Nucleation and growth of precipitates in demixing glass melts in the system NA2O-CAO-SIO2.

As an example of a first order phase transition with conserved order parameter the demixing of glass-forming quasibinary systems has been investigated by in situ measurement of light scattering during heat treatment. The relative supercooling is consistent with theoretical expectations. Using a two stage heat treatment, nucleation and growth are decoupled. Nuclei formed at a nucleation temperature Tn can grow to sizes detectable by light scattering at a higher temperature Tgr, where no more nuclei are formed. Reducing the nucleation time, one at last ends up with an incubation time, the temperature dependence of which is described by an Arrhenius ansatz. For low particle densities, the growth mechanism can be deduced from the initial increase of the scattering intensity. The proportionality of the latter to t5 is characteristic for diffusion controlled growth of spheres in a depleted zone. From extrema in the scattering a definite size is assigned to the aggregate. Then, the number of particles can be deduced from the absolute intensity. For the systems investigated, however, growth time is limited by the occurrence of crystallisation, thus allowing only the determination of relative nucleation rates

Tunneling Mechanism due to Chaos in a Complex Phase Space

We have revealed that the barrier-tunneling process in non-integrable systems is strongly linked to chaos in complex phase space by investigating a simple scattering map model. The semiclassical wavefunction reproduces complicated features of tunneling perfectly and it enables us to solve all the reasons why those features appear in spite of absence of chaos on the real plane. Multi-generation structure of manifolds, which is the manifestation of complex-domain homoclinic entanglement created by complexified classical dynamics, allows a symbolic coding and it is used as a guiding principle to extract dominant complex trajectories from all the semiclassical candidates.Comment: 4 pages, RevTeX, 6 figures, to appear in Phys. Rev.

Chaos assisted instanton tunneling in one dimensional perturbed periodic potential

For the system with one-dimensional spatially periodic potential we demonstrate that small periodic in time perturbation results in appearance of chaotic instanton solutions. We estimate parameter of local instability, width of stochastic layer and correlator for perturbed instanton solutions. Application of the instanton technique enables to calculate the amplitude of the tunneling, the form of the spectrum and the lower bound for width of the ground quasienergy zone

Detection and mobility of hafnium in SiO2

High-angle annular dark-field imaging in scanning transmission electron microscopy and x-ray photoelectron spectroscopy were used to investigate thermal SiO2 layers doped with Hf by ion-implantation. Hf was mobile under the focused electron beam in the asimplanted samples. After annealing for 5 min at 1200 °C, clusters of crystalline HfO2 were observed that were a few nm in size and surrounded by residual Hf that had remained trapped in the SiO2. Hf was not mobile under the electron beam in the annealed samples. Further annealing caused an expansion of the SiO2 that was damaged by ionimplantation. Hf rearrangement was confined to the ion beam damaged regions of the SiO2 layer. No diffusion of Hf into the undamaged SiO2 was observed. The implications of the results for complementary metal-oxide-semiconductor transistors with HfO2 gate dielectrics are discussed

Statistical analysis of scars in stadium billiard

In this paper, by using our improved plane wave decomposition method, we study the scars in the eigenfunctions of the stadium billiard from very low state to as high as about the one millionth state. In the systematic searching for scars of various types, we have used the approximate criterion based on the quantization of the classical action along the unstable periodic orbit supporting the scar. We have analized the profile of the integrated probability density along the orbit. We found that the maximal integrated intensity of different types of scars scales in different way with the $\hbar$, which confirms qualitatively and quantitatively the existing theories of scars such as that of Bogomolny (1988) and that of Robnik (1989).Comment: 22 plain Latex pages, 14 EPS figures (Figs. 4-6, 9,10,12 are included, others (too large) are availabe upon request.) to appear in J. Phys. A: Math. & Gen. 31 (1998

An efficient Fredholm method for calculation of highly excited states of billiards

A numerically efficient Fredholm formulation of the billiard problem is presented. The standard solution in the framework of the boundary integral method in terms of a search for roots of a secular determinant is reviewed first. We next reformulate the singularity condition in terms of a flow in the space of an auxiliary one-parameter family of eigenproblems and argue that the eigenvalues and eigenfunctions are analytic functions within a certain domain. Based on this analytic behavior we present a numerical algorithm to compute a range of billiard eigenvalues and associated eigenvectors by only two diagonalizations.Comment: 15 pages, 10 figures; included systematic study of accuracy with 2 new figures, movie to Fig. 4, http://www.quantumchaos.de/Media/0703030media.av

