measurement results demonstrate that all the elements used in the samples successfully introduce into the Bi-2223 structure, and the observed peaks of Ca, Cu and especially Pb reduce gradually with the Eu individuals in the Bi-2223 matrix, meaning that the Eu nanoparticles may substitute for the elements given above. This is enough to explain why the superconducting properties retrograde rapidly with the Eu impurities.

Role of Gd content in Cu(1) and Cu(2) sites on electrical, microstructural, physical, mechanical and superconducting properties of YBa2Cu3−xGdxO7−δ ceramics

This study deals with the effects of partial Gd3+ substitution for the Cu sites on the electrical, microstructural, physical, mechanical and superconducting properties of YBa2Cu3−xGdxO7−δ ceramic superconductors with x = 0, 0.025, 0.050, 0.100 and 0.150 with the aid of dc resistivity, transport critical current density (J c ), X-Ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-Ray (EDX), Vickers microhardness (H v ) and density measurements. The samples studied in this work are prepared by the standard solid-state reaction method. The resistivity (at room temperature), critical (onset and offset) temperature, variation of transition temperature, critical current density, hole-carrier concentration, grain size, phase purity, lattice parameter, texturing, surface morphology, element distribution, density, porosity, crystallinity, Vickers microhardness and elastic modulus (E) values of the samples are obtained and compared with each other. The obtained results show that the room temperature resistivity systematically increases with the increment of the Gd content as a result of the hole filling when the onset (T c onset ) and offset (T c offset ) critical temperatures determined from the resistivity curves are found to decrease from 95.2 to 93.6 K and 92.0 to 83.3 K, respectively, showing the presence of impurities and weak links between the superconducting grains. As for the critical current density measurements, the J c values decrease from 132 to 34 A/cm2 as the Gd doping increases. The XRD results give that although the Gd3+ ions substituted tend to occupy both the Cu(1) and Cu(2) sites, the ions are more favorable for the Cu(2) site as a consequence no change of the crystal structure. Besides, the peak intensities belonging to major phase (Y123) decrease monotonously with the increment of the Gd content in the system; however, new peaks belonging to the minor phases start to appear after the doping level of x = 0.0250 beyond which these peaks enhance monotonously, resulting in the decrement of the grain size. Further, the Lotgering indices calculated from the XRD patterns indicate that the texturing of the Y123 grains reduces systematically with the Gd content. According to the SEM investigations, the microstructures of the samples prepared degrade slightly with the content up to the doping level of x = 0.025 after which the morphology suddenly deteriorates due to the appearance of the different phases in the system. EDX measurements show that not only do the elements used for the preparation of the Y123 superconductors with and without Gd content distribute homogeneously but also the level of Cu element rapidly decreases with the increment of the Gd content compared to the other elements, illustrating that the Cu2+ ions may partly be substituted by Gd3+ ions. Moreover, the porosity analyses for the samples depict that the porosity increases with the Gd content, leading to the degradation of the grain connectivity. We also discuss on the mechanical properties of the samples to examine both the elastic modulus and the strength of connection between superconducting grains.

Effect of zirconium diffusion on the microstructural and superconducting properties of YBa2Cu3O7−δ superconductors

