Hydrogen in phosphorus- and carbon-doped crystalline silicon

The formation kinetics of the H-C complex in P-doped silicon have been studied using the DLTS and C-V profiling methods. The measurements show that the hydrogen species that is incorporated in the H-C complex originates from H-P complexes which act as a “hydrogen reservoir”. The dissociation energy of the H-P complexes is determined to be 1.13 eV. The results of C-V measurements clearly indicate that there exists a negatively charged H-species after the dissociation of the H-P complexes. H motion in an electric field seems to occur via a “hopping mechanism”.     

Positron annihilation in the hydrogenated granular superconductor of YBa2Cu3O7−δ

In this paper, we have used the sputtering neutral-particles mass spectroscopy (SNMS) and positron-annihilation technique to investigate the effect of hydrogenation on the physical properties of different oxygenated YBa₂Cu₃O_7−δ superconductors. Under the same of hydrogenation treatment, the hydrogenation effects on the superconductors are compared to the non-superconductors. It was shown that the hydrogen concentration in the superconductors is about eight times of the non-superconductor's. It was proven that the long lifetime of positrons in the annihilation process is determined by the variation of the concentrations of monovacancies and microvoids, which takes place in both of intragrain and intergrain samples. The hydrogenation effect can be classified into four stages. At the first stage, the hydrogen atoms fill both monovacancy and microvoid. At the end of the first stage, the long lifetime τ₂ reaches the maximum value which is determined by the lifetime of the positron in the monovacancy-free and nearly microvoid-exhausted YBCO sample. In the second stage, the hydrogen charging will lead to creation of new monovacancies; this will make the long lifetime τ₂ drop monotonically to its minimum value. In the third stage, further hydrogen charging promotes the formation of microvoids, and leads to an increasing τ₂ up to a saturation value, which indicates the equilibrium concentrations of monovacancy and microvoid at that temperature.     

The structure of dielectric β-SiC thin films of hollow glass waveguide for CO2 laser power delivery

A novel type of hollow glass waveguide with β-SiC dielectric films was manufactured by a modified chemical vapor deposition method. FTIR absorption spectra and SEM results show that the change of film structure is responsible for the phenomena of the blue shift and the narrow width of the fundamental absorption band of β-SiC, and that the microfissures at the films provide the heterocrystallization centers for promoting the formation of β-SiC crystal. The influences of the concentration of hydrogen gas passed through the system and the reaction temperature are discussed with regard to the film structure.     

Phase transitions and dimensional reduction

Using field theoretic methods a formalism is presented within which the critical behaviour of a system undergoing a dimensional reduction may be investigated. As a paradigm we study an Ising-like system on S¹ × R^3−ε. If the size of the system is L, and the correlation length ξ, then as L/ξ varies it is possible to get critical behaviour associated with two different fixed points. By exploiting a set of renormalization schemes which lead to manifest dimensional reduction in the loop expansion, and utilizing the renormalization group and an expansion about the fixed point of the finite system, we quantitatively investigate such crossover behaviour in its entirety. In particular, effective susceptibility and correlation length exponents are defined and computed. These exponents interpolate between those associated with a (4 − ε)-dimensional and a (3 − ε)-dimensional Ising model.     

Evidence for molecular hydrogen in single crystal silicon

Rutherford backscattering in channeling in combination with elastic recoil detection analysis has been used to study the formation and destruction of hydrogen “supermolecular” complexes (H₂)_n formed in single crystal silicon after hydrogen implantation and annealing in the range 150–800°C. Secondary ion mass spectroscopy has been used to confirm this interpretation by giving direct evidence for H₂. The supermolecular configuration can be interpreted as the nucleus for the formation of bubbles.     

Ultrasound in synthesis: natural products and supersonic reactions?

