Raman and photoluminescence characterisation of InxGa1−xP self-assembled quantum dots on GaP(100) substrate

We present here Raman and photoluminescence (PL) measurements of In_.5Ga_.5P self-assembled quantum dots (SAQD) on GaP, at each stage of the growth. Observation of confined acoustic phonons ∼32 and 49 cm⁻¹ in In₅Ga₅P SAQDs is the most important result of these Raman scattering measurements. The PL data at 12 K shows that the highest PL peak observed corresponds to bound exciton in the substrate, buffer layer and wetting layer (WL). We find that PL spectra from 2-D WL shows blue shift due to confinement and increased oscillator strength for the transition. These uncapped SAQDs introduce nonradiative transitions leading to quenching of PL from WL. Raman data at 12 K shows that interface layer at InGaP/GaP interface increases in In content as nominal thickness of InGaP layer increases.     

Facile synthesis of Ag/AgX (X = Cl,Br) with enhanced visible-light-induced photocatalytic activity by ultrasonic spray pyrolysis method

Ag/AgX (X?=?Cl, Br) plasmonic photocatalysts were synthesized via a facile one-pot ultrasonic spray pyrolysis method, wherein no additional issues such as high pressure, surfactants and reducing agents were required. The structure, morphology, and optical property of the as-prepared photocatalysts was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet–visible light absorption spectra and total organic carbon (TOC). The results showed that Ag/AgX photocatalysts have excellent photocatalytic performance for the photodegradation of methyl orange (MO) and methylene blue (MB) pollutants under visible light illumination, and the photocatalytic activity maintains a high level after seven cycles. Metallic Ag⁰ particles nucleate on the surface of AgX uniformly through the thermal decomposition of residual AgNO₃ solution, which enhanced the interaction between Ag⁰ and AgX. The outstanding photocatalytic activity benefits from the small size and high dispersion of Ag⁰ nanoparticles and the enhanced interaction between Ag⁰ and AgX.     

Influence of cerium oxide (CeO2) nanoparticles on the microstructure and hardness of tin–silver–copper (Sn–Ag–Cu) solders on silver (Ag) surface-finished copper (Cu) substrates

Nano-sized, non-reacting, non-coarsening CeO₂ particles with a density close to that of solder alloy were incorporated into Sn–3.0 wt%Ag–0.5 wt%Cu solder paste. The interfacial microstructure and hardness of Ag surface-finished Cu substrates were investigated, as a function of reaction time, at various temperatures. After the initial reaction, an island-shaped Cu₆Sn₅ intermetallic compound (IMC) layer was clearly observed at the interfaces of the Sn–Ag–Cu based solders/immersion Ag plated Cu substrates. However, after a prolonged reaction, a very thin, firmly adhering Cu₃Sn IMC layer was observed between the Cu₆Sn₅ IMC layer and the substrates. Rod-like Ag₃Sn IMC particles were also clearly observed at the interfaces. At the interfaces of the Sn–Ag–Cu based solder-Ag/Ni metallized Cu substrates, a (Cu, Ni)–Sn IMC layer was found. Rod-like Ag₃Sn and needle-shaped Cu₆Sn₅ IMC particles were also observed on the top surface of the (Cu, Ni)–Sn IMC layer. As the temperature and reaction time increased, so did the thickness of the IMC layers. In the solder ball region of both systems, a fine microstructure of Ag₃Sn, Cu₆Sn₅ IMC particles appeared in the β-Sn matrix. However, the growth behavior of the IMC layers of composite solder doped with CeO₂ nanoparticles was inhibited, due to an accumulation of surface-active CeO₂ nanoparticles at the grain boundary or in the IMC layers. In addition, the composite solder joint doped with CeO₂ nanoparticles had a higher hardness value than the plain Sn–Ag–Cu solder joints, due to a well-controlled fine microstructure and uniformly distributed CeO₂ nanoparticles. After 5 min of reaction on immersion Ag-plated Cu substrates at 250 °C, the micro-hardness values of the plain Sn–Ag–Cu solder joint and the composite solder joints containing 1 wt% of CeO₂ nanoparticles were approximately 16.6 and 18.6 Hv, respectively. However after 30 min of reaction, the hardness values were approximately 14.4 and 16.6 Hv, while the micro-hardness values of the plain Sn–Ag–Cu solder joints and the composite solder joints on Ag/Ni metallized Cu substrates after 5 min of reaction at 250 °C were approximately 15.9 and 17.4 Hv, respectively. After 30 min of reaction, values of approximately 14.4 and 15.5 Hv were recorded.     

