Photoluminescence properties and synthesis of a PZT mesostructure obtained by the microwave-assisted hydrothermal method

Micro-cube-shaped lead zirconate titanate was synthesized using the microwave-assisted hydrothermal method. Photoluminescence and field emission scanning electron microscopy were used for monitoring the formation of mesocrystals. Based on these results, a growth mechanism was then proposed which involved nanoparticle aggregation, nanoplate self-assembly on specific architecture and the final formation of mesoscopic micro-cube-shaped lead zirconate titanate.     

Influence of synthesis conditions on optical and electrical properties of CaTiO3:Pr3+ thin films deposited by radiofrequency sputtering for electroluminescent device

CaTiO₃:Pr³⁺ is a phosphor of great interest for electroluminescence application owing to its intense red emission characterized by CIE coordinates very close to those of the NSTC “ideal red”. In this paper, thin films of CaTiO₃:Pr³⁺ are deposited by radiofrequency sputtering technique in pure argon and post-treated by Rapid Thermal Annealing (RTA). The influence of the deposition pressure (0.125–4.5 Pa) and annealing conditions on the optical and electrical properties of the thin films is investigated. The chemical composition of the as-deposited films, checked by Rutherford Backscattering Spectroscopy (RBS), is close to that of the ceramic target used for the deposition. The crystal structure is confirmed to be orthorhombic by X-ray diffraction. We highlight an improvement of the optical and electrical properties of the films after RTA treatment. Moreover, a net gain is obtained by comparison with conventional thermal treatment procedures in classical furnaces, especially for the reduction of electrical defect densities.     

Structural,optical properties and optical modelling of hydrothermal chemical growth derived ZnO nanowires

ZnO nanowire films were produced at 90 °C using a hydrothermal chemical deposition method, and were characterised with scanning electron microscopy, optical transmission spectrometry and X-ray diffraction. The results showed that the optical band gap is 3.274–3.347 eV. Film porosity and microstructure can be controlled by adjusting the pH of the growth solution. ZnO nanowire films comprise a 2-layer structure as demonstrated by SEM analysis, showing different porosities for each layer. XRD analysis shows preferential growth in the (002) orientation. A comprehensive optical modelling method for nanostructured ZnO thin films was proposed, consisting of Bruggeman effective medium approximations, rough surface light scattering and O'Leary-Johnson-Lim models. Fitted optical transmission of nanostructured ZnO films agreed well with experimental data.     

Structural and optical properties of tellurium films obtained by chemical vapor deposition（CVD）

1 Introduction Te thin films have been extensively used in various technological areas, especially in microelectronic devices such as gas sensor [1?3], optical information storage [4] and other applications [5?7]. All these applications are due to remark…     

Structural dependence of the piezoelectric properties of KNbO3 nanowires synthesized by the hydrothermal method

Because of the presence of OH^? and H₂O in the KN unit cell, tetragonal KNbO₃ (KN) nanowires were formed when the synthesis was carried out at 120 °C for 48 h. However, when the fabrication was conducted at high temperatures (?150 °C) or at 120 °C for a long period of time (?72 h), orthorhombic KN nanowires were formed. Moreover, the KN nanowires synthesized at 120 °C for 60 h showed a morphotropic phase boundary (MPB) structure in which both tetragonal and orthorhombic structures coexisted. Tetragonal, orthorhombic and MPB KN nanowires were also grown on the Nb⁵⁺-doped SrTiO₃ substrate, and their d₃₃ values were measured for the first time. A tetragonal KN nanowire exhibited a d₃₃ value of 23.5 pm V^?1, which is larger than that of the orthorhombic KN nanowire (11.6 pm V^?1), probably because of the softening effect of the metal vacancies. The MPB KN nanowires exhibited a larger d₃₃ value of 40.0 pm V^?1. The d₃₃ values of KN nanowires increased to 104.5, 137.1 and 146.0 pm V^?1 for the orthorhombic, tetragonal and MPB KN nanowires, respectively, after the KN nanowires were poled along the [1 0 0] direction by application of a DC voltage of 10 V.     