Sonochemical syntheses of a number of useful reagents such as samarium diiodide, sodium phenylselenide, tertiary alkoxides and the reducing agent [(PPh₃P)CuH]₆ are discussed. The rates of these sonochemical reactions can be increased by the addition of electron-transfer agents, such as benzophenone ketyls. These results would not be expected on the basis of mechanical effects alone and lend support to proposals that ultrasound acts preferentially on single electron-transfer processes. Ultrasound also allows the rapid and efficient generation of tetracarbonyliron, which can be trapped by simple organic compounds, such as conjugated dienes, vinyl epoxides and allylic alcohols. In the latter cases, this allows the facile preparation of π-allyltricarbonyliron lactone and lactam complexes that can be converted to give a range of biologically active β-, γ- and δ-lactones, including a number of alkaloids and antibiotics. In addition, the δ-lactone products have been incorporated into several complex multi-step syntheses of macrocyclic natural products. The synthesis of key fragments of the potent antiparasitic agent avermectin B1a demonstrates that the sonochemical reaction conditions are fully compatible with the synthesis of highly functionalized molecules.     

Solid phase epitaxial growth of Si on Si---Sb surface phases for the formation of δ-doped layers and δiδi-superlattices

The SPE growth of Si on Si---Sb surface phases has been studied by LEED and AES techniques. The surface phases studied were the disordered Si(100)---Sb and the ordered one. Both surface phases have an Sb coverage of about one monolayer. Structures with single δ-doped layers and a δiδi-superlattice have been grown. The structural perfection of the grown Si films has been characterized on the basis of LEED data. The peculiarities of the annealing behaviour of Si films thinner than 10 nm have been detected.     

Characterization of heterogeneous interaction in binary mixtures of ethylene glycol oligomer with water, ethyl alcohol and dioxane by dielectric analysis

The associating behaviour of the binary mixtures of ethylene glycol oligomer (EGO), i.e. ethylene glycol (EG), diethylene glycol (DEG) and poly(ethylene glycol)s (PEG200, PEG300, PEG400 and PEG600) with water (W), ethyl alcohol (EA) and 1,4-dioxane (DX) over the entire concentration range at 25 °C have been investigated through their accurately measured values of dielectric constant. The static dielectric constant ε_o, high frequency limiting dielectric constant ε_∞, dielectric relaxation strength Δε, excess dielectric parameters ε^E₀ and ε^E_∞, effective Kirkwood correlation factor g^eff and corrective correlation factor g_f of EGO–W, EGO–EA and EGO–DX mixtures were determined to obtain qualitative and quantitative information about the complex formation through H-bond in these systems. Most of the evaluated dielectric parameters of EG and DEG in different ‘cosolvents’ have different characteristics as compared to the PEG–cosolvent mixture. The observed linear and non-linear behaviour of Δε against EGO monomer unit mole fraction X confirms the variation in the homogeneous structures in their binary mixtures with concentration variation. Appearance of the maximum in ε^E₀ against X plots indicates that a complex stable adduct is formed in the EGO–W mixtures at stoichiometric ratio 1:1.7 for lower oligomers but this ratio seems to be 1.7:1 for higher EGO molecules, which confirms that the EGO size and chain flexibility affects the complex formation between EGO and W. In case of EG–EA mixture 1:1 stoichiometric ratio form stable adduct whereas for higher EGO–EA, it is 3:1, at EGO monomer unit level. The complex formation behaviour of DEG–EA has entirely different characteristics when compared to the other studied EGO–EA mixtures. Although, 1,4-dioxane has weak polar behaviour dielectric properties of EG–DX and DEG–DX confirm the formation of stable adducts at the stoichiometric ratio 2:1 of EGO monomer unit mole fraction to the DX. For the higher EGO–DX mixtures, stable adduct forms at the stoichiometric ratio 9:1. Except DEG–EA mixtures, the EGO–W and EGO–EA form the complex with reduction in the effective number of dipoles. In EG–DX mixtures, the heterogeneous species form with a large reduction in the effective number of dipoles, which changes as the effective number of dipoles increases with the increase in monomer repeat units of EGO. Further the net electronic polarization in these binary mixtures increases due to heterogeneous interaction over the entire mixing concentration range.     