Effects of (TiB2 + ZrB2) nanoparticles on microstructure and properties of 7055Al matrix composites

The in situ (TiB₂?+?ZrB₂)/7055Al composites were successfully fabricated from the 7055Al-K₂TiF₆-K₂ZrF₆-KBF₄ system by a direct melt reaction method. Microstructural observations revealed that the nanoparticles were distributed relatively uniformly in the aluminium matrix, and that these nanoparticles exhibit various shapes such as spherical, hexagonal and cubic, with an average size of about 80?nm. Mechanical property testing showed that the strength and Young’s modulus of the composites increased significantly in comparison to the 7055 matrix alloy. The maximum ultimate tensile strength was approximately 361?MPa, with a yield strength of 323?MPa and an elongation of 3.6%, which constitute increases of 31.3%, 28.7% and 44% when compared to the 7055Al alloy, respectively. The strengthening mechanisms of the fabricated composites were also discussed.     

Synthesis and crystal structure of An(VI) complexes with cyclobutanecarboxylic acid anions and 2,2′-bipyridine [An(VI) = U,Np, Pu]

New complexes of hexavalent U, Np, and Pu of the composition [UO₂(bipy)(cbc)₂] (I) and [AnO₂(bipy)(cbc)₂]·0.5(bipy) [An = Np (II) and Pu (III)] with cyclobutanecarboxylic acid anions C₄H₇COO^– and 2,2′-bipyridine (bipy) were synthesized, and their structures were studied. The An atoms in I–III have the coordination surrounding in the form of distorted hexagonal bipyramids with the О atoms of AnO₂²⁺ cations in the apical positions. The equatorial plane of the bipyramids is constituted by the O atoms of two C₄H₇COO^– anions and N atoms of bipy.     

Electrophoretic deposition of Y2O3-stabilized ZrO2 nanoparticles on the surface of dense La0.7Sr0.3MnO3−δ cathodes produced by pyrolysis and solid-state reaction

La_0.7Sr_0.3MnO_3?δ (LSM) cathode materials have been prepared through pyrolysis of liquid precursors and by solid-state reaction. We examined the effect of the cathode material synthesis procedure on the growth of thin films of a solid electrolyte based on Y₂O₃-stabilized ZrO₂ (YSZ) nanopowder with an average geometric size of 10.9 nm on a dense surface of model cathodes by electrophoretic deposition. Using electron microscopy, BET surface area measurements, X-ray diffraction, thermal analysis, and dilatometry, we investigated the structure, specific surface area, phase composition, thermal properties, and sintering-induced volume changes of cathode materials differing in prior history. The results demonstrate that the starting cathode materials differed markedly in properties, but the cathodes produced by sintering them were identical in phase composition: they consisted entirely of a rhombohedral phase. The room-temperature electrical conductivity of the cathodes produced by solid-state reaction was 0.231 ± 0.01 S/cm, exceeding that of the cathodes produced through pyrolysis by an order of magnitude.     

Interpenetrating covalent and noncovalent nets in the crystal structures of [M(4,4′-bipyridine)2(NO3)2]·3C10H8 (M = Co,Ni)

The synthesis and crystal structures of [M(4,4′-bipyridine)₂(NO₃)₂]·3naphthalene (M = Co, 1·3naphthalene; Ni, 2·3naphthalene) are reported. 1·3naphthalene and 2·3naphthalene are isostructural and represent rare examples of interpenetrating planar networks that are chemically and topologically different. It appears that the networks coexist because the (4,4) topology of the cobalt and nickel square grids is complementary to the (6,3) topology of the naphthalene honeycomb network, resulting in an inclined interpenetrated 3D architecture. This observation is discussed in the context of rational design strategies for hybrid solids.     

