Xiuchun Yang

X-ray absorption spectroscopy analysis of formation and structure of Ag nanoparticles in soda-lime silicate glass

Abstract Ag nanoparticles of 2.8–7 nm mean size were fabricated in soda-lime glass of varying iron oxide content by Na + /Ag + ion exchange and subsequent thermal treatment. Fe 2+ ions have been identified as reducing agent for Ag ions by analysis of the X-ray absorption near edge structure at the Fe K-edge and of the extended X-ray absorption fine structure (EXAFS) at the Ag K-edge. EXAFS analysis accompanied by electron microscopy investigation has shown that crystalline Ag particles in glass with high content of iron oxide (0.865% Fe 2 O 3 ) exhibit a lattice dilatation. Furthermore, the calculated data demonstrate that with decreasing particle size lattice disorder and anharmonic effects, and hence also the thermal expansion coefficient, increase. This size effect is more distinctly pronounced for glass samples of reduced thickness as well as upon gradual thermal treatment applied for particle preparation. The results indicate substantial influence of the surrounding glass matrix on formation, structure and thermodynamic properties of Ag particles.

Nanoscaled ceramic powders produced by laser ablation

Abstract Copper oxide, silicon carbide and alumina–zirconia nanopowders have been produced by laser ablation in different atmospheres. Particle morphology, phase transformation and powder composition were investigated by X-ray diffraction, transmission electron microscopy, high resolution electron microscopy, and infrared spectroscopy. Targets used for producing the corresponding nanopowders usually melt, evaporate, decompose and oxidize during laser ablation, which lead to phase transformations and composition changes. A model has been proposed to explain the formation mechanism of nanoparticles, especially the nanoparticles embedded in amorphous matrices.

Recent progress in all-solid-state quantum dot-sensitized TiO2 nanotube array solar cells

All-solid-state quantum dot-sensitized TiO2 nanotube array solar cells have been drawing great attention to solar energy conversion, which break through restrictions in traditional solar cells, such as the high recombination at interfaces of porous TiO2 films/sensitizers/hole conductors/counter electrodes, instability of dyes, and leakage of solution electrolyte, and so the novel solar cells exhibit promising applications in the future. In this Minireview article, the assembling of solar cells including the preparation of TiO2 nanotube array photoanodes, quantum dot preparation and sensitization on photoanodes, filling of hole conductors in TiO2 nanotubes, and selection of counter electrodes are overviewed, and the development course of all-solid-state quantum dot-sensitized TiO2 nanotube array solar cells in recent years are summarized in detail. Moreover, the influences of TiO2 nanotube array photoanodes, quantum dots, solid electrolyte, and counter electrodes on photon-to-current efficiencies of solar cells are summarized. In addition, current problems of solid-state quantum dot-sensitized TiO2 nanotube array solar cells are analyzed, and the corresponding improvements, such as multisensitizers and passivation layers, are proposed to improve the photoelectric conversion efficiency. Finally, this Minireview provides a perspective for the future development of this novel solar cell.

OPAA template-directed synthesis and optical properties of metal nanocrystals

Ag and Cu nanocrystals (NCs) were assembled into ordered porous anodic alumina (OPAA) by a single-potential-step chronoamperometry technique. The composition, morphology, microstructure, and optical property were analyzed by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and optical absorption spectroscopy. The results indicate that metallic NCs/OPAA composite possesses a significant surface plasmon resonance absorption. For continuous electrodeposition, metallic nanowires are smooth and uniform with face-centered cubic (fcc) single-crystalline structure; however, for interval electrodeposition, the nanowires are bamboo-like or pearl-chain-like with fcc polycrystalline structure. The length of the nanoparticle nanowires or the single-crystalline nanowires can be controlled well by adjusting the experimental cycle times or the continuous depositing time. The transverse dipole resonance of metallic NCs enhances and displays a blue shift with increasing electrodeposition time or experimental cycle times, which is consistent with Zongs results but contradictory to Duans results. The formation mechanisms of the nanoparticle nanowires and the single-crystalline nanowires were discussed in detail.