This study reports not only the role of zirconium (Zr) diffusion on the superconducting, physical and microstructural properties of YBa2Cu3O7−δ (Y123) bulk superconductors prepared by the conventional solid-state reaction method with the aid of scanning electron microscopy (SEM), electron dispersive X-ray (EDX), X-ray diffraction (XRD), electrical resistivity (ρ–T) and transport critical current density (Jc) measurements but also the diffusion coefficient and the activation energy of zirconium in Y123 system for the first time. Zr diffusion is examined in the temperature range 500–945°C via the variation of the lattice parameters evaluated from the XRD patterns. It is found that while the room-temperature resistivity reduces in the presence of the Zr ions in the system, the critical transition temperature values measured enhance. The onset (Tconset) and offset (Tcoffset) critical temperatures are found to be about 94.4K and 91.5K for the Zr-diffused sample as against 93.7K and 89.4K, respectively, for the pure sample. The increase in the critical temperatures is due to the improvement of crystallinity and the enhancement in the grain size. Likewise, the presence of the Zr atoms in the system, the Jc value enhances from 128Acm−2 to 160Acm−2 at 77K owing to the increase of the flux pinning mechanism stemming from the stacking faults, planar and micro-defects. Further, XRD measurements display that the samples produced in this work exhibit the polycrystalline superconducting phase with the changing intensity of diffraction lines and contain the Y123 phase only, illustrating the incorporation of Zr atoms into the crystalline structure of the Zr-diffused sample. Based on the refinement of cell parameters done by considering the structural modulation, the Zr diffusion is confirmed by both a reduction of a and b lattice parameters and an enhancement of the cell parameter c (about 0.24%) of the sample in comparison with that of the pure sample. As for the SEM investigations, the crystallinity and grain connectivity improve with the Zr diffusion. According to the results obtained, the Tconset, Tcoffset and Jc values of the samples studied are found to depend strongly on the microstructure. Moreover, EDX measurements indicate that the elements used for the preparation of samples distribute homogeneously. Y3+ and Ba2+ cations may partly be substituted by Zr4+ ions and the substitution at the Cu site is less likely, presenting that the superconducting properties of the Zr-diffused sample are more superior to the pure sample. Further, the diffusion coefficient of the Zr in Y123 system in a range of 500–945°C is determined to change from 4.12×10−10 to 9.77×10−8cm2s−1 with activation energy of about 1.010eV, confirming that the Zr diffusion at lower temperatures is much less significant and the Zr ions primarily proceed through defects in the polycrystalline samples.

Role of Cerium Addition on Structural and Superconducting Properties of Bi-2212 System

This study examines the significant changes in the structural and superconducting properties of cerium (Ce) doped Bi-2212 superconductors via X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), electrical resistance and transport critical current density (Jc) measurements. Ce concentration is varied from x=0.0 until 0.1 in a general stoichiometry of Bi1.8Sr2.0CexCa1.1Cu2.1Oy. Zero resistivity transition temperatures (\(T_{c}^{\mathrm{offset}}\)) of the samples produced by the conventional solid-state reaction method are deduced from the dc resistivity measurements. Furthermore, the phase fractions and lattice parameters are determined from XRD measurements when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. The results show that \(T_{c}^{\mathrm{offset}}\) and Jc at self-field of the samples reduced gradually with the increase in the Ce addition. Maximum \(T_{c}^{\mathrm{offset}}\) of 79.7 K and Jc of 356.8 A⋅cm−2 at 77 K are obtained for pure sample as against 44.6 K and 18.7 A⋅cm−2, respectively, for the sample doped with 0.1 wt.% Ce. According to the refinement of cell parameters done by considering the structural modulation, the Ce doping is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample. As for SEM measurements, it is found that not only do the surface morphology and grain connectivity degrade but the grain size of the samples also decreases with the increase of the Ce addition. Moreover, EDX images indicate that the elements used for the preparation of samples distribute homogeneously and the Ce atoms enter into the crystal structure by replacing Cu atom. In addition, the variation of ΔTc (\(T_{c}^{\mathrm{onset}} -T_{c}^{\mathrm{offset}}\)) is investigated for the presence of impurities and weak links between superconducting grains of the samples. The possible reasons for the degradation in microstructural and superconducting properties are also interpreted.