Raman scattering analysis of disorder in heterogeneous (GaAs)1−x(SiC2:H)x films grown by metal-organic chemical vapour deposition

A chemical and structural analysis of (GaAs)_1−x(SiC₂:H)_x films is performed by using the Raman scattering probe. A multizone structural model is evidenced in accordance with previous X-ray and electron diffraction experiments. The ability of a spatial correlation model to account for the lineshape evolution of the spectra of the GaAs phase is discussed for the first time for both longitudinal optical and transverse optical modes. The values of the “Raman size” of the GaAs crystallites lie well below those deduced from diffraction experiments, revealing the presence of many internal defects which greatly influence the electron-phonon interactions.     

The Effect of Co Substitution on the Crystal Structure and Electrical Resistivity of (La0.85Ag0.15)MnO3 Compounds

The effect of Co substitution on the crystal structure and electrical transport properties of La_0.85Ag_0.15Mn_1−y Co _y O₃ compounds (0≥y≤0.50) has been studied. Structural transition from rhombohedral to orthorhombic symmetry has been observed with Co doping. The lattice parameters are found to increase with doping up to y=0.20, then it decreases. It is explained on the basis of transition from high spin state to low spin state of Co ions with increase in doping beyond y=0.20. Ferromagnetic (FM) metallic behavior with colossal magneto-resistivity has been observed up to y=0.10. However, for y≥0.15 compounds, the temperature dependence of resistivity ρ(T) follows semiconducting behavior. The electrical resistivity in the metallic region could be explained based on electron–electron and electron–magnon scattering mechanisms. The data in the semiconducting region could be explained based on the variable range hopping model for y=0.2 and adiabatic small polaron hopping model for y≥0.3.      

Design of an efficient uranyl ion optical sensor based on 1′-2,2′-(1,2-phenylene)bis(ethene-2,1-diyl)dinaphthalen-2-ol

A new optical uranyl (IV) selective sensor by incorporation of 1,1′-2,2′-(1,2-phenylene)bis(ethene-2,1-diyl)dinaphthalen-2-ol (PBED), dibutyl phthalate (DBP) and sodium tetraphenylborate (Na-TPB) in the plasticized poly vinyl chloride membrane matrices has been constructed. In the proposed optode, PBED functions as both ionophore and chromoionophore while DBP has synergistic effect on the complexation of uranyl ion (UO₂²⁺) by PBED. Following the optimization of influences of variables, the proposed sensor due to its high stability, reproducibility and relatively long lifetime has good selectivity and sensitivity for uranyl ion over a large number of alkali, alkaline earth, transition, and heavy metal ions. The response of the proposed optode is linear over the concentration range of 3.99 × 10^? 6 up to 8.06 × 10^? 5 mol L^? 1 of UO₂²⁺ within a detection limit of 9.99 × 10^? 7 mol L^? 1 and response time less than 10 min. The proposed optical sensor was applied successfully for the determination and evaluation of UO₂²⁺ ion content in water samples.     

Interpenetration of covalent and noncovalent networks in the crystal structures of {[M(4,4′-bipyridine)2(NO3)2]⋅2p-nitroaniline}n where M=Co, 1, Ni, 2, Zn, 3

The synthesis and crystal structures of {[M(4,4′-bipyridine)₂(NO₃)₂]⋅2p-nitroaniline}_n, M=Co, 1, Ni, 2, Zn, 3, are described. 1, 2 and 3 crystallize in the form of compounds that can be described as interpenetrating covalent and noncovalent networks. Analysis of the crystal packing in these compounds reveals that the p-nitroaniline molecules form a noncovalent network that is complementary from a topological perspective with [M(4,4′-bipyridine)₂(NO₃)₂] networks, which exist as square grids. These structures are interpreted in the broader perspective of crystal engineering strategies and development of new hybrid materials.     

Hydrothermal synthesis of Ca2(SiO3)(OH)2 microbelts and their transformation to β-Ca2SiO4 microbelts by microwave heating

Calcium silicates possess potential applications in biomedical fields such as drug delivery and bone tissue regeneration owing to their comparatively good bioactivity, biocompatibility and biodegradability. In this paper, we report the preparation of monoclinic β-Ca₂SiO₄ microbelts by microwave thermal transformation of Ca₂(SiO₃)(OH)₂ microbelts at 670 °C for 2 h. Ca₂(SiO₃)(OH)₂ microbelts are successfully used as both the precursor source material and the template for the preparation of β-Ca₂SiO₄ microbelts. The morphology and size of Ca₂(SiO₃)(OH)₂ microbelts can be well preserved during the microwave thermal transformation process. Ca₂(SiO₃)(OH)₂ microbelts are synthesized using Na₂SiO₃?9H₂O, NaOH and Ca(NO₃)₂?4H₂O in the solvent of water by a hydrothermal method at 200 °C for 24 h. The products are characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).     

