Showing papers on "Absorption (logic) published in 2006"

First principles simulations of the structural and electronic properties of silicon nanowires

Abstract: We report the results of first principles studies of the structural and electronic properties of hydrogen-passivated silicon nanowires with [001], [011], and [111] growth directions and diameters ranging from $1\phantom{\rule{03em}{0ex}}\text{to}\phantom{\rule{03em}{0ex}}3\phantom{\rule{03em}{0ex}}\mathrm{nm}$ We show that the growth direction, diameter, and surface structure all have a significant effect on the structural stability, electronic band gap, band structure, and band-edge effective masses of the nanowires The band gap is found to decrease with increasing diameter and to be further reduced by surface reconstruction While the electron and hole effective masses are found to depend on NW size for [001] and [111] NWs, they are almost independent of size for [011] NWs Our results suggest the possibility of engineering the properties of nanowires by manipulating their diameter, growth direction, and surface structure Finally, we use FEFF calculations to predict the extended x-ray absorption fine structure spectra produced by the relaxed atomic structure of the NWs and show that these spectra can serve as a tool for detecting surface reconstructions on NWs

Electronic and optical properties of nitrogen-doped multiwalled carbon nanotubes

Abstract: Highly nitrogen-doped carbon nanotube (${\mathrm{CN}}_{x}\mathrm{NT}$, $x=12\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$) was synthesized by the pyrolysis of acetonitrile on Co-Mo catalysts. The electronic structures and chemical bondings of ${\mathrm{CN}}_{x}\mathrm{NT}$ were studied using various spectroscopic techniques: Raman, photoelectron and x-ray absorption spectroscopies. The ultrafast pump-probe measurements of ${\mathrm{CN}}_{x}\mathrm{NT}$ exhibited a larger third-order susceptibility ${\ensuremath{\chi}}^{(3)}$, a relaxation time of ${\ensuremath{\tau}}_{2}=1\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ and improved saturable absorption, as compared with undoped multiple-walled carbon nanotubes, which indicate that N-doping can improve all-optical switching properties of carbon nanotubes.

Evidence for Temperature-Dependent Electron Band Dispersion in Pentacene

Abstract: Evidence for temperature-dependent electron band dispersion in a pentacene thin film polymorph on graphite is provided by angle- and energy-dependent ultraviolet photoelectron spectroscopy. The bands derived from the highest occupied molecular orbital exhibit dispersion of $\ensuremath{\sim}190\text{ }\text{ }\mathrm{meV}$ at room temperature, and $\ensuremath{\sim}240\text{ }\text{ }\mathrm{meV}$ at 120 K. Intermolecular electronic coupling in pentacene thin films is thus confirmed to be dependent on temperature and possibly crystal structure, as suggested by additional infrared absorption measurements.

Narrow Escape, Part II: The Circular Disk

Abstract: We consider Brownian motion in a circular disk Ω, whose boundary \(\partial\Omega\) is reflecting, except for a small arc, \(\partial\Omega_a\), which is absorbing. As \(\varepsilon=|\partial\Omega_a|/|\partial \Omega|\) decreases to zero the mean time to absorption in \(\partial\Omega_a\), denoted \(E\tau\), becomes infinite. The narrow escape problem is to find an asymptotic expansion of \(E\tau\) for \(\varepsilon\ll1\). We find the first two terms in the expansion and an estimate of the error. The results are extended in a straightforward manner to planar domains and two-dimensional Riemannian manifolds that can be mapped conformally onto the disk. Our results improve the previously derived expansion for a general domain, \(E\tau = {\frac{|\Omega|}{D\pi}}\big[\log{\frac{1}{\varepsilon}}+O(1)\big],\) (\(D\) is the diffusion coefficient) in the case of a circular disk. We find that the mean first passage time from the center of the disk is \(E[\tau\,|\,{\boldmath x}(0)={\bf 0}]={\frac{R^2}{D}}\big[\log{\frac{1}{\varepsilon}}+ \log 2 +{ \frac{1}{4}} + O(\varepsilon)\big]\). The second term in the expansion is needed in real life applications, such as trafficking of receptors on neuronal spines, because \(\log{\frac{1}{\varepsilon}}\) is not necessarily large, even when e is small. We also find the singular behavior of the probability flux profile into \(\partial\Omega_a\) at the endpoints of \(\partial\Omega_a\), and find the value of the flux near the center of the window.