Effect of Mn Addition on Structural and Superconducting Properties of (Bi, Pb)-2223 Superconducting Ceramics

This study deals with the effect of Mn addition on the structural and superconducting properties of Bi1.8Pb0.4Sr2MnxCa2.2Cu3.0Oy ceramics with x=0,0.03,0.06,0.15,0.3 and 0.6 by means of X-ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), resistivity, and transport critical current density (Jc) measurements. Zero-resistivity transition temperatures (Tc) of the samples produced via the standard solid-state reaction method are estimated from the dc resistivity measurements. Moreover, the phase fraction and lattice parameters are determined from XRD measurements while the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. It is found that Tc values are obtained to decrease from 109 K to 85 K; likewise, Jc values are observed to reduce from 3200 A/cm2 to 125 A/cm2 with increasing Mn addition. According to the refinement of cell parameters done by considering the structural modulation, the Mn addition is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample (Mn0). SEM measurements show that not only the surface morphology and grain connectivity are seen to degrade but the grain sizes of the samples are found to decrease with the increase of the Mn addition as well. The EDX results reveal that the elements used for the preparation of samples distribute homogeneously and the Mn atoms enter into the crystal structure by replacing Sr and Cu atoms. The possible reasons for the obtained degradation in microstructural and superconducting properties are also interpreted.

Vickers hardness measurements and some physical properties of Pr2O3 doped Bi-2212 superconductors

This study deals with the effect of Pr2O3 addition on the structural, superconducting and mechanical properties of Bi-2212 superconductor by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), Vickers microhardness and resistivity measurements. The samples studied are prepared using the standard solid-state reaction method. Onset transition temperatures (T onset ) of the samples are estimated from the dc resistivity measurements. Furthermore, the phase ratio and lattice parameters a and c are determined from XRD patterns when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. Additionally, vickers microhardness, elastic modulus, yield strength and fracture toughness values of the samples are deduced from microhardness measurements. It is found that T onset values of the samples increase from 87 to 97 K with the Pr2O3 addition. According to the refinement of cell parameters done by considering the structural modulation, the doping is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample. As for SEM measurements, it is obtained that the surface morphology and grain connectivity degrade with the increase of the Pr2O3 addition. Moreover, EDX images show that the elements used for the preparation of samples distribute homogeneously and the Pr atoms enter into the crystal structure by replacing Sr atoms. To sum up, the Pr2O3 addition is found to suppress the mechanical, microstructural and superconducting properties of the Bi-2212 superconductor.

Role of annealing time and temperature on structural and superconducting properties of (Bi, Pb)-2223 thin films produced by sputtering

This study reports the effect of annealing time (15 min, 1.5 and 3 h) and temperature (850, 860 and 870 °C) on the structural and superconducting properties of thin films by means of scanning electron microscopy (SEM), X-Ray analysis (XRD), electron dispersive X-Ray (EDX), resistivity and transport critical current density (Jc) measurements. Zero resistivity transition temperatures (Tc) of the films produced are estimated from the dc resistivity measurements. In addition, the phase and lattice parameters are determined from XRD patterns when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. The results indicate that Tc values of the films obtained are observed to be in a range of 23–102 K. The Tc of the film annealed at 870 °C for 3 h is found to be the smallest (23 K) while the film annealed at 860 °C for 3 h is noted to obtain the maximum Tc value (102 K). On the other hand, the maximum (minimum) Jc is found to be about 2068 A/cm2 (20 A/cm2) for the film annealed at 860 °C for 3 h (870 for 3 h). Moreover, according to the refinement of cell parameters done by considering the structural modulation, the greatest Bi-2223 phase fraction is noticed to belong to the film annealed at 860 °C for 3 h. Furthermore, SEM measurements show that the best surface morphology, largest grain size and grain connectivity are observed for that film. Based on these results, Tc and Jc values of the samples studied are found to depend strongly on the microstructure. As for EDX results, the elements used for the preparation of samples are observed to distribute homogeneously. The aim of this study is not only to investigate the changes of structural and superconducting properties of the films produced in the varied time and temperature but also to determine the best ambient for the film fabrication and show the feasibility of obtaining Bi-2223 film with tailored structure.