Surface modification of 2Cr13 oil pump steel by plasma immersion ion implantation–ion beam enhanced deposition (PIII–IBED)

2Cr13 martensite steel is often used as a piston material in oil pumps. In the harsh environment of an oil field, the materials and components undergo extensive and accelerated wear and tear. In this study, we employ Ti and N plasma immersion ion implantation and ion beam enhanced deposition (PIII-IBED) to enhance the surface wear resistance of 2Cr13 steel in an effort to prolong its working lifetime. To assess the technique efficacy and surface properties of the 2Cr13 steel samples treated by PIII-IBED using different voltages, the coefficient of friction, wear tracks, microhardness, anode polarization curves, chemical composition and elemental depth profiles were determined. The experimental data show that the wear resistance of the treated 2Cr13 steel samples is improved significantly by the method, and the nitride phases formed in the modified layer play an important role in the enhancement mechanism.     

Effects of single electrodes of Ni(OH)2 and activated carbon on electrochemical performance of Ni(OH)2–activated carbon asymmetric supercapacitor

Nickel hydroxide consisting of loosely packed nanospheres was synthesized as positive electrode material for an asymmetric capacitor based on Ni(OH)₂ and activated carbon (AC). Two series of supercapacitors were fabricated to investigate the effects of the single electrodes of Ni(OH)₂ and AC on the electrochemical performance of asymmetric Ni(OH)₂–AC capacitor. Parameters including cell voltage window, specific capacitance and cyclic stability were assessed. In one series of supercapacitors, mass of Ni(OH)₂ was excessive while mass of AC was varied, the AC electrode thus constrained both the capacitance and the upper limit of cell voltage. Deficiency of AC resulted in lower specific capacitance and narrower cell voltage window but benefited to cyclic stability. In the other series of supercapacitors, the mass of AC was excessive whereas the mass of Ni(OH)₂ was changeable in each cell, Ni(OH)₂ electrode thus dominated both the capacitance and the lower limit of cell voltage. As a consequence, deficiency of Ni(OH)₂ led to higher specific capacity and wider cell voltage window as well as lower cyclic stability. These results can contribute to improving understanding of and optimizing performance of asymmetric Ni(OH)₂–AC capacitor.     

Effect of ZnO nanoparticles addition on thermal, microstructure and tensile properties of Sn–3.5 Ag–0.5 Cu (SAC355) solder alloy

Regarding to the development of Sn–Ag–Cu (SAC) lead-free solders for advance electronic components, the effect of 0.5 wt% nano-sized ZnO particles on the thermal, microstructure and tensile properties of Sn–3.5 wt% Ag–0.5 wt% Cu (SAC355) lead-free solder alloy is investigated. The results showed that addition of 0.5 wt% nano-sized ZnO particles into the conventional lead-free SAC355 solder caused a slight increase of its liquidus temperature by about 1.1 K. Metallographic observations of SAC355–0.5 wt% ZnO (composite solder) revealed an obvious refinement in the microstructure compared with the SAC355 (non-composite) solder. Consequently, addition of nano sized-ZnO particles could improve the stress–strain characteristics proof stress (σ_y0.2) and ultimate strength (σ_UTS). This was rendered to suppressing effect of ZnO on the coarsening of the intemetallic compounds (IMCs) Ag₃Sn and Cu₆Sn₅ during the solidification process in the composite solder and subsequently dispersion strengthening is considered to be the dominating mechanism. This will allow the use of SAC355 composite lead-free solder alloy, to be consistent with the conditions of usage for conventional SAC solder alloys and to overcome the serious problem of the excessive growth of IMCs and the formation of microvoids in the SAC lead-free solder alloys.     

Comparative study of adatom induced relaxations and energetics for Si, Ge and carbon adsorption on a (2×1) Si(001) surface

Surface complexes involving silicon, germanium and carbon adatom on predefined adsorption sites of the 2×1 reconstructed Si(001) surface are investigated for their energetics and associated structural relaxations. Tersoff’s semi-empirical potential is used and the relaxations are obtained by employing the Monte Carlo simulated annealing technique. The results for the cases of Si, Ge and carbon adsorptions are compared. It is found that Si and Ge as adatoms on Si(001) 2×1 reconstructed surface behave in a similar fashion but the carbon adatom behaves in a markedly different way. Specifically, the carbon adatom induces a Si-C-Si chain configuration. It is also found that the adsorption sites between two dimer rows are the most favourable ones.     