Critical view on the deeply bound K − pp system

Abstract: We briefly review the situation around the claimed deeply bound ${K}^{\ensuremath{-}}$ states in different recent experiments and concentrate particularly on the state ${K}^{\ensuremath{-}}\mathit{pp}$ advocated by the FINUDA collaboration in nuclear ${K}^{\ensuremath{-}}$ absorption. We perform a theoretical simulation of the process and show that the peak in the $\ensuremath{\Lambda}p$ spectrum that was interpreted as a deep ${K}^{\ensuremath{-}}\mathit{pp}$ bound state corresponds mostly to the process ${K}^{\ensuremath{-}}pp\ensuremath{\rightarrow}\ensuremath{\Lambda}p$ followed by final-state interactions of the produced particles with the daughter nucleus.

Narrow escape, part I

Abstract: A Brownian particle with diffusion coefficient D is confined to a bounded domain Ω by a reflecting boundary, except for a small absorbing window \(\partial\Omega_a\). The mean time to absorption diverges as the window shrinks, thus rendering the calculation of the mean escape time a singular perturbation problem. In the three-dimensional case, we construct an asymptotic approximation when the window is an ellipse, assuming the large semi axis a is much smaller than \(|\Omega|^{1/3}\) (\(|\Omega|\) is the volume), and show that the mean escape time is \(E\tau\sim{\frac{|\Omega|}{2\pi Da}} K(e)\), where e is the eccentricity and \(K(\cdot)\) is the complete elliptic integral of the first kind. In the special case of a circular hole the result reduces to Lord Rayleigh's formula \(E\tau\sim{\frac{|\Omega|}{4aD}}\), which was derived by heuristic considerations. For the special case of a spherical domain, we obtain the asymptotic expansion \(E\tau={\frac{|\Omega|}{4aD}} [1+\frac{a}{R} \log \frac{R}{a} + O(\frac{a}{R})]\). This result is important in understanding the flow of ions in and out of narrow valves that control a wide range of biological and technological function. If Ω is a two-dimensional bounded Riemannian manifold with metric g and \(\varepsilon=|\partial\Omega_a|_g/|\Omega|_g\ll1\), we show that \(E\tau ={\frac{|\Omega|_g}{D\pi}}[\log{\frac{1}{\varepsilon}}+O(1)]\). This result is applicable to diffusion in membrane surfaces.

Growth of intact water ice on Ru(0001) between 140 and 160 K: experiment and density-functional theory calculations

Abstract: We report low-energy electron diffraction (LEED) and reflection absorption IR spectroscopy (RAIRS) results for water adsorption on $\mathrm{Ru}(0001)$ at temperatures between 140 and $160\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where water forms intact hydrogen bonded structures on the surface. We find that ${\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{D}}_{2}\mathrm{O}$ adsorption show identical behavior, with no evidence for a structural isotope effect. At low coverage LEED shows a diffuse $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ pattern, which becomes sharp and intense only as the coverage reaches 0.6 to 0.67 monolayer. The LEED pattern becomes broadened and diffuse as the surface saturates with a coverage of 0.76 monolayer. In RAIRS the low-frequency bands associated with the out of plane libration of hydrogen bonded water appear at low coverage, with the water stretch and scissors bands appearing as broad bands only as the coverage is increased. Water adsorbs flat on $\mathrm{Ru}(0001)$ at low coverage, forming small clusters which buckle to create an extended, hydrogen bonded structure only as the adlayer is completed. The free $\mathrm{OH}(\mathrm{OD})$ stretch band appears only as the monolayer approaches completion, indicating flat or H-down adsorption up to 0.67 monolayer with H-up water appearing as the $\sqrt{3}$ structure compresses. Density functional calculations at low coverage find that water forms stable clusters with water adsorbed flat on the surface. Calculations for a complete 0.67 monolayer structure find water adsorbed near the Ru atop site in a hydrogen bonded honeycomb network, containing chains of ``flat'' lying water, linked by upright chains bonded ``H down'' in the hexagonal, hydrogen bonded superstructure. This structure is $\ensuremath{\sim}20%$ more stable than the conventional ice bilayer structure and is expected to wet the $\mathrm{Ru}(0001)$ surface. We propose a model in which disordered, short chains of ``flat'' and H-down water are imbedded in a honeycomb network of hydrogen bonded water, which imposes long-range order on the adlayer but allows substantial local disorder, and discuss the agreement with existing experimental results.