Electrical and optical properties of phenylene vinylene oligomers obtained by vacuum evaporation

Optical absorption, photoluminescence and electrical impedance of phenylene vinylene (PV) oligomer films deposited onto indium—tin oxide (ITO) substrates by evaporation in vacuum were studied in a wide range of temperatures (10–450 K) and a.c. frequencies (0.3–10⁵ Hz). The material possesses an optical band of 2.8 eV. Photoluminescence spectra are Stokes shifted for 0.2 eV with respect to absorption and excitement luminescence. A.c. electrical properties of the material show some temperature-dependent hysteresis of the real part of dielectric permittivity, as well as several relaxation/conduction modes at low (− 100 to − 50 °C) and high (above 60 °C) temperatures.     

Structural stability, electronic and optical properties of Ni-doped 3C-SiC by first principles calculation

Structural stability along with the electronic and the optical properties of intrinsic 3C-SiC and Ni-doped 3C-SiC were studied by the first principles calculation. For the Ni-doped 3C-SiC, substitution of Ni in Si sub-lattice is energetically more favorable than that in C sub-lattice. Some new impurity energy levels appear in the band gap of Ni-doped 3C-SiC, which can improve the conductivity of 3C-SiC. The imaginary part of the dielectric function of Ni-doped 3C-SiC has three remarkable peaks at 0.69 eV, 2.35 eV, and 4.16 eV. This reveals that doping with Ni can improve the photo-absorption efficiency of 3C-SiC. In the absorption spectrum of Ni-doped 3C-SiC, the absorption edge red-shifts towards the far-infrared region. Furthermore, three new absorbing peaks emerge in the near-infrared region, visible region, and middle-ultraviolet region. These features confer Ni-doped 3C-SiC qualifications of a promising optical material.     

Optical properties of functionalized thiophenes: a theoretical and experimental study

The optical properties of ter-thiophene, diphenyl-thiophene, dithieno-thiophene and their analogues with the central sulphur atom functionalized with two oxygen atoms are investigated by first-principles time-dependent density-functional theory: absorption and emission energies and singlet–triplet energy-gaps are reported and compared with experimental results. Photoluminescence quantum yield measurements in solvents of different viscosity for the functionalized systems are reported. The non-radiative decay channels are discussed.     

Hydrothermal synthesis of MgCO3 and its optical properties

Well-crystallized magnesium carbonate micro-particles were successfully synthesized by a simple hydrothermal method. The structure of the as-synthesized products was characterized by X-ray diffraction (XRD), which is in good agreement with hexagonal rhomb-centered MgCO₃. Field emission scanning electron microscopy (FE-SEM) characterization indicates that the as-synthesized MgCO₃ micro-particles are of mean size about 30 μm. The photoluminescence properties of the as-synthesized MgCO₃ were measured at room temperature, which shows wide emissions with three emission centers ranging from violet to red. The violet emission center locates at 425 nm, the green emission center locates at 550 nm, and the red emission center locates at 698 nm.     

GaN/PMMA nanocomposite：synthesis and optical properties

High crystalline quality wurtzite-GaN nanoparticles, with diameters of about 11 nm, well dispersed in a poly-methyl methacrylate polymer matrix, were synthesized using a routine two-step route and were structurally and optically characterized.The as-prepared composite showed three broad overloading photoluminescence emission peaks with centers at 3.45, 3.29, and 3.10 eV.The 3.45 eV emission band is assigned to the recombination of the free exciton of GaN particles.The other two emission peaks possibly origi...     

Some physical properties of the Ti-Al and Ti-Al-Co composite materials obtained by shock-wave compacting

Ti-Al and Ti-Al-Co composite materials obtained by shock-wave compacting have been investigated. The powder mixture has been consolidated with the use of explosives ammonite and hexogen. The results of studying the microstructure and measuring the density, microhardness, and yield strength are presented.     

