Yiyang Xie

V5+ ionic displacement induced ferroelectric behavior in V-doped ZnO films

V-doped ZnO films have been prepared on Si(111) substrates by direct current reactive magnetron cosputtering. Hysteresis loops of polarization–applied field characteristics with a remnant polarization of 0.2μC∕cm2 were obtained in (2.5at.%) V-doped ZnO films, indicating the ferroelectric behavior exists in this system. This is demonstrated by displacement-voltage curves, which show typical butterfly shapes. X-ray absorption near-edge structure (XANES) spectrum at V K edge shows that V is in the 5+ state replacing Zn. Furthermore, the calculations of the XANES spectra indicate that a V5+ ionic displacement of 0.15A is responsible for the ferroelectric behavior.

Mechanical alloying of Fe-Mn and Fe-Mn-Si

The ball milling of Fe-24Mn and Fe-24Mn-6Si mixed powders has been performed by the high energy ball milling technique. By employing X-ray diffraction and Mossbauer measurements, the composition evolution during the milling process has been investigated. The results indicate the formation of paramagnetic Fe-Mn or Fe-Mn-Si alloys with a metastable fee phase as final products, which imply that the Fe and Mn proceed a co-diffusion mechanism through the surface of fragmented powders. The thermal stability and composition evolution of the as-milled alloys were discussed comparing with the bulk alloy

Bondlength alternation of nanoparticles Fe2O3 coated with organic surfactants probed by EXAFS

Abstract The nanoparticles γ-Fe2O3 coated with surfactants, DBS, ST and CTAB, repsectively, were synthesized by microemulsion method. The coated ferric oxides, which show enhanced nonlinear optical properties compared with their bulk counterpart, were probed by EXAFS in solution forms. The x-ray absorption spectra for Fe K edge were measured at room temperature by help of synchrotron radiation light source. Extended x-ray absorption fine structure analysis shows that the coating layers of organic molecules interact with surface atoms of nanoparticles, the Fe-O bond length was extended.

Study of the relationship between microstructure and performance for NOx storage catalysts

Aseries of Pt/BaAl2O4-Al2O3 NOx storage catalysts were prepared using the coprecipitation-impregnation method. XRD, XANES and EXAFS were used to characterize the microstructure of barium and platinum species in the samples. Barium exists in the forms of BaAl2O4 and BaCO3 crystallites. With the decreasing of calcination-temperature and barium content, the dispersion of BaAl2O4 phases becomes higher in the samples. In comparison with platinum standard compounds, the magnitude of the Pt-Pt coordination is significantly decreased, and the coordination distance is also shortened by about 0.01xa0nm. Platinum mainly exists as small atomic clusters, which possess a high dispersion, while some Pt (+ 4) species still present in the samples. A high dispersion of platinum and barium can greatly enhance the catalyst to store NOx.

Temperature effect of the local structure in liquid Sb studied with x-ray absorption spectroscopy

The temperature dependence of the local structure of liquid Sb has been studied by x-ray absorption spectroscopy. It is shown that about 10% of the atoms with coordination of 3 and weak Peierls distortion exist in liquid Sb just above its melting point. The Peierls distortion weakens gradually with increasing temperature and vanishes at about 750 degrees C. This structural variation in liquid Sb is different from the normal liquid-liquid phase transition. This work reveals the relationship between the variation in the local structure and the change in the physical properties, such as the electrical resisitvity of liquid Sb, with temperature. The complete agreement between the measured electrical resistivity values during heating and cooling processes suggests that the structural units with the features of a rhombohedron appear above the melting point of Sb during solidification.

GaN nanorod light emitting diodes with suspended graphene transparent electrodes grown by rapid chemical vapor deposition

Ordered and dense GaN light emitting nanorods are studied with polycrystalline graphene grown by rapid chemical vapor deposition as suspended transparent electrodes. As the substitute of indium tin oxide, the graphene avoids complex processing to fill up the gaps between nanorods and subsequent surface flattening and offers high conductivity to improve the carrier injection. The as-fabricated devices have 32% improvement in light output power compared to conventional planar GaN-graphene diodes. The suspended graphene remains electrically stable up to 300u2009°C in air. The graphene can be obtained at low cost and high efficiency, indicating its high potential in future applications.

Interface as the origin of ferromagnetism in cobalt doped ZnO film grown on silicon substrate

We have investigated the magnetic properties of Co-doped zinc oxide (ZnO) film deposited on silicon substrate by magnetron sputtering. Co ions have a valence of 2+ and substitute for Zn sites in the lattice. By using a chemical etching method, an extrinsic ferromagnetism was demonstrated. The observed ferromagnetism is neither associated with magnetic precipitates nor with contamination, but originates from the silicon/silicon oxide interface. This interface ferromagnetism is characterized by being temperature independent and by having a parallel magnetic anisotropy

High Beam Quality of In-Phase Coherent Coupling 2-D VCSEL Arrays Based on Proton-Implantation

Two-dimensional coherently coupled arrays of vertical cavity surface emitting lasers were fabricated using proton implantation. A 2 × 2 array with the far field beamwidth of 3.6° ( 1.18×diffraction limited), the output power of 0.45 mW, and the spectral line width of 0.2 nm was achieved for continuous wave operation at room temperature. It showed an excellent beam quality due to the in-phase coupling among the elements in the array. The array performance dependence on injection current level and thermal effects was discussed. The processing for the arrays is considerably simple and can be used as an alternative to other array implementations.

Implant-Defined 3

Two-dimensional in-phase coherently coupled vertical cavity surface emitting laser (VCSEL) array with high beam quality was fabricated by proton implantation. Indium-tin-oxide (ITO) current spreading layer was employed to improve the uniformity of the injection current. This makes a coherent array to operate in in-phase mode even in a relatively larger scale. The appropriate thickness of ITO current spreading layer was obtained by experiment (80 nm). The procedure of proton implantation defined array is considerably simple and low cost. A 3 × 3 in-phase coherently coupled array with 2.4° (1.28 × D.L.) of lobe beamwidth was achieved. It sufficiently demonstrates the advantages of the high beam quality of the in-phase coherently coupled arrays. The output power of the array was up to 4.5 mw under pulse-wave condition.

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We have designed an air-bridged PhC microcavity with high sensitivity and a high quality factor. The structure parameters of the microcavity are optimized by three-dimensional finite-difference time-domain method. We compare the performance of a silicon-on-insulator PhC microcavity and an air-bridged PhC microcavity, and analyze the effect of the thickness of the slab and the radius of the defect hole on the performance of the air-bridged PhC microcavity. For a thinner slab and a larger defect hole, the sensitivity is higher while the quality factor is lower. For the air-bridged photonic crystal slab, the sensitivity can reach 320-nm/RIU (refractive index unit) while the quality factor keeps a relatively high value of 120 by selecting the proper slab thickness and the defect hole radius, respectively, when the refractive index is 1.33. This is meaningful for low-detection-limit biosensing.