Strain induced x-ray absorption linear dichroism in La 0.7 Sr 0.3 Mn O 3 thin films

Abstract: Strain induced anisotropy in the electronic properties of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films was investigated by x-ray absorption spectroscopy at the Mn $2p$ and O $1s$ edges. Films on (100) $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ and (100) $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ substrates were grown by pulsed laser deposition with in situ reflection high energy electron diffraction diagnostic. At both absorption edges, clear features related to different anisotropic lattice strain effects as a function of the substrate were observed. On the average a negative (positive) linear dichroism was obtained for films grown under in-plane tensile (compressive) epitaxial strain conditions. Indeed, the structural macroscopic distortion induced by the substrate is responsible of the octahedra distortions with the resulting stabilization of ${x}^{2}\text{\ensuremath{-}}{y}^{2}$ $(3{z}^{2}\text{\ensuremath{-}}{r}^{2})$ orbitals. Enhanced linear dichroism at the Mn $2p$ edge in very thin films, only a few unit cells thick, is in agreement with a fully strained state which favors the formation of orbital ordered phase regions.

S~1 and S~2 Excited States of Gas-Phase Schiff-Base Retinal Chromophores

Abstract: Photoabsorption studies of 11-cis and all-trans Schiff-base retinal chromophore cations in the gas phase have been performed at the electrostatic ion storage ring in Aarhus. A broad absorption band due to the optically allowed excitation to the first electronically excited singlet state (${S}_{1}$) is observed at around 600 nm. A second ``dark'' excited state (${S}_{2}$) just below 400 nm is reported for the first time. It is located $\ensuremath{\sim}1.2\text{ }\text{ }\mathrm{eV}$ above ${S}_{1}$ for both chromophores. The ${S}_{2}$ state was not visible in a solution measurement where only one highly blueshifted absorption band corresponding to the first excited state was visible. Knowledge of the position of the excited states in retinal is essential for the understanding of the fast photoisomerization in, for example, visual pigments.

Electrons and hydrogen-bond connectivity in liquid water.

Abstract: The network connectivity in liquid water is revised in terms of electronic signatures of hydrogen bonds (HBs) instead of geometric criteria, in view of recent x-ray absorption studies. The analysis is based on ab initio molecular-dynamics simulations at ambient conditions. Even if instantaneous threadlike structures are observed in the electronic network, they continuously reshape in oscillations reminiscent of the $r$ and $t$ modes in ice ($\ensuremath{\tau}\ensuremath{\sim}170\text{ }\text{ }\mathrm{fs}$). However, two water molecules initially joined by a HB remain effectively bound over many periods regardless of its electronic signature.

J/ψProduction and Nuclear Effects ford+Auandp+pCollisions atsNN=200GeV

Abstract: $J/\ensuremath{\psi}$ production in $d+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{GeV}$ has been measured by the PHENIX experiment at rapidities $\ensuremath{-}2.2lyl+2.4$. The cross sections and nuclear dependence of $J/\ensuremath{\psi}$ production versus rapidity, transverse momentum, and centrality are obtained and compared to lower energy $p+A$ results and to theoretical models. The observed nuclear dependence in $d+\mathrm{Au}$ collisions is found to be modest, suggesting that the absorption in the final state is weak and the shadowing of the gluon distributions is small and consistent with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-based parametrizations that fit deep-inelastic scattering and Drell-Yan data at lower energies.

