Polarization modulation spectroscopy of surface plasmon resonance

The features of surface plasmon resonance in gold nanofilms deposited on the surface of a total-internal-reflection prism have been investigated theoretically, using the Fresnel equation, and experimentally, with application of the polarization modulation technique. The angular characteristics of the polarization difference of the reflection coefficients for s-and p-polarized light, Δρ = R _s ² ? R _p ² , were measured in the wave-length range λ = 0.4–2.0 μm. It is shown that the characteristics of Δρ, in contrast to the results of standard measurements by the surface plasmon resonance method, have a resonance peak. Due to this, the characteristics of the polarization difference contain nonresonant components whose magnitudes are determined by the internal reflection coefficients for the metal and insulator; these parameters depend on the film thickness. The calculated and experimental data coincide when the model assumes exponential dependence of the refractive indices and extinction coefficients on the thickness of the metal film. It is established that the characteristic parameter of the exponential is a metal film thickness of 11.0 ± 0.5 nm, at which the film optical parameters correspond to the bulk characteristics.     

Correlations of pions and kaons as a measure for delayed expansion due to the QCD phase transition

We study pion and kaon correlations in ultra-relativistic heavy ion collisions in a hydrodynamical model with transverse cylindrical and boost-invariant longitudinal symmetry. As a function of the initial energy density ε₀, the ratioR _out/R _side of the inverse widths of the two-particle correlation function in out- and side-direction reflects the behaviour of the lifetime of the system. The ratio shows an enhancement in the case of a delayed expansion caused by the QCD phase transition. We discuss how this time-delay signal depends on the average transverse momentum of the pair, and show that it appears particularly strong for pairs with large average transverse momentum,K _⊥～1 GeV and for initial energy densities ε₀ ? 10 ? 20 GeVfm^?3 GeVfm^?3, corresponding to nuclear collisions at RHIC.     

Electronic structure of gold nanoclusters on oxidized Ni(755) surface

The electronic energy structure of gold nanoclusters grown on oxidized single-crystal stepped surface Ni(755) is studied. It is shown that oxidation of the stepped Ni(755) surface results in the formation of a well-ordered continuous structure O(2 × 2) similar to that grown on a flat Ni(111) single-crystal surface. Evaporation of gold on such a surface leads to the formation of gold nanoclusters of a size determined by the size of the terraces on the Ni(755) surface. A comparison of the photoelectron spectra of the Au 4f _{5/2, 7/2} core levels in clusters grown on clean and oxidized Ni(755) surfaces reveals that the spectra obtained for a gold cluster system on an oxidized Ni(755) surface contain not only the spectral components characteristic of metallic gold but also additional components of Au^+δ. It is assumed that additional components for gold clusters on the oxidized Ni(755) surface originate from partial oxidation of gold atoms with the participation of defects inherent in the stepped relief of the nickel substrate.     

Spectra of negative particles and photons in collisions of p−W and16O−W at 200 GeV/u

p _⊥ spectra of negative particles were measured for p?W and¹⁶O?W collisions at 200 GeV/u in the rapidity range 0.9<y<1.9. Within the systematic errors of 20% the spectra are identical in the range 0.05<p _⊥<2.0 GeV/c. The p?W and¹⁶O?W spectra exhibit an exponential shape forp _⊥ >250 MeV/c. This is consistent with previous p?A data, but there is a significant excess above this exponential at lowerp _⊥. Photon spectra were measured using a conversion method. Theirp _⊥ distribution agrees in shape with the sum of known hadronic γ-sources.     

Saturation Approach in Top Production

The reduced cross section for the top production, in deep inelastic scattering, determined when we use the Kharzeev–Levin–Nardi (KLN) model of the low x gluon distributions. With respect to this model, a compact formula for the ratio R^t(τ) provided that it is approximately independent of τ behavior at low- τ values. For the top production where Q_sr_⊥ ? 1, the model reduced to color transparency.     

Spin-Hamiltonian parameters and tetragonal distortion due to the Jahn–Teller effect for Cu2+ centres in trigonal Zn(BrO3)·6H2O crystal

The spin-Hamiltonian parameters (g factors g_//, g_⊥ and hyperfine structure constants ⁶⁵A_// and ⁶⁵A_⊥) for the tetragonal Cu²⁺ centres in trigonal Zn(BrO₃)·6H₂O crystal are calculated from the complete diagonalization (of energy matrix) method (CDM) based on the cluster approach. In the CDM, the Zeeman and hyperfine interaction terms are added to the Hamiltonian in the conventional CDM and the contributions to the spin-Hamiltonian parameters from both the spin-orbit coupling parameter of central d⁹ ion and that of ligand ion are included. The calculated spin-Hamiltonian parameters of Zn(BrO₃)·6H₂O: Cu²⁺ show good agreement with the experimental values and the tetragonal elongation (characterized by ΔR=R_// ? R _⊥, where R_// and R _⊥ represent the metal-ligand distances parallel with and perpendicular to the C₄ axis) due to the static Jahn–Teller effect is obtained from the calculations. The results are discussed.     

