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All surface-excitation studies of Au in the past focused on the well-known 2.4 eV surface plasmon polariton in the visible spectral regime. The existence of surface exciton polaritons is believed to be pristine to the spectral regimes, showing strong excitonic absorptions. The presence of surface exciton polaritons in far-UV in Au (≥10 eV), where the optical and electronic properties of Au are dominated by broad interband transitions that display characters of rather weak and diffused excitonic oscillator strengths, is not expected and has never been discussed. Re-examining the reports of Yang and using electron energy-loss spectroscopy with a 2Å electron probe in aloof (optical near-field) setup and real-space energy-filtered imaging, we firmly establish the existence of surface exciton polaritons in individual Au nanoparticles in the far-UV spectral regime. These results indicate that surface exciton polaritons indeed can be excited in weak excitonic onsets in addition to their general believing for the sharp excitonic oscillations. Our experimental observations are further confirmed by the theoretical calculations of electron energy-loss spectra. The unmatched spatial resolution (2Å) of the electron spectroscopy technique enables an investigation of individual nanomaterials and their surface excitations in aloof setup. The surface exciton polaritons in individual Au nanoparticles thus represent an example of surface excitations of this type beyond the visible spectral regime and could stimulate further interests in surface exciton polaritons in various materials and applications in novel plasmonics and nanophotonics at high energies via manipulations of the associated surface near fields. © 2008 The American Physical Society., This work was supported by the National Science Council of Taiwan under Projects No. NSC94-2120-M-002-016 and No. NSC94-2119-M-002-025.

This paper aims to propose a 3D nanostructured organic-inorganic hybrid photovoltaic device based on the ZnO nanostructures/poly(3-hexylthiophene)(P3HT):TiO 2 nanorods hybrids by solution processes at low temperature. An array of ZnO nanorods with a larger size of ~50 nm in diameter and ~180 nm in length are grown to provide direct pathways for efficient charge collection. TiO 2 nanorods with a size of ~5 nm in diameter and ~20-30 nm in length are incorporated into polymer to facilitate charge separation and transport by providing increased interfacial area and more effective transport pathway. The device performance with the inclusion of TiO 2 nanorods exhibits a seven times increase in the short circuit current with respect to that without TiO 2 nanorods.

Irradiation with approximately 10 keV x rays or medium-energy electrons destroys long-range order of Ir spin dimers in CuIr2S4 while preserving the dimers locally. We find that as the order is destroyed, a new type of incommensurate structural correlations appears. This represents an intriguing example of order from disorder phenomenon, in which a previously unknown incommensurate order appears in the radiation-induced disordered state. These results suggest that two competing instabilities, one of which can be suppressed by radiation, are present in the system. Otherwise unrealized structural or electronic states can, therefore, be revealed in correlated systems by x-ray or electron irradiation.

Trilayer structures CoFe/Bi/Co were prepared by dc sputtering at room temperature. The samples were then annealed at temperatures from 50/spl deg/C to 250/spl deg/C for 30 minutes. The crystalline structure, microstructures and magnetization loops of the as-deposited and annealed samples were investigated by X-ray diffraction, transmission electron microscopy (TEM) and vibrating sample magnetometer respectively. The correlation of interface parameters with interlayer coupling was analyzed and presented as function of the different annealing temperatures.

A simple metallic bonding structure, has been developed consisting of a pure metal Nb and an alloy containing Sn, which can be employed to bond a semiconducting laser device and/or a silicon integrated circuit die to a submount with Au–Sn solder. Differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy reveal that the Nb layer acts effectively both as an adhesion layer to SiO2 and diamond submounts and as a perfect diffusion barrier against Au–Sn solder. The metallization structure shows no indication of dewetting of the Au–Sn solder. The excellent bonding characters have been attributed to the unique metallurgical properties of Nb.

Electron diffraction, magnetic susceptibility and electronic transport indicate the existence of charge-carrier ordering in (La, Sr)2NiO4. This is most pronounced for a hole concentration nh of 1 3 with a superlattice modulation vector δ of 1 3 and it is also suggested for n h = 1 2 with δ = 0 .