Universal features of terahertz absorption in disordered materials.

Abstract: Using an analytical theory, experimental terahertz time-domain spectroscopy data, and numerical evidence, we demonstrate that the frequency dependence of the absorption coupling coefficient between far-infrared photons and atomic vibrations in disordered materials has the universal functional form, $C(\ensuremath{\omega})=A+B{\ensuremath{\omega}}^{2}$, where the material-specific constants $A$ and $B$ are related to the distributions of fluctuating charges obeying global and local charge neutrality, respectively.

Determination of the high-pressure crystal structure of Ba W O 4 and Pb W O 4

Abstract: We report the results of both angle-dispersive x-ray diffraction and x-ray absorption near-edge structure studies in $\mathrm{Ba}\mathrm{W}{\mathrm{O}}_{4}$ and $\mathrm{Pb}\mathrm{W}{\mathrm{O}}_{4}$ at pressures of up to $56\phantom{\rule{03em}{0ex}}\mathrm{GPa}$ and $24\phantom{\rule{03em}{0ex}}\mathrm{GPa}$, respectively $\mathrm{Ba}\mathrm{W}{\mathrm{O}}_{4}$ is found to undergo a pressure-driven phase transition at $71\phantom{\rule{03em}{0ex}}\mathrm{GPa}$ from the tetragonal scheelite structure (which is stable under normal conditions) to the monoclinic fergusonite structure whereas the same transition takes place in $\mathrm{Pb}\mathrm{W}{\mathrm{O}}_{4}$ at $9\phantom{\rule{03em}{0ex}}\mathrm{GPa}$ We observe a second transition to another monoclinic structure which we identify as that of the isostructural phases $\mathrm{Ba}\mathrm{W}{\mathrm{O}}_{4}\text{\ensuremath{-}}II$ and $\mathrm{Pb}\mathrm{W}{\mathrm{O}}_{4}\text{\ensuremath{-}}III$ (space group $P{2}_{1}∕n$) We have also performed ab initio total-energy calculations which support the stability of this structure at high pressures in both compounds The theoretical calculations further find that upon increase of pressure the scheelite phases become locally unstable and transform displacively into the fergusonite structure The fergusonite structure is, however, metastable and can only occur if the transition to the $P{2}_{1}∕n$ phases were kinetically inhibited Our experiments in $\mathrm{Ba}\mathrm{W}{\mathrm{O}}_{4}$ indicate that it becomes amorphous beyond $47\phantom{\rule{03em}{0ex}}\mathrm{GPa}$

Mixed alkali effect in Li2O–Na2O–B2O3 glasses containing CuO – An EPR and optical study

Abstract: Electron Paramagnetic Resonance (EPR) and optical absorption spectra of 0.5 mol% CuO doped $xLi_{2}O-(30-x)Na_{2}O-{69.5}B_{2}O_{3}$ (5 \leq x \leq 25) mixed alkali glasses have been investigated. The EPR spectra of all the investigated samples exhibit resonance signals characteristic of $Cu^{2+}$ ions in octahedral sites with tetragonal distortion. It is found that the spin-Hamiltonian parameters do not vary much with x. It is interesting to observe that the number of $Cu^{2+}$ ions participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. It is observed that the temperature dependence of paramagnetic susceptibility (χ) obeys Curie–Weiss law. The paramagnetic Curie temperature $(\theta_p)$ is negative for the investigated sample, which suggests that the copper ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. A broad band corresponding to the transition $(^{2}B_{1g}\longrightarrow^{2}B_{2g})$ in the optical absorption spectrum shows a blue shift with x. By correlating the EPR and optical absorption data, the molecular orbital coefficients $\alpha^{2}$ and $\beta^{2}_{2}$ have been evaluated. It is interesting to observe that the optical band gap $(E_{opt})$ and Urbach energies $(\Delta{E})$ exhibit the mixed alkali effect. The theoretical values of optical basicity $({\Delta}_{th})$ have also been evaluated.