Fresnel filtering in lasing emission from scarred modes of wave-chaotic optical resonators

We study lasing emission from asymmetric resonant cavity (ARC) GaN micro-lasers. By comparing far-field intensity patterns with images of the micro-laser we find that the lasing modes are concentrated on three-bounce unstable periodic ray orbits, i.e. the modes are scarred. The high-intensity emission directions of these scarred modes are completely different from those predicted by applying Snell's law to the ray orbit. This effect is due to the process of ``Fresnel filtering'' which occurs when a beam of finite angular spread is incident at the critical angle for total internal reflection.Comment: 4 pages, 3 figures (eps), RevTeX 3.1, submitted to Phys. Rev. Lett; corrected a minor (transcription) erro

Localization of Eigenfunctions in the Stadium Billiard

We present a systematic survey of scarring and symmetry effects in the stadium billiard. The localization of individual eigenfunctions in Husimi phase space is studied first, and it is demonstrated that on average there is more localization than can be accounted for on the basis of random-matrix theory, even after removal of bouncing-ball states and visible scars. A major point of the paper is that symmetry considerations, including parity and time-reversal symmetries, enter to influence the total amount of localization. The properties of the local density of states spectrum are also investigated, as a function of phase space location. Aside from the bouncing-ball region of phase space, excess localization of the spectrum is found on short periodic orbits and along certain symmetry-related lines; the origin of all these sources of localization is discussed quantitatively and comparison is made with analytical predictions. Scarring is observed to be present in all the energy ranges considered. In light of these results the excess localization in individual eigenstates is interpreted as being primarily due to symmetry effects; another source of excess localization, scarring by multiple unstable periodic orbits, is smaller by a factor of $\sqrt{\hbar}$.Comment: 31 pages, including 10 figure

Structure and Sodium Ion Dynamics in Sodium Strontium Silicate Investigated by Multinuclear Solid-State NMR

© 2016 American Chemical Society.The high oxide ion conductivity of the proposed sodium strontium silicate ion conductors Sr0.55Na0.45SiO2.775 (>10-2 S·cm-1 at 525 °C) and its unusual alkali metal substitution strategy have been extensively questioned in the literature. Here, we present a comprehensive understanding of the structure of this material using a combination of XRD and multinuclear 17O, 23Na, and 29Si solid-state NMR spectroscopy data and a detailed investigation of the Na ion dynamics by high temperature 23Na NMR line shape analysis and relaxation rates measurements. Both 23Na and 29Si NMR spectra demonstrate the absence of Na doping in strontium silicate SrSiO3 and the presence of an amorphous phase identified as Na2O·2SiO2 glass as the Na-containing product. Devitrification at 800 °C yields crystallization of the Na2O·2SiO2 glass into the known crystalline α-Na2Si2O5 phase which was positively identified by its XRD pattern and the extensive and clear 17O, 23Na, and 29Si NMR fingerprints. High temperature 23Na NMR reveals that the Na ions are mobile in the Na2O·2SiO2 amorphous component below its glass transition temperature (∼450 °C). In contrast, 23Na NMR data obtained on the crystalline α-Na2Si2O5 shows limited Na dynamics below ∼650 °C, and this result explains the large discrepancy in the conductivity observed in the literature which strongly depends on the thermal history of the Sr0.55Na0.45SiO2.775 material. These insights demonstrate that the high conductivity observed in Sr0.55Na0.45SiO2.775 is due to Na conduction in the Na2O·2SiO2 glass, and this motivates the quest for the discovery of low temperature fast ion conductors in noncrystalline solids

Dynamical Tunneling in Mixed Systems

We study quantum-mechanical tunneling in mixed dynamical systems between symmetry-related phase space tori separated by a chaotic layer. Considering e.g. the annular billiard we decompose tunneling-related energy splittings and shifts into sums over paths in phase space. We show that tunneling transport is dominated by chaos-assisted paths that tunnel into and out of the chaotic layer via the ``beach'' regions sandwiched between the regular islands and the chaotic sea. Level splittings are shown to fluctuate on two scales as functions of energy or an external parameter: they display a dense sequence of peaks due to resonances with states supported by the chaotic sea, overlaid on top of slow modulations arising from resonances with states supported by the ``beaches''. We obtain analytic expressions which enable us to assess the relative importance of tunneling amplitudes into the chaotic sea vs. its internal transport properties. Finally, we average over the statistics of the chaotic region, and derive the asymptotic tail of the splitting distribution function under rather general assumptions concerning the fluctuation properties of chaotic states.Comment: 28 pages, Latex, 16 EPS figure