Template-free hydrothermal synthesis of single-crystalline SnO<Subscript>2</Subscript> nanocauliflowers and their optical properties

Large-scale single-crystalline SnO₂ nanocauliflowers were successfully synthesized using a hydrothermal growth method without any template. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). FE-SEM images show that the as-grown SnO₂ nanocauliflowers are constructed of tetragonal prisms with a width of 500–600 nm. XRD, EDS, and SAED results indicate that the as-grown SnO₂ nanocauliflowers are single crystalline with the tetragonal rutile crystalline structure. The growth mechanism of SnO₂ nanocauliflowers is also preliminarily discussed on the basis of different Sn(OH)₆²⁻ concentrations, and it is found that Sn(OH)₆²⁻ concentration plays an important role in determining the shape of the prepared SnO₂. Room temperature photoluminescence was further carried out on SnO₂ nanocauliflowers to investigate their optical properties. An intense blue luminescence centered at a wavelength of 424 nm is observed in the as-grown SnO₂ nanocauliflowers.     

Structural and optical properties of bandgap engineered bismuth titanate by cobalt doping

The wide band gap of complex oxides is one of the major obstacles limiting their use in photovoltaic cells. To tune the bandgap of complex oxides, nano-sized bismuth titanate-based powders were synthesized by conventional solid reaction method. X-ray diffraction patterns confirmed that all powders were crystallized in an orthorhombic structure. The photoluminescence signal shows that there was no contribution to the optical bandgap from unwanted oxygen vacancy. The UV-vis absorption spectra of LaCo-BiT powder showed that the optical bandgap drastically decreased from 3.1eV to 2.5eV, while those of of BiT and La-BiT showed change in the optical bandgap. From these observations, we could experimentally confirm that cobalt atoms were responsible for the modification of the electronic structure in BiT-based oxides. This approach to controlling the bandgap could be applied to other complex oxides materials, such as other types of Aurivillius phase materials for use in emerging oxide optoelectronic and energy applications.     

Shape-controlled synthesis of nanocubic Co3O4 by hydrothermal oxidation method

The nanocubic Co3O4 was synthesized by hydrothermal oxidation method. The effects of cobalt salt, precipitating agent, surfactant, solvent, pH value of the suspension and the amount of oxidant H2O2 on the morphology and structure of Co3O4 were investigated. The Co3O4 powders were characterized by transmission electron microscope and X-my diffraction. The results show that the morphology of Co3O4 is closely dependant on the anion in cobalt salts, but it is not so sensitive to the precipitating agents and solvents. The amount of H2O2 is the key factor to obtain Co3O4 with spinel crystal structure. The optimum synthetic conditions of uniform shape-controlled Co3O4 nanocubes are as follows： Co（CH3COO）2·4H2O as cobalt salt, KOH as precipitating agent, polyethylene glycol with relative molecular mass of about 20 000 as surfactant, water-n-butanol as solvent system, pH value of 8-9, the molar ratio of H2O2 to Co^2＋ above 2.5：1.0, hydrothermal temperature of 160 ℃ and hydrothermal holding time of 10 h. The tap density and apparent density of nanocubic Co3O4 obtained with the average particle size of 20 nm are 1.01 g/cm^3 and 0.70 g/cm^3, respectively.     

Growth and optical properties of ZnO nanorods prepared through hydrothermal growth followed by chemical vapor deposition

We report on the synthesis of high-quality ZnO nanorods by combining hydrothermal growth (HG) and chemical vapor deposition (CVD) processes. Vertically aligned and closely packed ZnO nanorods were grown by HG on a sputtered ZnO seed layer on a SiO₂/Si (0 0 1) substrate. The top surface of the HG-prepared ZnO nanorods showed very flat surfaces compared with that of the sputtered ZnO seed layer. Therefore, the HG-prepared ZnO nanorods were used as a new alternative seed material for the CVD growth of the ZnO nanorods. Vertical ZnO nanorods were grown by CVD on both the new HG-prepared nanorod seed material and the sputtered ZnO seed layer. The CVD-prepared ZnO nanorods on new HG-prepared nanorod seed material showed better crystalline quality and superior optical properties than the CVD-prepared ZnO nanorods on sputtered seed layer. The former showed negligible deep-level emissions at room temperature photoluminescence measurements. The intensity ratio of near-band-edge emissions to deep-level emissions from the former was about 910, but that from the latter was about 151. This implies that the HG-prepared ZnO nanorods can be used as a promising new seed material for nanostructure synthesis.     