Ten milliparsec-scale structure of the nucleus region in centaurus A

Abstract: We present the results of a VLBI Space Observatory Programme (VSOP) observation of the subparsec structure in Cen A at 4.9 GHz. The observation produced an image of the subparsec jet components with a resolution of three-times better than images from previous VLBI monitoring campaigns at 8.4 GHz, and twice better than the previous 22 GHz studies. Owing to its proximity, our Cen A space-VLBI image is one of the highest spatial-resolution images of an AGN ever made—0.01 pc per beam—comparable only to the recent 43 GHz VLBI images of M87. The elongated core region is resolved into several components of over 10 milliarcsec long (0.2 pc), including a compact component of brightness temperature $2.2 \times 10^{10} \,\mathrm{K}$ . A counterjet was detected: if we assume jet-counterjet symmetry, a relatively slow jet speed, and a large viewing angle, as derived from previous observations, the image allows us to investigate the distribution of ionized gas around the core, which is opaque at this frequency due to free-free absorption. We also analyzed the jet geometry in terms of collimation. Assuming the strongest component to be the core, the jet opening angle at $\sim 5000 \,r_{\mathrm{S}}$ from the core is estimated to be $\sim 12^\circ$ , with the collimation of the jet to $\sim 3^\circ$ continuing out to $\sim 20000 \,r_{\mathrm{S}}$ . This result is consistent with previous studies of the jet in M87, which favor MHD disk outflow models. Future space VLBI observations at higher frequencies will probably be able to image the collimation region, within $1000 \, r_{\mathrm{S}}$ of the center of Cen A, together with the accretion disk itself.

Phonon confinement and laser heating effects in Germanium nanowires

Abstract: We explore the combined effects of phonon confinement and local heating caused by laser beam absorption on the Raman spectra of Germanium nanowires of different diameters ($6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, $7\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, and $12\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$). The asymmetric broadening and downshifting of the first order Raman band is studied as a function of the average wire diameter and the local temperature of the nanowires. The basic phenomenological model with a modified confinement function incorporated with thermal effects is in good agreement with our experimental results. We also show the effects of the nanowire diameter, thermal conductivity of the underlying substrate, and the mediating substance (gallium in this case) on the local temperature of the nanowires.

Disorder and Cluster Formation during Ion Irradiation of Au Nanoparticles in SiO 2

Abstract: Au nanoparticles (NPs) have been formed by ion beam synthesis in $600\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thin $\mathrm{Si}{\mathrm{O}}_{2}$. Subsequently the NPs were irradiated with $2.3\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ Sn ions at liquid nitrogen temperature. Samples were analyzed using extended x-ray absorption fine structure (EXAFS) spectroscopy and small angle x-ray scattering (SAXS) as a function of Sn irradiation dose. Transmission electron microscopy shows that the NPs largely retain their spherical shape upon irradiation. However, we observe a reduction in average NP size and a concomitant significant narrowing of the size distribution with increasing irradiation dose as consistent with inverse Ostwald ripening. At lower irradiation doses, significant structural disorder is apparent with an effective bond length expansion as consistent with amorphous material. At higher irradiation doses, EXAFS measurements indicate dissolution of a significant fraction of Au from the NPs into the $\mathrm{Si}{\mathrm{O}}_{2}$ matrix (as monomers) and the formation of small Au clusters (dimers, trimers, etc.). We estimate the volume fraction of such monomers/clusters. Ion irradiation thus yields disordering then dissolution of Au NPs.