A first-principles study of surface and subsurface H on and in Ni(1 1 1): diffusional properties and coverage-dependent behavior

Periodic, self-consistent, density functional theory (GGA-PW91) calculations are performed for both surface and subsurface atomic hydrogen on and in Ni(1 1 1). At a low coverage (θ=0.25 ML), the binding energies (BEs) of a hydrogen atom in surface fcc, subsurface octahedral (first layer), and subsurface octahedral (second layer) sites are −2.89, −2.18, and −2.11 eV, respectively. The activation energy barriers for hydrogen diffusion from the surface to the first subsurface layer and from the first to the second subsurface layer are estimated to be 0.88 and 0.52 eV, respectively. In the entire coverage range studied, hydrogen occupies surface fcc and hcp sites and subsurface octahedral sites. In addition, the magnitude of the BE per hydrogen atom and the magnetization of the nickel slabs both decrease as hydrogen coverage increases. Vibrational frequencies of hydrogen at various surface and subsurface sites are calculated and are in reasonable agreement with experimental data. A phase stability calculation with a 2 × 2 surface unit cell shows that a p(2 × 2)-2H overlayer structure (θ=0.5 ML) and a p(1 × 1)-1H structure (θ=1.0 ML) are stable at low hydrogen pressures, in agreement with numerous experimental results. A very large increase in pressure is required to populate subsurface sites. After such an increase occurs, the first subsurface layer is filled completely.     

Steps and facets on annealed LaAlO3{100} and {110} surfaces

Lanthanum-aluminate (LaAlO₃) is one of the optimum substrates for epitaxic growth of thin oxide films. In this paper, the structures of the {100} and {110} surfaces of annealed LaAlO₃ are studied using reflection electron microscopy (REM). 010 steps have been observed on {100}, these are the lowest energy steps. The {100} surface is atomically flat, but the {110} surfaces exhibit high-density fine structures distributed on large surface terraces. These fine structures correspond to the formation of small width (100) and (010) facets on the (110) surface. A growth model is given to interpret the formation of large steps and large terraces on the {110} surfaces.     

The radiative decay of the Λ(1405)

A recent result for the branching ratio for the decay of the kaonic hydrogen atom to Λγ is used to derive a value for the transition moment for the decay Λ(1405) → Λγ. Two solutions are found, −0.29 < κ < −0.07 and 0.60 < κ < 0.81 proton magnetons, giving decay widths of Γ(Λ(1405) → Λγ) = 6 ± 6 and 74 ± 22 keV, respectively.     

A high resolution search for the tensor glueball candidate ξ(2230)

We report results of a high resolution search for the tensor glueball candidate ξ(2230) in a formation experiment. π⁰π⁰ and ηη decay channels were measured in a scan of the mass region 2220 MeV to 2240 MeV. No evidence for the existence of ξ(2230) was found. 95% confidence upper limits for the possible existence of ξ are presented.     

Contributions of atom probe tomography to the understanding of nickel-based superalloys

Atom probe tomography enables atomic level microstructural characterization to be performed on complex engineering materials such as superalloys. The technique provides information on the size, morphology and compositions of coexisting phases, the solute partitioning of the elements between the phases, and solute segregation to interfaces and grain boundaries. This information leads to a more complete understanding of nickel-based superalloys. The types of atomic level information that may be obtained with atom probe tomography are illustrated with examples of the formation of fine γ precipitates within the central region of the γ′ phase in PW 1480, the evolution of the dual γ′/γ″ nature of secondary precipitates in alloy 718, the interphase precipitation of the γ′ phase at the primary γ″–γ interface in alloy 718, and the quantification of the level and spatial extent of the boron segregation at grain boundaries in a nickel–molybdenum superalloy.     

No-go for detecting CP violation via neutrinoless double beta decay

We present a necessary condition on the solar oscillation amplitude for CP violation to be detectable through neutrinoless double beta (0νββ) decay. It depends only on the fractional uncertainty in the ν_e–ν_e element of the neutrino mass matrix. We demonstrate that even under very optimistic assumptions about the sensitivity of future experiments to the absolute neutrino mass scale, and on the precision with which nuclear matrix elements that contribute to 0νββ decay are calculable, it will be impossible to detect neutrino CP violation arising from Majorana phases.     