Inorganic compounds with the AB2X4 spinel structure have been studied for many years, because of their unusual physical properties. The spinel crystallographic structure, first solved by Bragg in 1915, has cations occupying both tetrahedral (A) and octahedral (B) sites. Interesting physics arises when the B-site cations become mixed in valence. Magnetite (Fe3O4) is a classic and still unresolved example, where the tendency to form ordered arrays of Fe2+ and Fe3+ ions competes with the topological frustration of the B-site network. The CuIr2S4 thiospinel is another example, well known for the presence of a metal-insulator transition at 230 K with an abrupt decrease of the electrical conductivity on cooling accompanied by the loss of localized magnetic moments. Here, we report the determination of the crystallographic structure of CuIr2S4 below the metal-insulator transition. Our results indicate that CuIr2S4 undergoes a simultaneous charge-ordering and spin-dimerization transition-a rare phenomenon in three-dimensional compounds. Remarkably, the charge-ordering pattern consists of isomorphic octamers of Ir83+S24 and Ir84+S24 (as isovalent bi-capped hexagonal rings). This extraordinary arrangement leads to an elegant description of the spinel structure, but represents an increase in complexity with respect to all the known charge-ordered structures, which are typically based on stripes, slabs or chequerboard patterns.

Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and (100) Si with an yttria stabilized zirconia buffer layer. The structures have been grown in situ by 90° off‐axis sputtering, which allows the growth of uniform stoichiometric films over large areas with excellent step coverage. X‐ray diffraction, Rutherford backscattering spectroscopy, and cross‐sectional transmission electron microscopy reveal high crystalline quality and coherent interfaces. They exhibit superior fatigue characteristics over those made with metal electrodes, showing little degradation over 1010 cycles, with a large remnant polarization.

The two fold degeneracy inherent to epitaxial growth of high Tc films on (101) perovskite substrates has been removed successfully. This is demonstrated by single domain, (103) oriented La2−xSrxCuO4 films of 0.04≤x≤0.34 on vicinal (101) SrTiO3 substrates using 90° off‐axis sputtering. (101) substrates that have the surface normal rotated about [010] by 0.5°–3.5° produced essentially single crystal films with the c‐axis direction determined by the sense of the miscut. Misoriented antidomains (103)’ have been eliminated effectively to a percentage less than 1 part in 104. The mechanism for symmetry breaking is understood on the basis of a surface step model in which the energetics promoting single domain growth is derived from nucleation and epitaxy on the (001) face found at surface steps of vicinal substrates. Furthermore, the incommensuration of the c axis interplanar spacings with the a, b, plane lattice parameters in the La2−xSrxCuO4 structure provides a natural selection of (103) domains over (103)’ d...

The surface plasmon (SP) excitations of gold/silica nanowire, investigated by electron energy-loss spectroscopy in conjunction with scanning transmission electron microscopy, are found to be anisotropic with stronger SP intensities observed along the transverse direction of the nanowire. This indicates that the charge carriers generated near the surface of the nanowires by the decay of SP resonance play a significant role to the enhanced photoconductivity. This conclusion is reaffirmed by the polarization dependent photoconductivity measurement.

Manganites with small rare earths (RE = Ho, Er, Tm, Yb, Lu, or Y) and hexagonal structures belong to a class of materials known as hexagonal ferroelectrics, in contrast to those with large rare earths and orthorhombic, perovskite-related structures showing different physical properties. In this work, we study the effects of growth conditions on the stabilization of HoMnO3 films with both hexagonal and orthorhombic structures. Based on our experimental results, a HoMnO3 film with a hexagonal structure can be stabilized on Si(111) at 850 °C and above. Pure orthorhombic phases grow on SrTiO3(100), SrTiO3(110), LaAlO3(100), and LaAlO3(110) in a temperature range from 750 to 850 °C. Multiphase samples can be grown on MgO(100) at all temperatures.

