ZnO–TeO2–Yb/Tm glasses with silver nanoparticles as laser operated quantum electronic devices

The incorporation of silver nanoparticles into a Yb/Tm codoped ZnO–TeO₂ glass is shown to lead to a substantial increase in optically stimulated second harmonic generation (SHG). The corresponding second order optical susceptibility is equal to 1.32 pm/V at a wavelength of 1064 nm. The optimal conditions required the thermoannealing of the sample for 48 h and the use of a pump-probe delaying time of 12 ns.     

Zinc impregnated cellulose nanocomposites: Synthesis,characterization and applications

Nanocomposite materials have broad applicability due to synergistic effect of combined components. In present investigation, cellulose isolated from citrus peel waste is used as a supporting material; impregnation of zinc oxide nanoparticles via co-precipitation method. The characterization of nano composite is carried out through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and Thermo-gravimetric analysis (TGA) resulting less than 10 µm cellulose fiber and approx. 50 nm ZnO NPs. Zinc oxide impregnated cellulose (ZnO–Cel) exhibited significant bacterial devastation property when compared to ZnO NPs or Cellulose via disc diffusion and colony forming unit methods. In addition, the ZnO–Cel exhibited significant total antioxidant, and minor DPPH free radical scavenging and total reducing power activities. The nano composite also showed time dependent increase in photocatalytic by effectively degrading methylene blue dye up to 69.5% under sunlight irradiation within 90 min. The results suggest effective utilization of cellulose obtained from citrus waste and synthesis of pharmacologically important nano-composites that can be exploited in wound dressing; defence against microbial attack and healing due to antioxidative property, furthermore can also be used for waste water treatment.     

Doped nanocrystalline materials — Physics and applications

The properties and applications of nanocrystals doped with transition and rare-earth impurities are reviewed. The high efficiency and ultrafast recombination times observed in these doped nanocrystals make these materials very attractive for optoelectronic applications.     

Field emission graphene–oxide–silicon field effect based photodetector

Silicon‐based devices keep moving into smaller dimension for improving the speed, efficiency, and low‐power consumption. Novel designed semiconductor device architectures are needed to overcome the physical limitations. An integration of well‐designed nanostructure and nanomaterials can potentially establish new principles and approaches to nanoelectronic and photonic devices. We herein demonstrate a graphene/SiO₂/p‐Si (GOS) heterostructure with an embedded nanoscale mesa, forming a GOS‐Mesa field‐effect photodetector. The proposed structure exhibits that multiple exciton generation (MEG) can occur in a quantum‐confined two‐dimensional electron gas (2DEG) region via impact ionization, leading to high internal quantum efficiency (η_IQE). The numerical simulation of the carrier multiplication (CM) factor in our designed structure finds a reasonable agreement with empirical data. Simulated and measured internal quantum efficiency demonstrate ～195% and ～135% of UV–Vis radiation, respectively. A vertically confined 2DEG plays an important role not only in enabling the electron emission process which is responsible for the flowing of electron current, but also in developing a highly localized electric field (up to ～10⁶ V/cm) at the SiO₂/Si interface, enabling an impact ionization process under photon energy of merely ～1.95 eV. Our findings demonstrate that carrier multiplication can be achieved in a suitably designed nanoscale structure in conjunction with nanomaterial on silicon‐based devices, providing incentive to better understand MEG within quantum wells in 2DEG systems, and being a research path to enhancing the efficiency of future solar harvesting technologies. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

EXAFS analysis of Er sites in Er–O and Er–F co-doped crystalline Si

We present extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) analyses of Er–O and Er–F co-doped Si. Samples were prepared by multiple implants at 77 K of Er and co-dopant (O or F) ions resulting in the formation of a2 μm thick amorphous layer uniformly doped with 1×10¹⁹ Er/cm³ and 3×10¹⁹ O/cm³, 1×10²⁰ O/cm³ or 1×10²⁰ F/cm³. EXAFS measurements show that the local environment of the Er sites in the amorphous layers consists of 6 Si first neighbors. After epitaxial regrowth at 620°C for 3 h, Er is fully coordinated with 8 F ions in the Er–F samples, while Si and O ions are concomitantly present in the first shell of O co-doped samples. Post regrowth thermal treatments at 900°C leave the coordination unchanged in the Er+F, while the Er+O (ratio 1 : 10) doped samples present Er sites with a fully O coordinated shell with an average of 5 O atoms and 4 O atoms after 30 s and 12 h, respectively. We have also found that the fine structure and intensity of the high-resolution PL spectra are strongly dependent on the Er-impurity ratio and on thermal process parameters in the Er–O co-doped samples, while this is not observed for the F-doped samples. The most intense PL response at 15 K was obtained for the 1 : 3 E : O ratio, suggesting that an incomplete O shell around Er is particularly suitable for optical excitation.     

