Generation of single-crystalline domain in nano-scale silicon pillars by near-field short pulsed laser

We observe laser-induced grain morphology change in silicon nanopillars under a transmission electron microscopy (TEM) environment. We couple the TEM with a near-field scanning optical microscopy pulsed laser processing system. This novel combination enables immediate scrutiny on the grain morphologies that the pulsed laser irradiation produces. We find unusual transformation of the tip of the amorphous or polycrystalline silicon pillar into a single crystalline domain via melt-mediated crystallization. On the basis of the three-dimensional finite difference simulation result and the dark field TEM data, we propose that the creation of the distinct single crystalline tip originates from the dominant grain growth initiated at the apex of the non-planar liquid–solid interface. Our microscopic observation provides a fundamental basis for laser-induced conversion of amorphous nanostructures into coarse-grained crystals.     

Narrow band quantitative and multivariate electroencephalogram analysis of peri-adolescent period

ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages.     

Charged pion spectra and energy transfer following antiproton annihilation at rest in carbon and uranium

The momentum spectra of charged pions following antiproton annihilation at rest in carbon and uranium have been measured. This information complements our previous measurement of the neutral pion spectra. The total charged pion multiplicity is 2.84±0.10 and 2.47±0.09 for carbon and uranium, respectively, in good agreement with recent INC model predictions of 2.96 and 2.48 for the same quantities. However, structures predicted by the model near 200 MeV/c and 300 MeV/c related to delta-resonance production are not seen in the data. The total energy transfers to the nucleus are calculated to be 119±59 MeV(carbon) and 455±50 MeV(uranium). The possibility of exciting multifragmentation with a¯p beam impinging on heavy nuclei is discussed.     

Effect of quantum entanglement on Aharonov-Bohm oscillations, spin-polarized transport and current magnification effect

We present a simple model of transmission across a metallic mesoscopic ring. In one of its arm an electron interacts with a single magnetic impurity via an exchange coupling. We show that entanglement between electron and spin impurity states leads to reduction of Aharonov-Bohm oscillations in the transmission coefficient. The spin-conductance is asymmetric in the flux reversal as opposed to the two-probe electrical conductance which is symmetric. In the same model, in contradiction to the naive expectation of a current magnification effect, we observe enhancement as well as suppression of this effect depending on the system parameters. The limitations of this model to the general notion of dephasing or decoherence in quantum systems are pointed out.     

Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Multinucleon phenomena and proton spectra characterizing antiproton annihilation at rest in nuclei

Spectra of protons with momenta greater than 500 MeV/c following antiproton annihilation at rest in carbon and uranium nuclei have been measured. They are compared to recent results from other experiments and to predictions of an intranuclear cascade model. Evidence is presented for a substantialB>0 component in the annihilation process, and an estimate of the magnitude of that component is made.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Metal speciation dynamics in colloidal ligand dispersions

In this work we propose a dynamic metal speciation theory for colloidal systems in which the complexing ligands are localized on the surface of the particles; i.e., there is spatial heterogeneity of binding sites within the sample volume. The differences between the complex formation and dissociation rate constants of complexes in colloidal dispersions and those in homogeneous solutions originate from the differences in kinetic and mass transport conditions. In colloidal systems, when the effective rate of dissociation of the surface complexes becomes fully diffusion controlled, its value is defined via the geometrical parameters of the particle. We assess the extent to which the conventional approach of assuming a homogeneously smeared-out ligand distribution overestimates the lability of surface complexes in colloidal ligand dispersions. The validity of the theory is illustrated by application to binding of lead and cadmium by carboxyl modified latex particles: our approach correctly predicts the formation/dissociation rate constants, which differ by several orders of magnitude from their homogeneous solution counterparts.     

Spectroscopic and electrochemical studies of transition metal tetrasulfonated phthalocyanines: Part V. Voltammetric studies of adsorbed tetrasulfonated phthalocyanines (MTsPc) in aqueous solutions

Cyclic voltammetric measurements of adsorbed Fe- and Co-tetrasulfonated phthalocyanine (TsPc) and Co-phthalocyanine (Pc) have been carried out on ordinary pyrolytic graphite and silver electrodes at different solution pH ranging from 1 to 13. Many voltammetric peaks were found to be pH dependent with a slope of ?59 mV/ unit pH. In some instances this dependence was observed in alkaline or acid solutions only. The influence of oxygen has been also examined.     

An automated activation analysis system

An automated delayed neutron counting and instrumental neutron activation analysis system has been developed at Los Alamos National Laboratory's Omega West Reactor (OWR) to analyze samples for uranium and 31 additional elements with a maximum throughput of 400 samples per day. The system and its mode of operation for a large reconnaissance survey will be described.