Characterization of composite materials based on Fe powder (core) and phenol–formaldehyde resin (shell) modified with nanometer-sized SiO2

Soft magnetic composites based on Fe powder and phenol–formaldehyde resin (PFR) modified with tetraethylorthosilicate are investigated in detail. The chemical synthesis of PFR, its modification with nanometer-sized SiO₂ particles created by sol–gel method and subsequent coating, enables a preparation of insulating PFR–SiO₂ (PFRT) layer on the surface of Fe particles. Thermal degradation and FTIR analysis of PFR and PFRT with different amount of SiO₂ was examined. Mechanical hardness and flexural strength of FePFRT composites was studied depending on the amount of nanosized-SiO₂ in the coating. SEM serves in evidence of a defectless microstructure if the coating contains at least 2% of silica particles. The morphology of Fe particles implies uniform coating without any visible exfoliation. A presence of fine SiO₂ particles was verified by TEM. The best magnetic properties were found in Fe–PFRT composite with 2% of SiO₂ in the insulating layer on behalf of its uniform arrangement and homogeneity.     

Synthesis and photoluminescence properties of the Eu(III)-containing silica nanoparticles via a mechanochemical solid-state reaction between SiO2 and EuCl3·6H2O

In this study, Eu³⁺-containing amorphous silica nanoparticles and Eu compounds were successfully synthesized via a mechanochemical solid-state reaction between silica nanoparticles and EuCl₃·6H₂O. This reaction was induced by a grinding process, and the states of Eu³⁺ in the silica/europium composites were investigated. The silica/europium composites exhibited orange–red color luminescence owing to the ⁵D₀–⁷F₀, ⁵D₀–⁷F₁, and ⁵D₀–⁷F₂ transitions, which indicated the presence of Eu³⁺ in the silica framework and the newly formed Eu compounds such as EuOCl and Eu(OH)₂Cl. The mechanochemical reaction because of the grinding process effectively induced an interaction between the silica surface and europium chloride; subsequently, Eu(OH)₂Cl was formed in the silica/europium composites. Additionally, the Eu(OH)₂Cl in the silica/europium composite exhibited a higher thermal stability than that of simple Eu(OH)₂Cl, indicating that the mechanochemical reaction mediated the formation of Eu(OH)₂Cl and new chemical bonding between the newly formed Eu(OH)₂Cl and the silica surface, providing improved thermal stability to Eu(OH)₂Cl. Thus, we successfully prepared silica nanoparticles containing not only Eu(III) in the silica framework but also Eu compounds that exhibit unique chemical bonding during a mechanochemical reaction.     

The hydrothermal synthesis of beta-Ni(OH)(2) nanoflakes on carbon cloth and their electrochemical properties北大核心CSCD

Carbon cloth (CC) coated with beta-Ni(OH)(2) nanoflakes was prepared by a hydrothermal method using nickel nitrate, urea and ammonium fluoride as the reaction system, and was characterized by SEM, XPS and XRD. Results indicated that the acid treatment of the CC introduced more active functional groups on its surface, which was beneficial to the coating of the beta-Ni(OH)(2). The beta-Ni(OH)(2) nanoflakes were of high purity; and their formation mechanism on the CC was investigated by observing their morphology at different reaction times. It was revealed that the beta-Ni(OH)(2) were initially present in the form of discrete nanoparticles and nanoflakes and after 6 h formed a continuous and well-crystallized beta-Ni(OH)(2) nanoflake with diameter and thickness of 1 mu m and 10 nm, respectively. Nanoflakes continued to form, grow and overlap and after 12 h the thickness had increased to 200 nm. The sample at 6 h had the highest specific capacitance of 815. 67 F.g(-1) at a current density of 1 A.g(-1) and retained 98. 1% of its initial capacitance after 4 000 cycles.     

Correction to: Co-sputtering of Al1−xScxN thin films on Pt(111): a characterization by Raman and IR spectroscopies

Journal of Materials Science -