Magnetic hydrophobic nanocomposites: Silica aerogel/maghemite

Magnetic hydrophobic aerogels (MHA) in the form of nanocomposites of silica and maghemite (γ-Fe₂O₃) were prepared by one step sol–gel procedure followed by supercritical solvent extraction. Silica alcogels were obtained from TEOS, MTMS, methanol and H₂O, and Fe(III) nitrate as magnetic precursor. The hydrophobic property was achieved using the methytrimethoxysilane (MTMS) as co-precursor for surface modification. The so produced nanocomposite aerogels are monolithic, hydrophobic and magnetic. The interconnected porous structure hosts ∼6 nm size γ-Fe₂O₃ particles, has a mean pore diameter of 5 nm, and a specific surface area (SSA) of 698 m²/g. Medium range structure of MHA is determined by SAXS, which displays the typical fractal power law behavior with primary particle radius of ∼1 nm. Magnetic properties of the nanoparticle ensembles hosted in them are studied by means of dc-magnetometry.     

Polymer electrolytes based on ethylene oxide–epichlorohydrin copolymers

In this work we studied the ionic conductivity for three copolymers of the title co-monomers as a function of LiClO₄ content, temperature and ambient relative humidity. We also investigated the interactions between the salt and the co-monomer blocks in the copolymers and its effect on the morphology and thermal properties of the copolymer/salt complexes. Our data indicate that the Li⁺ ion predominantly interacts with the ethylene oxide repeating units of the copolymers. The copolymer with the highest ionic conductivity was obtained with an ethylene oxide/epichlorohydrin ratio of 84/16 containing 5.5% (w/w) of LiClO₄. It showed a conductivity of 4.1×10⁻⁵ S cm⁻¹ (30°C, humidity< 1 ppm) and 2.6×10⁻⁴ S cm⁻¹ at 84% relative humidity (24°C). The potential stability window of the copolymer/salt complex is 4.0 V, as measured by cyclic voltammetry. For comparison, we also prepared a blend of the corresponding homopolymers containing LiClO₄; it showed higher crystallinity and lower ionic conductivity.     

Fabrication and characteristics of solution‐processed graphene oxide–silicon heterojunction

We demonstrate the fabrication of a solid state heterojunction photovoltaic device with solution‐processed graphene oxide (GO) and n‐Si. Partially reduced GO with a high optical gap (2.8 eV) was spin‐coated on the n‐Si substrate and a heterojunction device was fabricated with the structure of Au/pr‐GO/n‐Si. In the fabricated device, incident light was transmitted through the thin GO film to reach the junction interface, generating photoexciton, and thereby a photovoltaic action was observed. By means of a built‐in electric potential at the GO/n‐Si junction, photoexcited electrons and holes can be separated, transported and collected at the electrodes.

     

Spectroscopy of II–VI nanocrystals at high pressure and high temperature

We review experimental measurements of CdS, CdSe, and CdS_xSe_{1 − x} nanocrystals which address the properties and phase stability of both powder and embedded nanoparticles under extreme conditions. We address the high pressure phase transition of wurtzite or zincblende phase to the rock salt structure; the high temperature solid to liquid phase transition; and the homogeneous nucleation of nanoparticles in glass from dissolved reactants. We also review the use of high pressure optical measurements to study electronic states.     

Synthesis and optical characterization of c-axis oriented GaN thin films on amorphous quartz glass via sol–gel process

c-Axis oriented GaN nanocrystalline thin films were fabricated by nitridation of three different thin films of -GaO(OH), -Ga₂O₃ or β-Ga₂O₃ obtained by sol–gel technique on amorphous quartz glass substrates. All these GaN thin films showed near band edge emission at 390 nm and yellow luminescence at 570 nm. The crystalline nature and c-axis orientation as well as luminescence properties of the GaN thin films increased by several times by using a buffer layer of GaN on the substrate.     

Synthesis and characterization of hydroxyapatite/titania nanocomposites using in situ precipitation technique

Hydroxyapatite/titania nanocomposites were successfully synthesized by in situ precipitation of precursor matters from hydroxyapatite and titania at 70 °C with different hydroxyapatite/titania ratios. X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller surface, scanning and transmission electron microscopes were employed to characterize the prepared nanocomposite powders. X-ray diffraction results indicated that hydroxyapatite and anatase (TiO₂) were the major crystalline phases. By increasing the amount of titania nano-particles, Fourier transform infrared spectroscopy revealed that (PO₄)³⁻ bands at 567, 1033 cm⁻¹ decreased. Brunauer–Emmett–Teller surface results also showed a reduction in surface areas of nanocomposites. Transmission electron microscope observations revealed that the aspect ratio of hydroxyapatite/TiO₂ nanocrystals increased by increasing TiO₂ proportion in nanocomposites. The observed nanorod crystals tended to thin, elongated and plate-like in shape.     

Luminescent properties of Dy-doped and Dy–Tmco-doped phosphate glasses

Phosphate glasses doped with Dy³⁺ ions and co-doped with Dy³⁺–Tm³⁺ ions are successfully prepared in the present work. Their photoluminescence properties have been studied by absorption, excitation and emission spectra. A combination of blue and yellow emissions has emerged in the glasses, which allows the observation of white light when the glasses are excited by the ultraviolet light. The emission intensity of Dy³⁺ is influenced by the system ionicity, while the intensity ratio of yellow to blue emissions from Dy³⁺ can be tuned by varying both the concentration of Tm³⁺ ion and the glass matrix composition.     