57Fe,119Sn and151Eu Mössbauer study of EuBa2(Cu1−x−y 119Sn x 57Fe y )3O7−δ superconductor

¹⁵¹Eu,¹¹⁹Sn and⁵⁷Fe Mössbauer spectroscopy was used to study a EuBa₂(Cu_1?x?y Sn _x Fe _v )₃O_7?δ superconductor in which sites were replaced by all three Mössbauer isotopes in the same sample in order to get information about the site preferences and structural changes. We have found changes in the Mössbauer parameters of the⁵⁷Fe,¹¹⁹Sn and¹⁵¹Eu spectra compared to those recorded in the separately substituted EuBa₂Cu₃O_7?δ, EuBa₂(Cu_1?x Sn _x )₃O_7?δ, YBaCu_3?x Fe _x O_7?δ YBaCu_3?x Sn _x O_7?δ materials. These results can be interpreted as a consequence of the site preferences and the changes in the structure due to the presence of other additional substitutional elements.     

Enhanced oxygen binding through surface mediated ionic bonds

Palladium clusters deposited on TiO₂ supports constitute important oxidation catalysts. Addition of O₂ in presence of deposited palladium clusters results in dissociated O atoms whose binding strength controls the activity of a catalytic oxidation reaction. Here we demonstrate how the presence of even remote Pd sites can more than double the energy required to remove surface O atoms from a surface. This unusual increase in binding is shown to originate in a Coulomb interaction between Pd^δ+ and O^δ? where the otherwise semiconducting support remains almost neutral acting to mediate a charge transfer from Pd to O sites. The O atoms supported on lattice Ti sites are further shown to form composite TiO motifs that can exchange sites with Pd atoms with a minimal energy, opening the pathway to Ti migration. This behavior is proposed to be linked to their identical valence pool containing d-states.     

Production of pion and muon pairs in e±e− colliding beams. Extension of the equivalent photon approximation

The reactions e^?e^?→e^?e^?π⁺π^?(μ⁺μ^?) are considered here in the situation where only pions (muons) are recorded and k_⊥ (total transverse momentum of the pair) is not too small (roughly speaking m_e²?k_⊥²?m_π²); this domain gives the main contribution to the cross section. In this paper the differential cross sections have been obtained to an accuracy of (Ink_⊥²/me²)^?1k_⊥/m_π. The amplitudes with one scalar photon have to be taken into account in this approximation. Also the charge asymmetry appears due to the interference of the two-photon and bremsstrahlung diagrams. It is shown what information on amplitudes of the reaction γγ→π⁺π^? and on the pion electromagnetic form factor can be obtained from an experiment in the given set-up.     

Square Fermi surface model for conduction in linear chain mercury compounds: Hg3−δAsF6

The unusual temperature dependence of the electrical resistivity of Hg_3?δAsF₆ (δ = 0.18?0.22) is discussed in the framework of a nearly square Fermi surface model. This model predicts a T³ dependence of the resistivity, in close agreement with the recently observed T^2.8 dependence.     

Inclusive φ-meson production in 93 and 63 GeV hadron interactions

The inclusive reactions h+p→φ+X, (h=π^±,,K^±,p^±), are studied for 0?x_F?0.3 and p⊥ ? 1 GeV at 93 and and 63 GeV incident momentum. Differential cross sections dσ/dp_⊥² anddσ/dx_F are presented and are compared with predictions of the naive parton model.     

Luminescence spectra and crystal structure of high-temperature superconductors

A study is reported of the effect of temperature (4.2 K≤T≤150 K), the content of weakly bonded oxygen [6.1≤(7?δ)≤6.9], illumination [E _exc=3.4 eV, (Φt)_max～1.5 ×10²⁰ photon cm^?2, and substitution (Cu → Ag, Cr, Fe, Mn) on the luminescence spectra of the high-T _c superconductor YBa₂Cu₃O_7?δ. Only two bands with E _lum～2.4 and ～2.8 eV were observed in the luminescence spectra in all these cases. A clearly pronounced correlation between the electronic and structural changes in YBa₂Cu₃O_7?δ, caused by the influence of temperature, illumination, doping with oxygen or metal ions, and the spectral parameters (peak position E _lum, width Δλ _lum, and intensity I _lum of the luminescence bands), has been established. It is shown that luminescence spectra of HTSCs can be employed as a fairly reliable optical probe to study the electronic processes occurring in these substances, in particular, the electron (hole) transfer between the CuO₂ plane and the CuO_1?δ chain plane serving as a charge reservoir.     