Characterization of saturable absorbers using an open-aperture Gaussian-beam Z scan

Abstract: We present a theoretical investigation on the open-aperture Gaussian-beam $Z$-scan technique for two dominant saturable absorption models, by using the Adomian decomposition method. Analytic expressions of the $Z$-scan traces are deduced for a cw laser and a pulsed laser, respectively; in particular, for performable simulations, the optimal sum upper limit is found. We give an experimental demonstration, in which a side-chain azobenzene polymer poly [6-[1-(4-(4-nitrophenylazo)phenyl) piperazine] hexyl methacrylate] (Pda) film behaves as a test sample. The results manifest that our theory is reasonable and the Pda film is a good saturable absorber at the wavelength of $532\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

Direct Experimental Evidence for Atomic Tunneling of Europium in Crystalline Eu 8 Ga 16 Ge 30

Abstract: M\"ossbauer-effect and microwave absorption experimental evidence unambiguously demonstrates the presence of slow, $\ensuremath{\sim}450\text{ }\text{ }\mathrm{MHz}$, tunneling of magnetic europium between four equivalent sites in ${\mathrm{Eu}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$, a stoichiometric clathrate. Remarkably, six of the eight europium atoms, or 11% of the constituents in this solid, tunnel between these four sites separated by 0.55 \AA{}. The off centering of the atoms or ions in crystalline clathrates appears to be a promising route for producing Rabi oscillators in solid-state materials.

Experimental comparison of the structural, magnetic, electronic, and optical properties of ferromagnetic and paramagnetic polycrystalline Zn 1-x Co x O (x=0,0.05,0.1)

Abstract: Ferromagnetism at room temperature is observed in one case whereas paramagnetism down to $12\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is observed in the second case when polycrystalline ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{O}$ is synthesized under almost identical conditions. Identical x-ray diffraction, optical absorption, and x-ray photoelectron spectroscopy results indicate the incorporation of ${\mathrm{Co}}^{2+}$ ions in the ZnO lattice in both cases. However, electron diffraction studies show the presence of Co metal impurities in the ferromagnetic samples, indicating that pure Co doped ZnO is not likely to be ferromagnetic.

X-ray absorption fine structure (XAFS) analyses of Ni species trapped in graphene sheet of carbon nanofibers

Abstract: Metal impurities in the carbon nanotubes and carbon nanofibers play an important role in understanding their physical and chemical properties. We apply the Ni $K$-edge x-ray absorption fine structure analyses to the local electronic and geometric structures around embedded Ni impurities used as catalysts in a carbon nanofiber in combination with multiple scattering analyses. We find almost Ni catalysts as metal particles are removed by the purification treatment. Even after the purification, residual $100\phantom{\rule{0.3em}{0ex}}\mathrm{ppm}$ Ni species are still absorbed; most of them are in monomer structure with Ni-C bond length $1.83\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, and each of them is substituted for a carbon atom in a graphene sheet.

Determining neutrino mass hierarchy by precision measurements in electron and muon neutrino disappearance experiments

Abstract: Recently a new method for determining the neutrino mass hierarchy by comparing the effective values of the atmospheric {Delta}m{sup 2} measured in the electron neutrino disappearance channel, {Delta}m{sup 2}(ee), with the one measured in the muon neutrino disappearance channel, {Delta}m{sup 2}({mu}{mu}), was proposed. If {Delta}m{sup 2}(ee) is larger (smaller) than {Delta}m{sup 2} ({mu}{mu}) the hierarchy is of the normal (inverted) type. We re-examine this proposition in the light of two very high precision measurements: {Delta}m{sup 2}({mu}{mu}) that may be accomplished by the phase II of the Tokai-to-Kamioka (T2K) experiment, for example, and {Delta}m{sup 2}(ee) that can be envisaged using the novel Moessbauer enhanced resonant {bar {nu}}{sub e} absorption technique. Under optimistic assumptions for the systematic uncertainties of both measurements, we estimate the parameter region of ({theta}{sub 13}, {delta}) in which the mass hierarchy can be determined. If {theta}{sub 13} is relatively large, sin{sup 2} 2{theta}{sub 13} {approx}> 0.05, and both of {Delta}m{sup 2}(ee) and {Delta}m{sup 2}({mu}{mu}) can be measured with the precision of {approx} 0.5 % it is possible to determine the neutrino mass hierarchy at > 95% CL for 0.3{pi} {approx}< {delta} {approx}< 1.7 {pi} for the current best fit values of all the other oscillation parameters.