Far‐infrared spectroscopy,the wavenumbers of metal–ligand vibrations and the characterisation of inorganic pigments

Extensive far‐infrared studies of inorganic materials and pigments in the early 1960s are highlighted and related to the many subsequent Raman studies of the same materials, studies which led to the formulation of Raman spectral libraries for use in conservation science. The need for complementary infrared/far‐infrared libraries is recognised. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis, characterization and infrared emissivity study of polyurethane/TiO2 nanocomposites

In this study, polyurethane/titania (PU/TiO₂) nanocomposites were prepared in ultrasonic process and characterized by fourier transform IR spectroscopy (FT-IR), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared emissivity analysis. The TEM and SEM results indicated that the nanoparticles were dispersed homogeneously in PU matrix on nanoscale. TGA-DSC confirmed that the heat stability of the composite was improved. Infrared emissivity study showed that the nanocomposite possessed lower emissivity value than those values of pure polymer and nanoparticles.     

The effect of solvent on the crystal structure and size distribution of cadmium sulfide nanocrystals

CdS nanocrystals with different structures were synthesized by the method of solution precipitation using thiourea and cadmium acetate as starting materials in different solvents: water, methanol and N,N-dimethylformamide (DMF). Our results show that the solvent has direct effect on the structure and size of the final nanoparticles. It was found that using DMF, as a solvent, results in producing smaller nanoparticles with the cubic structures, while using the other solvents gives rise to larger nanoparticles with the hexagonal structure. It was also found that using heat during washing the precipitate results in a more homogenous size distribution of CdS nanocrystals. On the basis of our experimental results we also suggest a critical structure transformation size.     

CdS:Mn/SiO2复合纳米颗粒的反常的磁学特性

采用反胶束法,合成了硅土包裹的Mn2+掺杂的CdS纳米颗粒。利用高分辨透射电镜(HRTEM)和电子自旋共振谱 (EPR) 对这些纳米颗粒的结构进行了表征。利用超导量子干涉磁力计（SQUID）测量了这些纳米颗粒在低温下的磁学特性。研究结果表明：扩散在硅土基质中的CdS:Mn纳米颗粒的磁滞回线相对于磁场轴有明显的偏移,而有致密包裹层SiO2的CdS:Mn纳米颗粒却使磁滞回线的偏移消失,对于磁性纳米颗粒在磁化过程中出现的这一奇特的现象进行了合理的解释。     

CdS:Mn/SiO2复合纳米颗粒的反常的磁学特性

采用反胶束法,合成了硅土包裹的Mn2+掺杂的CdS纳米颗粒。利用高分辨透射电镜(HRTEM)和电子自旋共振谱 (EPR) 对这些纳米颗粒的结构进行了表征。利用超导量子干涉磁力计（SQUID）测量了这些纳米颗粒在低温下的磁学特性。研究结果表明：扩散在硅土基质中的CdS:Mn纳米颗粒的磁滞回线相对于磁场轴有明显的偏移,而有致密包裹层SiO2的CdS:Mn纳米颗粒却使磁滞回线的偏移消失,对于磁性纳米颗粒在磁化过程中出现的这一奇特的现象进行了合理的解释。     

Dielectric behavior of TiC–PVDF nanocomposites

TiC/PVDF nanocomposite is prepared via simple blending and hot pressing route. Percolation theory was employed to explain the dielectric behavior of the TiC/PVDF composites. The dependence of the dielectric properties of the composite on both volume fraction of the filler and frequency is investigated. High dielectric constant (? = 540) and low loss (tan δ = 0.48) of the composites at 100 Hz have been observed near the percolation threshold (0.12). The composites show a weak frequency dependence towards the high frequency range (10–100 kHz), regardless of the TiC content. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

CdSnO3-graphene nanocomposites: Ultrasonic synthesis using glucose as capping agent and characterization for electrochemical hydrogen storage

Nanoscale cadmium stannate (CdSnO₃) structures were productively synthesized via a facile and rapid sonochemical route using an eco-friendly capping agent of glucose. In order to optimize the size and structure of products, the various effective factors were inquired such as ultrasound waves, calcination temperature and solvent. The all samples were synthesized under ultrasonic probe for 30 min and different power (frequency) of 80 (24 KHz), 60 (18 KHz) and 40 W (12 KHz). The properties and characteristics of as-fabricated samples were examined by proficient techniques to identification the purity, structure, shape, optical, electrical and surface features. The ability of CdSnO₃ nanostructures and representative graphene based nanocomposites as potential hydrogen storage materials was considered by electrochemical methods. According to the obtained results, the CdSnO₃/graphene nanocomposites demonstrated higher hydrogen storage capacity than pristine CdSnO₃ nanostructures.