Superconducting oxide formation in the Yb---Ba---Cu---O system

Conditions for forming YbBa₂Cu₄O₈, Yb₂Ba₂Cu₃O_7−δ and YbBa₂Cu₃O_7−δ were determined in oxygen at 1.0 atm pressure by experiments with oxidized Yb---Ba---Cu---Ag alloys. YbBa₂Cu₃O_7−δ formed in less than 10 s when oxidized alloy ribbons were baked in the 805°C–890°C range. Large amounts of Ba₂Cu₃O₅ formed below 870°C. Yb₂Ba₄Cu₇O_15−δ and YbBa₂Cu₄O ₈ then formed in the 10²s–10³s range at temperatures in the 840°C–870°C and <840°C ranges, respectively. Ba₂Cu₃O₅ decomposition supplied Cu²⁺ and O²⁻ for the rapid transformation of YbBa₂Cu₃O_7−δ grains into Yb₂Ba₄Cu₇O_15−δ grains by intercalation. Intercalation was much slower in the absence of Ba₂Cu₃O₅. All of these transformation products underwent coarsening with increasing bake time. Rapid YbBa₂Cu₄O₈ and Yb₂Ba₄Cu₇O_15−δ formation, compared to the slow formation of these phase types when Yb was substituted by Y, Is due to the differing effects of Y and Yb on formation kinetics. Superconducting oxide-silver composite ribbons containing mainly YbBa₂Cu₃O_7−δ, Yb₂Ba₄Cu₇O_15−δ or YbBa₂Cu₄O₈ can be prepared from Yb---Ba ---Ba---Cu---Ag alloys.     

Solid-state synthesis of potassium β- and β″-gallates

Direct synthesis of K-β- and β″-gallates by Ga₂O₃–K₂O solid-state reaction is described. The formation of K-β- or β″-gallates depends on the initial Ga₂O₃ phase. -Ga₂O₃ leads to K-β-gallate; β-Ga₂O₃ leads to K-β″-gallate. K-β″-Gallate is stable <1200°C. The high temperature stability of K-β″-gallate can be enhanced by doping with aliovalent ions.     

Chord length analysis of the fragments of a 'dead leaves' tessellation

Let the (homogeneous) fragments of a puzzle, resulting from a 'dead leaves' tessellation, be embedded in a homogeneous medium (constant density). The application of elastic scattering methods allows the determination of second-order characteristics and derived functions of these particles (set covariance, geometric covariogram, chord length distribution). The second-order characteristics of the grains of the 'dead leaves' model, closely interrelated with those of the resulting tessellation pieces, can be considered as puzzle particles (PPs). A discussion of the behaviour of the chord length distribution of the PPs allows the origin of the shape of the PPs to be characterized. For fitting PPs, the mean small-angle scattering correlation function γ_P(r) of the PPs fulfills γ_P^'(0)/[γ_P' (0)]² = 1.     

Stress relaxation in crumpled surfaces

The stress relaxation in crumpled surfaces maintained at a fixed compressive strain is investigated. The experiments indicate a slow relaxation of the mechanical stress in these non-equilibrium disordered systems. The experimental data indicate an anomalous stretched exponential decay with exponent β=0.28±0.03 along six decades in the rescaled variable t/τ, for a wide interval of strain. The results are compared with the similar behaviour of glassy materials, among others.     

Vibrational Spectra of Hydrogen Bonded Complexes Between Acetophenone and Some Phenol Derivatives

The hydrogen bonded complexes between hydroxylic derivatives and carbonyl bases have been extensively studied by infrared spectroscopy but meager Raman spectroscopic results are available for such complexes. This work reports on a study of the Raman intensity of the v_C[dbnd]0 stretching vibration of hydrogen bonded complexes formed between acetophenone and some phenol derivatives. The formation constants of these complexes are calculated from infrared spectroscopy.     

The Higgs boson: shall we see it soon or is it still far away?

The status of the Higgs boson mass in the Standard Model and its supersymmetric extensions is reviewed and the perspectives of Higgs searches are discussed. The parameter space of the Minimal Supersymmetric Standard Model (MSSM) is analysed with the emphasis on the lightest Higgs mass. The infrared behaviour of renormalization group equations for the parameters of MSSM is examined and infrared quasi-fixed points are used for the Higgs mass predictions. They strongly suggest the Higgs mass to be lighter than 100 or 130 GeV for low and high tan β scenarios, respectively. Extended models, however, allow one to increase these limits for low tan β up to 50%.