Role of local disorder in the dielectric response of BaTaO2N

Abstract: Short-range structural disorder of the high-$\ensuremath{\kappa}$ dielectric $\mathrm{Ba}\mathrm{Ta}{\mathrm{O}}_{2}\mathrm{N}$ is revealed by the analysis of the extended x-ray-absorption fine-structure (EXAFS) spectroscopy measured at the Ta ${L}_{\mathit{III}}$ edge. Although previous neutron, x-ray, and electron diffraction studies have shown $\mathrm{Ba}\mathrm{Ta}{\mathrm{O}}_{2}\mathrm{N}$ to crystallize in a centrosymmetric, cubic structure, these EXAFS spectra show a wide distribution of first shell Ta-(O,N) distances with further implications to nonuniformity of the existing octahedral distortions. A distortion model based upon a density functional theory energy minimization for a $4\ifmmode\times\else\texttimes\fi{}4\ifmmode\times\else\texttimes\fi{}4$ supercell of $\mathrm{Ba}\mathrm{Ta}{\mathrm{O}}_{2}\mathrm{N}$ was used to successfully interpret these EXAFS data. We find that structural distortions with very short correlation lengths exist in this material and that these distortions are consistent with the large dielectric permitivity of $\mathrm{Ba}\mathrm{Ta}{\mathrm{O}}_{2}\mathrm{N}$.

Resonant-Raman intensities and transition energies of the E 11 transition in carbon nanotubes

Abstract: We observed the lowest optical transitions $({E}_{11}^{S})$ in separated carbon nanotubes by resonant Raman spectroscopy. Radial breathing mode spectra were collected varying the excitation energy in the near-infrared from $1.15\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1.48\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. From resonance profiles we obtained the ${E}_{11}^{S}$ energies of 11 nanotubes, extending the experimental Kataura plot. Strong Raman signal from tubes with $\ensuremath{ u}=(n\ensuremath{-}m)\mathrm{mod}3=+1$ and from tubes that were absent in photoluminescence support the theory of exciton resonance. The measured Raman intensities agree well with the calculated optical absorption and electron-phonon coupling obtained with first-principles and empirical methods. A remaining factor of $\ensuremath{\sim}3$ can be due to a higher abundance of armchairlike tubes or differences of the absorption and vibrational coupling between correlated (excitons) and uncorrelated electron-hole pairs.

Origin of ferromagnetism in semiconducting ( In 1 − x − y Fe x Cu y ) 2 O 3 − σ

Abstract: We systematically measure and analyze x-ray absorption fine structure and the anomalous Hall effect of recently discovered room-temperature ferromagnetic semiconductor thin films, ${({\mathrm{In}}_{1\ensuremath{-}x\ensuremath{-}y}{\mathrm{Fe}}_{x}{\mathrm{Cu}}_{y})}_{2}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\sigma}}$. The x-ray fine structure demonstrates that divalent Fe ions exist in ferromagnetic samples but not in nonmagnetic ones, suggesting a mobile-electron-mediated ferromagnetism. The anomalous Hall behavior is found to be consistent with that of ferromagnets, in which carriers are delocalized, but qualitatively different from that of double-exchange manganites, in which carriers are bound to magnetic ions, confirming that the ferromagnetism in ${({\mathrm{In}}_{1\ensuremath{-}x\ensuremath{-}y}{\mathrm{Fe}}_{x}{\mathrm{Cu}}_{y})}_{2}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\sigma}}$ is mediated by mobile electrons.