Waves in a superlattice with anisotropic inhomogeneities

Dependences of the dispersion laws and damping of waves in an initially sinusoidal superlattice on inhomogeneities with anisotropic correlation properties are studied for the first time. The period of the superlattice is modulated by the random function described by the anisotropic correlation function K_?(r) that has different correlation radii, k _∥ ^?1 and k _⊥ ^?1 , along the axis of the superlattice z and in the plane xy, respectively. The anisotropy of the correlation is characterized by the parameter λ=1?k_⊥/k_∥ that can change from λ=0 to λ=1 when the correlation wave number k⊥ changes from k_⊥=k_∥ (isotropic 3D inhomogeneities) to k_⊥=0 (1D inhomogeneities). The correlation function of the superlattice K(r) is developed. Its decreasing part goes to the asymptote L that divides the correlation volume into two parts, characterized by finite and infinite correlation radii. The dependences of the width of the gap in the spectrum at the boundary of the Brillouin zone δν and the damping of waves ξ on the value of λ are studied. It is shown that decreasing L leads to the decrease of δν, and increase of ξ, with the increase of λ.     

Production and decay of quark-gluon strings: inclusive distributions of hadrons in p⊥ and x

The dependence of inclusive cross sections of the production of hadrons $\text{p}\text{p}\text{→ hX}$ on p_⊥ (and also on x and √s) is calculated at high energy in the region of small p_⊥ ? 1–2 GeV. The model of production and decay of quark-gluon strings is used under the simplest assumptions about the k_⊥ dependence of the quark distributions in nucleons ～ exp(?γ₁k²_⊥) and about the form of the string fragmentation function $\text{G}\text{?}{}^{\mathrm{<mtext>h</mtext>}}\text{～}\text{exp}\text{[?γ}{}^{\mathrm{<mtext>h</mtext>}}\text{(}\text{p}{}_{\mathrm{\perp }}\text{? z}\text{k}{}_{\mathrm{\perp }}\text{)}{}^2\text{]}$ where γ₁ and γ^h are some constants. The theory reproduces all existing experimental data and yields the “seagull effect” for the dependence of 〈p_⊥〉 on x. Predictions are given for the p_⊥ dependence of the spectra of π^± mesons produced at high energies at SPS and other future colliders.     

FTIR sensitivity enhancement on Pt/SiO2/Au layered structures: A novel method for CO adsorption studies on Pt surfaces

Specular reflectance FTIR study of carbon monoxide adsorbed on platinum is performed on Pt/SiO₂/Au layered structures prepared by deposition of thin films on silicon (1 0 0) wafers. The layered structures consist of 5 nm thick platinum films over SiO₂ films of varying thicknesses with 50 nm thick reflecting gold films underneath. Due to optical interference effects, the reflectance of each of these structures varies with the incident infrared wavelength and goes through a minimum at a wavelength that depends on the thickness of the SiO₂ layer. The decrease in the reflectance R causes an effective increase in the ΔR/R value resulting in a large increase in the infrared absorption band intensity of linearly-adsorbed CO. The peak height changes with changing the SiO₂ thickness in the structures and is greatest for the sample which has lowest reflectance near the absorption wavelength of CO (∼2100 cm⁻¹). This improvement in the ratio of FTIR signal to background reflectance can be very useful for probing low surface area model catalytic surfaces at atmospheric pressures and under reaction conditions. A spectrum of CO adsorbed on nanofabricated Pt nanowire catalysts on TiO₂ support is also shown as an example of the sensitivity enhancement on layered structures.     

Gold‐Cluster‐Based Dual‐Emission Nanocomposite Film as Ratiometric Fluorescent Sensing Paper for Specific Metal Ion

A dual‐emission ratiometric fluorescent sensing film for metal ion detection is designed. This dual‐emission film is successfully prepared from chitosan, graphitic carbon nitride (g‐C₃N₄), and gold nanoclusters (Au NCs). Here, it is shown that the g‐C₃N₄ not only serves as the fluorescence emission source, but also enhances the mechanical and thermal stability of the film. Meanwhile, the Au NCs are adsorbed on the surface of chitosan film by the electrostatic interaction. The as‐prepared dual‐emission film can selectively detect Cu²⁺, leading to the quench of red fluorescence of Au NCs, whereas the blue fluorescence from g‐C₃N₄ persists. The ratio of the two fluorescence intensities depends on the Cu²⁺ concentration and the fluorescence color changes from orange red to yellow, cyan, and finally to blue with increasing Cu²⁺ concentration. Thus, the as‐prepared dual‐emission film can be worked as ratiometric sensing paper for Cu²⁺ detection. Furthermore, the film shows high sensitivity and selectivity, with low limit of detection (LOD) (10 ppb). It is observed that this novel gold‐cluster‐based dual‐emission ratiometric fluorescent sensing paper is an easy and convenient way for detecting metal ions. It is believed that this research work have created another avenue for the detection of metal ions in the environment.     