Indentation of lipid-based particle gels: An experimental,theoretical and numerical study

The rheological properties of lipid-based particle gels are critical in defining end-use properties. Although indentation is commonly utilized to investigate the end-use properties of these materials, a comprehensive methodology for acquiring and characterizing fundamental rheological properties via indentation is lacking. This study sought to develop the indentation method for obtaining the large-strain viscoplastic characteristics of three lipid systems that vary in composition and structure: shortening, margarine and butter. Uniaxial compression and conical indentation tests were performed at various rates. Constitutive behaviour was fitted with a viscoplastic model, with the rate-dependent plasticity defined by the overstress power law equation. The static stress–strain curve was defined by a linear elastic region, a strain hardening plastic deformation region, and a subsequent region of perfect plasticity. Forward predictions of the indentation load–displacement response were obtained via finite element analysis using compression test data. Good reverse predictions of the stress–strain properties from the indentation response were obtained through a novel method developed in this study.     

Structural size effects of intermetallic compounds on the mechanical properties of Mo-Si-B alloy: An experimental investigation

In general, size, shape and dispersion of phases in alloys significantly affect mechanical properties. In this study, the mechanical properties of Mo-Si-B alloys were experimentally investigated with regards to the refinement of intermetallic compound. To confirm the size effect of the intermetallic compound phases on mechanical properties, two differently sized intermetallic compound powders consisting Mo₅SiB₂ and Mo₃Si were fabricated by mechano-chemical process and high-energy ball milling. A modified powder metallurgy method was used with core-shell intermetallic powders where the intermetallic compound particles were the core and nano-sized Mo particles which formed by the hydrogen reduction of Mo oxide were the shells, leading to the microstructures with uniformly distributed intermetallic compound phases within a continuous α-Mo matrix phase. Vickers hardness and fracture toughness were measured to examine the mechanical properties of sintered bodies. Vickers hardness was 472 Hv for the fine intermetallic compound powder and 415 Hv for the coarse intermetallic compound powder. The fracture toughness was 12.4 MPa·√m for the fine IMC powders and 13.5 MPa·√m for the coarse intermetallic compound powder.     

Structural and electrochemical properties of LiV3O8 prepared by combustion synthesis

LiV₃O₈ powders were prepared by combustion synthesis, using metallic nitrates as the oxidant and metal sources and urea as fuel. The effect of (Li + V)/CO(NH₂)₂ ratio and heat-treatment temperature on the structure and electrochemical properties were discussed. The electrochemical behavior of the product showed that sample B₁ synthesized at 300 °C with 1:0.5 ratio of (Li + V)/CO(NH₂)₂ showed the highest initial discharge capacity of 317.3 mAh g⁻¹ and the best cycle ability with 238.9 mAh g⁻¹ after 30 cycles.     

Radiation-induced precipitation in a ferritic model alloy: An experimental and theoretical study

The radiation embrittlement of low-alloyed reactor pressure vessel steels is partly due to the formation of nanometer-sized solute clusters (Mn, Si, Ni, Cu and P). In order to determine if radiation-induced mechanisms can take part in the solute clustering, an under-saturated binary Fe–1 at.% Mn alloy was irradiated with Fe ions at 400 °C. After irradiation, atom probe tomography experiments revealed that a high density of Mn-rich clusters is formed. This observation clearly demonstrates that, under these irradiation conditions, Mn clustering in this model alloy is radiation-induced and not radiation-enhanced. Mn-rich clusters were not distributed homogeneously in the analyzed volume but were heterogeneously precipitated on a planar object, suggesting a grain boundary (GB) or a dislocation loop. In parallel, a rate theory model calibrated on the population of point defect (PD) clusters measured by transmission electron microscopy has shown that the dominant sinks for mobile PDs are PD clusters. Thus Mn clustering could be explained by Mn atoms dragged by mobile PD fluxes towards sinks such as PD clusters or GBs. According to the model, most of the dragging occurs via isolated interstitials. These results are in very good agreement with previous studies, suggesting a correlation of position between solute-rich clusters and sinks.