Intrachain photoluminescence properties of conjugated polymers as revealed by long oligothiophenes and polythiophenes diluted in an inactive solid matrix

Abstract: The intrinsic intrachain photoluminescence (PL) dynamics of conjugated polymers in the solid state is investigated. We focus on the PL properties of long $\ensuremath{\beta}$-substituted oligothiophenes (8-mer, 12-mer, and 16-mer) and regio-regular (RR) and regio-random poly(3-octylthiophenes) (P3OTs) diluted in the inactive solid matrix polypropylene (PP). The oligothiophenes have well-resolved 0-0 PL and absorption peaks at $4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and show a good linear relationship with the reciprocal of the ring number. Franck-Condon analyses on the PL spectra reveal that the strength of the electron-phonon coupling represented by the Huang-Rhys factor becomes weak with increasing chain length in the oligomers. In contrast, the presence of stronger electron-phonon coupling is confirmed in RR P3OT despite it being of a much longer chain length than oligomers. This is probably due to its stereoregular chain conformation. The materials used in this work diluted in PP exhibit single-exponential PL decays with lifetimes that decrease with increases in the chain length. The presence of intrachain exciton migration is shown by the time-resolved PL measurements, except for the case of RR P3OT. The energy shifts attributed to intrachain migration are much smaller than those ascribed to interchain migration. We conclude that a change in the torsion angle around the thiophene ring bonds occurs within $50\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ following the absorption transition in thiophene derivatives and that the torsional change gives rise to a constant Stokes shift $(60\char21{}70\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$, regardless of the chain length. We propose that the Stokes shift can be utilized for estimating the magnitude of exciton migration in thiophene derivatives, even in the case of undiluted films.

Inelastic quantum transport and peierls-like mechanism in carbon nanotubes.

Abstract: We report on a theoretical study of inelastic quantum transport in $(3m,0)$ carbon nanotubes. By using a many-body description of the electron-phonon interaction in Fock space, a novel mechanism involving optical phonon emission (absorption) is shown to induce an unprecedented energy-gap opening at half the phonon energy, $\ensuremath{\hbar}{\ensuremath{\omega}}_{0}/2$, above (below) the charge neutrality point. This mechanism, which is prevented by Pauli blocking at low bias voltages, is activated at bias voltages on the order of $\ensuremath{\hbar}{\ensuremath{\omega}}_{0}$.

Local atomic structure of martensitic Ni 2 + x Mn 1 − x Ga : An EXAFS study

Abstract: The local atomic structure of ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1\ensuremath{-}x}\mathrm{Ga}$ with $0\ensuremath{\le}x\ensuremath{\le}0.16$ alloys was explored using Mn and Ga $K$-edge extended x-ray-absorption fine-structure (EXAFS) measurement. In order to study the atomic re-arrangements that occur upon martensitic transformation, room-temperature and low-temperature EXAFS were recorded. The changes occurring in the $L{2}_{1}$ unit cell and the bond lengths obtained from the analysis enables us to determine the modulation amplitudes over which the constituent atoms move giving rise to the shuffling of the atomic planes in the modulated structure. The EXAFS analysis also suggests the changes in hybridization of $\mathrm{Ga}\text{\ensuremath{-}}p$ and $\mathrm{Ni}\text{\ensuremath{-}}d$ orbitals associated with the local symmetry breaking upon undergoing martensitic transition.

Local Co structure and ferromagnetism in ion-implanted Co-doped LiNbO 3

Abstract: A ferromagnetic oxide ${\mathrm{Co}}_{0.05}(\mathrm{LiNb}{)}_{0.95}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ was prepared by Co ion implantation into (104) ${\mathrm{LiNbO}}_{3}$ wafers. Co is uniformly distributed to a depth of $\ensuremath{\sim}220\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ by implanting at three different energies and doses. Electron energy loss spectroscopy and x-ray absorption near-edge structure (XANES) spectra reveal a solid solution of cobalt in an implanted layer, where Co is not metallic but in the 2+ state. Furthermore, full multiple-scattering ab initio calculations of Co XANES at the $K$ edge clearly provide a structure fingerprint to determine Co substitution at Li lattice sites rather than Nb. The ${\mathrm{Co}}_{0.05}(\mathrm{LiNb}{)}_{0.95}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ system exhibits room temperature ferromagnetism of $1.3{\ensuremath{\mu}}_{B}∕\mathrm{Co}$ ion with an easy in-plane axis and a high Curie temperature of $710\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.