From our study of the evolution of charge ordering in Bi 0.5 Ca 0.5- x Sr x MnO 3 ( x = 0–0.5) with chemical pressure, we found the detailed nature of two distinct charge ordering schemes, associated with the structural change from P n m a - to I m m a -type symmetry at x = 0.2–0.25. Charge ordering for x = 0–0.2 ( P n m a ) is consistent with the checkerboard-type pattern, commonly observed in half-doped manganites. On the other hand, a large tolerance factor for x = 0.25–0.5 ( I m m a ) stabilizes a double-stripe charge ordering scheme. These findings indicate the bicritical nature of two competing charge ordered states and provide further insight towards understanding the dominant charge ordering mechanism in half-doped manganites.

We report a direct observation of dramatic mass transport due to 1.5 MeV Au2+ ion impact on isolated Au nanostructures of an average size 7.6 nm and a height 6.9 nm that are deposited on Si (111) substrate under high flux (3.2x10^10 to 6.3x10^12 ions cm-2 s-1) conditions. The mass transport from nanostructures found to extend up to a distance of about 60 nm into the substrate, much beyond their size. This forward mass transport is compared with the recoil implantation profiles using SRIM simulation. The observed anomalies with theory and simulations are discussed. At a given energy, the incident flux plays a major role in mass transport and its re-distribution. The mass transport is explained on the basis of thermal effects and creation of rapid diffusion paths at nano-scale regime during the course of ion irradiation. The unusual mass transport is found to be associated with the formation of gold silicide nanoalloys at sub-surfaces. The complexity of the ion-nanostructure interaction process has been discussed with a direct observation of melting (in the form of spherical fragments on the surface) phenomena. The transmission electron microscopy, scanning transmission electron microscopy and Rutherford backscattering spectroscopy methods have been used., Comment: 16 pages, 6 Figures

We report the synthesis of single crystals of a metallorganic coordination compound, [Zn 2 Cl 4 (μ-bipy) 2 ], where bipy is 4,4'-trimethylene bipyridine, which is capable of producing white light as a single component. The coordination compound was crystallized by the hydrothermal synthesis of zinc chloride and bipy ligand, and the structure was determined by single-crystal x-ray diffraction refinement. The [Zn 2 Cl 4 ( F -bipy) 2 ] coordination complex crystallizes into a monoclinic crystal system in the P2 1 /m space group. The coordination compound is a distinct single-component, white-light-emitting phosphor upon excitation by UV-light-emitting diodes. The internal quantum efficiency was found to be 32%. The crystal structure and photoluminescence properties of the coordination polymer are discussed.

In this article, we have proposed a nanostructured photovoltaic device based on the ZnO nanostructures/poly(3-hexylthiophene)(P3HT):TiO2 nanorod hybrid by solution processes at low temperature. An array of ZnO nanorods with a larger size of ∼50 nm in diameter and ∼180 nm in length are grown to provide direct pathways for efficient charge collection. TiO2 nanorods with a size of ∼5 nm in diameter and ∼20–30 nm in length are incorporated into polymers to facilitate charge separation and transport by providing an increased interfacial area and a more effective transport pathway. The device performance with the inclusion of TiO2 nanorods exhibits a seven times increase in the short circuit current with respect to that without TiO2 nanorods. The device performance can be further enhanced after completely removing the residual surfactant on the TiO2 nanorods using the ligand exchange method, giving a short circuit current density of 2.67 mA cm−2 and a power conversion efficiency of 0.59% under Air Mass 1.5 (100 mW cm−2) illumination.

A “step-edge” model has been proposed to explain the growth of solid nanotips of aluminum nitride (AlN) and indium nitride (InN) grown by thermal and metal organic chemical vapor depositions, respectively. The model predicts a set of apex angles that solid AlN and InN nanotips can have. A statistical distribution of the apex angle in InN nanotips indicates the discrete set of apex angles and its probability of nucleation.