Optical Properties of Ag Nanoparticle-Glass Composites

Silver nanoparticles doped glass composites were prepared by ion-exchange and subsequent thermal treatment processes. The optical properties of silver nanoparticle-glass composites were investigated by UV-VIS spectrophotometer and z-scan technique. The results show that the optimal Ag+/Na+ ion-exchange temperature range is between 310°C and 380°C, higher ion-exchange temperature or higher AgNO3 concentration in melt or longer ion-exchange period favors the introduction of more Ag+ ions into soda lime silicate glasses. The higher Ag+ concentration introduced into silicate glass, the larger the volume fraction of Ag nanoparticles in glass after annealing will be. Ag nanoparticles size and volume fraction become larger with increasing the annealing temperature and extending the annealing time. The off-resonant third-order nonlinear optical susceptibility of Ag nanoparticle-glass composite exhibits a value of 1.16×10-10esu where the real part is -1.15×10-10esu, and imaginary part is 1.4×10-11esu.

XAFS Studies of Silver Environments in Ion‐Exchanged Glasses

The X‐ray absorption fine structure (XAFS) technique was used to analyze the structural geometry of Ag atoms introduced into soda‐lime silicate glass and soda aluminosilicate glass by ion‐exchange methods. The results show that Ag+ ions in aluminosilicate glass are coordinated by about two oxygens and the nearest‐neighbor Ag‐O distance increases when the Ag+‐for‐Na+ ion‐exchange ratio is larger than 0.47. When the exchange ratio is low, the introduced Ag+ ions are stabilized at the non‐bridge oxygen (NBO) site with a Ag‐O distance of 2.20 A, and the Na+ ions in the AlO4 site are exchanged by Ag+ ions after full replacement of the NBO sites with a Ag‐O distance of 2.28 A. The disorder of Ag‐O coordination increases with increasing ion‐exchange ratio in aluminosilicate glass where Ag+ ions are coordinated by NBO and bridge oxygen (BO).

Effect of NO2 Concentration on Sensitivity for High Temperature Impedancemetric NOx Sensors

With the growing problem of automobile exhaust pollution, the study of automotive oxygen sensor is very meaningful, nitrogen oxides accounts for a large proportion of automobile exhaust. AC impedance spectroscopy of the NOx sensor in different temperature(500°C，600°C，700°C) and NO2 of different concentrations （100ppm，500ppm，1000ppm）in this paper, the influence of temperature and gas concentration on NOx sensors is explored.

Preparation of AgBr Nanowire Arrays in Porous Anodic Aluminium Oxide Template by Paired Cell Deposition

Firstly, porous anodic aluminum oxide template was prepared by a two-step anodization process, then AgBr nanowire arrays were successfully synthesized by paired cell deposition. X-ray diffraction (XRD) indicates that the as-synthesized samples are composed of face-centered AgBr. Field-emission scanning electron microscopy (FESEM) shows that the average diameter of the nanowire arrays is about 70nm.

The Influence of Y2O3 Calcined Temperature on the Performance of ZrO2

Semiconductor gas sensors utilize porous polycrystalline resistors made of semiconducting oxides.The working principle involves the receptor function played by the surface of each oxide grain and the transducer function played by each grain boundary. In addition, the utility factor of the sensing body also takes part in determining the gas response. Therefore, the concepts of sensor design are determined by considering each of these three key factors.ZrO2 is one of the most commonly used sensitive material, The performances of the different components Y2O3-ZrO2 are studied in this paper.The performances of YSZ Prepared with different Y2O3 powder(untreated and 1300°C preburned) and the Mechanism are explored in this paper.

Formation and Mechanism of Ag/Cu Nanoparticles in Silicate Glass via Ion-Exchange and Reduction Treatment

Ag-Cu nanoparticles/silicate glass composites are synthesized by twice ion-exchange and reduction treatment. The as-produced glass slides were characterized by UV–Vis spectroscopy, electron probe microanalysis (EPM) and high resolution transmission electron microscopy (HRTEM). The studies show that Ag-Cu nanoparticles aggregate on the surface of the silicate glass, which size is from 2 nm to 8 nm. The copper layer on the surface of glass matrix is about 20 m by compared to Ag layer (120 m), indicating that it is more difficult for copper ions to enter into the interior. Ag-Cu migration in glass matrix cannot be simply ascribed to a direct interaction with hydrogen, but to a more complex process involving a charge balancing mechanism during hydrogen-sodium ion-exchange.