Local tetragonal distortions of the (CrF6)3− and (FeF6)3− octahedral clusters in Cr3+- and Fe3+-doped tetragonal Rb2KGaF6 crystals

The local tetragonal distortions (α???α₀) (where α is the angle defined as tgα?=?R_⊥/R_//, R_⊥ and R_// are the metal–ligand distances parallel with and normal to the C₄ axis, α₀?=?45° is the same angle in cubic symmetry) of (CrF₆)^3? and (FeF₆)^3? octahedral clusters in the tetragonal Rb₂KGaF₆ crystals are estimated by analyzing their electron paramagnetic resonance (EPR) zero-field splittings D. The results indicate that the two impurity octahedra and hence the host (GaF₆)^3? octahedra are tetragonally elongated. The distortion (α???α₀) in magnitude differs from impurity to impurity because of the different sizes and natures of these impurities. These results are analogous to those in ABX₃ and doped ABX₃ perovskite crystals where the cubic-to-tetragonal phase transition is due to the rotation of BX₆ octahedra associated with the release or elongation of B–X bond along the C₄ rotational axis.     

Semi-empirical analysis of magnetic moments of single-particle (or-hole) states around the 208Pb core

Magnetic moments of single-particle (or-hole) states around the ²⁰⁸Pb core were fitted by three state-independent parameters δg_l^(p), δg_l⁽ⁿ⁾ and α, where α is a parameter that is connected closely with δg_S and g_p. The analysis was performed under the assumptions that (i) the state-dependence of radial integral I((nl)²(n'l')²) involved in δg_s and g_p is calculated by the harmonic-oscillator potential, and (ii) δg_s is taken as being equal to ?4g_p, as expected from the δ-force type core polarization. An excellent fit was obtained when δg_l^(p) = 0.10(2), δg_l⁽ⁿ⁾ = ?0.05(1) and α = 1.2(1), which show that the main contributor to δg_s is the M1 core polarization and δg_l⁽ⁿ⁾ is certainly smaller than 0. B(M1)'s for allowed transitions calculated with the use of the same parameters as above are smaller than the observed B(M1)'s whereas α = 1.01(1) explains well the observed B(M1)'s.     

Carbon isotopic signature reveals the geographical trend in methane consumption and production pathways in alpine ecosystems over the Qinghai–Tibetan Plateau

On the Qinghai–Tibetan Plateau, isotopic signatures in soil–atmosphere CH₄ fluxes were investigated in nine grasslands and three wetlands. In the grasslands, the fractionation factor for soil CH₄ uptake, α_soil, was much smaller than the usually reported value of 0.9975–1.0095. Stepwise multiple variation analysis indicates that α_soil is higher for higher soil water contents but is lower for higher C/N ratios of soil surface biomass. In the three wetlands, the soil-emitted δ¹³C–CH₄ was similar (?55.3?±?5.5?‰ and ?53.0?±?5.5?‰) in two bogs separated by >1000?km but was lower (?63.4?±?6.3?‰) in a marsh. Environmental factors related to intrasite variations in soil-emitted δ¹³C–CH₄ include the soil C/N ratio, oxidation–reduction potential, soil C concentration and soil water contents. Geographical isotopic surveys revealed environmental constraints on the CH₄ consumption pathways in grasslands and the biome type-specific consistency in CH₄ production pathways in wetlands.     

Preparation and properties of Y1−xHoxBa2Cu3O7−δ thin films by TFA-MOD method

Y_1?xHo_xBa₂Cu₃O_7?δ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) thin films were prepared on LaAlO₃ (0 0 1) substrates by trifluoroacetate metal organic deposition (TFA-MOD) without change of the processing parameters. The highest J_c was attributed to the sample of Y_0.6Ho_0.4Ba₂Cu₃O_7?δ thin film, whose critical current density is about 1.6 times as compared to that of YBa₂Cu₃O_7?δ thin film at 77 K and self field. The flux pinning type was not varied with Ho substitution and can be attributed to δl pinning model, which is attributed to the close ionic radius between the Y³⁺ and Ho³⁺ ions. The improvement of J_c by Ho substitution without change of the processing parameters will provide an effective route to enhance the J_c of YBCO-based thin films using TFA-MOD method.