Recently, a commensurate superlattice modulation characterized by a wave vector of= (l/4, l/4, 0) was observed in both pure Nd2CuO4and electron-doped Nd2CuO4−xFx/Nd2−xCexCuO4compounds. The orthorhombic superlattice phase was found to exist in four possible variants with its c-axis parallel to the four equivalent zone-axes of the underlying tetragonal lattice. The origin of this modulation which is commonly observed in the beginning members of the rare-earth-based T' —214 compounds is not yet known. Gd2CuO4which represents the end member to this series has shown to exhibit anomalous magnetic properties.The present study was undertaken to investigate the superstructure in Gd2CuO4single crystals.Thin plate-like crystals of Gd2CuO4were grown from PbO- and CuO-based flux. TEM samples were prepared by ion-milling with a liquid-nitrogen-cooled sample holder.In-situheating experiments were carried out in a JEOL 2000FX electron microscope equipped with a Gatan hot stage.

Rapid progress has been made on thin films of high-Tc superconducting perovskites. Here we focus on the results from one of the most studied oxide systems, 125 K TlBaCaCuO. We have produced single-phase high-Tc superconducting Tl2Ba2Ca2Cu3O10 films 0.2–1.0 microm thick on MgO(100) and SrTiO3(100) substrates by sputtering using a single oxide target. The Tl2Ba2Ca2Cu3O10 films have a Tc onset at 125K and a Tc(R=0) at 116 K. Transport critical current densities of these films on SrTiO3 substrates are as high as 105 A cm−2 at 100 K. These thallium-based films are not only strongly textured with the c-axis perpendicular to the film plane, but also epitaxial to SrTiO3(100) substrates.

We have studied the microstructures of epitaxial YbBa2Cu3O7 superconducting films grown on SrTiO3[100] and [110] substrates by a new liquid‐gas‐solidification processing technique. Films grown on SrTiO3[100] and [110] substrates are epitaxially oriented with [001] and [110] axes normal to the film surface. Twinned domains of ∼200 A in size are observed in the [001] oriented films. Most defects observed can be attributed to the presence of stacking faults along the c axis. The presence of Cu‐O bilayer defects is also observed. Rapid oxygen diffusion in the liquid phase is found to play an important role in the microstructure of the thin films.

We compare the superlattice modulation, microstructure, and epitaxy of Tl2Ba2Ca2Cu3O10 thin films grown on MgO [100] and SrTiO3 [100] substrates by dc diode sputtering. Films grown on MgO were found to be quite clean with the c axis perpendicular to the substrate. However, no in‐plane orientational relationship to the substrate was found. Films grown on SrTiO3, on the other hand, showed very good epitaxy to the substrate despite the presence of second phases. Films grown on MgO also exhibited a longer coherence length of the superlattice modulation than those grown on SrTiO3 under identical conditions.

The pyrolysis of organic dianhydrides (e.g., 3,4,9,10‐perylenetetracarboxylic dianhydride) in an evacuated system results in the loss of hydrogen, CO, and CO2 and the deposition of a chemically inert, metallic‐appearing mirrolike film. The films are highly conducting (σRT250 Ω−1 cm−1) and can evidence either metallic or semiconducting behavior, depending on the preparation temperature. Superconducting films are obtained when niobium is used as a dopant. Preparation of films on doped silicon semiconductor chips results in the formation of p‐n junctions. ESR spectra exhibit a moderately strong line at g=2.0025. The resonance intensity remains almost constant to 20 °K, characteristic of a highly delocalized spin system.

We have used metal molecular beam epitaxy, sputter deposition with single composite target, and spin‐on/pyrolysis with metallo‐organic precursors to prepare thin films of high Tc oxide superconductors mostly in the Y‐Ba‐Cu‐O system. We report the superconducting properties and the structural characteristics of the films. The processing parameters of these thin‐film techniques are also discussed.

The authors found dynamic ferromagnetic correlations at the room temperature in perovskite manganites which have an antiferromagnetic insulating ground state. They are replaced by antiferromagnetic correlations when the electrons order. The results indicate that the double exchange mechanism is turned off by electron localization at low temperatures.

The formation of a charge-density-wave (CDW) superlattice in the blue molybdenum oxide bronze K/sub 0.30/MoO/sub 3/ is found to be extremely sensitive to electron-beam irradiation. Short exposure of the samples to an electron beam completely destroys the CDW superlattice whereas the underlying main lattice remains largely intact. The radiation damage in the CDW superlattice is believed to be electronic in origin.